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Minneapolis Moline Tractors Discussion Forum
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JAHNS PISTONS FROM WELTERS

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LAZY RAY

10-12-2006 08:39:34




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Hey guys. I was wandering if someone could shed some light on this problem I have. I called the ladies out at welters to get some info on their oversized pistons for my 50 utu. The lady I spoke with said I would have to bore my blocks out to a finished bore of 4.375 or 4.475. I cant remember wich she said. I know the ladies out there know their stuff. But this sounds like a huge amount to cut out of the bore. From what I underdstood. That would mean .185 would have to be cut from the block. Help me out here guys. Thanks in advance.

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UB-ToMMy

10-12-2006 19:06:37




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 JAHNS PISTONS FROM WELTERS in reply to LAZY RAY, 10-12-2006 08:39:34  
I bought a set of the Jahns pistons from Welters. They are 4.375� +0.060� over. ie. essentially a 3/16� overbore. The thing to be careful about is to make sure that when the blocks are rebored the recommended diametral clearance between piston and bore is maintained. As I recall .008� is recommended. Initially my blocks were mistakenly rebored with a 0.006� clearance. The result was disastrous. The engine would seize when run wide open for any length of time. I thought and hoped the problem was something other than the pistons. Upon disassembly, I found #1 piston severely damaged well beyond usability. The others were fine. I was able to buy one more piston from Welters�it was their display piston from the counter. I had to machine a substantial amount of the inside of the skirt to make it match the other 3 in weight and I fine tuned the weight so that all 4 weighed within about 3 grams of each other. One other thing, I had to machine the wrist pin boss openings on the inside so that the rod would fit between the two bosses on all 4 pistons. I had the bores honed to give 0.010� diametral clearance except for the bad hole which was machined 0.012� over. I wasn�t too concerned about piston slop since the tractor use was for pulling not field work.

I also have 4207 heads on the tractor. With the Jahns pistons and the high compression heads I�ve finally gotten the engine to the point where it doesn�t power out-at least not easily. After 3 years of trying to get it right, this year was the payoff in that the tractor was 1st place successful in a number of pulls. And, by the way, it never, never overheats and barely gets into the run zone when run without a thermostat. One other point: it runs best on race gas.

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AGCO AVENGER

10-12-2006 18:43:31




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 Re: JAHNS PISTONS FROM WELTERS in reply to LAZY RAY, 10-12-2006 08:39:34  
Nothing against Welters, but if I were rebuilding your U, I would get the Ross forged pistons from Everetts in Ohio. Ross pistons are a LOT higher quality and available in many oversizes.
Avenger



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MM Collector

10-13-2006 04:06:59




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 Re: JAHNS PISTONS FROM WELTERS in reply to AGCO AVENGER, 10-12-2006 18:43:31  
Everetts is the most over priced person out there. If you want Ross pistons, go to Ross.



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T.R.K.

10-13-2006 06:27:42




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 Re: JAHNS PISTONS FROM WELTERS in reply to MM Collector, 10-13-2006 04:06:59  
How do we get in touch with them and do we have to be a reseller?



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ken in texas

10-12-2006 17:29:43




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 Re: JAHNS PISTONS FROM WELTERS in reply to LAZY RAY, 10-12-2006 08:39:34  
Back in the 50,s and 60,s we would bore the utu to 125 thousand,s and install aluminum pistons and then turn up the rpm,s.The blocks have a lot of metal in them.I think we used M and W pistons.



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SWMoline

10-12-2006 08:46:53




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 Re: JAHNS PISTONS FROM WELTERS in reply to LAZY RAY, 10-12-2006 08:39:34  
4-3/8 (4.375") is a common over-size bore for the MM 283 blocks. Some will even bore them to 4.435" which is 4.375 + 0.060".


You are correct. Those ladies know their stuff.



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LAZY RAY

10-12-2006 09:42:17




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 Re: JAHNS PISTONS FROM WELTERS in reply to SWMoline, 10-12-2006 08:46:53  
Will the 4.435 overbore cause the enine to run any hotter?



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SWMolines

10-12-2006 10:14:47




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 Re: JAHNS PISTONS FROM WELTERS in reply to LAZY RAY, 10-12-2006 09:42:17  
I do not believe you will notice any difference.



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