720World

Little Trucks, Big World

I can't seem to find a definitive answer to my query.

I know the min/max bearing clearances from my FSM

 

Con rod clearance is 0.0005" - 0.0021"

The limit is 0.0047"

Or..0.012 - .054mm

What is the target bearing clearance when rebuilding an engine?

I'm assuming it should be around .0015"

 

My machinist says the clearance is fine.....but.. by looking at my OP gauge when the engine was warm....I'd say nay. About 35 lbs at idle

Main bearing clearance were right on.

I plastigaged the con bearings....

 

Looks on the verge for 'replacement'

Engine/bearings have about 5000 km on it, block was returned to machinist.

The head has been there 3 times already.

Rings never seated, cylinder walls and piston skirts were scuffed.

 

Upper and lower con rod bearing halves had opposite wear patterns on them.

Wear on top half, towards back on engine.

Wear on bottom half, towards front of engine.

 

Rod also had wear near cap

 

He blames all the issues on the larger Z22 rod on the Z24 piston, which only has  clearance of about .012.

That's 'fine'...but I think he should of noticed this when he pressed the rods on the pistons.

Big mistake taking my engine there in the first place.....but...I'm too far into it now.

So....new pistons (again) and cast iron rings....excellent...not

Anywho.....back to the query....con rod bearing clearance

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Oh......He's going to shave each side of the rod by 1mm for piston clearance

Ah, missed this post.

Doug I'd take a grinder to the pistons and open up the rod/piston clearance some like the Z22. This is likely why the piston scuffed and the upper/lower rod bearing shells had opposite wear patterns. If the rod and piston touch they may bind and the piston won't rotate on the pin very well adding a side load to the skirts.

The manual says just under 0.001" to 0.002" roughly, With a limit of just under 0.005" so you are at the upper end allowable. I would try for 0.0015" or 0.038mm or so.

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