Engine difficult to turn over

[Fred99]

I have just completed assembling my new 750cc, 277 degree engine. But it is difficult to turn over. With the spark plugs out and a quirt of oil down the bores I cannot turn it over by hand with the kick starter. The engine is at waist height in a stand so using my foot to try to kick it over is not an option at the moment. I have applied a torque wrench to the crankshaft nut and it takes around 35 lbft to turn the engine over. That seems way too much to me but what to you regular rebuilders reckon?
And then, of course, the next question: where do I start looking for the cause? The 750cc pistons, rings and block came as a kit from MikesXS. I checked the ring end gaps in the bores and they were all within tolerance. The cam chain has been adjusted and the tappets set. The gearbox has all new bearings but nothing else and appears to be changing gears ok and spinning freely.
Ideas anyone?
Thanks
Greg

 

[rebel542]

With a fresh engine I'm not sure 35 would be an outrageous number. I've never checked mine to see what torque it turns at but I will soon. Sounds like you did your homework so install it and fire it up.

 

[Punkskalar]

I ALWAYS make sure that the pistons move freely in the bore before installing the top end... Those MikesXS 750 kits have the thinnest oil control rings I've seen, and even I find myself ruining one occasionally (I've installed TONS of pistons/rings in the past few years) and binding a ring between the cylinder and piston. So make sure none of that is an issue.

Also, with new or heavier valve springs, it will be harder to turn over... Leave the camchain tension slightly on the loose side, make sure the valves are properly adjusted and the cam/crank is timed properly, and you should be good.

Also, check that the clutch basket was installed properly. There is a thin shim that if left out will cause the basket to drag on the cases..

Hugh

 

[Fred99]

Hugh.

Thank you, thank you, thank you.

I went through your list of suggestions: "yep done that, yep done that" etc until I got to the end. Then knowing I had everything right I felt around the clutch basket with a 0.020" feeler gauge and doubt started to creep in. I took the clutch apart and found a rather severe witness mark on the casing. I will now go back to the book and study even harder and put that ##!!@ shim back in the right place.

Thanks again for your help and money-saving suggestions.

Greg in NZ

 

[retiredgentleman]

This is the diagram I followed for my 78 SE clutch.

A PO had left out the "A" shim washer, which is 1 mm in thickness. That allowed my clutch basket to rub on the engine, as seen in the picture.

 

[Fred99]

That is the diagram I am using (now).

I think my main problem is that I had to replace the cush drive springs and it is the nuts from that kit that are fouling the case. The witness marks are at between 2:30 and 3:30 from the clutch shaft i.e. towards the crankshaft where there is a slight change in the case profile. I have realigned the nuts so that the flats are outermost thereby giving the maximum sideways clearance from the case and tidied up the case.

FWIW the cranking torque has changed very little - from about 35 ftlb mentioned above to around 28 ftlb.

GP

 

[Fred99]

In reference to your engine photo, Retiredgentleman, my witness marks are further to the left, on the "shoulder" of the engine case casting and much slimmer. i.e the points of the cush drive nuts are wearing away the edge of the casing at that point rather than the face of it.

 

[CDNTX650]

I has the same problem with my rebuilt clutch basket nuts. I could see one spot where they were rubbing the cases...small stone in the dremel took a little off the case and voila. Even with no rubbing and new top end...i can barely get it to turn by hand with the kicker on my work bench. Thats only 680cc. Plugs out or ratchet on stator.

 

[Fred99]

I put it all back together, filled it with oil including a squirt down the plug holes (but left the spark plugs out), took it out of the stand and put it on the floor. I stood on the kick starter and nothing moved.
If I jump on it the engine will turn but not much. The resistance is constant i.e. not like a nut hitting the engine case.
I guess there is nothing for it but a bit-by-bit dismantle until I find some stupid thing I have done.

 

[CDNTX650]

Could be a pinched oil control ring....done that.

 

[Fred99]

I found the problem. The new PMA alternator rotor is rubbing against its backing plate. As the rotor is mounted on the taper of the crankshaft its position along the crankshaft cannot be changed. Does that then mean that the backing plate is incorrectly mounted on the engine cases? I haven't got that off yet to see if I have mounted it incorrectly or can somehow move it. Any suggestions?
Thanks
Greg