Author Topic: list of all the seals to rebuild an engine  (Read 2216 times)

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Offline _mark

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list of all the seals to rebuild an engine
« on: September 20, 2020, 03:00:43 PM »
Hi. I'm rebuilding the engine of my 750.
I was thinking that CMSNL sells a unique package comprehensive of all the seals (06112300000P Gasket Kit   and 90000300010 Oil Seal Kit)

but I have some doubts for example of the items in the pics attached. Are such kits complete?

if not, is there a list of all the needed seals to avoid to make multiple orders ? Thanks and Regards.

 
« Last Edit: September 20, 2020, 03:08:52 PM by _mark »

Offline trigger

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Re: list of all the seals to rebuild an engine
« Reply #1 on: September 20, 2020, 03:13:16 PM »
loads of seals and o'rings on a 750 engine and then there are the seals and stopper in the oil pump.

Offline PeWe

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Re: list of all the seals to rebuild an engine
« Reply #2 on: September 20, 2020, 11:39:36 PM »
I have attached an Excel file I have found here about o-rings.
http://forums.sohc4.net/index.php/topic,172646.msg2010189.html#msg2010189
http://forums.sohc4.net/index.php/topic,181124.msg2098510.html#msg2098510

If cylinder has been milled, do not use thicker o-rings for oil feed since the recessed areas for these 2 o-rings are more shallow.
Always measure both sides of where the knock pins will sit, case-cylinder, cylinder-head. There are different versions depending on year. If this has not enough space, it will leak, parts not properly assembled.
CB750 K6-76  970cc (Earlier 1005cc JMR Billet block on the shelf waiting for a comeback)
CB750 K2-75 Parts assembled to a stock K2

Updates of the CB750 K6 -1976
http://forums.sohc4.net/index.php/topic,180468.msg2092136.html#msg2092136
The billet block build thread
http://forums.sohc4.net/index.php/topic,49438.msg1863571.html#msg1863571
CB750 K2 -1975  build thread
http://forums.sohc4.net/index.php/topic,168243.msg1948381.html#msg1948381
K2 engine build thread. For a complete CB750 -75
http://forums.sohc4.net/index.php/topic,180088.msg2088008.html#msg2088008
Carb jetting, a long story Mikuni TMR32
http://forums.sohc4.net/index.php/topic,179479.msg2104967.html#msg2104967

Offline Progas

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Re: list of all the seals to rebuild an engine
« Reply #3 on: September 21, 2020, 05:04:27 AM »
There is a guy selling a complete o-ring kit on E-bay, I have used it and it is very complete and the o-rings are very good quality .Search for Honda 750 o-ring kit

Offline _mark

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Re: list of all the seals to rebuild an engine
« Reply #4 on: September 22, 2020, 02:09:15 AM »
Yamiya reports also a list

https://www.yamiya750.com/index.php?main_page=product_info&cPath=246_21_250_66&products_id=124

Engin Gasket Set Instructions
(MADE IN JAPAN)
1   GASKET, CYLINDER HEAD   1pc
2   GASKET, BREATHER COVER   1pc
3   O-RING 30.8mm(TAPPET CAPS)   8pcs
4   SEAL, VALVE STEM   8pcs
5   GASKET, CYLINDER HEAD COVER   1pc
6   K0-K2 O-RING (CYLINDER HEAD)   4pcs
7   K4 O-RING (CYLINDER HEAD)   4pcs
8   RUBBER, SEALING   6pcs
9   PACKING, CYLINDER STUD BOLT (K4)   8pcs
10   GASKET, CYLINDER   1pc
11   O-RING 61.8x2.0(PISTON)   4pcs
12   O-RING 11x2.5   4pcs
13   GASKET, CAM CHAIN TENSIONER HOLDER   1pc
14   GASKET, POINT COVER   1pc
15   O-RING (SPARK ADVANCER SHAFT)   1pc
16   GASKET, CLUTCH COVER   1pc
17   GASKET, DYNAMO COVER   1pc
18   PACKING, STARTING MOTOR COVER   1pc
19   GASKET, MISSION COVER   1pc
20   GASKET, OIL PAN (K0 Sand cast)   1pc
21   GASKET, OIL PAN (K0)   1pc
22   GASKET, OIL PAN   1pc
23   O-RING 15x2.5   4pcs
24   O-RING 5x2.4   1pc
25   O-RING 18x3   2pcs
26   GASKET, EXHAUST PIPE   4pcs
« Last Edit: September 22, 2020, 02:13:31 AM by _mark »

Offline _mark

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Re: list of all the seals to rebuild an engine
« Reply #5 on: September 22, 2020, 02:17:51 AM »
I have attached an Excel file I have found here about o-rings.
http://forums.sohc4.net/index.php/topic,172646.msg2010189.html#msg2010189
http://forums.sohc4.net/index.php/topic,181124.msg2098510.html#msg2098510

If cylinder has been milled, do not use thicker o-rings for oil feed since the recessed areas for these 2 o-rings are more shallow.
Always measure both sides of where the knock pins will sit, case-cylinder, cylinder-head. There are different versions depending on year. If this has not enough space, it will leak, parts not properly assembled.

Thanks a lot. Appreciated.

Offline Old Moe Toe

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Re: list of all the seals to rebuild an engine
« Reply #6 on: September 23, 2020, 02:52:50 PM »
The Yamiya kits do not have the 4 o-rings 5.5mm x 3mm that go between the cylinders and crank case on the 750 F2 motors, also the final drive seal is a bigger size on that model. So beware if you have an F2.

Offline HondaMan

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Re: list of all the seals to rebuild an engine
« Reply #7 on: September 23, 2020, 06:21:33 PM »
Hi. I'm rebuilding the engine of my 750.
I was thinking that CMSNL sells a unique package comprehensive of all the seals (06112300000P Gasket Kit   and 90000300010 Oil Seal Kit)

but I have some doubts for example of the items in the pics attached. Are such kits complete?

if not, is there a list of all the needed seals to avoid to make multiple orders ? Thanks and Regards.

The O-rings around the dowel between the engine cases (up front, behind the oil filter site) is 3x18mm, same as the one around the Neutral Switch. These are not in kits. The ones around the oil pump's (3) dowels are 15x2.5 (some are listed as 15x2.4, but you don't want those), same as the ones in the oil hose fittings that bolt to the engine (you need 5 of these). The ones that fit into the oil port holes between the cylinders and head MUST be 2.6x10.5mm minimum, because all modern head gasket are at least 0.2mm thicker than OEM, some are even thicker (like MLS gaskets). The original head gasket was 0.8mm thick, now you will find your new one to be at least 1.0mm thick instead. So, the extra thickness must either be milled off the tops of the cylinders, or use a thicker O-ring (I do both).

The Oring between the countershaft bearing housing and the engine case is 1.9x5.9 minimum: I use 2x6. Same for the oil jets in the later heads: in the early heads the larger oil jets use a smaller O-ring (1.5x3) but I usually add another 2x7 outside of that because many of the early rocker towers were not perfectly flat: this helps prevent loss of oil flow in a hot engine at high speed.

When you install the seal at the engine's countershaft, spread some Hondabond on the seal's outer rim before installing. There are some seals out there that are a hair on the thin side of rubber over that rim, and those will weep a bit around the edges on a hot day. While it just falls mostly on the chain, it can also dribble down the kickstand when parked hot, making a mess until it drains away.

Edit (in 2023): I forgot to mention about the final-drive countershaft seal: when you put sealant on it, like Hondabond or Permatex, be sure to press the seal inward against the cases several times as you snug the cases shut. Every now and then I have seen this seal squeeze itself out of the cases when lubed up with Hondabond, and you must make sure it is flush with the outside of the cases when everything is tightened down. Many of the cases have dead-square boring for these seals, but not all, especially starting with the K5 engines. This is why Honda made the custom lipped seal on the crankshaft by the points: it could otherwise do this, too.
« Last Edit: July 30, 2023, 07:56:23 PM by HondaMan »
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

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Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
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Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

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Offline _mark

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Re: list of all the seals to rebuild an engine
« Reply #8 on: September 24, 2020, 01:36:05 AM »
Thank you all guys. You are awesome.

Offline _mark

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Re: list of all the seals to rebuild an engine
« Reply #9 on: September 24, 2020, 02:02:46 AM »
The ones that fit into the oil port holes between the cylinders and head MUST be 2.6x10.5mm minimum, because all modern head gasket are at least 0.2mm thicker than OEM, some are even thicker (like MLS gaskets). The original head gasket was 0.8mm thick, now you will find your new one to be at least 1.0mm thick instead. So, the extra thickness must either be milled off the tops of the cylinders, or use a thicker O-ring (I do both).
Thanks. Is there a particoular reason why you tell to mill the cylinders instead of the head (operation generally more frequent) ?
The new gaskets are thicker due to the asbestos free materials ?
thanks

Offline bryanj

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Re: list of all the seals to rebuild an engine
« Reply #10 on: September 24, 2020, 06:18:17 AM »
Because the groove for the O ring is in the barrel and making it shallower makes the O ring stick up more
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Offline HondaMan

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Re: list of all the seals to rebuild an engine
« Reply #11 on: September 24, 2020, 06:39:53 PM »
The ones that fit into the oil port holes between the cylinders and head MUST be 2.6x10.5mm minimum, because all modern head gasket are at least 0.2mm thicker than OEM, some are even thicker (like MLS gaskets). The original head gasket was 0.8mm thick, now you will find your new one to be at least 1.0mm thick instead. So, the extra thickness must either be milled off the tops of the cylinders, or use a thicker O-ring (I do both).
Thanks. Is there a particoular reason why you tell to mill the cylinders instead of the head (operation generally more frequent) ?
The new gaskets are thicker due to the asbestos free materials ?
thanks

Yep, the head gaskets got thicker when asbestos was outlawed in the USA. Since this is the biggest single market worldwide, all the manufacturers followed our laws everywhere. This has made for a LOT of leaky engines, and mysteries, but the cause is easily sorted out and fixed. The gaskets are thicker now because a paper-based fiber is used instead, and it is not as strong nor as heat-resistant.

Milling the head won't solve it because the O-rings sit in a pocket on the top of the cylinders. The top of the cylinders must be milled off to make that pocket shallower so the O-rings can fill in the gap (it makes them sit taller). It gets a little more complicated in this: Honda always lists the MINIMUM size of O-ring that will work in a given site, and gasket kit makers use Honda's parts fiche to make up kits. Well, the 2.4x11.0 O-ring that is spec'd here could be anywhere form 2.4 to 2.6mm thick and still work in production engines, and most of the O-rings came in (to Honda) around 2.5mm thick. When you take apart the old one, you can measure them and find this: they will usually be 2.4mm tall (from being flat and heated hard now) and 2.6+mm wide: this works out to 2.5mm diameter when new. This is the scenario all over these engines, and the clue to how to fix them up again. ;)
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book

Link to website: www.SOHC4shop.com

Offline _mark

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Re: list of all the seals to rebuild an engine
« Reply #12 on: September 26, 2020, 12:55:48 PM »
The ones that fit into the oil port holes between the cylinders and head MUST be 2.6x10.5mm minimum, because all modern head gasket are at least 0.2mm thicker than OEM, some are even thicker (like MLS gaskets). The original head gasket was 0.8mm thick, now you will find your new one to be at least 1.0mm thick instead. So, the extra thickness must either be milled off the tops of the cylinders, or use a thicker O-ring (I do both).
Thanks. Is there a particoular reason why you tell to mill the cylinders instead of the head (operation generally more frequent) ?
The new gaskets are thicker due to the asbestos free materials ?
thanks

Yep, the head gaskets got thicker when asbestos was outlawed in the USA. Since this is the biggest single market worldwide, all the manufacturers followed our laws everywhere. This has made for a LOT of leaky engines, and mysteries, but the cause is easily sorted out and fixed. The gaskets are thicker now because a paper-based fiber is used instead, and it is not as strong nor as heat-resistant.

Milling the head won't solve it because the O-rings sit in a pocket on the top of the cylinders. The top of the cylinders must be milled off to make that pocket shallower so the O-rings can fill in the gap (it makes them sit taller). It gets a little more complicated in this: Honda always lists the MINIMUM size of O-ring that will work in a given site, and gasket kit makers use Honda's parts fiche to make up kits. Well, the 2.4x11.0 O-ring that is spec'd here could be anywhere form 2.4 to 2.6mm thick and still work in production engines, and most of the O-rings came in (to Honda) around 2.5mm thick. When you take apart the old one, you can measure them and find this: they will usually be 2.4mm tall (from being flat and heated hard now) and 2.6+mm wide: this works out to 2.5mm diameter when new. This is the scenario all over these engines, and the clue to how to fix them up again. ;)
Thanks

Offline Erny

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Re: list of all the seals to rebuild an engine
« Reply #13 on: September 27, 2020, 12:42:06 AM »
Interesting information, will take into account when I'll do top end (maybe this winter)
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Offline Maltboy

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Re: list of all the seals to rebuild an engine
« Reply #14 on: September 27, 2020, 04:53:13 AM »
« Last Edit: September 27, 2020, 04:57:23 AM by maltboy1 »

Offline HondaMan

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Re: list of all the seals to rebuild an engine
« Reply #15 on: September 27, 2020, 09:25:49 AM »
I have attached an Excel file I have found here about o-rings.
http://forums.sohc4.net/index.php/topic,172646.msg2010189.html#msg2010189
http://forums.sohc4.net/index.php/topic,181124.msg2098510.html#msg2098510

If cylinder has been milled, do not use thicker o-rings for oil feed since the recessed areas for these 2 o-rings are more shallow.
Always measure both sides of where the knock pins will sit, case-cylinder, cylinder-head. There are different versions depending on year. If this has not enough space, it will leak, parts not properly assembled.

Thanks a lot. Appreciated.

This is WRONG, period.
The modern head gaskets for these engines are all at LEAST 0.2mm thicker than OEM. This in turn requires that this distance either be milled off the tops of the cylinders, or else a thicker O-ring be used, to prevent oil leaks from the main oil journals.

I have rebuilt MANY, MANY of these 750 engines that leaked because of this issue. Whoever wrote this was born after 2002, because those of us who have been working on these bikes since they appeared know better....
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book

Link to website: www.SOHC4shop.com

Offline mblutcher

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Re: list of all the seals to rebuild an engine
« Reply #16 on: September 27, 2020, 09:26:11 PM »
How does a person buy quality gaskets and oRings in the correct size for a CB750? Seems to be a problem from standard suppliers.

Offline HondaMan

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Re: list of all the seals to rebuild an engine
« Reply #17 on: November 06, 2020, 06:13:07 PM »
How does a person buy quality gaskets and oRings in the correct size for a CB750? Seems to be a problem from standard suppliers.

The seal kits have been mostly good for the 750 engines. The 500/550 often gets an incorrect shifter-shaft seal (14mm inner that should be 13.8mm, leaks because of it).

The gasket kits: I've rebuilt several leaky engines that had been rebuilt using Athena gaskets, which is why I don't like them. the Vesrah gasket kits have been good since 2010, when they dropped out the parts they were selling that were wrong (head pucks, cylinder deck O-rings.) But, NONE of these kits include the correct, thicker O-rings needed at the head joint to prevent oil journal leaks at the head. They still supply the 2.4x12 (some are 2.4x11) size as shown in the Honda parts fiche. The problem of leakage from the head is due to the thicker head gaskets made today, but none of them seem to know it.

Only one gasket set I have ever seen included enough O-rings to do the whole 750 engine (except for the afore-mentioned thicker ones at the head joint, the oil passages, and the oil pump), it was the red-packaged "Made in Japan" kits you see now and then. I don't know its brand.
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book

Link to website: www.SOHC4shop.com

Offline HondaMan

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Re: list of all the seals to rebuild an engine
« Reply #18 on: August 03, 2023, 08:51:58 PM »
OK, how many years later am I?
Does $7 mailed (in the USA) sound fair for this kit? These are all the O-rings that don't come in any CB750 gasket sets.
This will let me turn $1 of each one sold back into the forums' Donations.
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book

Link to website: www.SOHC4shop.com

Offline CycleRanger

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Re: list of all the seals to rebuild an engine
« Reply #19 on: August 03, 2023, 09:02:07 PM »
That's brilliant!  :D

$7 is a steal.
Do you have a copy of the Honda Shop Manual or Parts List for your bike? Get one here:
https://www.honda4fun.com/materiale/documentazione-tecnica
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Offline newday777

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Re: list of all the seals to rebuild an engine
« Reply #20 on: August 04, 2023, 02:52:24 AM »
OK, how many years later am I?
Does $7 mailed (in the USA) sound fair for this kit? These are all the O-rings that don't come in any CB750 gasket sets.
This will let me turn $1 of each one sold back into the forums' Donations.
I'll take 5 of the kits Mark

BTW, the neutral switch O-ring 3x18, are they actually 3mm? I bought one from Honda a couple weeks ago that came 3.4mm and wouldn't fit the neutral switch back in the hole..... The O-ring was listed as 3mm.
« Last Edit: August 04, 2023, 02:57:00 AM by newday777 »
Stu
Honda Parts manager in the mid 1970s Nashua Honda
My current rides
1975 K5 Planet Blue my summer ride, it was a friend's bike I worked with at the Honda shop in 76, lots of fun to be on it again
1976 K6 Anteres Red rebuilding project, was originally my brother's that I set up from the crate, it'll breath again soon!
Project 750s, 2 K4, 2 K6, 1 K8
2008 GL1800 my daily ride and cross country runner

Prior bikes....
1972 Suzuki GT380 I had charge of it for a year in 1973 while my friend was deployed and learned to love street riding....
New CB450 K7 after my friend returned...
New CB750 K5 Planet Blue, demise by ex cousin in law at 9,000 miles...
New CB750 K6 Anteres Red, to replace the totaled K5, I sold this K6 at 45k in 1983, I had heavily modified it, many great memories on it and have missed it greatly.....
1983 GL1100A, 1999 GL1500 SE, 1999 GL1500A

Offline dave500

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Re: list of all the seals to rebuild an engine
« Reply #21 on: August 04, 2023, 04:02:38 AM »
thats a great deal Mark!im guessing the original suppliers of Hondas oddball uneven sized o rings and oil seals have gone west?close enough may fit and not leak for some low pressure or splash lubed areas?ive said it before and ill say it again,any proper diesel pump and injector service centre will have oddball seals and o rings and copper washers on hand,ive often walked out of those places with a handfull of stuff for loose coins!

Offline HondaMan

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Re: list of all the seals to rebuild an engine
« Reply #22 on: August 04, 2023, 05:35:54 PM »
OK, how many years later am I?
Does $7 mailed (in the USA) sound fair for this kit? These are all the O-rings that don't come in any CB750 gasket sets.
This will let me turn $1 of each one sold back into the forums' Donations.
I'll take 5 of the kits Mark

BTW, the neutral switch O-ring 3x18, are they actually 3mm? I bought one from Honda a couple weeks ago that came 3.4mm and wouldn't fit the neutral switch back in the hole..... The O-ring was listed as 3mm.

Yeah, I've been thru that, too. It's been Honda's doing, but I think I know how it's happened, knowing other things about them (more about that in a minute...).
The Oring for both the Neutral Switch and the Case Main Oil Port (between the upper and lower halves) is actually 3.0x18mm, despite having been variously listed as 3.1x18, 3.2x18, and 3.3x17.8 at various times in the Honda Parts Fiche system(s) over the last 30 years or so. You'll find similar confusion with the Orings for the intake manifolds of the CB500/550 and the valve caps that fit all these SOHC4 bikes.

(...the more:) In the Old Days, when dirt was young and I used to walk my dinosaur on his leash in the summer evenings before that big asteroid hit Yucatan and killed him, Honda specified their Orings as the 'minimum acceptable size', which was the same way they ordered their parts from their vendors. With Orings they have (or HAD, before ISO came along) an implied tolerance in JIS terms, which was -0%/+8% (some say it was +10%, but I disagree...) give or take. So, if spec'd an Oring that was, say, 3x20mm (and specified the material separately) then this meant they would accept O-rings of 3x20 minimum up to 3.2x21.6 maximum in production buys of parts - and they had LOTS of Honda people measuring incoming parts in those days to ensure quality was #1 there (Suzy/Yamy/Kawi, not so much...). This let their vendors calculate the wear factor for their molds in real numbers so they could tell what their tooling costs would be, and then they could negotiate block purchases for millions of Orings at a firm cost.

This easy-to-understand system was all destroyed when JIS was halted suddenly in 1996 as the world (mostly driven by EU, via Belgium and their endless regulations) decided to kill most all industrial communications and go to ISO, which still wasn't yet defined for these sorts of things. After all, what the f#$k is a BUREAUCRAT doing defining Engineering terms when he/she/it doesn't even understand what mechanical tolerances ARE? ...but, I digress...

So, if you are lucky enough to have [paper] copies of the old Honda parts fiche from the early 1980s era (some which, I am that lucky) you can look thru all of the Orings in all of the bikes and soon you'll see this built-in pattern showing up.

Then came the 'new kids' to Engineering Support (worldwide) in the late 1990s. Since they didn't understand ANY of the history of JIS nor the bikes (nor Japanese cars, etc.) they would go out and tear down an engine to get a measurement for a part if it wasn't available via their burgeoning (but woefully incomplete) photocopies of old manuals and engineering notes. We see some of these 'notes' when we find stamped letters and numbers inside these engines, which told us sometimes WHO, or HOW, or WHICH TOOL SET, or WHICH MOLD was involved with the build of the part(s). This practice in Honda was being phased out with the advent of the 'new era' of bikes in the CX500 V-Twin and the GL1000, when Honda's Engineering groups were split into 3 parts: Vintage Support (that was our guys), Recreation Vehicles (bikes and ATVs, boats, etc.), and Honda Automobile. Some of their 'new' practices then appeared in the bikes, starting for example with the 750F1 and the CB550K3: the last of these bikes designed the "old way" was the CB350F. That's why the post-1976 SOHC4 bikes look and 'feel' so different when you're working on them: they were transition products between what Honda WAS, and what Honda BECAME, i.e., that we know now. Everything in their Engineering became codified, specified on a per-part basis (like Americans have since 1965 or so) and tracked with long chains of people and paper - until microfiche came along, and later computerized listings. Each of these latter 2 changes lost more of the lore of the pre-1976 bikes, to the point now that Honda doesn't even display any parts fiche for them anymore.

This particular Oring on the Neutral Switch started out as 3.1x18. It became 3.2x18 in the early K1 parts fiche, and the Neutral Switch became almost impossible to install, while mating the upper and lower case halves with the 3.2 thick O-ring resulted in the outer edges of the rubber getting pinched into a thin film around the Oring (seen when the cases get opened nowadays) and sometimes a damaged (cracked) Oring, causing mysterious loss of oil PSI when the engines were hot. This was seen as 60 PSI when cold, 30-35 PSI at hiway speeds, and a flickering OIL light when sitting at a freeway offramp on a hot day after riding at speed for a while. Normally these numbers should be 60+ PSI cold, 40-60 PSI at hiway speeds, and 5-12 PSI at that same stop (no OIL light flicker). So, now you know why that mysterious 'legend' got started...and Honda had to address it with a "...don't worry if the light flickers..." message beginning in the 1972 750K2 Owner's Manuals. Dang it, you'd BETTER worry about it, as the loss of pressure was REAL...but, that's more digression...

This same sort of situation has led to the many differently-sized Orings we see in carb rebuild kits today. An example: the intra-carb fuel tees in the 750 roundtop carbs started out as 1.9x7.8mm in the K0 bikes, and one on each tee end. Well, the material was also spec'd as Buna 70 when our gasolines didn't attack Buna, but as lead began to disappear, starting in 1971, the Buna started shrinking a bit when it dried out during a winter park-in. Then the tees weeped gas in the Spring startup until it swelled a bit, presuming the same gasoline was being used. If not, they could continue to weep. So, Honda added another Oring on each end of the fuel tees and re-spec'd the size as 1.9x7.9mm instead, starting in the summer-of-1971 Parts Listings. So, if you buy a carb kit today that is listed as being specifically for the K0 bikes (hard to find now) you can get undersized Orings (and not enough in some cases) for those tees if they are 'faithful to spec', (but won't work well now). I got 4 of these about 4-5 years ago, which were the rubber-only kits first sold at PartsNmore. Those kits vanished, and now only the later ones with 4 Orings per tee are used, and they are usually 1.9x7.9 to 2.0x8.0 in size. The latter, thicker ones will not ever leak with the modern fuels attacking them in the future, but can take a bit more effort to assemble: lube them with silicone of grease during a rebuild to prevent breaking off the fuel hose's spigot because they don't rotate easily at first, either.

The latest manifestation of the errors caused by the loss of the man-to-man information exchange for these parts is: leaking shifter shaft seals on the CB500/550 bikes, and weird fork seals in 'kits' for these bikes. If you buy most seal kits today, they have been 'generalized' using "reduction of inventory" rules to become the most-commonly-available, closest-fit standard part that a lazy designer/engineer/clerk can't be bothered to research further to see if it actually works, so, in this example, it becomes:
1. Shifter shaft seal: the ID was 14mm on the CB500K0 bike's earliest offerings. The bike made a puddle of oil when parked hot in Cycle Magazine's parking lot and Honda traced it to the shifter shaft: when the bike leans over, parked, with hot oil, the cooling shaft sucks oil past the seal's lips. So, the embarrassed Honda changed it to a custom-made seal with a 13.8mm ID hole by the time the HONDA logo plate on the 500 alternator cover also stopped falling off by itself (i.e., by the first month of production), NOT an industry-standard part. Today you will likely get a 14mm ID hole in your generic seal kit, and a puddle of oil by the kickstand from a rebuilt, parked, hot engine. Finding the 13.8mm ID seal will fix it, every time.
2. Fork seals: in the late 1970s and into the 1980s Honda changed the fork seals for the CB750 5 times in their parts fiche. The original seals lasted as long as the forks (and the CB750 bikes) were thought to be living, i.e., about 20k miles. When riders everywhere were quadrupling this mileage by 1975 with their K0/1/2 bikes and suffering oily riding boots, Honda was supremely embarrassed and changed the seal from its first design of 2 inner lips (the upper one for dust removal) to first 3 lips (not a standard seal), to 4 lips, and then 5 lips (also not a standard seal) , the latter which almost locked the forks in position unless you hit a curb, or something almost that big! They then changed back to a 3-lip seal with Teflon coating, which were seals to die for, copied from a Suzuki bike design circa 1976. So, until about 1995 we got these fine seals from Honda for these bikes. They were discontinued in 1997 but picked up aftermarket for about 10 years, now gone again, too bad. They were not a standard part, so today we just find 2-lip standard Parker-style seals, since they are the world's seal giant. While there are some tricks to make the front end work better (see my book), those tricks are lost to today's computerized Parts Clerks.

The list of these little things goes on and on, but they make the difference between these bikes working right, or working OK (or not so much) after a rebuild. Lots of us have become those 'gurus' (to steal a 1960s dubbing) just to make them the fine machines they have long been, again. ;)
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book

Link to website: www.SOHC4shop.com

Offline HondaMan

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Re: list of all the seals to rebuild an engine
« Reply #23 on: August 04, 2023, 05:51:02 PM »
OK, how many years later am I?
Does $7 mailed (in the USA) sound fair for this kit? These are all the O-rings that don't come in any CB750 gasket sets.
This will let me turn $1 of each one sold back into the forums' Donations.
I'll take 5 of the kits Mark

BTW, the neutral switch O-ring 3x18, are they actually 3mm? I bought one from Honda a couple weeks ago that came 3.4mm and wouldn't fit the neutral switch back in the hole..... The O-ring was listed as 3mm.

Oh, I forgot: PM me your address! I think I can send them in regular envelopes, or maybe one big one.
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book

Link to website: www.SOHC4shop.com