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Max Piston Protrusion / Notches
#1
I have searched the net and all the forums and need some guidance since I can't find anything.

I have a Bobcat 751 skid steer with the XUD9(A?) normally aspirated engine in it and beyond the shop manual no one here in the US knows anything about the motor.  I'm doing a full rebuild on the motor, had a spun bearing and then someone left it sitting with no injectors in it so rusted the cylinders etc.  I got the block machined for larger pistons, and got the crank turned and got the matching bearings.  Was just about to order a new head and was measuring piston protrusion.  Three cylinders are in spec for a three notch gasket.  The #1 cylinder (crank pulley end) is measuring at 0.040" protrusion (1.016mm) using a dial indicator.  It isn't the piston/rod/bearing as I swapped it with #3 and the measurements stayed the same for the respective cylinders.  I measured the crank and both rod journals are the same size so that isn't the problem.  Next step will be to pull the crank out but I'm afraid I'll have to get new gaskets so wanted to see if that amount of protrusion would cause slap with a five notch.  Bobcat's implementation of the engine is only rated at Gross: 41 HP (31 kW) Net: 38 HP (28 kW) and governed to max 3100rpm so far from a high performance implementation.

If it will cause interference issues I would appreciate any guidance of the next thing to check?

Thanks,

Calvin
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#2
I would seriously just put a 5 notch on. I wuoldnt have even measured with these engines. Ive not seen one spin a bearing beofre though, The only thing that could cause the slight variation now would be the crank or mains being out. Assuming youve checked them as its been rebuilt you should be fine. Specially at that little power output.
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#3
(01-08-2017, 09:01 PM)bashbarnard Wrote: I would seriously just put a 5 notch on. I wuoldnt have even measured with these engines. Ive not seen one spin a bearing beofre though, The only thing that could cause the slight variation now would be the crank or mains being out. Assuming youve checked them as its been rebuilt you should be fine. Specially at that little power output.

Thanks, I just ordered a 1.7mm which appears thicker than the five notch at other places and should give me a bit more clearance.  As to the spun bearing from what I've read these motors seem to be prone to spinning bearings in this application.  No one seems sure why but one theory is that long periods at low to mid RPM ranges are somehow starving them.  Thanks again.
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