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#1
08-16-2005, 03:55 PM
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Need new ideas about oil leak
I have been fighting oil leaks since I rebuilt my 455. It has been rear mains and oil pan leaks. I have replaced an oil pan that I found to be bent and also a couple of rear main seals. I am using a BOP rear main and followed the instructions carefully when I installed it. The leak is not as bad this time but after about 20 minutes I could see a line of oil slung off the fly wheel. I am looking for new ideas as to what could be causing my problem. I have pulled the motor 4 times trying to solve this and am not having any luck. The block was fully machined before starting so I know it was straight.
Any ideas of what I could have missed? (several times) |
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#2
08-16-2005, 06:53 PM
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The lifter cover gasket can leak in the back and look like a rear main seal...
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--------------------------------------------------------- "And he Asked, Who Owns This Car? With The Peace Sign, Mag Wheels, and the Four on the Floor?? --------------------------------------------------------- |
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#3
08-16-2005, 07:57 PM
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You may have one of the weird blocks like I have. I kept having leaks with my BOP seals no matter how carefully I prepped the installation. Finally discussed it with BOP and they had me measure the groove for the seal all the way around. Turns out it was cut at an offset. You can see in the photos that the passenger side of the groove is about .026" deeper than the driver's side. The max allowable is .005. You can see how this affects the seal itself. You can have the block machined to correct this if you happen to live near a large city. I tried in vain to get a local (within 100 miles) shop to fix it but all I got was "it needs a line-bore" answer (which won't fix the problem). I finally cut it myself using a die grinder with 2 wheels attached. Took a whole day - light pass, measure - light pass, measure. However, it seems to have fixed the leak. If you pull the block again I'd measure the groove, including the cap.
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  1967 Firebird ragtop, 464, Weiand 8-71, ported 6H heads, Hyd roller, 4L80E, paddle shifter, Moser 9", Cal-Tracs, Vintage Air, Corbeau seats, 13"/12" disk brakes, Hydraboost, electric cutouts and M&H drag radials. 
Last edited by Sporter; 08-16-2005 at 08:29 PM. Reason: Add attachments |
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#4
08-16-2005, 11:04 PM
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this is interesting. I have been fighting one that isnt CONCENTRIC to the crank, is .015 off to the side (just the rope seal grove) this is like a .007 squish and a .007 (loose) on the sides, which, btw leaks like a small stream running.
seems the machine work on the later 455 blocks was kinda poor, now im wondering if it was done in Mexico , like some other GM cars and truck engines. Ill have to look at the "offset cut" of that grove again. Great post!! |
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#5
08-17-2005, 08:39 AM
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Thanks for the pictures, I will check the grove when I pull the motor out. If it is bad I will put in a rope seal, I do not want to pull the motor apart to do more machineing on it.
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#6
08-17-2005, 10:14 AM
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Also someone stated that you should put some silicone between the main cap and the block. Any one haerd of this, is it good? I have always gone on do not put silicone on a machined surface.
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#7
08-17-2005, 10:34 AM
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I run a SMALL bead of silicone at the very back edge of the block where the cap sets to help seal up the cap to the block. Also one other thing is the stock rubber rear oil pans gaskets tend to leak. I always replace them with the cork rear oil pan gasket and glue them in place. No leaks what so ever. I would look into those if you find that your block is ok.
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#8
08-17-2005, 02:07 PM
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Do you have a breather in the valve cover? Dave K.
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#9
08-17-2005, 02:51 PM
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Breather in valve cover and working PVC.
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#10
08-17-2005, 08:30 PM
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after a little research, Ive found this problem only to exist on 75 and 76 455 blocks. When the machining took place (cap off block) the procedure was shoddy at best as the rope didnt care. Having a concentricity issue, like this one here, and few Ive seen now that leak, all have their oil seal hole off to the side by 15-25 thousands. This CANNOT be fixed by Align boring block. The block centerline must be maintained ( NO side to side movement), Align boring typically moves crank up in block a couple thousands.
All that being said, there IS a fix. The Engine builder I go to, and know personally, has verified the claim above , and has the equipment (CnC etc muti angle milling and boring) and can bring the hole to centerline of crank. this will make your BOP seal work well. It does require a shim sealed in the grove behind the seal, the shim would be different for each block as some are off more than others. I believe hes going to be discussing this with the AERA this weekend (engine rebuilders conference) This fix may or may not be happening out there as Ive now heard a bunch tossed good blocks. He would buy some tooling, rather than the 1st made stuff, if the interest is there in getting your block right. So, if theres interest, speak up!!.l Last edited by Formulabruce; 08-17-2005 at 11:35 PM. |
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#11
08-17-2005, 10:35 PM
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Taht may explain alot since the 455 block I am using is a '76. Thanks for the info I will mike it out and see when I pull the motor next.
Looks like I might need a rope seal if it is off since I do not want to totally take it apart and do more amchineing right now. |
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