Author Topic: Two '77 CB750K projects... or maybe just one...  (Read 564 times)

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Offline onepieceatatime

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Two '77 CB750K projects... or maybe just one...
« on: March 21, 2019, 11:56:23 pm »
I suppose I should record my progress.
I bought 2 non-running, titled '77 CB750Ks and part of a K5 for $500.
I intend to work on both of these at the same time, and hopefully within the next 2 years have them on the road.
All 3 engines were stuck, I got the 2 '77s freed up with ATF/acetone and rocking the bikes in gear. The first one shot the ATF/acetone at least 15 feet across the garage and covered 3 other bikes with it. I figured out that I should put rags over the spark plug holes on the other one.
The one missing the exhaust, unfortunately the valves are not moving either, so that engine is going to have to come apart, and it will likely get an 836 kit in the process. That engine has already been apart at some point so I am curious to see what is in there.







All of this was included in the sale




« Last Edit: October 22, 2020, 01:56:29 am by onepieceatatime »
1972 CB750K
1974 CB450K7
1977 CB750K
1977 CB750K
1978 CB400A
1980 CB650C
1980 CB650
1982 CM450A
1997 GL1500SE

Offline onepieceatatime

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Re: Two '77 CB750K projects
« Reply #1 on: March 22, 2019, 12:02:14 am »
The grey bike had the bags and fairing on it when PO bought it, but he took them off. I plan on putting them back on, but may use another fairing that I have.
I have gathered a few other parts, and several rebuild kits, but know I need a few more rebuild kits that I have not bought yet.
The other fairing:

I want to remove the comstar wheel and put these on:


and one of these tanks:


and this Corbin-Gentry seat that I bought for it:
1972 CB750K
1974 CB450K7
1977 CB750K
1977 CB750K
1978 CB400A
1980 CB650C
1980 CB650
1982 CM450A
1997 GL1500SE

Offline onepieceatatime

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Re: Two '77 CB750K projects
« Reply #2 on: March 22, 2019, 12:10:45 am »
The air-brushing was done by a place called Vantastics in Carlisle, PA (it is signed). This is the one that will have to have the engine torn apart, and will likely get the 836 kit. It has 6" oversized forks with a fork brace, but  they are bad, so I got some new stock size fork tubes for it. It also has Lester wheels which I plan to keep on it.
I need an exhaust for it still. I either want to find a factory exhaust for the grey bike and use its headers and these NOS Jardines on the black one, or find some other period correct aftermarket exhaust to go on it.

This bike is getting this Corbin-Gentry seat:

some finned engine covers:

and probably these floorboards and highway pegs:

The speedometer is messed up so it will probably get some '75 gauges.


And the other set will go on the grey bike to replace the DOHC gauges that are on it now.
 
1972 CB750K
1974 CB450K7
1977 CB750K
1977 CB750K
1978 CB400A
1980 CB650C
1980 CB650
1982 CM450A
1997 GL1500SE

Offline onepieceatatime

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Re: Two '77 CB750K projects
« Reply #3 on: March 23, 2019, 06:14:27 pm »
Before I spend any money on new spokes, can anyone confirm that the front wheel from a '76 CB550 and the rear wheel from a CB750K5 will fit the K7? I know I'll have to switch to a 630 sprocket on the rear, but otherwise will it all work?
1972 CB750K
1974 CB450K7
1977 CB750K
1977 CB750K
1978 CB400A
1980 CB650C
1980 CB650
1982 CM450A
1997 GL1500SE

Online seanbarney41

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Re: Two '77 CB750K projects
« Reply #4 on: March 23, 2019, 08:41:02 pm »
On the back, you have to keep the k7 sprocket carrier with the k7 engine so that front and rear sprockets align...use the k7 wheel spacers with that too.
If it works good, it looks good...

Offline onepieceatatime

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Re: Two '77 CB750K projects
« Reply #5 on: March 23, 2019, 10:13:18 pm »
On the back, you have to keep the k7 sprocket carrier with the k7 engine so that front and rear sprockets align...use the k7 wheel spacers with that too.

Thank you. will the one from the comstar fit the spoke wheel?
1972 CB750K
1974 CB450K7
1977 CB750K
1977 CB750K
1978 CB400A
1980 CB650C
1980 CB650
1982 CM450A
1997 GL1500SE

Online seanbarney41

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Re: Two '77 CB750K projects
« Reply #6 on: March 23, 2019, 10:27:53 pm »
On the back, you have to keep the k7 sprocket carrier with the k7 engine so that front and rear sprockets align...use the k7 wheel spacers with that too.

Thank you. will the one from the comstar fit the spoke wheel?
yes it should, as long as the comstar is from a 77/78 cb750f..but you do know that the k7 never came with comstars?
If it works good, it looks good...

Offline onepieceatatime

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Re: Two '77 CB750K projects
« Reply #7 on: March 23, 2019, 10:33:59 pm »
On the back, you have to keep the k7 sprocket carrier with the k7 engine so that front and rear sprockets align...use the k7 wheel spacers with that too.

Thank you. will the one from the comstar fit the spoke wheel?
yes it should, as long as the comstar is from a 77/78 cb750f..but you do know that the k7 never came with comstars?

Yeah, that's why I want to get them off of it. I have no idea what the comstars are originally from.
1972 CB750K
1974 CB450K7
1977 CB750K
1977 CB750K
1978 CB400A
1980 CB650C
1980 CB650
1982 CM450A
1997 GL1500SE

Online seanbarney41

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Re: Two '77 CB750K projects
« Reply #8 on: March 23, 2019, 11:03:39 pm »
okay, I went back and looked at your pics of the grey bike...that rear wheel is what as known as a reverse comstar.  It came on certain 79 and later dohc4's, certain models of sohc 650, and some honda twins...so no idea if that sprocket carrier will work or not
If it works good, it looks good...

Offline onepieceatatime

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Re: Two '77 CB750K projects
« Reply #9 on: March 23, 2019, 11:13:23 pm »
okay, I went back and looked at your pics of the grey bike...that rear wheel is what as known as a reverse comstar.  It came on certain 79 and later dohc4's, certain models of sohc 650, and some honda twins...so no idea if that sprocket carrier will work or not


Thanks for checking. I guess I'll figure it out when I get to that point. The reverse comstars might end up as spares for my 650, if they will work for that. Either way I want to have spokes on the K7.
1972 CB750K
1974 CB450K7
1977 CB750K
1977 CB750K
1978 CB400A
1980 CB650C
1980 CB650
1982 CM450A
1997 GL1500SE

Offline onepieceatatime

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Re: Two '77 CB750K projects
« Reply #10 on: October 22, 2020, 01:47:27 am »
I guess it is time to resurrect this thread. I have finally started working on one of the K7s (the black one with the air brushed tank).
A friend wants the grey one, but wants help getting it going, so it may end up in this build thread, or one of his if he joins up here.

I have been accumulating parts that were missing, and rebuild kits for brakes, carbs, etc.

I rebuilt the forks (actually a different set of lowers too, since I hate chrome) with new stock length uppers, bought a weldless frame kit, cut the frame to be able to pull the top end off in frame.
I have the master cylinder and caliper taken apart and ready for cleanup and rebuild.
I decided to use the K5 gauges on my K2 Ol' Sarge project, so I bought another good set of K7 gauges.

The carbs are seized solid on this bike, but I bought a good rebuilt set a while back, so I can put those on and worry about these ones later.
I did buy a set of factory 4 into 4 exhaust pipes for the grey bike, so the Jardines are going on this one.

I will be replacing the chrome covers as I get this engine ready to run again. I got a black '78 F head cover to put on this engine, and will be putting a set of finned covers in place of the other covers.

I pulled the head cover off. There is plenty of orange silicone for me to clean up before I put it back together. the exhaust valve on #4 is stuck wide open.

The cam and rockers look ok, and I pulled the head off to have a look at the cylinders and pistons.

There is a bunch of gunk in #4.

A closer look reveals what looks to be rolled up leaves.

I also noted a nicely patinaed cam chain tensioner. A new one is on the way, along with a cam chain and gasket kit.


No major dings in the pistons, but I'll still pull the cylinders off and check piston to cylinder tolerance, since there is plenty of orange silicone at the bottom of the cylinders to clean off too.
Here is the head with no cam present. Looks like #3  exhaust is stuck partly open too.


I think I'll end up sending this head out for new valve guides, valve work, etc.
1972 CB750K
1974 CB450K7
1977 CB750K
1977 CB750K
1978 CB400A
1980 CB650C
1980 CB650
1982 CM450A
1997 GL1500SE

Offline 754

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Re: Two '77 CB750K projects... or maybe just one...
« Reply #11 on: October 22, 2020, 12:15:19 pm »
With the  amount of rust on that tensioner, I would be really wondering what the inside of cases looks like,  not the gears  so much as the bearings ..
Maker of the WELDLESS 750 Frame Kit
dodogas99@gmail.com
Kelowna B.C.       Canada

My next bike will be a ..ANFOB.....

It's All part of the ADVENTURE...

73 836cc.. Green, had it for 3 decades!!
Lost quite a few CB 750's along the way

Offline onepieceatatime

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Re: Two '77 CB750K projects... or maybe just one...
« Reply #12 on: October 22, 2020, 03:09:49 pm »
With the  amount of rust on that tensioner, I would be really wondering what the inside of cases looks like,  not the gears  so much as the bearings ..

Yep, I was hoping to get away with just doing top end stuff on this one, but seeing that made me realize that I have to split these cases for a proper inspection.
1972 CB750K
1974 CB450K7
1977 CB750K
1977 CB750K
1978 CB400A
1980 CB650C
1980 CB650
1982 CM450A
1997 GL1500SE

Offline PeWe

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Re: Two '77 CB750K projects... or maybe just one...
« Reply #13 on: October 24, 2020, 04:22:52 am »
Good idea to take all apart for a good clean.
If pistons/rings/bores are worn, cheap alternative available from Cruzinimage.
My K2 has K7/K8/F/F1 (392) pistons. 61.5mm (+0.5).
Max 0.025mm total clearance.

https://www.cruzinimage.net/2017/08/17/77-78-honda-cb750k-k7-k8-0-5mm-over-size-pistons-set/

If any of the bores have much rust, go bigger. I had to replace 2   sleeves due to the rust was deeper than expected on an old cylinder.

https://www.cruzinimage.net/2017/08/17/77-78-honda-cb750k-k7-k8-1-0mm-over-size-pistons-set-62-00mm/

Their clutch work fine too. My K2 has it (+56whp) and my K6 had too when 836cc and 81whp.
https://www.cruzinimage.net/2017/11/16/76-78-honda-cb750k6-cb750k7-cb750f2-clutch-friction-plate/

When apart replace all chains and tensioners. Stock Honda tensioners.

My K2 build got BMW timing chains as primary chains (2 chains needed) which are stronger than stock. Some sell these for 2-3 x price as HD chains.
These chains can be found cheap here at internet car part dealers.

Details
BMW 530 d,  184 HP,  [E39],  Production: 1998/08 - 2000/09,  Engine code: M57 D30 (306D1)
Original partno: 11 31 2 248 729

You can find more about primary chains in this thread
http://forums.sohc4.net/index.php/topic,154183.100.html
« Last Edit: October 24, 2020, 04:25:28 am by PeWe »

Offline onepieceatatime

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Re: Two '77 CB750K projects... or maybe just one...
« Reply #14 on: October 24, 2020, 05:02:37 am »
Thanks for the info Pewe. Looks like I have more reading to do.

Yesterday I ordered a set of primary chains, just in case either engine I currently am working on needs them, and 2 primary chain tensioners, one for this engine and one for my K5 engine. It seems as though you are suggesting I just replace the chains as a matter of principle since I am in there anyways.

I have a set of RC 64mm pistons and rings that I might put in this engine, and a set of 1st over NOS pistons and rings, and a nameless 836 kit that I bought 2nd hand but unused which includes that bored cylinders. Unfortunately none of them are the K7/K8 style pistons, so I need to figure out what to do to the head, or replace the head to use them. I am waiting on my ball hone to show up so I can clean up these cylinders as well as the K5 cylinders. Once I have done that I will check the piston to bore clearance and make a solid decision on how to proceed.
I still have the K2 engine that I have to tear down and update as well. Right now, my inclination is to put the RC parts in the K7, the 836 kit in the K2 engine and either stock or first over in the K5 engine. The K5 is going in my K2 frame, but the K2 will eventually be swapped in once I get the oil filter bolt threaded bung welded back onto the lower case.
1972 CB750K
1974 CB450K7
1977 CB750K
1977 CB750K
1978 CB400A
1980 CB650C
1980 CB650
1982 CM450A
1997 GL1500SE

Offline PeWe

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Re: Two '77 CB750K projects... or maybe just one...
« Reply #15 on: October 24, 2020, 05:54:18 am »
Better to overdo it instead of redo it shortly after.
Pull engine and take apart cost some in gaskets and seals only. Plus oil. Do it again new gaskets and seals.
MLS and RCS gaskets can be reused which is one reason to use them.

If using old pistons. Check if ring groves are worn. Rings should not have play up-down.

Offline onepieceatatime

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Re: Two '77 CB750K projects... or maybe just one...
« Reply #16 on: October 24, 2020, 06:06:51 am »
Better to overdo it instead of redo it shortly after.
Pull engine and take apart cost some in gaskets and seals only. Plus oil. Do it again new gaskets and seals.
MLS and RCS gaskets can be reused which is one reason to use them.

If using old pistons. Check if ring groves are worn. Rings should not have play up-down.

Thanks.
I haven't been this far into an engine before, so I don't have the experience with pistons, cylinders, etc. The most I have done is heads, valves, timing chains, etc.
1972 CB750K
1974 CB450K7
1977 CB750K
1977 CB750K
1978 CB400A
1980 CB650C
1980 CB650
1982 CM450A
1997 GL1500SE

Offline onepieceatatime

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Re: Two '77 CB750K projects... or maybe just one...
« Reply #17 on: October 29, 2020, 07:52:09 am »
I didn't do anything too exciting last night. I took apart, cleaned, and rebuilt the front caliper and master cylinder for both this bike and the K2. Then I searched through my bolt bins for some fender and caliper mounting bolts that were missing. I messed around with a couple other little things in the garage, then bent the mount on the kickstand back straight and replaced the missing spring on it. Then I pulled the cylinders. The rods look as lovely as the cam chain tensioner. I guess next time I am in the garage (after I finish the Subaru, since got the other parts I was waiting on) I'll have to clear some bench space for this engine to come out of the frame and be split apart.
1972 CB750K
1974 CB450K7
1977 CB750K
1977 CB750K
1978 CB400A
1980 CB650C
1980 CB650
1982 CM450A
1997 GL1500SE