Topic: CB 750 Project 1 - Rides Well but a few tweaks needed

[Terry in Australia]

Yeah mate, the cap nuts were used on most big fours in the 1970's, probably just to stop the outside studs from rusting to the nuts. Suzuki GS1000 OEM gasket sets came with 16 copper washers for the cylinder studs. From memory, the theory about using  captive nuts on the 750 head was to stop hot oil under the cam cover from seeping back down the studs, and dripping out thru the fins at the rear of the head/cylinder block? Cheers, Terry.    

[knottedknickers]

Terry, I didn't read a lot, I usually follow the theory that a picture tells a thousand words. I have an electronic copy of the factory workshop manual and it doesn't mention much, however I did find a picture that shows not cap nuts. I also checked the Yamiya site and he mentions them being for the sandcast and shows them on the outside studs.

Here's another picture (of my '76 top end):

You can see 'flange nuts', not 'cap nuts' (maybe they have a different meaning of 'cap nut' down under?) And I didn't have any copper washers--all steel. For what it's worth.

Oh, this might be worth something: do remember that the nuts and the bolts have different torques--15 lb/ft and 8 lb/ft respectively. I almost screwed that up... [pun intended]. Good luck! It's fun to see progress! ;-)

[timbo750]

Here is a picture of the cap nuts and the suggested location by Yamiya, they also mention they are recommended for sandcast engines. not going worry about them but I would like to know how you torque the short bolts on the head, I cant get a socket on to them.

[knottedknickers]

Here is a picture of the cap nuts and the suggested location by Yamiya, they also mention they are recommended for sandcast engines. not going worry about them but I would like to know how you torque the short bolts on the head, I cant get a socket on to them.

Oooh, funky. I've never seen that before; NOT that I've "seen it all"--not even close!--but just in my following other peoples' builds here, this is the first time. As for tightening the 6 short head bolts, I'm pretty sure I used a 1/4" drive socket and extension with a 3/8 x 1/4 reducer at my torque wrench.

[timbo750]

Yeah funky describes it well. I still am not sure why you need it on the outer studs as I would think that there is not much oil passing through them. From memory I didn't have a socket that would get on those outside bolts. Ended up using a screwdriver and spanner combination to get them loose.

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[Terry in Australia]

Here is a picture of the cap nuts and the suggested location by Yamiya, they also mention they are recommended for sandcast engines. not going worry about them but I would like to know how you torque the short bolts on the head, I cant get a socket on to them.

Yep, that proves that I'm not mad, ha ha! I know that I ditched the OEM 6mm bolts and replaced them with cap head screws (allen bolts) so I could torque them properly. It makes it way easier to get them in and out too. Looking good Tim, keep up the good work! Cheers, Terry.

[timbo750]

Glad you mentioned that Terry, I will get some 6mm alan bolts tomorrow. My local bolt shop calls them 'socket head' screws.

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[colined2]

Hello Timbo
Greetings from South Morang Melbourne.
I have been following your rebuild and thought you might be interested in some mods I am doing to a cylinder and cylinder head I am preparing for an 836 kit.
I have already replaced the 4 cam tower bolts with studs on my restored CB750 K4 so I know they work and I have replaced the bolts under the rubbers under the cam towers with studs and also the long bolt at the front of the head and the small one at the back.Easier to tighten down and less chance of stripping the thread in the cylinder head.
I have attached 2 pics. to show you what I mean.
Good luck with your rebuild.
Regards
Colin Edwards.

[colined2]

Having trouble sending attachments

[colined2]

cylinder head

[timbo750]

Colin
Where did you get the studs from, I have been searching this morning and having no luck. I have used 'Small Parts' before but if they don't have it in stock they are pricey.

[colined2]

Good morning Tim
I will take them out and measure them.
I used to be a spare parts manager at Peter Stevens Springvale and Geoff Taylor Motorcycles for many years in the past so I had a good idea that they were available. I went to my local Honda dealer (Moto GC in Thomastown) and gave them the part numbers and they got them in. They were only a couple of dollars each, but they had to go on back order which took a couple of weeks to get in. The only stud I had trouble with was the long one at the front of the cylinder. Jack the spare parts man at Evolution Motorcycles in Epping had a good secondhand one from his collection of old Honda parts. I also believe that a Kawasaki KV400 also has the same stud.  I will get back to you with the length and part numbers later this morning.
Colin

[timbo750]

Colin, thanks. I had a look on Yamiya and CMS and they dont have yhem listed so I figure they may be discontinued. I have also searching bolts supplier web sites and there is not much range in the 6mm available.

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[timbo750]

Colin don't go out of your way removing them, I can measure thread depths and also depth through the head. I think will have to start ringing around to find them.

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[colined2]

Tim me again
The replacement studs for the cam tower bolts are 6x65mm.Honda part number #92700-060650B (4 of)
The replacement studs that go under 4 of the rubber discs under the cam tower  are 6x50mm. Honda part number #92700-060500B (4 of)
The replacement stud for rear of cylinder is 6x50mm.Honda part number #92700-060500B. (The same as above).
The replacement stud for front of cylinder is 6x102mm.The Honda part number is #92700-061020B. Good luck finding this one. I know that a certain model Kawasaki KVF400 uses this size but I could not find the part number,you might have to ring around or spend some time on the internet looking for one. I was lucky and found a good secondhand one.
Hope this helps.
Colin

[timbo750]

Colin. That's awsome. I will let you know how I go.

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[timbo750]

Got them all ordered including enough for the next engine. They all needed to go on back order so hopefully have them in 2 weeks.

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[timbo750]

Also ordered flange nuts while as well. I will try to get all the engine and covers painted while I am waiting for these.

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[timbo750]

After looking closely at photos of Colins cylinders and head I realised a difference in the cylinders. Mine will not take small rubber dowels/sleeves around some of the studs. I know that this was not on the original K0 but  did it also disappear on later model engines?

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[Terry in Australia]

You've got an early top end on your engine Tim, I picked that when I saw your valve guides without valve guide seals, I'm not sure when they discontinued them, but I'm guessing K1 or very early K2. Same for your cylinder block, later (K3 onwards, but of course we didn't get K3-K5 in Oz, we jumped straight from K2 to K6) cylinder blocks had bigger dowels and seals than on the earlier engines, to stop any possible oil leaks.

As you've seen, the CB750 "evolved" over it's 9 year life, I can't remember how many subtle mods there were, but there were a lot. No biggie, if you torque your head properly, then re-torque it again before you install it, it won't leak. Cheers, Terry.

[timbo750]

Thanks Terry. I was considering changing the studs and nearly did but I shied away for fear of breaking one and having to get it machined out. Now I am wishing I did so I can torque without fear of a leak.

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[timbo750]

The other thing I would like to do before assemply is straighten a fin on the head. Its not baddly bent but I am painting the head and cylinders black and would like to sand the fins back and the bent fin is at one of the front corners.
I  was thinking of warming the engine in the oven to about 70 to 80 degrees C. They try to manipulte the fin with additionalheat from a heat gun. If the chance of breaking the fin is too high then I wont try,  so someone please let me know if I should not try this method.

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[Terry in Australia]

Best of luck with that Tim, the fins on our engines are usually very brittle, and require way more heat than that to make them soft enough to manipulate.

I heat cylinder blocks to around 200 deg C to pop out the sleeves and I can tell you that's not even close to hot enough. If you've got an oxy/acytelene torch (not just a gas torch, you need the oxy to increase the heat to soften the alloy) you can give it a go, but be careful even then, you could do more damage than good. Sucks, don't it? Cheers, Terry.  

[timbo750]

I thought it was a long shot. I was of the thinking that the bent most likely happened when the engine was hot and got knocked and that the end of a fin would only be about 100c.

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[Terry in Australia]

Yeah, it always surprises me that you can bend a fin by accident that will then break when you intentionally try to straighten it. Yes I understand that some metals become more brittle the more you try to manipulate them, but even so.......