JD M engine Tight

330 Standard · Apr 9, 2012

This is my first upright 2 cyl rebuild. I put together a JD M engine back from the machine shop with all new rings bearings etc. It was supposed to be .10 on rods and mains. I have double checked main and rod bolt torques as well as bearing sizes and used plastigage and I have .003 clearance as the IT manual states but this motor is tight. It is what I feel like is hard to turn through. Just watched the 420 rebuild video and those guys are turning theirs through effortlessly. Any suggestions or should I just attribute it to all new stuff and finish the build and fire it up?

barnE · Apr 9, 2012

Is everything oil or grease coated like it should be.??? Dave

cbt1124 · Apr 9, 2012

As stated in previous reply, ensure all moving parts have some sort of assembly lube on them. Also, I have seen this before so please just confirm that there is nothing on the back side of the bearings or the caps where the bearings rest they MUST be clean and dry!!!If the previous is ok,check crankshaft end play(thrust bearing clearance) engine rebuilders overlook this critical clearance quite often. If that is ok,continue by loosening all rod and main bearing caps, roll the crank over to check resistance then tighten 1 cap at a time starting with the main bearing caps and roll the crank 1 complete turn after eack cap being tightned. The resistance will increase each time and should be consistent. If you get to one where it really tightens the engine,remove that cap and inspect the wear surface of both halves of the bearing. You could have a bent connecting rod too. Good luck and let us know what you find...

gbs · Apr 9, 2012

what you were seeing on the video was most likely the crank only installed,if the bearing clearances are to spec. including thrust bearing, and the piston to cyl clearance is correct and the ring gap is correct the engine will still have some resistance with all these parts installed but not to the point of binding

Unruh · Apr 9, 2012

Is the engine assembled? I did one once that had a missing bolt in the flywheel when I disassembled it. While I assembled it, I put in a bolt that was a little too long and the back side was up against the block making the engine very difficult to turn. Took the too-long bolt out, ground it down shorter and all was well. Sometimes it's something so simple we overlook it!

BCnT · Apr 9, 2012

do you have the correct rod caps and mains on their mates? if they are mismatched it wont work.

huntingreen2day · Apr 9, 2012

Did you check the end gap on the rings? If gaped wrong that will make it hard to turn over.

330 Standard · Apr 10, 2012

Much thanks to all who replied. I really appreciate the help. I finally found the problem late last night after your help. I completely took everything apart again and plastigaged clearances etc. All checked out. Then I finally noticed a very faint and small 1 and 2 stamped on the main bearing caps. Even though they were the same casting/part number I swapped them and swapped the bearings so the correct one would still be in the rear and re-torqued and problem solved. Engine turns through as I would expect. Again many thanks to all who offered advice to help. Just proves YT forums is a great place with great folks.

JD M engine Tight

330 Standard

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BCnT

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