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AC model B low / no compression

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Bill Copeland

05-26-2005 09:29:15




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Getting my 1938 "B" together and after freeing up the stuck valves and lapping them in i still have only 30lbs on cyl. # 1 & # 4 with nothing on #2 & #3.This machine sat for 10 yrs with a full tank of gas indoors.Could the rings be stuck? and what do you suggest to free them without tearing down the bottom end? Where is the old " Gumout " that works? This new aresol stuff is for killing bugs!




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37WC

05-27-2005 19:06:51




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 Re: AC model B low / no compression in reply to Bill Copeland, 05-26-2005 09:29:15  
I have done what the others have said to loosen up the rings for better compression and it works well. I think they have it well covered. When you removed the valves from the head did you buff them with a wire wheel, check them ease of travel in the guides, and lube the stems before installing them. I would suggest to also check the valve clearance again. I usally set them real loose(.025)after installing the head and reset them after the motor has run awhile and things have settled in. I would also check that the rocker arms have full movement by cranking the engine. This would check the cam shaft for flat spot and cam gear to make sure that area is moving.
Good luck
37WC

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Texas Denny

05-27-2005 13:12:59




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 Re: AC model B low / no compression in reply to Bill Copeland, 05-26-2005 09:29:15  
Very interesting suggestions that are worth trying. I haven't done this. But I have had engines where I pulled them down, cleaned (and honed) the cylinders (in spec with no ridge), put in new rings and had the same problem you are having because the rings weren't seated. When that happens to me, I get a tractor hooked up and pull it for a while. After a bit of spinning, it will start. And after running a reasonably short time, the rings should break free (in my case they seated pretty quickly). If they don't, try one of the ideas below. Don't forget to prime the oil pump. If it has set that long, you won't get any oil pressure if you don't prime the pump - and that could be disaster.

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Kent of SW MO

05-27-2005 05:55:11




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 Re: AC model B low / no compression in reply to Bill Copeland, 05-26-2005 09:29:15  
You have already had the head off once. I would pullit again then pull the pan and take out each piston /rod assssy. and do the job right.

Kent



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Paul Shuler

05-27-2005 16:36:19




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 Re: AC model B low / no compression in reply to Kent of SW MO, 05-27-2005 05:55:11  
Hey Kent, where you at in SW MO? I'm in Springfield.I spend most of my time over on the Farmall board but I like ALL old Iron.
Paul



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Kent of SW Mo

05-27-2005 16:50:33




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 Re: AC model B low / no compression in reply to Paul Shuler, 05-27-2005 16:36:19  
I am 20 miles North on H Highway in Pinhook ( Pleasant Hope ).

Kent



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Okieboy

05-26-2005 19:47:11




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 Re: AC model B low / no compression in reply to Bill Copeland, 05-26-2005 09:29:15  
Best thing on the market for that is a product called "Sea Foam". I pick it up at the local Napa store, pour some in, let it soak a while the try to start your engine, if you can get it to start, remove the air cleaner hose, hold the throttle open and pour it in fast enough to kill the engine, let it set for 15 or 20 minutes, resart and it will surprise you how well it works. Oh yeah, when you do that, it will smoke like crazy for a few minutes. Okie

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old

05-26-2005 19:22:03




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 Re: AC model B low / no compression in reply to Bill Copeland, 05-26-2005 09:29:15  
Both the other guys are right on track. Fill each cylinder with tranny fluid and let it sit a few days. Then say after 3 day turn it over with out the plugs in, check compression. If its not up fill the cylinders with turpentine and let sit a few days and check again. Another thing you can do if you can get it started after doing the tranny fluid thing is to run it with out water in the Rad for about 10 minutes, that heats up the engine but not hot enough to hurt things, don't put it under a load that way jusy idle it. Let a cool back off, the heat will most likely pop the rings loose if they are going to loosen up.

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russ1

05-26-2005 11:32:33




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 Re: AC model B low / no compression in reply to Bill Copeland, 05-26-2005 09:29:15  
I would say the rings are stuck. Transmission fluid or Marvel mystery oil would be your best bet. Pour it in the plug holes and let it set for a few days. If you have cranked it very much it is possible that the cylinder walls are scored. That happened to me on an engine that had set for several years.

Hope this helps.
Russ



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steve(ill)

05-26-2005 16:01:18




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 Re: AC model B low / no compression in reply to russ1, 05-26-2005 11:32:33  
i agree i would pour some fluid in the cylinder and let it set and soak into the ring grooves. after a couple days, remove most of the oil (just let ist squirt out the plug hole.) leave a spooon full in each cylinder. you will find the oil helps to seal and get more compression. that should make the motor start. then set at half throttle and see if it will keep running after the oil has burn out. run for 10-15 minutes and recheck the compression. might need to do this a couple times.

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