When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
Hey guys I built a 350 with a aggressive cam, high flow heads etc etc and I have this rear main seal oil leak that absolutely CAN NOT get rid of. Replaced the 2 piece rear main seal with the poly top of the line two different times, have done all the tips and tricks with sealant in the corners and joints and I still have this damn leak. Currently I'm not running any PCV Valve and just have a breather on both valve covers. I deleted the PCV years and years ago for some reason I cant remember... since the crank case can flow freely I feel like this wouldn't contribute to the rear main leak but technically the crank case doesn't have a vacuum since it's free flow. I've heard of people putting the Wagner PCV Valve on and it curing weird leaks like this. Any chance this could be causing my issue?
Last edited by propaintball96; 01-28-2024 at 09:24 PM.
Put in the pcv if this is a street car, doesn't hurt.
How are you sealing the rear main cap to the block?
what oil pan and gasket ?
I'll put it back in but I remember specially deleting for a certain reason... I'm sure it'll come right back to me once I throw it in. Black silicone between the rear cap and block especially in the corners. This thing should be bullet proof and just won't stop the drip. Very frustrating
2 piece RMS? Are the seal lips facing the engine?
Did you offset the parting lines?
If YES to all, then remove and clean the rearmost oil pan bolts and apply a sealer to them.
Please report back.
2 piece RMS? Are the seal lips facing the engine?
Did you offset the parting lines?
If YES to all, then remove and clean the rearmost oil pan bolts and apply a sealer to them.
Please report back.
Yes, Yes, Yes. I'm removing the whole oil pan in a couple weeks and going to add RTV the gasket in all of the corners, front seal, and in all of the corner bolt holes to see if that does the trick. Going to add a PCV valve as well to get some vacuum in the crank case. Will let you guys know how it turns out!
2 piece RMS? Are the seal lips facing the engine?
Did you offset the parting lines?
If YES to all, then remove and clean the rearmost oil pan bolts and apply a sealer to them.
Please report back.
Well guys, ended up pulling the entire engine to get the F**KING rear main seal out. Oil pan couldn't drop without raising the motor and removing the trans. It sucked but its out. Absolutely zero signs of why this thing is leaking. Everything looks nice and dry when I popped the cap. I just reinstalled and did the following. Let me know if you guys have any input.
1. Cleaned with carb clean and then wiped all silicon and seal surfaces with rubbing alcohol.
2. Brand new seal
3. Front lip forward.
4. Offset seal 3/8"
5. Dap of RTV on each end of RMS.
6. Dap of RTV on rear main cap in the corners.
7. I even put a thin strip of RTV on the backside of the seal just incase it was coming around the back side which is super doubtful.
8. Re-Installed cap and torqued to 75 ft/lbs.
Rear china wall, or rear cam plug leak will look like a rear main seal leak too
Back of the engine block is total dry. I've seen it leak out of the RMS so I'm 99& sure thats it. Just saying that when I tore it apart there was nothing apparent. Anyone see any issues with my installation method? Should be bulletproof...famous last words.
Have you done a compression test and/or leakdown test?
Could be that despite your best efforts with quality parts and cautious assembly, that there's simply too much crankcase pressure to contain. That's regardless of the engine's mileage.
FTR, the PCV circuit can rectify some of that excessive pressure when it's allowing vacuum to the crankcase.
Have you done a compression test and/or leakdown test?
Could be that despite your best efforts with quality parts and cautious assembly, that there's simply too much crankcase pressure to contain. That's regardless of the engine's mileage.
FTR, the PCV circuit can rectify some of that excessive pressure when it's allowing vacuum to the crankcase.
I have not performed either of those tests but I could once I get the engine back together. I also did buy the Wagner PCB valve so excited to see if those two items combined correct my issue
I've looked into that Wagner valve. Interesting item. At one time there was group purchase organized (by a member here possibly) but I missed the boat. I've spent many hours tuning with various valves looking for the operation that would have suited my last engine.
I was dealing with a lot of blow-by from a worn shortblock. If I removed the valve from the rocker cover, it would puff like a little chimney.
There are some accounts of people setting up the PCV system to act as a sort of vacuum pump. It takes more than the OEM 3rd gen arrangement to replicate but it was an interesting approach.
Esp on the driver's side. Note that there are 4 holes in the cap register surface: 1 on each side is for the bolts, the other on the pass side is for the pump drive rod to pass through, and the other on the driver's side is for the pressurized oil to come up from the pump, through the cap, and into the block. On that side therefore, there is pressurized oil trying to get out through that crack.
Use a VERY THIN schmeeer of non-hardening sealant such as thread sealer w PTFE or Permatex 200 (brown gooey gunk), NOT RTV since the parts constantly move, making sure to lay a large enough bead in the corners of the register step to seal up to the cap, where NoE drew the yellow lines. ESPECIALLY on the driver's side. The pass side can leeeeek a bit, butt the driver's side can literally SPEW if you don't get it sealed up. Obviously you don't want to use so much that it affects the main bearing clearance, or gets forced into the gap between the bearing halves or behind the shells. Those should be offset slightly anyway, much like the seal halves should be.
Note also that there should be a plug in the pressure passage on the driver's side, about an inch or so up into the block from the cap surface. That passage goes all the way from top to bottom of the block. Oil is supposed to come up into the block, be stopped by the cap, detour over to the oil filter, come back into the block above the plug, and continue upward toward everything that gets lubed. If that plug is not there, then the oil is not forced to flow through the filter; and instead of having an oil filter, you merely have a small reservoir of stagnant oil sitting off to the side, while all the oil remains dirty.
01-28-2024, 09:17 PM
I’ve had good results with anaerobic sealer on the 2 piece rear main cap. 
