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1940 flathead motor compression question

Discussion in 'The Hokey Ass Message Board' started by guy1unico, Jan 23, 2013.

  1. guy1unico
    Joined: Aug 30, 2006
    Posts: 709

    guy1unico
    Member

    All but 2 of my cylinders are at 100 psi there are 2 together on the passenger side at 60 psi....the car runs out pretty well... at idle it shakes a bit and right at immediate acceleration it back flows alittle before taking off smoothly.No smoke blowing out the rear. I put some Marvel oil in the 2 cylinders with no better results. Could there be a major problem here or should i forget about it?
     
  2. Flatman
    Joined: Dec 20, 2005
    Posts: 1,975

    Flatman
    Member

    Did the compression come up in the cylinders you put the oil? Sounds like you may have some valves sticking open a bit. Any ticking sounds? A cylinder leakage test (putting air into the cylinder at TDC and finding where your compession is going) is your best bet!

    Flatman
     
  3. Rich Wright
    Joined: Jan 9, 2008
    Posts: 3,922

    Rich Wright

    If the wet test shows a higher compression reading it is an indication of a problem with the rings. If there is no difference between the two tests then you most likely have a valve train problem.
     
  4. Typically this is a valvetrain problem for me. If it's not annoying the absolute crap out of you, though, I might be tempted to leave it alone 'til it does.

    Last time that happened it took a while for the valves to unseat enough for it to matter, and even then the car was running OK. One was out .030, the other .100

    Two years since the last valvetrain repair and she's running great, compression is great.
     
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  5. guy1unico
    Joined: Aug 30, 2006
    Posts: 709

    guy1unico
    Member

    One fellow on the Ford Barn said if the 2 cylinders are together it more than likely is just a gasket leak.

    Can I take out all the head bolts but maybe a couple ...loosen those , turn over the engine and dislodge the head?
     
  6. Rich Wright
    Joined: Jan 9, 2008
    Posts: 3,922

    Rich Wright

    Head bolts or studs with nuts???

    They can be a bit tough to get over the studs but if it has bolts a little careful prying will usually pop it loose.

    You might try a leak down test before pulling the head. Easy enough to make a fitting with a short length of hose to attach to a quick coupler. Use regulated air and pump up those two cylinders one at a time. Look for an air leak at the intake and exhaust..or even into the adjoining cylinder if the gasket is the cause and it's bad enough.
     
  7. guy1unico
    Joined: Aug 30, 2006
    Posts: 709

    guy1unico
    Member

    studs with nuts
     
  8. Rich Wright
    Joined: Jan 9, 2008
    Posts: 3,922

    Rich Wright

    Soooo...... How's it going with your compression/leak down/tear down project???

    I have an 8BA that I drove for a couple thousand miles with two very sick cylinders and the thing ran pretty well. #2 had a wrist pin float back and forth digging deep grooves in the cylinder wall. During a long hibernation on a farm in Colorado all 8 cylinders accumulated some nasty rust pits.
    Some yahoo screwed the person I bought it by selling him a "rebuild" that consisted of honing #s 2 and 8, replacing the rings in those cylinders only and...surprising ...installing a new cam. Nothing else:eek::eek:
    #8 was so loose it made only 40lbs while #2 only made compression above the grooves...about 20lbs. The other 6 managed between 85 and 95.
    When we finally tore the engine down for a correct rebuild the rods and mains were completely worn out. Not spun or anything, just serious long term wear, same with the crank journals.

    This engine had been down the road many times.

    Yet, amazingly, it ran quite well. Never did overheat and would roll down the road 65-70 pretty much all day.

    Maybe the earlier suggestion that you just keep driving and enjoying your car for a while is the best solution as long as it runs OK and is not in the process of self destruction due to broken pieces floating around.

    Analyze the problem so you know what's going on and then enjoy it til it really needs to came part.

    These engines are far more stout than a lot of people think. They put up with a lot and keep on going.

    So, what's the status??? What have you found out so far?
     

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