crankshaft moving

[carolinamudwalker]

Was under the car looking for an oil leak when I noticed about a 1/8th inch of shiny crankshaft indicating that it has moved forward. Is this normal or do I have a problem? Car runs fine. Bob

[Marshall V. Daut]

That's called crankshaft endplay and should not exceed about .004"-.006", the less the better. The Babbitt along the back and front edges of the rear main bearing controls this fore-and-aft movement and was set to this tolerance when the Babbitt was poured - or should have been set. As the Babbitt is worn down through engine operation, the crankshaft's movement becomes more and more pronounced. This causes oil to leak from the rear main bearing slinger "seal" because the crankshaft is now acting as a pump to the rear. The slinger and drainage system in that area can't handle all that extra oil, so the oil follows the path of least resistance and goes out the rear main bearing area, down the flywheel housing and eventually out of the bell housing. There are fixes for this condition short of re-pouring new Babbitt, but they are all quasi-Rube Goldberg stopgap measures. Until you are able to reduce the fore-and-aft crankshaft movement to an acceptable amount, your leaking will become more acute.
Marshall

[H. L. Chauvin]

Hi Walker,

Your findings are the same as an untold amount of Model A owners who have had this same crankshaft condition since 1932, did nothing about it, and just kept on driving for thousands and thousands of miles thereafter.

Forum member opinions and corrective actions are generally related to: "What's in your wallet?"

[George Miller]

Good explanation Marshall.

[Bob Bidonde]

https://www.youtube.com/watch?v=N5kDrtTJGsU

This presentation by Antique Engine Rebuilding of Skokie, Illinois is worth watching multiple times until the nuances sink in.

[Tom Wesenberg]

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Riding the clutch while parked at a red light is good for wearing out the rear thrust babbit. That exerts a lot of forward pressure on the babbit.

[Bob Bidonde]

Hi Tom,
You make a good point. In my opinion, the action of the clutch and the inertia of the driveline due to engine acceleration, deceleration and braking are the primary loads on the crankshaft bearing thrust faces.

When the crankshaft has excessive fore-aft motion due to worn thrust bearing surfaces, it forces the connecting rods to slide on their journals and induces bending stresses in the rods and wrist pins. The pistons and cylinders also see loads as they tend to resist the connecting rod motions.

Marshal Daut gives us an excellent explanation of what goes on in the rear and front main bearings when crankshaft thrust motion becomes excessive.

[George Miller]

Along with what Tom said, plus Parade driving.

[Jim Brierley]

Also the babbitt can come off in pieces, perhaps caused by poor bonding. I was preparing for a race years ago and noticed the same thing. Not wanting to miss the race, I patched it using some flattened copper tubing, on the cap only. It lasted thru the race and still looked good. Get it fixed whatever you do.

[George Miller]

Originally Posted by forever4

Not the best fix, but something you can do without an engine rebuild is the replace the thrust. This can even be done in cases without removing the crankshaft, depending on why has cracked and what is missing.

click> www.fordgarage.com/pages/Abronzerearthrust.htm
Model A Ford Garage ~ Bronze Rear Main Bearing Thrust

I have had good luck with those. They work well with inserts, along with the half round thrust sold by the venders.

[Fullraceflathead]

Don't ride the clutch pedal while stopped at a light and Learn to shift without double clutching. You will cut down wearing out the Babbitt thrust surfaces by 50%.
It's not that hard to shift without double clutching. I count roughly 3 seconds when shifting gears. 1st then at 7 to 10 mph shift to 2nd, then 20 to 25 mph shift to 3rd.
The lower speed level ground and the higher speed for uphill. Remember 25mph in high gear with 3.78 is 1000rpm engine speed. Don't lug in high gear below 20 mph if pulling hard.

[40 Deluxe]

Originally Posted by Tom Wesenberg

Riding the clutch while parked at a red light is good for wearing out the rear thrust babbit. That exerts a lot of forward pressure on the babbit.

How about the forward pressure exerted on the thrust surface by a propeller?? Pietenpol (Bernard?) himself stated that the thrust surface was just fine for aircraft use! Anybody know what is done these days for aircraft use?

[carolinamudwalker]

Thanks every one, I am learning more every day. Will nurse it until this winter. Bob Bidonde, Great link, I was leaning in that direction already. What a great bunch of people on this forum. Bob Reid