Wrist Pin Question

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xraycajun

Well-known member
Hey Guys,

I am nearly ready to-reassable my '53 Cub engine. I am ready to order rings, rod bearings, front seal, and gaskets. I have measured all parts to confirm that my orders will be correct. I am left with only one question. How do I measure for wrist pin play? I honestly hadn't thought of replacing them until I saw some on the Steiner site... so its kind of an afterthought. Is there a left-to right tolerance between the rod and inside of the piston. Some feel kinda loose... but I have nothing to compare to. Any guidance would be much appreciated.

Thanks!
 
The connecting rods have bushings in them that are replaceable. That should tighten up the wrist pins. Mic the center and the ends of the wristpins to be sure there is no wear on them. They should be the same diameter the full length of the wrist pin.
 
I ordered new parts and had a machine shop press the old bushings out & install new ones. They have to fit the new pins to the bushings by honing them for correct clearance. I gave them a copy of the Cub service manual specs. That work isn't for novices. The last thing you want is a knock from loose pins.
Larry
 
Cubfriend":4ff7ytej said:
The connecting rods have bushings in them that are replaceable. That should tighten up the wrist pins. Mic the center and the ends of the wristpins to be sure there is no wear on them. They should be the same diameter the full length of the wrist pin.
Click to expand...
:Dito:
 
they are correct, when new rod bushings are installed they need to be "burnished" to make sure they fit correctly
 
Thanks guys...

Yeah, I would have a machinist do the work... I just don't know how to determine for sure if they are in need of replacement. It sounds like I have to disassemble the pin/bushing/rod to make the determination? No way to measure the assembled piston and rod for wear?
 
did you measure the bore? if you can feel loose wrist pins I would suspect that the engine has some time on it and the bore is worn, check it for taper wear top to bottom
 
Hi,
I think the engines with cast iron pistons are supposed to have some side to side movement of the connecting rod on the piston pin. The amount it can move is more than the length of the bushing.

The wear would be felt holding the piston upright, and twisting the connecting rod in a direction that would be front to rear, when the piston is in the engine, or crossways to the pin.
Also check for any up and down looseness.

Below is a page from the Cub service manual, showing the size of the bushing when installed in the connecting rod. It is about half way down the page. The best way is to measure the ID of the bushings in the connecting rods.

http://www.farmallcub.info/manuals/gss- ... 001-05.jpg

Below is the Cub service manual, if you don't have it. It has lots of info. The engine is in section 1, I would read it if you are rebuilding the engine.

http://farmallcub.com/rudi_cub/www.clea ... index.html
 
I have the manual. I was hoping for a sure-fire way to measure the wear without disassembly. To answer your question... I did take measurements on the bore. It is within spec on the bore and is not out-of-round. I also measured the rod journals. The tractor will be getting new standard rings and rod bearings.... and perhaps new wrist pin bushings.
 
I was one that measured but didn’t change bushings. If I recall clearance is suppose to be 0.0005 t 0.0010 give or take a tenth. I had them in the 0.0015 to 0.002 range. I have a slight knock when cold but I didn’t know whether I was feeding a money pit or rebuilding an engine. Turns out it didn’t really need them but would have made it more correct. I’m going on 5 years with no issues. Measure them decide
 
Good news is, there was no knock before. The engine ran well, started well too. It just had low power/compression and blue burned oil. I mostly pulled the pistons because I had already re-worked the valves. I did have a rattle in the engine. I later discovered the hydraulic pump gear retainer nut in the oil pan I think the gear had been held on by the front cover and was rattling around in there!
 
I had a stuck piston from water leakage but found excessive ring end gap like you did. Mine came in with std rings. Po beat the hockey stick out of the poor tractor. You should probably plan on rebuilding the pump. May even need a rebuild able donor. The gear is probably is worn but sleeve retaining loctite will fill nearly 0.010 clearance. It did on mine.
 
I have the pump rebuild kit on the way. It was obvious after pulling the front cover that the o-ring was leaking hyd. fluid into the crankcase. Another "might as well" project.
 
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