[Ragtop Man]

The 100K+ engine in the '67 GTO is stock as a rock, runs fine, starts easy and doesn't smoke.

Main issue - leaks oil like a sieve from every join and gasket ... as in "Next thing you know old Jed's a millionaire" after a run.

While I'd love to pull the engine and hit it with a stroker kit, that's not in the budget. And since we are finally pretty well unpacked from our move, I'm running low on cardboard to soak up the eeerll.

Engine HAS to come out for a number of other services, so it's house money on that labor - engine mount rubber is rotting and the exhaust manifolds clickety clack like the junk pickers on trash night. That's all lined up so far.

Planning to do the external gaskets for pan, valve covers, throw a timing set at it, etc. but it would burn like fire if the rear main was still leaking on fire up.

So - can the rear main seal be addressed with the BOP 1-pc. without removing the crank? Or is there a better solution? Also any ideers for helping keep all of the joints sealed is very welcome.

Thanks!

[Murf]

If I was going to try what you’re doing. I think I would use the Best brand seal

https://butlerperformance.com/i-2445...tegory:1234758

But, I am not an expert.

Good luck!

[mgarblik]

I think a 2-piece BOP seal gives you your best chance of success without removing the crankshaft. I would still remove all the main caps or at least lift them off the dowels so you can move the crank up enough to clean out the seal groove, get it clean and dry so you can fill the anti-rotation pockets in the block with RTV. I have had very good success with the BOP 2 piece seals. The 1 piece seal would be much more difficult to flex into place with the crank more or less still in the block. If you want to go the replacement rope route, the Best Gasket rope seal is an option as well. Pack it as tight as you can in the cap then carefully remove it and transfer it to the block. Then pack the other half in the cap and cut with a NEW single edge razor.

[tom s]

FWIW,im 50-50 on the Best gasket rope seal,50-50 on the BOP 2pc seal and 100% on the BOP 1 pc seal.Tom

[carcrazy]

I've used the BOP 1 pc on the last two builds...no issues....one has been in for several years.

[Vroom_vroom]

My two piece leaks, going to the one piece next

[kingbuzzo]

My two piece BOP leaks but I didn't put it in...maybe he didn't smooth the crank serrations or follow the directions not sure...good luck!

[grandam1979]

When you guys are saying leaks do you mean it drips as it’s running or you see a drop hanging in the rear pan area. I had one leak years ago you could not pull it on to the driveway without leaving a quarter size puddle.

[Formulas]

A bone stock 1967 GTO will will be easy to ping and rattle creating alot of internal pressure trying to push oil out of everywhere as well...

i would do a compression test to verify cylinder health is there before going this deep... no since on beating a dead horse if something is amiss

[steve25]

Once the pan is off the first order of business is to look at the number 1 and 2 rod bearing and then decide if it’s worth struggling to get a rear seal in there and working right with the crank in.

[kingbuzzo]

Mine drips and drabs similar to the way the old rope seal did...i'd pull it and do a one piece if I did it all over again...then put it on a tilt for a week before she went back in!

[Formulajones]

Like formula mentioned I'd prefer to make sure the 100k mile engine is healthy with a leak down test first. If there is any excess crank case pressure it's just going to find a place to leak no matter what you do.

If you're confident with that then the rear main choice weighs on several factors for me.

A factory crank has serrations that don't play well with the modern seals.. now with 100k miles those serrations are somewhat polished from a rope seal riding on it, which is why I believe the success rate with a modern seal on a factory crank is 50/50. Some are more worn than others. Myself I always have them polished before a modern seal goes on. Either that or I'm using an aftermarket crank that has a smooth surface.
Ive had 100 percent success with the 2 piece seals as long as those guidelines are followed. Ive never used the one piece or found a need to. Honestly it still has to be cut somewhere to get it in so it still has a joint in it, youre only eliminating one joint.
Up to you but that one piece is likely going to require crank removal to install. Depends on how deep you want to drive.

[steve25]

Even if you tare it all down and go with a rope seal to better deal with the serrations, modern seals are fiberglass not Asbestos like the original ones .

The original ones because of the Asbestos can handle the ware from the serrations, where as the fiberglass ones just tare in a microscopic way .
Basically a modern fiberglass glass seal is no better then then one or two piece seal and you get the pleasurable experience of a more difficult installation due to having no choice but to remove the crank.

[67Lemons]

So it seems no matter what if the crank comes out for any reason it’s a smart idea to have the serrations polished or dealt with in some way? Good to know as I am going to have the crank polished on a 455 I’m working on.

[78w72]

Something to be aware of on these older engines that use the 3 prong rubber U seal is that they are notorious for leaking and will look or act just like a leaking rear main... Ive posted before about my rear leak on a fresh 400/467 stroker build, I have a milodon 7 qt pan that uses the older style rubber U seal on the pan, only has 1 raised bead to crush seal on the main cap vs 2 beads of the later 5 prong design which still isnt the best option.

Short story is I installed the pan & top end on the short block the machine shop did using a 2 piece BOP rear main, after break in & ~50 miles I noticed a small 2-3" spot on the ground when sitting overnight, called the shop thinking it was the rear main, they had me bring it back to replace rear main and they reinstalled the oil pan... got it home & after just idling for a few minutes there was a much bigger 5" spot on the ground! So pulled it again & brung back for another rear main, this time I decided to go with the 1/4" cork gasket for the rear U seal on the pan like Mr Pbody explained years ago & others have mentioned on here. Shop said the rear main was good so I had them reinstall the pan with the cork gasket, they ran it on the dyno to verify no leaks & got a few free pulls out of it, was bone dry & still is ~8 years later, well not bone dry, it will seep just a bit after a season of driving that I just wipe off the pan, but no spots on the ground.

So its a good idea to avoid that rubber U seal if youre regasketing everything & use the 1/4" cork seal.

[John Milner]

I've replaced one rear main seal with the engine put together. After I took out the junk Fel Pro rope seal, I used a Best rope seal. It really wasn't all that hard with the engine on the stand. I removed all of the main caps and was able to work the crank up enough to slide the new rope seal in. I then torqued every main cap up but the rear. That seemed to pack the new seal in fine. After trimming it, I then installed the rear main cap/seal. I also used a 1 piece pan gasket from BOP. The engine has been leak free for a long time now.

[77 TRASHCAN]

Originally Posted by John Milner

I've replaced one rear main seal with the engine put together. After I took out the junk Fel Pro rope seal, I used a Best rope seal. It really wasn't all that hard with the engine on the stand. I removed all of the main caps and was able to work the crank up enough to slide the new rope seal in. I then torqued every main cap up but the rear. That seemed to pack the new seal in fine. After trimming it, I then installed the rear main cap/seal. I also used a 1 piece pan gasket from BOP. The engine has been leak free for a long time now.

That's exactly how I would do it!!!

Milner, you get that 409 into the 57 yet?

[VCho455]

I've managed to significantly reduce oil leaks on several engines over the years by installing a new PVC valve, valve grommet, and hose.

[steve25]

The PCV valve only works when there’s manifold vacuum.
Once the throttle is open far enough that manifold vacuum drops to zero then since the top side of the carb has vacuum the tube from the valve cover to the air cleaner takes over to move the crankcase pressure and oil vapors out.

This is why on many motors that have had aftermarket air cleaners and or no tube valve covers put on what was a dry or minor drip motors start to leak worse, and this is especially true of high mileage motors.

[J GLASGO]

We do 1 piece rear main seals without removing crankshaft all the time. I would be wary of a 100000 mile Gto engine though. It’s got to be huffing oil out fill cap