Model A Lower end

J

JBohannon

Senior Member
For the first time I am going to pull the pan on my 28 Model A and see what condition the bottom end is in. I am doing this for 2 reasons. At higher engine speeds I get a terrible vibration and it feels like engine is going to come apart. Also I have a bad rear seal leak. My compression is ok and the car runs ok but I think it is time I see what condition it is in. Any ideas on what I should look for when I get the pan pulled. Should I check for extreme looseness in the rods or use plastigage? Thanks for any help.
 
i believe the spec is .003-.008
to much end play can contribute to a rear main oil leak and vibration.
of course many other things can cause that also.
 
I was under the assumption that most of the vibration would have been from a bad rod bearing but I am now reading in this and other post that it might well be the mains also? Any thing else to look for.
 
Some average, completely stock Model A's, many time has vibrations/rattles, that sounds as if you're "tearing" up the engine, usually above 45 MPH. Many small things can cause "disastrous" sounding noises. Minerva had a bad noise for about a week, once! The locking knob for the windshield slide bar was NOT TIGHT enough. The tail pipe hanger can cause BAD noises sometimes. If you rig up a rubber hanger on the pipe, it helps a lot.
On crankshaft end play, it helps prevent some wear on the bearing thrust area, IF when you're waiting at LOOOONG stop lights, put it in neutral & let the clutch out. With the clutch pushed in, it puts a LOT of pressure on the thrust area of the MAIN BEARING & causes extra wear.
You can get a FAIR idea of lower end bearing condition, by holding the idle to about 900 to 1100 RPM & "feather" the speed, UP & DOWN, slightly & listen for KNOCKING type sounds. A rod knock can be narrowed down by grounding out 1 cylinder at a time. If you SUSPECT a loose CENTER MAIN, usually it quiets down SOME, when you ground out # 2 or # 3 & will quiet down completely, when you ground out # 2 & # 3, AT THE SAME TIME, while "feathering" the throttle. Claude, (RIP) our REAL GURU, had a rebuilt engine with a center main knock, SOMEONE FORGOT TO ADJUST THE CENTER MAIN!! The shim pack was TOTALLY undisturbed!!! After adjusting it, the engine sounded "PRIMO"!!!
Bill W.
 
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Correct me if I'm wrong, but I don't think a bad bearing will cause a vibration. Or at least a loud knock way before that? Has this engine ever run smooth? I think the vibration is u joint, out of balance crank/rods or pressure plate ect.
 
JBohannon said:
For the first time I am going to pull the pan on my 28 Model A and see what condition the bottom end is in. I am doing this for 2 reasons. At higher engine speeds I get a terrible vibration and it feels like engine is going to come apart. Also I have a bad rear seal leak. My compression is ok and the car runs ok but I think it is time I see what condition it is in. Any ideas on what I should look for when I get the pan pulled. Should I check for extreme looseness in the rods or use plastigage? Thanks for any help.
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What does high engine speed mean ? And, does this vibration happen while sitting still in neutral or only when driving ?
 
I always sit at a light with my foot off the clutch, also helps me from getting T boned people like to run red lights hear. also I start up the motor with my foot off the clutch, I like to get some oil in there before I step on it
 
the vibration is the same in neutral or driving. It starts at mid throttle. I think my laymen thoughts are it is in the rods?
 
JBohannon said:
the vibration is the same in neutral or driving. It starts at mid throttle. I think my laymen thoughts are it is in the rods?
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Model A's have so much stuff that's mounted almost solid and/or metal to metal & some noises are almost impossible to find/correct. Each car has different personalities/sounds. Once in awhile I ACCIDENTALLY find/correct a noise, after it's driven me NUTS, for month. Minerva had a loose vertical wood piece, behind the R/H quarter window, that would only noise off @ 40 MPH, in second gear. I almost NEVER found that sucker! I used to know the part # for that individual wood piece. BUT, I DO know the part # for the oil pressure sender for Early Jaguars--PT-1801/06 & the short stepped radumator hose fur a Jag-XKE is--C15099! The English made POOR rubber. I hope their condoms are better.
Bill W.
 
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