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Engine wont turn forwards...

  • Thread starter Thread starter NigeW
  • Start date Start date
N

NigeW

Guest
Hi all

Just starting rebuild of a 750 (last owned one back in the 80's) - will post some pics, but it's a bit of a shed.

I've just rebuilt top end (fitted new base and head gaskets, valve-grind etc). All was ok then when cams put back in and used kick starter to turn it over the engine locks...
I can turn the engine backwards all day long, so a bit puzzled on this one. Tensioner not refitted yet but don't think that's it - could be wrong.

Any ideas before I remove the cams and try again?

Thanks,

Nige
 
you should not be turning the engine backwards. without the tensioner fitted the chain will be slack and could be snagging on the crank at the bottom. or the cam timing is incorrect.
check the timing and fit the tensioner before you try and turn it again
 
Cam Chain was the first thing that came to mind. One thing that you might need to worry about now is weather or not the chain has skipped any teeth on the cams or crank now that you've been rolling it around without the tensioner... :-k
 
NigeW said:
All was ok then when cams put back in and used kick starter to turn it over the engine locks...
Click to expand...

How hard did you kick it? It can't be good for the chain to stop the engine by binding on the sprocket, it certainly isn't good for the valves to hit the pistons hard enough to stop the engine.
 
Thanks for the ideas.

Haven't kicked it over as such - just turning by hand, using the kickstart lever and haven't forced it beyond the point of resistance.

Turning it backwards for a short time shouldn't harm as the chain is under tension (jockey wheel is in place) and chain seems to be running on all teeth correctly.

Cam timing is set up correctly as far as I know so there should be no issues with valves hitting pistons, and this would happen whether the engine was being turned either way.

I'm wondering if the front chain guide/blade is sited incorrectly at the bottom and locking the chain somehow. I'll remove the cams and check the chain-run and blade to ensure everything's turning freely.

Nige
 
Without the tensioner engaged, the cam chain is bunching up at the crank.

I would pull the valve cover off & verify the timing is spot on (it's easy to be a tooth off). Might have to pull a cam to free up the chain...

Then engage the tensioner & it should turn forward by hand without any problem.
 
Update...

Taken a look this morning. Fitted tensioner, still the same (but now notice it locks both back and forwards if rotated far enough). So I removed the inlet cam and now it turns fine - so it could be valve/piston contact!

Will take it apart and check eveything.

Cheers
 
Last edited:
Now sorted - thanks for the input.

Well, I had used the right marks (T 1/4) so not sure what the problem was. Now all reassembled/reset again and everything turning over fine.

Nige
 
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