312 rear main seal


http://209.208.111.198/Topic38026.aspx 		Print Topic | Close Window

By carl - 15 Years Ago
I know this subject has been covered a lot but i want to add this information.i have replaced the  rear main seal in my 312 three times and it still leaked.one time i installed the bottom seal in the retainer backwards and it really leaked.the other two times i really took my time and followed Teds tips and it still leaked.when i took it apart this time i noticed that the two halves  of the neoprene seal were a different width and there is a .025 gap between the retainer and the thinner seal.i still had the one that leaked before and it was the same.  apparently the oil pressure pushed the seal back and let oil seep between, the seal and retainer.I called Armin Brown at Best Gasket and he said that they had been (recently) aware of that problem.he did send me new seals,both rope and also neoprene and the neoprene are both the same width and are a tight fit in the block and retainer.now i have to decide which to use,rope or neoprene.   Carl    Ohio 
By Ted - 15 Years Ago

Carl.  I’m going to suggest you give the neoprene seal one more shot.  The fact that you found one of the seal halves narrower than the other at least gives you an idea of what was causing this last rear main seal oil leak.  Just something else to watch out for but sounds like you’re on the right track now.

 

If anyone else has any suggestions, be sure to post them as Carl has been struggling with this for awhile.  Carl’s ’56 is just drop dead gorgeous and it makes me cringe at the thought of the engine coming in and out while trying to rectify this problem.

By paul2748 - 15 Years Ago
No other suggestions, but the neophrene seal in mine is a Best Gasket unit and I haven't any problems in the three years it been on the road. They probably had a bad manufacturing run after they made mine.
By marvh - 15 Years Ago
I had a problem with the best gasket seal on one of the 312's I rebuilt. I pulled the engine out twice before I found the seal groove in the block was deeper than the seal was. It previously had a rope seal.



If you install the seal so the ends are staggered that when one end is above and the other end below the casting parting line you will not notice this. I found the problem when I pushed the seal down so both ends were level at the casting parting line. The seal end sat about 3/16" below the parting line so had a big leak. To fix it I had to do it the long time method of using a Dodge 318 seal as they have a higher seal crush than the Best seals do and you trim it till it fits.



Today whenever I do an engine I check to see if the groove has not been machined deeper than normal.

marv
By carl - 15 Years Ago
Marv  Never checked the seal groove depth but i will tomorrow.Maybe if i get it fixed this time  i can get rid of the velcro motor mounts  LOL  Carl
By Ted - 15 Years Ago
Marv.  Thanks for the heads up on the 312 seal groove depth.  That’s an item that’s easily overlooked but also easy enough to check out during the initial assembly now that it’s known that the groove depth can be a factor.  I’ll edit the seal installation tips on my own website to incorporate this as this is a good piece of info.
By marvh - 15 Years Ago
Your welcome Ted.



It was the only 312 I have seen like that. It was Canadian 312 block from a 56 Merc.

marv
By aussiebill - 15 Years Ago
Ted (1/21/2010)
Marv.  Thanks for the heads up on the 312 seal groove depth.  That’s an item that’s easily overlooked but also easy enough to check out during the initial assembly now that it’s known that the groove depth can be a factor.  I’ll edit the seal installation tips on my own website to incorporate this as this is a good piece of info.

Ted, i have mentioned in the past of finding in some 272,s the rear seal depth in the block being shallow but ok in the seal cap, resulting in the neoprene seal elongating upon tightening and leaking straight off, a worthy note to check all depths on all of them! The jets are on the way. regards bill.

By Ted - 15 Years Ago

Bill.  Thanks for the additional piece of info on the 272 seal.  You gotta love manufacturing variances.  I have appropriately modified the seal installation instructions on the eatonbalancing site to include checking seal groove depth on all Y’s.  Here’s the link.

http://www.eatonbalancing.com/blog/2008/09/10/neoprene-rear-seal-installation-for-the-y-and-others/

And thanks again for the jets.