Unusual oil leak in a Model A motor

Topics Last Day Last Week Tree View    Getting Started Formatting Troubleshooting Program Credits    New Messages Keyword Search Contact Moderators Edit Profile Administration
Model T Ford Forum: Forum 2012: Unusual oil leak in a Model A motor
Top of pagePrevious messageNext messageBottom of page Link to this message  By Scott Kramer on Friday, May 04, 2012 - 08:36 pm:

I was talking to a friend who owns a 1931 Model A (he also owns an early T).He had his Model A motor rebuilt last year.The problem is that it is leaking oil at the center main bolt where it comes out of the block.It leaks about 3 quarts in about 30 miles.
Does anyone have any idea why it is leaking oil ?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Gregush Portland Oregon on Friday, May 04, 2012 - 08:57 pm:

Even with the center main bolt snugged up to specks there would be no way to have that much oil pump out it. It might weep. That is a big oil leak. I would be looking for a hole between the valve gallery and the area between the cylinders or a hole in the crank case in that area. The Model A pumps oil at about 4 PSI from the pan into the valve gallery which then feed the 3 tubes to the mains, the over fill then goes through a hole in the front and fills the windage/dipper tray. The main bolts only have their head exposed like a T so any oil would need to get past there to make it outside.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bill Stephan Two Rivers Wisc. on Friday, May 04, 2012 - 09:05 pm:

Can you put a copper or brass washer as a gasket under the nut? ws


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Gregush Portland Oregon on Friday, May 04, 2012 - 09:16 pm:

I think they would be too soft. You would have to drop the pan to do that now anyway. You can put some sealer at the base of the threads where they come out the block when you assemble the engine. Without putting a lot of pressure on the wrench, can you move the nut in any way. Were cotter pins (correct way) or lock washers (wrong way) used?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kohnke Rebabbitting on Friday, May 04, 2012 - 11:09 pm:

The likely cause is who ever rebuilt the motor, probably pressurized the center Main, and that is why all the oil. Don't waste your time with any thing to seal it it with, except a lead washer over the bolt, and under the nut. Yes you will have to take the pan off, and torque the main bolt to 80 foot pounds. Herm.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bill in Adelaida Calif on Friday, May 04, 2012 - 11:10 pm:

How rebuilt is it? Was the engine modified for full pressure to the mains?

Bill


Top of pagePrevious messageNext messageBottom of page Link to this message  By Deron Shady on Friday, May 04, 2012 - 11:25 pm:

Scott,

I had a customer's Model A in the shop several years ago with exactly the same problem. Ask your friend if it's a stock rebuild or one that's been modified and monkeyed with. The problem that I found with my customer's car was that he'd had someone (who apparently wasn't exactly qualified) build him a pressurized motor with a high dollar billet oil pump, counterweighted crank, aftermarket rods, etc. You know, all that stuff that a Model A really doesn't need.....

Anyway, I found two distinct problems that were causing the oil leak. First was that the bypass on the oil pump was adjusted too high, and it was making way too much oil pressure.

The second thing I found was that the machinist had been careless when line boring the block for inserts, and the area between the main bearing saddle and the main cap bolt hole was paper thin on two bolts & had a small chip missing out of the third. This was a problem on the center and front mains only, but the one leaking was the one with the small chunk missing. The way they had converted it to inserts was to lay two conventional narrow main bearings beside each other with about a 3/16" space between them. As soon as the motor built up oil pressure this gap would fill up and channel the oil directly to the main bolt hole and right out the top.

Adjusting the bypass valve on the oil pump only helped to slow down the leak. What I ended up doing to stop the leak was to take some main bolt nuts and back cut the bottom side to contain an o-ring. That way you still have a solid bearing surface on the bottom of the nut, but there's a small groove that will capture the o-ring and squeeze it tight against both the stud and the block. Best I recall, I think I also coated the sides of the main bolts with RTV before installing them because I wasn't about to pull the oil pan a fourth time....

Keep us posted as to what he finds!


Deron


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Weir on Saturday, May 05, 2012 - 04:19 am:

Go to McMaster catalog online and type in _ standard sealing washers and then pick the size you want. Their shipping is great.

Sincerely

Jim Weir


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bob Shirley on Saturday, May 05, 2012 - 06:50 am:

The Toyota 4.7 Tundra around 2000 uses a aluminium washers on their fuel rail that fit just right. Soft enough to seal, but hard enough to hold up, and cheap.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Howard D. Dennis on Saturday, May 05, 2012 - 08:25 pm:

I could be wrong, and it's been a long time since I saw an open Model A crankcase but if memory serves me correctly, the rear main cap on a Model A has a screw in tube to drain the oil back into the pan and IF that tube falls out it blows oil out of the rear main.

Howard Dennis


Top of pagePrevious messageNext messageBottom of page Link to this message  By David Dewey, N. California on Sunday, May 06, 2012 - 02:01 pm:

Howard,
You are right, and it's a detail that seems to be lost on many nowadays. That tube was originaly threaded into the cap and spot ark welded to keep it from turning, and coming out. One thing one has to be careful when installing the tube is that it doesn't block the drain, so I usually grind a V in the back side of the threaded portion so the oil has a free flow from the cast in drain galley down the tube.
The Center main leak makes me suspect the shims on the center main are the type that has a C cut for the bolt instead of a bolt hole. This is often done so you can pull the shim out without taking the bolt out, so adjustment is easier. However, like all modifications, it then allows the bearing oil pressure access to the bolt hole, and voila, a leak out the top where the nut is.
Easiest solution--change out the shim pack.
T'
David D.


Posting is currently disabled in this topic. Contact your discussion moderator for more information.
Topics Last Day Last Week Tree View    Getting Started Formatting Troubleshooting Program Credits    New Messages Keyword Search Contact Moderators Edit Profile Administration