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Allis Chalmers Discussion Forum
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Allis Chalmers C: Low Compression

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rkr29kracing

10-08-2007 07:07:07




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My C only has 65 lbs on the 1 and 2 cylinder and 45 lbs on the 3 and 4 cylinders.

This tractor didn't run when I bought it, and I did a complete tear down. The cylinders looked great and I put new piston rings in. The head was cracked so I took one off another tractor. The valve seats were a little pitted so I polished them up. The valves seemed to seat well after that.

I put it back together and used the existing valve spings. I think maybe a couple of these spings could be weak, and that may be causing the low compression. Either that or I didn't do a good job cleaning up the valve seats.

The carb is also bad (rebuild kit on the way) but I had the tractor running for 2-3 seconds on spray.

Does anyone have any advice on the low compression? Or why I am seeing that huge differential between the 1-2 and 3-4. Will it run for any length of time with compression this low?

Thanks!

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Gene

10-08-2007 18:21:31




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 Re: Allis Chalmers C: Low Compression in reply to rkr29kracing, 10-08-2007 07:07:07  
Go ahead and get the engine running. Do the compression test, dry and wet. This should tell you where the problem is. If this test is not positive, then do the vacuum test/check. This should isolate the problem even further.



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l gehring

10-08-2007 17:23:23




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 Re: Allis Chalmers C: Low Compression in reply to rkr29kracing, 10-08-2007 07:07:07  
i had a case head with bad pits on the valve seats from being full of water. wanted to see if it would run before i spent any money on it. i blocked the head upside down on my work bench.put lapping compound on the valves and hung my 1/2 drill on the stem and locked the trigger for a while. i know it was the wrong way to do it, but it worked! it starts right off and runs great. someday i will have the job done correctly.

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Gene

10-08-2007 08:21:46




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 Re: Allis Chalmers C: Low Compression in reply to rkr29kracing, 10-08-2007 07:07:07  
Go ahead and rebuild and install the carb. Add a bit of oil to the top of each piston. Start and run the engine for an hour or so, then do an other compression check. Dry and wet.

Engine will start and run on 45 PSI.

Check your valve tappet clearance.

Also do a vacuum gauge check with the engine running.



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rkr29kracing

10-08-2007 08:14:54




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 Question for Dick L in reply to rkr29kracing, 10-08-2007 07:07:07  
Dick L

What is your method for checking the valve seating/seal when you have the tractor apart? Can you do this?

Also, do you feel the tranny fluid will help if I already know the rings are free? I thought this was just for getting a stuck tractor turning again without taking it apart?

Thanks in advance for your great help. I have seen a lot of your posts on here, all very helpful!



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Dick L

10-08-2007 10:42:45




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 Re: Question for Dick L in reply to rkr29kracing, 10-08-2007 08:14:54  
spotting blue. It is a blue ink paste for this purpose. You wipe a thin coat on the valve face and set the valve down against the seat. Without turning the valve you lift the valve up and look at the blue transfer to the seat. We buy it from Production Tool. The list it as Hi-spot Blue



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JMS/.MN

10-08-2007 07:45:18




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 Re: Allis Chalmers C: Low Compression in reply to rkr29kracing, 10-08-2007 07:07:07  
Did you hone the liners with a crosshatch pattern before installing the rings? Try putting some tranny fluid in each cylinder, let it set for a couple days and see if it tightens up.



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Dick L

10-08-2007 07:25:17




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 Re: Allis Chalmers C: Low Compression in reply to rkr29kracing, 10-08-2007 07:07:07  
Takes magic and luck to polish valve seats and get them to seal with out a valve lapping tool, lapping compound and bluing. I have never had good luck getting them correct and I have had all the above for many years. It takes a lot of care to get a proper seal with my valve grinding machines.



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