1982 CB750F...Better Devil

Jimbonaut

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Dropped the seat pan off at my upholsterers yesterday, had this beauty parked up in the shop -



60's Continental, definitely a bucket list car. Thing is, this beast is in no way small and he's re-doing a lot of the upholstery. I guess I'll just have to be patient.

Also picked up some Spraymax 2K satin clear - hope to get the fenders, side covers and a few odds and sods painted over the weekend. 35 degrees here today in the shade, that's over 100 in the blazing. Hotter than the hinges on the gates of hell's whorehouse. Riding the bike yesterday (similar temps) and damn it was something. I'm all for hot weather, but fully kitted up on a bike in slow moving traffic is...hallucinatory at best.
 
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Jimbonaut

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The cylinder stud o-rings showed up last week - I was going to paint the fenders and side covers but the weather took a dump today so I turned attentions to the motor. Deep breath, round two. New OEM base gasket, no dicking about with jobber shite this time -



The OEM cylinder stud o-rings are a considerably different size to the jobber ones (OEM on the right) -



Piston ring gaps all in the right places, lowered the cylinder block - without an extra set of hands lying around I use cable ties on the outer studs to help hold the block in place -



Ease it down over 2 and 3 pistons at TDC, everything going swimmingly -



until the motherf*cking bastard of a sh*t sucking f*ck knuckle w*nk tw*tting cam chain tensioner acorn nut fell into the lower case when I was loosening it. Bad fucking scene. Even worse because I did the exact same thing last time, except that time it was the washer. Turns out the washer is worse to dig out - it's lighter and not magnetic. Still, had to drop the pan and mercifully the little shite was in there. Anyone reading this working on a CB750 engine - don't do what I did, twice. Thread the upper acorn and washer onto the tensioner thread, leave the lower one off until the cylinder in seated. That way you can push the tensioner inside the lower case as you're lowering the cylinder (it won't clear if both acorn nuts are tightened) , and then thread the lower nut once you're done.

Bollocks.

However -

When I dropped the pan I was that there was a bunch of aluminium shavings in there too, not chunks but tiny shavings. I think they've come from one of the cam holders - I switched out the 750 cams for 900 cams and maybe there was a slight clearance issue - on inspection one of the holders is definitely a bit scarred. Cleaned out and re-installed the pan, got the block installed, with the correct head gasket this time -



then the head and then torqued up the bolts to spec.



Praying that ally in the pan was from that cam holder.
 
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Jimbonaut

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My mate Jimmy when he saw the junk in the pan - "there's more glitter in there than a 10 year old's birthday party".

Not what you want to hear. I'll take a photo of the cam holder later - I don't have any where near the experience to know for sure, but I think it's a clearance issue between the 900 cam and one of the holders. The head itself looks fine, just one of the holders. I'm thinking once that cam has done its dirty work to that holder then it should be ok? I'll drain and change the oil several times in the first few kilometres and get whatever crap I can out. Any thoughts?
 

Jimbonaut

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Another hot and humid one. If there's another place on earth with an 75 degree C spread between summer and winter then shit, good luck to them too.

Got the cams and top end buttoned up. Getting the hang of this now, but really hope that's the last time for this lump. This is the scoring on the cam holder and head (maybe it wasn't quite so fine after all) -




- pretty sure neither were like that before. So this time I borrowed some way thicker assembly lube (Bel Ray) and gave all the cam journals and camshafts themselves a thorough coat. Cam installation went fine, punch marks on the cam sprocket and notches on the cam aligned -







Neato. Guess time will tell if I got that noise taken care of, and hope to god whatever aluminum shavings I found in the pan aren't anything too awful. Hope the base gasket doesn't leak this time either.

Lots of hope happening here.
 

Maritime

Well-Known Member
Jim, after looking at this on the PC screen vs phone the issue with the oil leak was more than likely the aftermarket o-rings being oversized and not allowing the base to fully seat on the gasket.
 

Jimbonaut

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Something was skewing the clearances Mike for sure - the size difference between the o-rings wasn't huge but enough to bugger up the tolerances. I'll find out soon enough - one thing's for sure, I won't be using aftermarket parts on such crucial aspects of an engine rebuild again.

The good news is I can take apart the top end of a DOHC CB engine now fairly easily. Dumping nuts and washers into the cases is one way of honing your skills in that department.
 

Maritime

Well-Known Member
Its fun. I had to do plugs on the pilot and the back 3 are a bitch. Dropped the extension into the engine bay 3 times and finding it was not fun so I feel your pain. Lots of swears that afternoon
 

Jimbonaut

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DTT SUPPORTER
Lots of swears, all of them in fact. Some of them more them once and all of them loud. Miraculously (really, he was celestial in his timing) my moto mechanic mate came by to say hi just as I was hauling the engine onto its front to get at the pan. Another set of (qualified) eyes on the prize really was a godsend.
 
Glad you got it buttoned up. I cant even imagine the frustration of losing that bolt on a hot, sweaty day like that. At least for me patience runs thin on hot days.

Are those gaskets on the stator reusable? Mine has been sitting without oil for a little while and I wanted to give it a few hand cranks to start. That bolt on the stator is the right place to do that on these engines, right?
 

Jimbonaut

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Those gaskets are totally reusable, as long as you can get them off cleanly (sometimes they tear, or get stuck to one of the surfaces). You turn the crank from either side - although the bolt on the spark advancer side is bigger (24mm I think) and therefore stronger than the rotor bolt (17mm) - I prefer to turn the spark advancer bolt (counterclockwise). If you turn the rotor bolt on the other side of the engine instead, turn it clockwise.
 

Jimbonaut

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With the help of a burly mate got the engine muscled back into the frame -



I'll get the carbs installed tomorrow, the bike re-wired etc etc then fire up the bastard. Time will tell.
 

Jimbonaut

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DTT SUPPORTER
Brake lines are on - the rear line is a few inches too long so that'll have to go back and the front line from the master cylinder to the splitter may or may not work, undecided. The mc is a Nissin retro model, really nice unit. I'll upload some photos later.
 

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