HELP CB750 SOHC Only turns 1 & 1/2 rotations (540 degrees)

Frankenfe

Frankenfe

Coast to Coast
I picked up a 1975 CB75F0 engine for my current build. Cosmetically a Very nice engine, but there is a problem.

The Crank will only turn 1 & 1/2 rotations (540 degrees) before it hits or stops against something. it can be turned 1 & 1/2 turns either direction lock to lock.

I am very suspicious that it has to do with the kick start gearing / return spring, as it does not seam to operate properly. won't return fully and does not dseem to provide a "Full Stroke".

I would like to adress this issue before anything else.

1) What could cause this scenario?
2) If it is the kick start, would it possibly be a bad tooth on the kick start gear? or simply an issue with the return spring?
3) If it is the Kick Start gear, this requires splitting the case, Correct?

Anyone who has experienced and resolved this issue, I would appreciate your advise.
 
Any number of bad things can cause it. Like you mentioned, screwed up and/or missing teeth on any of the gears. Dropped valve would probably be my biggest worry though. You're definitely going to want to disassemble that thing.
 
Sonreir, thanks for the reply. I too cosidered a valve had dropped, or badly adjusted valve, and made sense to me considering the 1 & 1/2 rotations.

If I am visualizing correctly though, wouldn't a dropped valve restrict rotation to one revolution or less?

but an over adjusted valve only occur @ 1 & !/2 rotations, on the exhaust stroke for example?

I did pop the vale cover and all lloks good up there.

This engine has few miles on it and I am hoping to do only a focused tear down to resolve the issue.
 
I would say cam timing.
crank has to turn twice for cam to turn once.
Check cam bolt isn't backed out
Top end will look good if you remove cam cover, you'll have to remove rocker arms to find out if valve is damaged though.
 
Thanks all for chiming in. I will dig in a little deeper up top. Specifically Cam Chain Tension. and paying particular attention to the valves that function fully and the valve it is on at lock up. Again if I am visualizing right, I would think Cam Timing would render issues in less than 1 & 1/2 Turns. Even if cam and crank rotate at 2 to 1 rotation that still would put 4 valves out of time and I would think restrict crank rotation to under 1 & 1/2 turns.

I really think the fact that it is exactly 1.5 turns is the key to the problem.

Does anyone know the ratio of a full kick stroke to crank revolutions?
 
Why don't you just pull the right side cover off and look inside? You could do that in less time than reading this thread. <G>

Seriously, if you feel there is a problem with the kick start anyway, then look in there before you start committing to buying a bunch of engine gaskets.
 
Alpha, thanks for…….? Thought it was the other Café site that had all the Bored Post Flamers. How long did it take you to read a 1 page 6 post thread? I would assume you took the time to read this because you were either hoping to learn something or had something to actually contribute, instead of just making it unnecessarily longer.

Yea, I will be pulling the side off since there is obviously an issue with the Kick, and I still hope someone with some real knowledge can answer my specific questions I posted. 1) Ratio of a full kick stroke to crank revolutions. 2) Confirmation it will take splitting of the case if I need to address the Kick Gear or Shaft. I know there is a Pin that bridges the cases that acts as a retainer for the shaft, but maybe someone has a “trick” way to do it.

But since I have plenty to work on before I start on the engine I thought I would post this to get some constructive suggestions on “What would cause this Scenario” or possibly find “Anyone who has experienced and resolved this issue” The reason for this post is to hopefully narrow the possible cause to “only a focused tear down to resolve the issue” and NOT “committing to buying a bunch of engine gaskets” as you suggest.
 
Ya know what, you arrogant little shit... Go fuck yourself.
I gave you good advice, and you act like a turd. Way to fuckin' go!
 
I guess I should have expected the articulate response you just posted after the obvious "Advice" you rendered. I guess it is hard to have a battle of wits with an unarmed person.

Bitchin' Rat tail by the way, bet it gets you lotsa babes at the local bowling alley lounge.
 
We will let this thread speak for itself:

TROLL = Someone who gets pleasure by typing annoying/controversial/offensive words at strangers on internet forums, for them to read.

ARROGANT = Having or displaying a sense of overbearing self-worth or self-importance.

“Why don't you just pull the right side cover off and look inside? You could do that in less time than reading this thread” = Troll

“Ya know what, you arrogant little shit... Go fuck yourself.
I gave you good advice, and you act like a turd. Way to fuckin' go!” = ARROGANT TROLL

To all others who opened this thread for the right reason, my apology.
 
kickstart shouldn't be engaged when the clutch is pulled in, transmission as well, so by clutching it and turning the engine over via the crankshaft, you can narrow the problem to either

a-something in the case or b-something in the crank/cam

by 1-1/2 turns, you've probably got a valve contact issue, though if the cam chain had slipped my guess is that it would be less than 1-1/2 turns because it would probably be getting stuck on more than one cylinder. could also be something in the primary drive chain, if there were something lodged in one of the chains, it could stop the crank in the same fashion. the primary chains should be visible by remving the oil pan iirc.
 
Rock City you Rock, thanks for getting this thread back on track. Your post is the kinda suggestions and clear explanation I was lookng for. Sorry you had to wade through the mud to respond.

I should have stated more clearly that the engine is out of bike & on a stand. Should not be difficult to hook up a clutch cable though.
 
You already have cam cover off, check cam timing.
TDC is marked on the advancer unit, pull points cover.
Kickstart is a pretty major job, cases need splitting if I remember right (haven'tdone one since the 80's ;) )
 
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