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gs850 engine rebuild, tight spot in rotation

  • Thread starter Thread starter micahcondon
  • Start date Start date
M

micahcondon

Guest
Hi -

I'm reassembling an '80 gs850 engine, and now that I'm to the point of adjusting the valve clearances, when I rotate the engine I'm finding a tight spot in the rotation

It occurs at the two rotation points just as a pair of pistons is coming toward the top of the stroke. I know knothing was tight before I installed the cylinders and top end, and I've got it in neutral w/ the clutch disengaged to be sure it's not in the transmission. So, I'm pretty sure it's related to the pistons or head. I don't remember whether I rotated the engine at all after I put on the pistons and cylinders before I put the head on - I don't think I did, so can't say for sure if it was tight at that point.

It's not completely binding, just gets a little tighter at two spots in the rotation - if I push a little harder on the wrench then it keeps on turning and seems to jump past the tight spot, but it takes about 25 lbs of torque to do it. No noticeable noises except the slight noise of everything suddenly turning again. I have the spark plugs out, so it's turning against compression.

So, probably I'll take the head and cylinders off to test. But, just wanted to see if anybody has any experience/suggestions with this first
 
that's what I was afraid of, and seems to be the case. thought I had the timing dead on, but apparently not or else the valve clearances are way too tight.

oh well, I really didn't intend to put it back in the frame today . . . :-)
 
micahcondon said:
that's what I was afraid of, and seems to be the case. thought I had the timing dead on, but apparently not or else the valve clearances are way too tight.

oh well, I really didn't intend to put it back in the frame today . . . :-)
Click to expand...

If the valve timing is out, using a torch you should be able to see the valves touching the piston, through the spark plug hole! If there is adequate piston to valve clearance, you need to investigate other areas. Have you done any radical mods to the engine?
 
Thanks - it was the valve timing, retimed it and it's fine now. Now just need to see if I bent any of the valves - I was planning to do a compression test anyway before I fire it up
 
Will twenty-five pounds of tourque bend a valve? Maybe but probably not.
 
Now, for the really curious ones out here...which cam was it, how many teeth off was the cam, and which direction? :-s

Just something to toss into the old memory bank. Would be nice to know that 1 tooth or 2 teeth off might be OK, but 3 teeth definitely touches. That sort of thing. 8-[

.
 
Steve said:
Now, for the really curious ones out here...which cam was it, how many teeth off was the cam, and which direction? :-s

Just something to toss into the old memory bank. Would be nice to know that 1 tooth or 2 teeth off might be OK, but 3 teeth definitely touches. That sort of thing. 8-[

.
Click to expand...

Steve, You have posed some interesting questions. micahcondon could run a book on this!!
Ok, I should have suggested using a flashlight instead of and open flame (torch). But hey, he hasn't even got the carbs or tank fitted yet so the torch might still be a safe option. You need to be careful not to singe your eyebrows though!

My bet is on the exhaust valve. If it were the inlet valve, it would be still advancing (opening) after TDC and trying to jamb tighter into the top of the piston. On the other hand, the exhaust valve is continuing to close after TDC. On my 850 cams, the opening and closing figures between them both differ by only 0.5degs at TDC.

So, my bet is the exhaust cam being ???? teeth advanced!!
 
Last edited:
the exhaust cam was off, I think maybe two teeth, due to slack in the chain when I first timed it. So, since the intake cam was still timed correctly with the exhaust , it was off by the same amount. Not sure which one was hitting
 
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