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420 Low Compression

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Prune Picker

04-11-2000 17:43:56




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My 420 has 110 psi compression (cold) on the rear cylander and only 40 psi on the front. A few squirts of motor oil in the front jug makes no difference. Does this sound like a problem a valve job will correct? Any advice on re-ring without a re-bore? This tractor runs pretty well, starts right up, doesn't appear to burn any oil. Plugs look good, although both have a light coat of oil on the center. I'm not a crack mechanic but love this tractor and have plenty of patience!
Any of you tractor wrenches have some advice??

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clooney

04-11-2000 18:05:31




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 Re: 420 Low Compression in reply to Prune Picker, 04-11-2000 17:43:56  
Prune Picker, sounds like it could be a valve, but to make sure take an old spark plug & break the top off then punch the center out, then weld or attach an air fitting that fits your air hose. Bring the rear cylinder up on the compression stroke until TDC then put it in high gear with the wheels blocked & brakes on. Insert the modified plug in the rear spark plug hole & put in about 50-60 psi of air pressure & listen to the exhaust, carb. intake & crankcase to see where the air is going. That will tell you what is leaking.

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Prune picker

04-12-2000 17:35:55




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 Re: Re: 420 Low Compression in reply to clooney, 04-11-2000 18:05:31  
Thanks, Clooney. This is a great idea and I'll give it a shot this weekend. If I do find leakage past the rings, is it a waste of time to re-ring without a re-bore, assuming the cyl bores look OK? I don't work this tractor more than 100 or so hours a year. Thanks again for the advice. I'll post a follow up for future reference.



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Doug D

04-11-2000 20:35:16




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 Re: Re: 420 Low Compression in reply to clooney, 04-11-2000 18:05:31  
Clooney, you truly are the great one. Where do you come up with all this stuff? I have heard a lot of tricks, but this one takes the cake! Keep it up, I sure do enjoy and learn a lot from your posts!



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