Swapping rear main seal on an assembled engine
 

455 I've had together for a few years finally got to the dyno last week. Had an oil leak at rear driver's corner. Plate sized puddle after 11 pulls. Looked like pan bolts. Now looking more like rear main seal. 2 piece BOP machine shop did when they assembled sort block. They have assembled most of my motors, even using the old Caddy seal with luck before BOP came out.

How bad a deal is it to swap seals with crank in the motor. Loosen caps let it hang down, or pry up a little?

Have you tried the Wagner Dual Adjustable PCV valve? I got rid of a few leaks on my Pontiac that I had never been able to fix before.

No it id have a regular PCV valve in it tapped into main plenum of T2.

Do a tilt test before disassembly

Tilt test after pulling the bolts was totally negative. Now definitely positive at mid rear main carp and below pan. But motor was totally on its butt for a few minutes as I readjusted the chains on the lift. So I don't think even a vacuum pump or different PCV will help much

I put a Best rope seal in a 421 of mine several years back and did not pull the crank. I took the main caps off and gently pried the crank up high enough to get the leaky seal out. I then worked in the new rope seal. Once I was confident that it was in the groove, I tightened up the main caps to seat the crank and pack the new seal in. From there, I trimmed the ends of the rear main seal very carefully with a razor blade. It has been leak free for around 7 years. It is certainly possible to change one without completely disassembling the engine.

Used to remove and install rope seals in GM’s glorious front wheel drive engines while engine in car with crank in place. Had a keen threaded tool with handle to pull the top half out. This was a Kentmore kit that also had a “Chinese finger” installer with a thin cable to work over the crank and draw the seal into place. On some that felt loose I’d jamb and pack the loose ends into the block to ensur that half of the rope was tight in the groove and against the crank. Then trim the excess. The bearing cap half I’d pack the rope in tight also and used a big socket to ensure that half was firmly seated and packed into the groove. Leaving slack in the rope to continually pack in place until it was obvious that it had enough to ride firm against the crank. A small smear of RTV where the cap meets the clock and torque it down. And this has to be oiled so the rope won’t burn up on restart…

Talked to Wade at BOP today. He has seen lots of "false positives" with the tilt test. Rear main seals the do no leak when the motor is running but when tilted drip as oil wicks down the crank serrations. So might have to put it on a run stand to be sure,especially since the dyno shop and I felt it looked more like a pan leak on when running.

I would put an evap. smoke machine on it before taking the engine apart. They find the leak almost every time.

I've had good luck with replacing them in car without removing the crank. I use the neoprene seals, with anaerobic sealer on the joining sections. I usually offset the halves slightly from even with the main cap/block as well. As stated above, make sure it's actually a problem when the engine is running before jumping in. It sucks fixing something that ain't broke.

Could not having the normal pcv valve and hose hooked to the intake and valley pan cause a rear main leak on the dyno? Say the grommet was in the valley pan but just open to the air?

As long as there is a breather in the valve cover the crankcase will see the same conditions at WOT with or without a PCV valve. I dont think not having a PCV valve would cause a main seal leak.

Normal PCV valve, hooked to a stock type(Butler/Tomahawk) valley and and into intake main plenum.

Amazon has a bunch of testers Summit has one any suggestions?

Do they work finding water leaks in the cab of a truck?:)

I'm in the same boat with the bop two piece hair piece...subscribed and defeated 👀

Normal PCV valve was factory calibrated for stock engine, with stock valve covers/breathers. Wagner allows for non stock calibration. Seems to work for many to cure small leaks, drips. Worked for me!

[QUOTE= I dont think not having a PCV valve would cause a main seal leak.[/QUOTE]

It does for many!

But it is leaking just sitting there also.
Stock valve covers and breather also.

suggest to wipe the engine clean and then run it again. this way you can spot a fresh oil trail and trace it up to its highest point to find the source of the leak.

Got a smoke tester ordered be here next week I'll keep you posted.

I don't know but, swapping the rear main on a assembled Pontiac., I am not doing that. Almost none of them are daily drivers these days, fun toy cars. Its a lot of work pulling the pan on a engine in a car, let alone sealing it properly.
Heck, before I put a mid plate, elephant ears and multi piece headers I could pull my 455 in a hour- hour and a half. One time my oil pressure dropped to 10 lbs on a Saturday at the track. Put it on the trailer and took it home, pulled the engine, changed the pump, re installed the engine and raced it Sunday.

This is part of why I dyno them . Tuning some trying a few parts, letting rings seat with a load, and leak checking. This is my first leaker.

Smoke machine showed it is rear main. Passenger side main cap just below parting line with block, but moves when rotate the crank.

Change the seal, use anaerobic sealer on the cap to block and between the mating halves of the seal.

I do this with a tiny change. I use a dot of RTV on the ends of the seal instead of anerobic sealer. Not sure the seal ends would be air tight enough for it to dry on the seal ends.

Slight leak at fuel pump block off plate too. Man garage still smells of the mineral oil smoke! But better that what I get when I use it for dog or cat enemas at the clinic!

I guess pull all the mains loose and pry the crank up to get the old one out and new one in. Never had a main leak before even using the old Caddy seals!

Yesterday spent hours swapping the 455 off the cradle , the 557 400 on the engine stand and onto a a cradle. Had on old cradle for ealry blocks I had modified to take the late model block-but the deel GTO pan on th e400 would not clear but the 455 would bolt up to I could pull the 400 off the engine stand and put it in the good cradle I have gotten form our member. Down side the front passenger side cradle bolt does not use the front bolt hole and the 557 block middle hole is 0.25 behind and 1.5" above! so made a bracket to use a nut on back of the cradle bolt and a bolt into the block hole!
Now to pull the pan and main cap and see what we have. What an ordeal!

Got it swapped yesterday putting pan back on today. Popped all the mains loose and pried crank up some at the back. It looked OK correct on gaps sticking up. Good silicon placement in cap, could not see under crank in the groove. Took awhile to scrape out silicone residue there. Not sure how much got in the rotation holes using the method in the BOP instructions of putting silicon in then using a seal(used the old one) to push it though into the holes-hopefully. New one on the cap was perfect block side stuck up too much so had to mess with that. Hopefully will solve the issue and not leak worse!

Got it swapped yesterday putting pan back on today. Popped all the mains loose and pried crank up some at the back. It looked OK correct on gaps sticking up. Good silicon placement in cap, could not see under crank in the groove. Took awhile to scrape out silicone residue there. Not sure how much got in the rotation holes using the method in the BOP instructions of putting silicon in then using a seal(used the old one) to push it though into the holes-hopefully. New one on the cap was perfect block side stuck up too much so had to mess with that. Hopefully will solve the issue and not leak worse!

Like Button Notice (view) Damn, skip i wish i had your motivation, talked to you before on the rms deal, did you notice anything off with that, im not sure of what to even look for on my deal. lol.............also any thoughts on your oil pan gasket, on mine im using the bop 1 pcs oil pan gasket, it thought the builder would cut that rubber piece off the back and put the cork pc in the main cap, yeah, that didnt happen..............so i take it its almost impossible to see if the rms is bad or not, boy this is getting old fast, but let me know how it works out for you, would be a big help for me in the future

Thanks Rich

Sorry, about that skip, thought i was sending that thru a pm,

Rich

Update. I pondered smoke testing or hoping for the best on the run stand. Smoke tested it as curiosity got to me. Found a rear oil pan corner leak fixed by snugging bolts up.

BUT mid cap main seal smoke! And I know I got the cap half of the seal in good! This time it did not move rotating crank.
Going to finish up my run stand and fire it up in it before I jump on it again.
For those of you using an aftermarket pan one of the repop corner braces needs grinding to lay flat. The canton on this one and the moroso on the 400 I just put together both needed the radius ground where the black is.

So smoke tested the 400 i put together a few months ago. Had a few pan bolts and a valve cover bolt that needed to be snugged up but no smoking anywhere after that! That makes me worry more about the 455 leaking again.