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Old 04-15-2014, 01:02 PM   #1
Tom Endy
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Default Rear main thrust

Bratton's new 2014 catalog shows a new part on page 2, called a "Brass replacement main with thrust surface". Part number 8949.

The description states that "This replaces the original style rear main oil seal #8960. This provides a superior crank thrust surface than the original babbit. Also if the babbit thrust surface has cracked off your cap this will now act as the crank thrust surface".

Has anyone had experience with this modification?

Tom Endy
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Old 04-15-2014, 02:09 PM   #2
CarlG
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Default Re: Rear main thrust

I have this in my engine and so far (1,500 miles) seems to be working fine. Reason I went that way was, as you stated, the babbit thrust surface was pretty much gone. Almost completely solved my rear main "spotting". Only get a drop or 2 every now and then. Before it was a teacup full every time I parked it.
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Old 04-15-2014, 02:57 PM   #3
Dave in MN
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Default Re: Rear main thrust

Tom,

This part has been available for quite a few years now from other sources.
I use them in my insert bearing design. I machine for a 1/2 circle thrust (Bratton's part # 08946) into the cap for a full surface thrust at the rear. The combination rear main seal/thrust and the machined recess in the main cap capture the 1/2 circle thrust keeping the 1/2 circle thrust from moving.

They work good for my purposes. I use them because they keep any small amount of oil coming through the rear main bearing in contact with the thrust surfaces for a longer period of time....thus providing more lubrication to the rear thrust.

Photo helps my description.

Good Day!
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Old 04-15-2014, 08:32 PM   #4
SteveB31
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Default Re: Rear main thrust

Tom,

We have made those for about 20 years now, and sold appx. 9,000 of them. Many babbit engine builders use them on every engine they build. They do generally last longer then most babbited rear thrusts.

Steve Becker
Berts Model A Center
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Old 04-16-2014, 04:25 AM   #5
colin1928
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Default Re: Rear main thrust

Yes I have used them when the Babbitt thrust was cracked but the rest of the bearing was ok they work well checked 1 after 10,000 miles minimal wear put it back in still working
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Old 04-16-2014, 08:27 AM   #6
John Stone
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Default Re: Rear main thrust

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Think I need some enlightenment. Almost all the engines I take apart (90%)have the rear main cracked on the forward part of the thrust surface. The brass thing is for the rear thrust surface. How does this help the forward part? I believe the crank puts more pressure on the front surface and generally the rear surface is only contacted when the clutch is depressed.

Also, how the the clearance set when replacing the oil seal in the back with the new one?

Thanks--John
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Old 04-16-2014, 12:47 PM   #7
Dave in MN
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Default Re: Rear main thrust

Quote:
Originally Posted by John Stone View Post
Think I need some enlightenment. Almost all the engines I take apart (90%)have the rear main cracked on the forward part of the thrust surface. The brass thing is for the rear thrust surface. How does this help the forward part? I believe the crank puts more pressure on the front surface and generally the rear surface is only contacted when the clutch is depressed.

Also, how the the clearance set when replacing the oil seal in the back with the new one?

Thanks--John
John , You are correct in your observation...
Installing the rear thrust will not help an engine with the front thrust failing.

If you install the rear combination thrust and seal, you will need to modify the front thrust to adjust the clearance. You could build up or remove from the front thrust to set the clearance. I have not tried to build-up a front thrust but I have heard of it being done...I do not know the process. Another option would be to install a 1/2 circle bronze thrust in the cap. The cap can be mounted on a stub shaft in a lathe (turned to the ID of your rear main cap) and the recess for the thrust can be machined to allow for the suggested .003" oil clearance. This modification to the cap will remove the front Babbitt thrust from the cap only. The bronze thrust will be captured by/between the crankshaft and the combination of the cap and block. (You do not need to stake the thrust to the cap.) The block will keep the bronze from rotating. The bronze 1/2 circle thrust should float in the recess you create in the cap. Leave a couple thousandths clearance in the machining so the 1/2 circle thrust is not a force fit into cap recess. It is a good idea to slightly bevel the leading edge of the bronze thrust contacting the thrust surface of the crankshaft. Leaving the edge at a sharp 90 degrees could cause the bronze thrust to wipe the oil from the crankshaft. It is likely that the bronze thrust surface will be proud of the Babbitt thrust on the block so the edge profile is important. (See post #3 above for a photo of a cap modified for a bronze thrust. The cap in the picture has one installed at the rear but the installation technique and "look" is the same at the front of the cap. This photo was of one of the first engines we installed inserts into...we now dowel all of our caps to the block.)

Thrust Washers

These half circle shaped brass thrust washers are used when converting a babbitt style motor over to modern inserts.

These thrust washers are available from many of the national vendors or the manufacturer, Antique Engine Rebuilding in Skokie, IL.
Good Day!

Last edited by Dave in MN; 04-16-2014 at 02:55 PM.
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Old 04-17-2014, 08:24 AM   #8
old splicer
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Default Re: Rear main thrust

Doe anyone make this for a Model B?
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Old 04-17-2014, 08:43 AM   #9
John Stone
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Default Re: Rear main thrust

After reading post #7 (which I agree with), I believe the people that advertise the rear thrust insert should point out it does not correct excess thrust if the front is worn or broke. To fully correct the problem, it is a much more involved process. Either the machine work is required to essentially install inserts or a new babbit job.

Nothing is as easy as someone says when they are trying to sell you something.
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Old 04-17-2014, 12:59 PM   #10
Dave in MN
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Default Re: Rear main thrust

Quote:
Originally Posted by old splicer View Post
Doe anyone make this for a Model B?
The 1/2 circle trust washers are available for "B" engines but not the bronze combination seal and thrust....to my knowledge anyway.
Good Day!

Last edited by Dave in MN; 04-17-2014 at 03:06 PM.
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Old 04-19-2014, 03:04 PM   #11
drumyn29
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Default Re: Rear main thrust

Quote:
Originally Posted by SteveB31 View Post
Tom,

We have made those for about 20 years now, and sold appx. 9,000 of them. Many babbit engine builders use them on every engine they build. They do generally last longer then most babbited rear thrusts.

Steve Becker
Berts Model A Center
Can a rear main be installed without removing the crank? I changed the oil pan gasket today and it still leaks bad. DAMMIT.
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Old 05-07-2014, 02:49 PM   #12
kentdepe
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Default Re: Rear main thrust

I have a newly rebuilt engine in my Model A and believe the rear main oil seal casting in the block was not RTV'd into place. Can I remove the oil pan, clean up the rear main seal casting with a good solvent and add RTV without removing the crankshaft? Kent
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Old 05-08-2014, 07:42 AM   #13
Dave in MN
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Default Re: Rear main thrust

I don't know if RTV would bond well enough to keep this area sealed. I have used Permatex "Right Stuff" as a gasket replacement and find it takes a stiffer set and bonds very well to cast iron if it is clean. IMO: I would use this product instead of the RTV. Try to work some of this same product along the seam between the cap and the block to halt any oil movement. I think it may solve your problem. Let the Right Stuff set up 36 hours before running the engine and try to keep the Stuff no less than 1/16" thick over the area to be sealed and beyond to help support and bond the fix.
Good Day!

Last edited by Dave in MN; 05-08-2014 at 07:59 AM.
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