SC crank grinding

[Erik OK]

The crank on my SC that I am putting together has a little light rust on the rod journals but the mains are clean and shiny, the engine sat with the rods out for a while. It has .010 undersize mains and rods in it, the mains and rods both have about .025 clearance checking with plastigauge. I have a set of .020 undersize rod bearings, should I have the rod journals ground to clean up the rust or will they clean up with running? I have heard that hardening on these cranks didn"t go .020 deep but this tractor won"t be used on a regular basis so wearing out won"t be too much of a concern

 

[mEl]

I would suggest getting a set of mics and getting exact measurements of the journals checking at TDC and at 90 degrees and also across the journal to find taper wear. If you have the shaft out now's the time to do it right. Surface rust if not pitted can be removed with fine emery cloth. If your plastigage readings are accurate that is on the loose side with .020 brgs. You probably wouldn't hear loose bearings but oil pressure certainly would suffer. I just wouldn't go by plastigage readings but rather hard measurements. I would look at the inside measurement of the bearings in the rods after installing them and torqueing the caps. You will then know the exact oil clearance. mEl

 

[rlp]

.025 is right on the limit to where you need to regrind the crank. I built an engine once with that amount of clearance on a car once and didn't have problems. A tractor with lower rpms should be all right. If you let it idle for more than a minute, bump up the idle a little bit. If you do decide to regrind be aware that you can have the machinist offset grind the crank to give you a little more cubic inches, but you have to make sure that the piston won't hit the head or valves. On most tractors, that is no problem.

 

[onestout]

I think you may want to double check those numbers, .025" is waaaaaay too much clearance, it will rattle very bad if put together like that. I am guessing that was a typo, at least I hope so. If it was mine I would grind it and put it together right. Also check out the oil pump closely, maybe add a shim to the spring to bump up the oil pressure a little.

 

[Erik OK]

Yes it should have been .0025 instead

 

[mEl]

that typo makes all the difference in the world, sounds like youre good to go