f2 rebuild...help...

[whiteylfc]

Can anyone help?..I took apart a 26k mile cb750 engine in my Phil Read Replica and had the crankcases bead blasted. ...now it's going back together I can't remember whether there should be any of the 3 semi circular clips (?)on the 3 bearings on the main shaft to the drive sprocket.There is a groove in the top and bottom crankcases.secondly...when I finally put the 2 crankcase halves together,should I put any bonding on the joints?I don't remember their being any when I split the crankcases...many thanks John white

[K2-K6]

The manual shows three location semi circular collars fitted to the top of the gearbox mainshaft, this is fitted into the top crankcase with it upside down and then the bottom case placed onto it for assembly.
They use a sealant between the cases,  there's differing opinions as to which is the best choice. Someone may be able to offer a current choice to help you.

[adriangsmith]

threebond works well. Ive used it on 2 engines so far and had no leaks or weeps.

[whiteylfc]

COLLARS.....I couldn't think of a word to describe them..!!I could see them on exploded diagrams on the Internet but couldn't work out why there would be a groove in the lower crankcase half is something didn't go into it.I bought and stripped another f2 engine and I don't remember that having any collars in it which is what threw me.Is Honda bond any good?    Many thanks

[Trigger]

I call them Half Rings  Should fit in the casings and early 750's had 5 of them, 2 being on the final drive.

[K2-K6]

Yeh Trigger,  I didn't know what to call them either. Guess they are more rings as they're like half a piston ring in large scale.

The bottom cases have the groove as well as during machining it's not possible to bore the groove halfway round because the crankcase are machined bolted up as a pair to ensure accuracy and tolerance is achieved whiteylfc. Easiest route during production is to leave that lower half there but redundant, looks like something should be in there later though.

[MrDavo]

The half rings (aka oriental hobbits) stop your gearbox clusters from wandering sideways. As you say you can have more slot than ring, but you shouldn't have none.

I put my crankcases back together using a tube of Harley Bond I had left over, I don't think it was any the wiser.

[K2-K6]

"wandering gearbox clusters " seem eye wateringly painful,  you can probably get ointment for that,  or perhaps syrup of figs may help 

It's the clutch mech that tries to push that shaft sideways that's the principal reason for the design. You get similar thrust resistance in car cranks to stop the clutch pushing the crank along as well.

There must be a double meaning in "thrust resistance " I'm sure 

[whiteylfc]

Cheers boys...thrust resistance!!!sounds like a cheap date gone wrong...looks like I can torque down the conrod bolts and put the lid on this thing..👍