Engine Rebuild Question

[JP31]

I have removed the engine in my 31 Cabriolet because of a rear main oil leak (modern seal). I have opened the engine and removed the crank to inspect the babbitts and to possibly replace the "modern rear seal" The best I can guess is that the engine was rebuilt about 20 years ago and the slinger was removed and a Burtz rear seal was used. The engine has performed well and the seal just began leaking. I can't afford to put a lot of money in the engine right now but wanted to get recommendations on what I should do while it is open. I would like to clean and repaint, I had an exhaust and intake gasket leak that was pretty obvious when I removed the manifolds. What to do and where do I stop? Thanks in advance for your advise.

[Terry Burtz, Calif]

After 20 years of good performance, your rear main bearing most likely has excessive clearance. Clearance should be .0015 inch.

With excessive clearance, the crankshaft is wobbling around and the seal lips cannot respond quick enough to maintain contact with the rubbing surface.

Check the condition of the Babbitt, shim for .0015 inch clearance, install a new seal, pressure check, and you should be good for another 20 years or equivalent mileage.

[JP31]

Thank you Terry

[Dave in MN]

While you have it opened, check the valve guide clearance to the valves. Replace the components that show excessive clearance. Refresh the valves with lapping compound to the seats.
You know this but I'm going to say it...keep everything clean during your work and re-assembly.
Good Day!

[JP31]

Thanks Dave. Should I also check cylinders and replace piston rings? Would new rings help or hurt me if I don't rebore the cylinder walls?

[Dave in MN]

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Originally Posted by JP31

Thanks Dave. Should I also check cylinders and replace piston rings? Would new rings help or hurt me if I don't rebore the cylinder walls?

If you were not experiencing blow-by you could re-use. If you replace the rings, you should de-glaze the cylinder walls with a flexible hone. Time your up and down motion with the rpm of the hone to create a cross-hatch pattern. IMO: Rings do not cost much ....I would replace the rings and deglaze as described if it were my engine.

Flex-hone used to de-glaze cylinders.

120 Grit Standard Flex-Hones, 2" to 4-5/8" Diameters
Order No.: BG-210
$24.69 Go to Goodson Tools ( http://www.goodson.com/Flex-Hones/ )


Make sure you carefully clean the carbon from your existing pistons, including cleaning the ring grooves. Wash and re-wash to remove traces of the carbon dust you will raise prior to assembling. Fully wash/clean the block after deglazing the cylinder walls. Clean is critical!
Good Day!

[Tom Wesenberg]

As Dave said, clean is important. After you think the cylinder walls are clean I oil them and run a white paper towel up and down. If the paper towel comes out clean then the walls are clean. You'd be surprised at how much cleaning it usually takes before the paper towel remains white.

[colin1928]

Installing new rings when you engine apart is a good idea but you must check for a ridge in the bore if it has a ridge remove it or it may break your new rings
also inspect and measure everything possible from timing gears to head

[garyjohn]

You might want to check and see if the cam shaft is leaking oil also This can me-mick a rear main seal leak also. I have pulled my engine and found that the cam was leaking into the flywheel housing. I am going to seal it with a brass freeze plug before I reinstall my engine.

[James Rogers]

Originally Posted by garyjohn

You might want to check and see if the cam shaft is leaking oil also This can me-mick a rear main seal leak also. I have pulled my engine and found that the cam was leaking into the flywheel housing. I am going to seal it with a brass freeze plug before I reinstall my engine.

To do that you will have to remove the cam and have some cut off the rear to make room for the plug.You also won't use a freeze plug since freeze plugs have a flange. You will need to find a welsh plug of the correct diameter.