piston weighing

riveroadrat

Well-known Member
Does anyone weigh pistons when they are replacing one of the original ones in an engine. I had a block done by a machine shop but it seems like it has a low speed vibration that it didn't have before.
 
I have never replaced just one piston. I always replaced the whole set. The only time we weighed pistons -rods and balanced the crank and flywheel together was in racing engines. We had a 4 cyl that would turn 9000 RPM in a Mini stock. I would think that there would have to be a big weight difference to create a vibration in a tractor engine. Did you get the balancer timed correctly?
 

I weigh out pistons often. I just did a set of chevy 327 30 over. I'm going to do another set here before to long for a 327 also. I weight out my pistons, then the wrist pins, then put the into sets, and weigh them each as a unit again. I also weigh out my rods separate. I do all the small ends first, then the large ends.

Then I tell the engine balancer the weight, and have him spin the weight on the crankshaft, so that he can balance the crankshaft & the flywheel/flex plate & damper as one. It's the only true way to do it.

I have done it this way since I was shown how to by a funny car engine builder/driver back in '76 for my race car. Bill Schifsky & The Bear Town Shaker. I do all my engines this way, whether it's a stock engine, street car, or if my race engine.

It's the way the engine balancer does it here, that does the final balancing for me also. I don't have a spinner, and the bob weights to do it myself.

I have also replaced only one up to four pistons. If you weigh them out right, the engine will never know. One bad piston, does not mean their all bad. If you have one that is to light, you cut welding rod, and set it with it, till it weighs the same, then weld on to the inside of the piston, just a tad more then you weighed out, and grind it back to weigh the same.

My 327 in my '27 coupe is able to turn 8000 rpms. But where I'm building it to run, it will never go past 6000, with 513 rear end gears, and my built 200R4 trans. No, not a 700R4

I'm not new to engines, just working on tractors, and tractor engines. :)

Pat
 

Yea, but Pat, this is a tractor, or at least we assume so since the question was posted in a tractor forum. For a high rpm race engine that will be balanced and blueprinted, yes, weight everything, balance everything, but a tractor? It's not turning that many RPM to matter.

It's likely, the vibration is a tuning issue.
 

I agree, it's a tractor, but I still do it with any engine.

David's question was, "Does anyone weigh pistons when they are replacing one of the original ones in an engine." Not whether it was in anything.

A answer he was given was, "
I have never replaced just one piston. I always replaced the whole set.

That was what I was answering to. Not that it was in a tractor, lawn mower, or race engine.

I have repaired engines for people that can't afford to replace everything, but had to have it fixed. I have never done anything that would not be right.

I just rebuilt a Case dozer for a neighbor that used his up most his savings, by buying a engine that was crap, but was still installed by what everyone around he say's he's the best at tractor repair around here. After this, I would not let him fix anything. He just screwed him over.

After I got the dozer to repair the governor for him, I found out the engine was no good! I could not believe when I drove it to my house, it was not knocking, and falling a part. I have never seen bearings as bad as these. All bearing , even the cam bearings were beyond shot.

I rebuilt if for him free, he had to pay for the parts. He bought everything new, except piston rings. He just had no more money to buy them for $154.00, for a 4 cyl engine. The engine ran good, and did not smoke at all. The cylinders all looked great. So I used them. I had the engine machinist carefully remove the rods, and recondition them, gave them back to me, and I weighed everything out as I always do, gave them back to him, and had him put them back on. I had marked all the pistons & rods as I always do, before pulling it apart.

I have it running, and it runs great good power, and no smoke.

He is very happy.
Case say's there is not a engine of the bore. I had called Hasting ring company, and they told me there is nothing that has that bore. They had rings that were for a .015 bigger bore, that I would have to sit down, and file all 20 of the rings down to fit. They were $154.00, and weren't the right ones.

If the engine had a bad piston, he would have had to scrap the engine, and buy a different engine.

So my answer had nothing to do what it was for. It's just what I do, when I pull a engine apart. Heck, I did it to my twin cyl engine on my JD rider lawn mower last year. I had to replace a piston & rod in it, because of governor failure.

It can never hurt to do it, but it may help to do it.

Pat
 

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