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[JPP]

Hello, I have my '29 AA on the road, and have actually driven 550 miles, lots of fun. Ok well, I seem to be burning oil and my compression tests at 40 psi across all four cylinder. I had added oil to one cylinder head, and tested again, no help on compression. Do I need rings? What is best techniques, my Model A manual, Vol. dosn't talk to this much. I can drive empty on flat road to 45-50 mph, steep hills not so much. all advice appreciated.

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[BrianT]

Hello JPP,
You didn't say our much oil you used in that time, if adding oil to a cylinder didn't change the reading it generally indicates leaky valves, I would try with another compression gauge before deciding a course of action, worn valve guides are a possible cause but often cause intermittent rough idle. have you noticed any blue smoke when coasting, or oily spark plugs ?

[gunmetal 2]

Did you ever think about it being a bad head gasket. Nice truck I got one in pieces restoring it. Do you have a worm gear rear end. Is your truck gunmetal blue. e-mail me at 1929oldlady@gmail.com I live in upper Indiana.

[Stakebed]

yea if adding oil to any engine then redoing the compression test and it doesnt change its a valve issue. stuck or broken rings will get temporarily "fixed" when you add the oil and change the compression test.

if you can hook shop air up to the spark plug hole when the piston is TDC (valves are supposed to be closed) and keep it regulated or turned way way down you can feel/hear air escaping thru the valve thats the culpret. (intake leak will allow air hiss out of the carb, exhaust valve would allow air hiss out the exhaust pipe)

your sure you have the correct amount of oil in it right? too much and it will burn/blow out. ive heard SOME aftermarket dipsticks are improperly marked on the scale side of the stick..

[JPP]

Hey thanks for the help.. let's see, yes I have oily spark plugs. As for how much oil, from full to low on 2 tanks of fuel. The truck paint is midnight blue. I have a high speed rear out of a 30 AA. I have an original dipstick and a 29 AA motor 2. Million serial number. I lean towards rings, as I haven't touched them yet. Head gasket is new, not that it makes a difference, could still be leaking.. can`t wait to try air pressure test. Will know Saturday. Thanks

[Stakebed]

yea if its leaking thru the rings bad you will hear it hiss out of the oil fill tube.(you will hear some due to them being rings with splits in them) when i say keep it regulated down i mean like 30psi. you can do almost the same with a 1/4 turn valve hooked in with the air line and just barely crack it open. Use an old spark plug or a big rubber cork on the end of the air hose/whatever you have to regulate it.

take all the plugs out when you do this and keep the ign off.

if its a leaking headgasket into the water jacket, it will create bubbles in the water (keep radiator cap off - should be NO bubbles in water)

if you hear hissing from an adjacent cylinder you got a leak between cylinders in the headgasket (or warped head or block)

your burning oil due to leaky/loose/stuck valve and or broken rings. something is allowing oil to be sucked into the cyl.

when you did the "wet" compression test did you use at least 1/2 cup of oil down into the cylinder? your sure it got into the cylinder and not all over the valves that are directly below the spark hole?


my gut feeling is something in the valve arrangement (cracked valve, worn seats, worn guides, worn valvestems)

[JPP]

Stakebed, et al , Thanks for your insight. 1/2 a cup of oil, no I certainly did not use that much. As for oil placement, I can't be sure of that either. I have an old plug with an air compressor fitting welded to it, and I can regulate my air pressure, so i can bring it up from 5 psi to 30, when I do the experiment. As for sticky or cracked valves, i took the valve cover off and they all seem to go up and down no problem as I crank the engine manually.

[Stakebed]

Stakebed, et al , Thanks for your insight. 1/2 a cup of oil, no I certainly did not use that much. As for oil placement, I can't be sure of that either. I have an old plug with an air compressor fitting welded to it, and I can regulate my air pressure, so i can bring it up from 5 psi to 30, when I do the experiment. As for sticky or cracked valves, i took the valve cover off and they all seem to go up and down no problem as I crank the engine manually.

good good. yea valves can move freely (could be too freely due to worn stems or guides) but still not seal due to the valve seat having a crack or valve head itself having a crack or burnt spot (not setting advance right when crusing or too little fuel)

could also bea a warped valve not sealing completely or has just the right amount of pitting.

the valve and or seat cracking is pretty common on all engines. If your cylinder leakdown test (actual name of what im suggesting you try) says its a problem with a valve not seating your going to have to pull the head and get a better look to find out if its a seat or a valve. if its a valve its MUCH easier to replace.

yea when ti comes time to get the oil out of the cylinders leave the plugs out and put an old towel over the head covering the spark plug holes (not plugging them) and crank it, should expell most of the oil (i say use a towel so it doesnt spray oil residue over everything under the hood. will still smoke quite a bit on initial startup so dont do it with the truck in the garage haha.

[JPP]

Ok I did the test. Motor turned to top dead center. Spark plug 1, closest to radiator, air is leaking through oil fill tube. In cylinder 2,3,4 I hear air going to muffler. Does that mean I need valves and rings?

[Bob C]

Did you bring each cylinder to TDC and make sure it was on the compression
stroke before testing it??

Bob

[JPP]

Sorry, no only top dead center on # 1, how do I get that for the other three, only one indent on timing gear. Please advise.. obviously new at this. Thanks

[Jazzjr]

Remove the Top of the Distributor Cap, rotate the engine with the crank or have some one help you bump the Starter, until the Rotor comes in line with the next pin in the Distributor Body. The Firing order is 1-2-4-3 then test each cylinder. It turns in a Counter Clock Wise Rotation.
The Photo below shows how to set the Timing, so put the center of the rotor, across each pin to obtain Top Dead Center (TDC)

[JPP]

Ok, now I tested all the cylinders at top dead center and all four cylinders leak through the oil fill tube. So does that mean rings for all four cylinders? How do I determine what size rings to buy? Does my test tell me my valves are ok?

[flatford39]

Looks like you need to pull the head and take a look at what's in there.

[BrianT]

John,
A couple of thoughts before you take the engine apart, is the engine oil fresh and not to thin?, it seems odd that the compression at 40 psi and even on all cylinder runs and starts OK, you did not mention if there was any change in compression when retesting with the oil in the cylinders.
Did you notice if there was a lot of blue smoke coming out of the filler tube or exhaust when the engine was running, any major oil leakage?,