Topic: 77 CB750 F2 Top End Rebuild Advice

[spmc]

Hey all, looking again to the wisdom of the elders and more experienced…

Backstory bought this bike apart from a shop that was doing a head gasket replacement but never got around to it… I bought it and did that replacement and has been my daily rider for about 5/6 years. Problem is the new head gasket didn’t fix the leak, it still slowly weeped oil on rides throughout that time, getting worse to a point last summer I decided I had to pull the engine again and fix it.

So plan is to pull of the top end and get the faces resurfaced. And while I’m at it gonna have the machine shop do a valve job for good measure as I didn’t touch them last time.

My question for you guys is what should I be looking out for to try to identify the source of the leak, or is it likely near impossible for the naked eye to spot?

Also side question, all my tubes like breathers and drainage and stuff are all rock solid now so was wondering if anyone has tips on what to use as replacements and is there a source in the GTA? (I’m DT)

Thanks for any advice in advance!

[bryanj]

Most common oil leaks in order
1 the rubber pucks under the cam towers

2 the studs and bolts holding the cam towers if the holes have been helicoiled or bolts mixed up

Rocker cover gasket can, and has been, fitted backwards

Tach drive seal


You say you will have the valves done, budget for exhaust valve guides and make sure it is a good honda motorcycle person doing it.

Have fun and report back

[newday777]

"is there a source in the GTA? (I’m DT)" GTA, DT???

[Scootch]

Might mean Greater Toronto Area  🥴😏

[denward17]

Read this thread, it is a sticky in this sub-forum:

http://forums.sohc4.net/index.php/topic,107040.0.html

[spmc]

"is there a source in the GTA? (I’m DT)" GTA, DT???

Might mean Greater Toronto Area  🥴😏

Winner winner haha, sorry yeah downtown Toronto.

Most common oil leaks in order
1 the rubber pucks under the cam towers

2 the studs and bolts holding the cam towers if the holes have been helicoiled or bolts mixed up

Rocker cover gasket can, and has been, fitted backwards

Tach drive seal


You say you will have the valves done, budget for exhaust valve guides and make sure it is a good honda motorcycle person doing it.

Have fun and report back

Big help, will check and double check!

Read this thread, it is a sticky in this sub-forum:

http://forums.sohc4.net/index.php/topic,107040.0.html

Thanks for the reminder I forgot about this thread!

[Tracksnblades1]

"is there a source in the GTA? (I’m DT)" GTA, DT???

Might mean Greater Toronto Area  🥴😏

Winner winner haha, sorry yeah downtown Toronto.

Most common oil leaks in order
1 the rubber pucks under the cam towers

2 the studs and bolts holding the cam towers if the holes have been helicoiled or bolts mixed up

Rocker cover gasket can, and has been, fitted backwards

Tach drive seal


You say you will have the valves done, budget for exhaust valve guides and make sure it is a good honda motorcycle person doing it.

Have fun and report back

Big help, will check and double check!

Read this thread, it is a sticky in this sub-forum:

http://forums.sohc4.net/index.php/topic,107040.0.html

Thanks for the reminder I forgot about this thread!

BryanJ has probably already identified your oil seep. However you would’ve had to replace those rubber pucks after removing them to get to the hidden head bolts during your last head gasket replacement.

[bryanj]

True but hondaman has identified there was a batch of too thin ones that leaked and was hondabond or any compound used under them

[spmc]

True but hondaman has identified there was a batch of too thin ones that leaked and was hondabond or any compound used under them

Yes I did replace them and used Hondabond last time if memory serves as I remember them being called out as a sore spot. Re-reading the leak free top end thread refreshed a bunch of the stuff I hadn't thought about in 6 years since I did the work. I think I payed special attention to those but they were aftermarket from an Athena kit if I recall so who knows, maybe 1 is off. Thinking about it more now I alway thought the leak looked like it originated up around the No. 4 spark plug and if I'm not mistaken that is the general area a leak from one of those damn pucks would present, maybe?

[BenelliSEI]

Regarding your leak location, “around the #4 spark plug”. I had the same issue on the cb750K4 engine that I’m using in my Rickman Honda CR project. This engine coincidentally had been “freshly rebuilt” by a very well known shop in the GTA!

It was not the rubber pucks that were leaking, but the cam box hold down hardware. The threaded hole in the cylinder head goes through the casting into an airflow space. Oil was weeping down the threads and out. A small dab of Hondabond on the threads cured it.

[BenelliSEI]

Go to page six of my Rickman Project Post to see the full details of the oil leak….

« Reply #129 on: March 23, 2020, 06:10:04 am »
QuoteModifyRemove
OIL LEAK! Yesterday I spotted a small oil leak on the hoist table. The RHS frame down tube, clutch cable and “triangle” engine mounting plate were spotted with oil. Started the bike up and there is a small drip hanging off the head fin, next to #4 exhaust, inside stud. LASH was visiting and suggested a leaking cam box stud. It’s either that or a “puck” rubber gasket under the cam block.

So, apparently one advantage of the Rickman frame is the space to work on the top end. We’ll see. I’m going to try resealing the studs in the area (quick fix?) or eventually pull off the cam and do it all, in the frame. We’ll see.
[/quote]

[spmc]

Regarding your leak location, “around the #4 spark plug”. I had the same issue on the cb750K4 engine that I’m using in my Rickman Honda CR project. This engine coincidentally had been “freshly rebuilt” by a very well known shop in the GTA!

It was not the rubber pucks that were leaking, but the cam box hold down hardware. The threaded hole in the cylinder head goes through the casting into an airflow space. Oil was weeping down the threads and out. A small dab of Hondabond on the threads cured it.

Love this info! Will definitely add that hondabond!

[spmc]

Regarding your leak location, “around the #4 spark plug”. I had the same issue on the cb750K4 engine that I’m using in my Rickman Honda CR project. This engine coincidentally had been “freshly rebuilt” by a very well known shop in the GTA!

It was not the rubber pucks that were leaking, but the cam box hold down hardware. The threaded hole in the cylinder head goes through the casting into an airflow space. Oil was weeping down the threads and out. A small dab of Hondabond on the threads cured it.

And just to make sure I'm doing the right bolt were you referring to the bolt my index is pointing to or my pinky?

[spmc]

Also trying to figure out the issue I was having with the number 3 cylinder before the winter where it didn't seem to be firing (pipe wasn't hot, running poorly overall). I've got new coils caps and wires I'm going to replace the originals, but looking at the exhaust valves on 3 and 4 they have a white/beige soot on them,  I'm not experienced enough to translate what that means so would love any guidance/thoughts!

[spmc]

And lastly something a little worrying... As I was removing the cam holders and stuff I noticed some sitting in the groove next to the valve spring. It looks like tappet adjuster nut to me, but every one on the tappets were on and untouched. I didn't take this apart originally, I bought it with the top end torn down, but the valves were untouched when I rebuilt it, so maybe it bounced in there in the groove and I never noticed but a loose nut slopping around in there would surely do some damage would it not?

So it makes me think it fell in there while I was tearing it down, but I don't know where in the world this came from.

Anyone have any ideas?

[HondaMan]

That looks like a rocker adjuster locknut. It probably came off one of the adjusters and the Mr. WrenchIt working on it said, "Hey, I found the source of the tapping noise" and put another nut on the adjuster. The F2/3 engine was famous for loosening those, and here's why:
1. The top spring retainers for the extra-strong valve springs used in the F2/3 engine are not strong enough, and after years of heat-anealing by the engine they are now warped a bit, which can make vibrations that will loosen those nuts (and sometimes the springs will pull the keepers right thru the retainers, dropping the valve into the engine - bad day at best). An absolutely brilliant "fix" for this is Ken's (CylceX) Valve Spring Retainers that he sells now, about $100 USD, to replace the old stamped-steel ones. I've used many of them to 'fix' F2/3 engines.
2. The top-end oil leaks have 3 sources. One is noted above (the too-thin rubber pucks we all suffered form circa 2002-2008 or so). You can get good ones today from PartsNmore (Ontario) or CB750Supply (Florida, USA). The second source is the O-rings in the head gasket that [are supposed to] seal the oil fed to the top end. The new head gaskets made after 1990-something are all (ALL) thicker by at least 0.2mm over Honda's version (some of the MLS are even thicker than this) so you need to use a correspondingly thicker O-ring in those 2 ports: 2.6x10.8mm (Parker# 02-111) to make up the extra thickness with sealing pressure. I also mill the top of the cylinders down 0.010" on EVERY build to ensure the deck is flat, and have the head milled flat as well. This also helps improve the oil seal at those ports. The third place is: the bottoms of the cam bearing (rocker tower) studs that stick thru the head. These 4 studs have a long end of threads and a short end. The long end goes down into the head with sealant on the threads: many leak now from age, or were removed-reinstalled by someone who didn't use sealant.

[BenelliSEI]

Regarding your leak location, “around the #4 spark plug”. I had the same issue on the cb750K4 engine that I’m using in my Rickman Honda CR project. This engine coincidentally had been “freshly rebuilt” by a very well known shop in the GTA!

It was not the rubber pucks that were leaking, but the cam box hold down hardware. The threaded hole in the cylinder head goes through the casting into an airflow space. Oil was weeping down the threads and out. A small dab of Hondabond on the threads cured it.

And just to make sure I'm doing the right bolt were you referring to the bolt my index is pointing to or my pinky?

Index finger (ON MINE). When everything is apart and clean, poke a small poker in each hole. If the bottom is blind (sealed, not drilled right through) don’t worry about it. If you can see the end of your poker in an airway, that one needs to be sealed. Check ‘‘em all.

[spmc]

That looks like a rocker adjuster locknut. It probably came off one of the adjusters and the Mr. WrenchIt working on it said, "Hey, I found the source of the tapping noise" and put another nut on the adjuster. The F2/3 engine was famous for loosening those, and here's why:
1. The top spring retainers for the extra-strong valve springs used in the F2/3 engine are not strong enough, and after years of heat-anealing by the engine they are now warped a bit, which can make vibrations that will loosen those nuts (and sometimes the springs will pull the keepers right thru the retainers, dropping the valve into the engine - bad day at best). An absolutely brilliant "fix" for this is Ken's (CylceX) Valve Spring Retainers that he sells now, about $100 USD, to replace the old stamped-steel ones. I've used many of them to 'fix' F2/3 engines.
2. The top-end oil leaks have 3 sources. One is noted above (the too-thin rubber pucks we all suffered form circa 2002-2008 or so). You can get good ones today from PartsNmore (Ontario) or CB750Supply (Florida, USA). The second source is the O-rings in the head gasket that [are supposed to] seal the oil fed to the top end. The new head gaskets made after 1990-something are all (ALL) thicker by at least 0.2mm over Honda's version (some of the MLS are even thicker than this) so you need to use a correspondingly thicker O-ring in those 2 ports: 2.6x10.8mm (Parker# 02-111) to make up the extra thickness with sealing pressure. I also mill the top of the cylinders down 0.010" on EVERY build to ensure the deck is flat, and have the head milled flat as well. This also helps improve the oil seal at those ports. The third place is: the bottoms of the cam bearing (rocker tower) studs that stick thru the head. These 4 studs have a long end of threads and a short end. The long end goes down into the head with sealant on the threads: many leak now from age, or were removed-reinstalled by someone who didn't use sealant.

I can't tell you how valuable this info is! I was planning on getting both the cylinder and head resurfaced and this confirms the necessity. I got the kit from 4into1 so I will check the head gasket and the o rings and make the correct adjustments. I believe I gave the pucks a good coat of hondabond around the edges last time but I'll pay very special attention this time. Also would be a real shame to drop a valve into the motor so I'll check out the CycleX retainers! Thanks again very much!

[spmc]

Index finger (ON MINE). When everything is apart and clean, poke a small poker in each hole. If the bottom is blind (sealed, not drilled right through) don’t worry about it. If you can see the end of your poker in an airway, that one needs to be sealed. Check ‘‘em all.

Will absolutely do! Thanks for the clarity!

[spmc]

Okay, any machine shop in my part of town is a black hole of time in terms of when "they could get to it". I don't know why everyone doesn't open an machine shop if the demand is so high, seems like a license to print money!

Anyway I digress. I wanted to check the exhaust valves/guides to see if in fact they need replacing as reading about the F2 engine the wisdom seems to be that they wear out commonly. So got the exhaust side disassembled and aside for the seals being hard as a rock everything looks to be in really good shape to my untrained eye. I checked all four valves and there's next to no play on any of them. Judging from the video below do you think I'm okay to skip the exhaust guides replacement I was thinking of doing?
https://drive.google.com/file/d/1kufxmEv1pqoDHvvp-dv6ZQRwVYcI0YFx/view?usp=share_link

Secondarily, and due to my untrained eye, how do these valves look to you guys? Clean em up and run em or replace?
https://drive.google.com/drive/folders/1eIUJ3EHpFv0QeRGP0aL7FAj90jMG_jQc?usp=share_link

And lastly there was some odd yellowing on the spring under the retainer, anything to worry about or just common?
https://drive.google.com/file/d/10bxbHR_M1hDZKffXpTzx1-gew8946EiJ/view?usp=share_link

[grcamna2]

subscribed

[MRieck]

That yellow paint indicated which end of the spring goes on top. When the factory is building hundreds of heads and has thousands of springs it makes it easy to know which end goes up.
 That 45 degree valve face is hammered. The contact width should be .060....that looks to be about double that and it is recessed as well. Dynoman sells F2 valves for cheap and they are better quality. OEM Honda valves are as soft as a grape.

[HondaMan]

Okay, any machine shop in my part of town is a black hole of time in terms of when "they could get to it". I don't know why everyone doesn't open an machine shop if the demand is so high, seems like a license to print money!

I've  worked for a couple of machine shops (building machinery, not engines - well, not 'officially' engines, we did a few there) here in the Denver Metro area over the last 30+ years. Ever since Obama was king, they have been subjected to more and more and more REAL expensive regulations concerning their cutting and washing fluids, instigated by the 'O' administration. In the shop I use now almost half of the shop's floorspace has had to be reconfigured and dedicated to newly-required EPA crap to 'preclean' solvents, etc., from their parts washing machines, alone. Their cutting fluids now have to be handled like they were some sort of instantly-lethal liquid (or something), totally outrageous requirements. Most of the stuff isn't even toxic if you drank it full strength. All of this nonsense slows them down on every step they do, and costs them a fortune in overhead $$ just to support operations that have been done for 100 years without hurting nor killing anyone.

So, no one wants to open a new one around here, while the population increases. Hence, lead times do, too.
If you open one, be prepared: the customers will line up all the way down the block on Day 2 after word gets around.

[spmc]

Okay, any machine shop in my part of town is a black hole of time in terms of when "they could get to it". I don't know why everyone doesn't open an machine shop if the demand is so high, seems like a license to print money!

I've  worked for a couple of machine shops (building machinery, not engines - well, not 'officially' engines, we did a few there) here in the Denver Metro area over the last 30+ years. Ever since Obama was king, they have been subjected to more and more and more REAL expensive regulations concerning their cutting and washing fluids, instigated by the 'O' administration. In the shop I use now almost half of the shop's floorspace has had to be reconfigured and dedicated to newly-required EPA crap to 'preclean' solvents, etc., from their parts washing machines, alone. Their cutting fluids now have to be handled like they were some sort of instantly-lethal liquid (or something), totally outrageous requirements. Most of the stuff isn't even toxic if you drank it full strength. All of this nonsense slows them down on every step they do, and costs them a fortune in overhead $$ just to support operations that have been done for 100 years without hurting nor killing anyone.

So, no one wants to open a new one around here, while the population increases. Hence, lead times do, too.
If you open one, be prepared: the customers will line up all the way down the block on Day 2 after word gets around.

Haha, well now I'm out!

[spmc]

That yellow paint indicated which end of the spring goes on top. When the factory is building hundreds of heads and has thousands of springs it makes it easy to know which end goes up.
 That 45 degree valve face is hammered. The contact width should be .060....that looks to be about double that and it is recessed as well. Dynoman sells F2 valves for cheap and they are better quality. OEM Honda valves are as soft as a grape.

Ah that makes sense, and glad I asked as I wouldn't have thought there was a right/wrong way up!

I'll order a set of new exhaust valves ASAP.

[bryanj]

Sorry cant watch videos, with valves only just perceptible play between stem and guide is allowable, if you can see movement its probably too much.
We are talking way less clearance than cars here

[grcamna2]

Sorry cant watch videos, with valves only just perceptible play between stem and guide is allowable, if you can see movement its probably too much.
We are talking way less clearance than cars here

 

[spmc]

If the mating surfaces are clean and flat is there any need for liquid gasket as insurance or could that just cause other issues?

I just think a new gasket should be enough to keep everyone sealed no? Or does most everyone add a little liquid gasket on a rebuild?

[PeWe]

That yellow paint indicated which end of the spring goes on top. When the factory is building hundreds of heads and has thousands of springs it makes it easy to know which end goes up.
 That 45 degree valve face is hammered. The contact width should be .060....that looks to be about double that and it is recessed as well. Dynoman sells F2 valves for cheap and they are better quality. OEM Honda valves are as soft as a grape.

I have used F2 in valves in my K6 head.
The first set got mushroomed tips within 10000 km so the tips had to be grinded to take out.
Engine got new the year after. Same thing shortly.

So stock F2 valves are wrongly made. Cannot be hardened, soft as a mushroom.

Dynoman valves as Mike wrote.
They also have titanium retainers that keep up better.

[spmc]

That yellow paint indicated which end of the spring goes on top. When the factory is building hundreds of heads and has thousands of springs it makes it easy to know which end goes up.
 That 45 degree valve face is hammered. The contact width should be .060....that looks to be about double that and it is recessed as well. Dynoman sells F2 valves for cheap and they are better quality. OEM Honda valves are as soft as a grape.

I have used F2 in valves in my K6 head.
The first set got mushroomed tips within 10000 km so the tips had to be grinded to take out.
Engine got new the year after. Same thing shortly.

So stock F2 valves are wrongly made. Cannot be hardened, soft as a mushroom.

Dynoman valves as Mike wrote.
They also have titanium retainers that keep up better.

Justin installed the Cycle X retainers last night actually! Make it look a little more Mad Max haha.

[spmc]

The second source is the O-rings in the head gasket that [are supposed to] seal the oil fed to the top end. The new head gaskets made after 1990-something are all (ALL) thicker by at least 0.2mm over Honda's version (some of the MLS are even thicker than this) so you need to use a correspondingly thicker O-ring in those 2 ports: 2.6x10.8mm (Parker# 02-111) to make up the extra thickness with sealing pressure.

I'm having a hell of a time trying to find the right O-Ring to address the potential head gasket gap... If I'm correct you're referring to part no. 91310300000 which is 2.5x11? Can't find any source for a 2.6x10.8mm in Canada currently. And to make me more confused the rebuild kit I got from 4into1 has the following listed

91302-001-020 - O-Ring 30.8mm - x8 (tappet rings)
91305-323-000 - O-Ring 5.8 x 1.9mm - x4
91304-286-000 - O-Ring 61.8 x 2mm - x4 (Cylinder)

I'm assuming 2.6 x 10.8 is because you're thickening the ring by .2mm so that means you subtract .2 from the diameter right? Can I order this from a marine store or something?

[grcamna2]

The second source is the O-rings in the head gasket that [are supposed to] seal the oil fed to the top end. The new head gaskets made after 1990-something are all (ALL) thicker by at least 0.2mm over Honda's version (some of the MLS are even thicker than this) so you need to use a correspondingly thicker O-ring in those 2 ports: 2.6x10.8mm (Parker# 02-111) to make up the extra thickness with sealing pressure.

I'm having a hell of a time trying to find the right O-Ring to address the potential head gasket gap... If I'm correct you're referring to part no. 91310300000 which is 2.5x11? Can't find any source for a 2.6x10.8mm in Canada currently. And to make me more confused the rebuild kit I got from 4into1 has the following listed

91302-001-020 - O-Ring 30.8mm - x8 (tappet rings)
91305-323-000 - O-Ring 5.8 x 1.9mm - x4
91304-286-000 - O-Ring 61.8 x 2mm - x4 (Cylinder)

I'm assuming 2.6 x 10.8 is because you're thickening the ring by .2mm so that means you subtract .2 from the diameter right? Can I order this from a marine store or something?

Bump.  Yes,I hope HondaMan will give you a source for these.

[spmc]

The second source is the O-rings in the head gasket that [are supposed to] seal the oil fed to the top end. The new head gaskets made after 1990-something are all (ALL) thicker by at least 0.2mm over Honda's version (some of the MLS are even thicker than this) so you need to use a correspondingly thicker O-ring in those 2 ports: 2.6x10.8mm (Parker# 02-111) to make up the extra thickness with sealing pressure.

I'm having a hell of a time trying to find the right O-Ring to address the potential head gasket gap... If I'm correct you're referring to part no. 91310300000 which is 2.5x11? Can't find any source for a 2.6x10.8mm in Canada currently. And to make me more confused the rebuild kit I got from 4into1 has the following listed

91302-001-020 - O-Ring 30.8mm - x8 (tappet rings)
91305-323-000 - O-Ring 5.8 x 1.9mm - x4
91304-286-000 - O-Ring 61.8 x 2mm - x4 (Cylinder)

I'm assuming 2.6 x 10.8 is because you're thickening the ring by .2mm so that means you subtract .2 from the diameter right? Can I order this from a marine store or something?

Bump.  Yes,I hope HondaMan will give you a source for these.

Closest I can find right now is an SAE version which is

ID 0.437 or 11.09mm
OD 0.625 or 15.875
CS 0.103 or 2.616mm

Which the part number I got from them was also 02-111 so I'm guessing thats the one HondaMan was referencing
https://www.sealsonline.com/sealtech/en/2-xxx/81378-2-111-n70.html?search_query=2-111&results=9

So if that is the one I'll grab it, or rather a little more than 100 of em cause they have a minimum order of $15 haha

[spmc]

Okay can confirm I was able to source that odd oversize o-ring plus the goofy 3mm x 5.5mm ones for the studs on the F at SealTech Supply in Mississauga (sealsonline.com)

For any future lurkers here's the part numbers!