Rear main oil leak
I have had a steady, but small, oil leak from my rear main on my '67 L71 for a few years. It is not a big deal, but I get annoyed (especially at flight judging) when the leak is pointed out t me once again. A little oil, like a little blood, always looks like alot. I probably lose about 1/2 -3/4 quart a year. The question is, how difficult (and thus expensive if I can't do it) is this to fix? I assume it is the rear main seal with lots of parts to remove to get to it. Guess there is no oil additive to fix it like in the old days. Any ideas welcome, thanks.
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Big Tanks In the High Mountains of New Mexico -
Re: Rear main oil leak
Michael,
Not easy, the distributer has to be removed along with the schroud, fan, and front mount bolts. Then the engine has to be lifted to remove the pan. The rest is easy but there a few tricks that will insure that it does not leak again.
getting to it is the work.
DOM -
Re: Rear main oil leak
It's been years since I've dropped the pan on a 67 427, but I think disconnecting the idler arm from the frame and pulling down the steering linkage was the only thing necessary to get enough clearance for the pan to be removed. Pan removal in a Corvette was much easier than in other Chevys because the engine is behind the front crossmember and therefore raising the engine is not necessary.Comment
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Re: Rear main oil leak
Patrick,
I hope your right for Michael's sake.
I'm sure he has the larger volume pan that is a bit longer, but never the less it should be outlined in the manual.
I was speaking about the passenger car now that I think of it.
DOMComment
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Re: Rear main oil leak
always put the TDC mark on the damper at the 6:00 o'clock position the get the counter weight out of the way of removing the panComment
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Re: Rear main oil leak
Pat hit the nail on the head. Only thing special you need it a tie rod separator (tuning fork(Dick WhittingtonComment
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Re: Rear main oil leak
Dick: It's actually simpler than that. Just removing the bolts that hold the idler arm to the frame allows one to pull the whole steering linkage assembly down with the idler arm still attached. There is now enough clearance to remove the oil pan, especially if the crank is turned to get the front counterweight out of the way according the Clem's clever tip.Comment
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Re: Rear main oil leak
Thats good news for Michael.
When you pull the rear cap off see if there is oil where it touches the block. A lot of rear main leaks are there where it is a metal to metal between the cap and block. If so that is a leak also.
The rear main cap should have a thin layer of sealant under it all the way to the edges.
I loosten the main caps (all but the front) and lower the back of the crank a bit to allow the new seal to slip in without shaving the rubber bead that is on the outside of the seal.
Use a double lip seal with a good rtv sealer or what ever you decide works best. You will get a lot of advice from everyone on the sealer.
I also use brake cleaner or equal and spray the oil out of the channel.
A thin piece of plastic apx 3/16 wide and about 3" long will also protect the outside bead from shaving off as you feed it around the crank. Just put the plastic between the outer part of the seal and the sharp machined surface that seals the outer part of the seal.
Put some assembly lube on your finger and lightly lube the lip that seals to the crank but about 1/4 " from the edge so it won't mix with the sealer. Don;t let the oil touch the sealer or the sealer touch the crank.
Once you re-torque, rotate (by hand) the crank to get the oil around the lip that touches the crank so there is lube around the entire seal.
Locktite makes a good metal sealer that will seal the main cap to the block.
I am on the way to the shop now, feel free to contact me as I can make things confusing at times.
DOMComment
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Re: Rear main oil leak
Well, I really haven't. It is just that I have had and seen so many Chevy engines with this same problem, I assumed the worst. Not sure how I can tell the difference without dropping the pan, steering, etc., as described here anyway. Is there an easy way to know? Tighten the oil pan bolts? Replace gasket and see? How about the Lucas oil leak stop additive or similar?Big Tanks In the High Mountains of New MexicoComment
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Re: Rear main oil leak
I can't really say.
I thought that I had a rear main leak until I pulled the trans/clutch/bellhousing/flywheel for alignment refacing/new pressure plate and disk. When I examined the area of where the crank exits the rear of the block, I found the area to be dry. There was also no evidence of splash. I can only assume that the leak was coming from the rear radius of the pan or near the rear section of the rail(s) and getting blown aft.
In comparing the design of the rear main cap and seal to that of the cheap, flimsy sheet metal oil pan, you would think that the weak link would be the oil pan. My rear seal is only a couple years old, and is the more expensive red, flouoelastomer material. The lower-rear of the engine was always dry before I started using full synthetic oil. The seal was correctly installed, and correctly sealed at the parting lines.
Tightening the bolts of a sheet metal item like oil pans/timing covers/rocker covers usually exacerbates rather than alleviates the problem because it causes further deformation of the flimsy sheet metal flange surface. I would say that your best bet is to install a one-piece pan gasket and coat both sides, all around with Permatex Aviation #3 sealant. The one piece gasket is a dead giveaway, so if you use an OEM style gasket, then apply the same type sealer in the same manner, as well as applying a dab of RTV red to each corner.Comment
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Re: Rear main oil leak
My leak happens just sitting and with the engine running. Would a rear main seal only leak with the engine running with pressure on the system?Big Tanks In the High Mountains of New MexicoComment
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Re: Rear main oil leak
if the leak is the rear seal they most often leak when the engine is not running because with oil pressure pushing on the inside of the seal it should tighten up against the crank. if the seal is old and hard this will not happen. i fixed rear seal leaks in boat engines because there is a real problem if this happens by machining a couple of small grooves in the bearing insert allowing the oil to have a clear path back into the pan when you shut off the engine. seem to cure most but not all leaks. if sealer was not used on the rear bearing cap in the proper place you will have a leak under pressure and do not use RTV use non hardening permatexComment
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Re: Rear main oil leak
In your first post you asked if there was an additive to stop the leak . My local mech swears by a product called AT-205 reseal . I bought two bottles for my 58 and 70 but havent tried it as you have to run it for 45 min after you add it and have not driven either with this weather were having . StanComment
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