Another rear main seal leak?

69banana · Jun 16, 2023

I think I may have another 2 piece rear main seal leak. I have a fairly new crate engine that had a rear main seal leak last year ( half the seal was installed backwards). I pulled the engine and replaced the seal and was fine for about 700 miles but now I seem to have a leak again.

I plan to add dye again but right now after extended drives I get a little oil running down the outside of the scattershield to the base of the bell housing. I also see a little oil on the bottom of the starter and oil on the back of the bell housing. On the bell housing it seems to start on the passenger side at the lowest engine bolt for the bell housing right below the dowel above the starter. It looks like it is running down the outside back of the housing around the starter bubble and then down to the lowest part of the housing then drips.

I don't see any oil at the valve covers, intake, distributor or oil pressure sending unit. I can't tell if there is any oil inside the bell housing or the back of the flywheel but I don't see any.

Since I don't see any leaks up top I am guessing that its the rear main seal and the oil is getting spun over to the starter area and coming out there. I guess that's possible although the bolt where I see the oil start seems pretty high. Hopefully after I add some dye it will be more obvious but based on last time if I see no dye up top it's probably the rear main.

I do have a working PCV system.

If anyone has any thoughts let me know. I'll probably add some dye in the next few weeks and drive it for a few weeks and see if I learn more.

rp930 · Jun 16, 2023

What seal did you use?
Did you seal the rear cap to the block?
Did you offset the seal and apply sealant to the ends?
What direction did you orient the seal in?
Did the crankshaft surface look ok?

Georgia68 · Jun 16, 2023

Low mileage engine?

Bar's Leaks Rear Main Seal Repair, 16.9 oz

INSTRUCTIONS: Add entire bottle of Rear Main Seal Repair to engine crankcase (where you add oil) at or between oil changes. Do not overfill. Most leaks will stop within 100 miles or 2 days of driving.

To prevent future leaks, install Rear Main Seal Repair every 5,000 miles or with every oil change.

DOSAGE: One bottle treats 4 to 6 quarts of oil. Larger systems use 1 bottle for every 5 quarts of oil capacity. For small engines including 4 cycle / stroke motorcycle, ATV, lawn mowers and other engines use approximately 3 to 4 ounces per quart of capacity.

69banana · Jun 16, 2023

I used the fel pro blue seal ( 2900 I think).
I used the shoehorn to carefully install the block half of the seal.
I applied oil to the crank side of the seal and offset it a little.
I used a q-tip to apply a haze of Permatex optimum black to the ends of the seal.
I put a thin line of Permatex Optimum black on the rear main cap as recommended.
I am sure that the seal is facing the correct direction.
The crankshaft looked pristine. It was new with under 2000 miles.

I'm reluctant to use a leak repair additive in a new engine. It I don't find another source of the leak I'll probably try a new rear main seal again. I assume the fel-pro 2900 is still the best option? It is a Dart Block if it matters.

Georgia68 · Jun 16, 2023

Here are a few tips to all who might not have this knowledge.

Check the mfg date of your new replacement seal.

Gaskets & seals should be stored in a cool, ambient location, between 4⁰C and 27⁰C. Excessive humidity (40% to 75% relative humidity), direct sunlight and any chemical vapours should not be present. Most are stored in warehouses and not climate controlled storage facilities.

[TD]Silicone[/TD]
[TD]20 years[/TD]

1st Gen Camaro rear main seal - TWO PIECE SEAL Neoprene or called rubber Silicone
Fel-Pro Performance Rear Main Bearing Seals 2900 made from silicone also.

Take a big wad of assembly lube or wheel bearing grease and pack the garter spring cavity. This keeps the spring in place during installation. Seal lips should be generously lubricated to where they are wet during start-up, especially if an engine, transmission, or rear axle is going to sit for a while before operation. Dry seals and spinning shafts don’t mix. A dry seal will tear and then leak.

rp930 · Jun 16, 2023

I would use the Viton Fel-2918. Permatex right stuff and offset per directions. And seal the cap per directions.

Forget the leak fix in a bottle.

Georgia68 · Jun 16, 2023

It has been shown and reported on Corvair engines thet the Viton seal is not durable as a crankshaft seal. The ones available to the Corvair owners just do not last in the rotating enviroment.

I read similar main seal leaks on SBC engines also. Just a heads up on Viton use. Corvair people limit the use of Viton to static seals, gaskets and valve stem seals.

69banana · Jun 16, 2023

It looks like the 2912 is the Fel-pro Fluoroelastomer seal that is similar to the Fel-pro 2900 Silicone seal.
Is the 2912 considered a better seal for a street engine? From what I have read it is good for race engines with vacuum pumps. I have a nice street motor but if the 2912 might be less likely to leak I will try that one.

Rallegreen · Jun 16, 2023

69banana said:
I think I may have another 2 piece rear main seal leak. I have a fairly new crate engine that had a rear main seal leak last year ( half the seal was installed backwards). I pulled the engine and replaced the seal and was fine for about 700 miles but now I seem to have a leak again.

I plan to add dye again but right now after extended drives I get a little oil running down the outside of the scattershield to the base of the bell housing. I also see a little oil on the bottom of the starter and oil on the back of the bell housing. On the bell housing it seems to start on the passenger side at the lowest engine bolt for the bell housing right below the dowel above the starter. It looks like it is running down the outside back of the housing around the starter bubble and then down to the lowest part of the housing then drips.

I don't see any oil at the valve covers, intake, distributor or oil pressure sending unit. I can't tell if there is any oil inside the bell housing or the back of the flywheel but I don't see any.

Since I don't see any leaks up top I am guessing that its the rear main seal and the oil is getting spun over to the starter area and coming out there. I guess that's possible although the bolt where I see the oil start seems pretty high. Hopefully after I add some dye it will be more obvious but based on last time if I see no dye up top it's probably the rear main.

I do have a working PCV system.

If anyone has any thoughts let me know. I'll probably add some dye in the next few weeks and drive it for a few weeks and see if I learn more.

you say another rear main leak in a manual transmission car. You could check for excessive end play in your crankshaft at the harmonic balancer with a large screw driver. The thrust bearing might need to be replaced along with a new seal.

69banana · Jun 16, 2023

I checked my build sheet and if I read it correctly the crankshaft endplay was .002". I'm not sure how the thrust bearing works. Should I tap the harmonic balancer with a hammer and block of wood to push it back, put a dial indicator on the balancer and pry it out with a screwdriver and see if it is still close to .002" ?

rp930 · Jun 17, 2023

69banana said:
It looks like the 2912 is the Fel-pro Fluoroelastomer seal that is similar to the Fel-pro 2900 Silicone seal.
Is the 2912 considered a better seal for a street engine? From what I have read it is good for race engines with vacuum pumps. I have a nice street motor but if the 2912 might be less likely to leak I will try that one.

2912 was dry for 10 years in mine. Not a “race” engine, no vacuum pump. No offense I really don’t care what the Corvair guys are doing.

Rallegreen · Jun 17, 2023

69banana said:
I checked my build sheet and if I read it correctly the crankshaft endplay was .002". I'm not sure how the thrust bearing works. Should I tap the harmonic balancer with a hammer and block of wood to push it back, put a dial indicator on the balancer and pry it out with a screwdriver and see if it is still close to .002" ?

You just want to see if it moves in and out at all. You won’t see 2 thousandths, if it’s bad you will be able to move it back and fourth.

Georgia68 · Jun 17, 2023

rp930 said:
2912 was dry for 10 years in mine. Not a “race” engine, no vacuum pump. No offense I really don’t care what the Corvair guys are doing.

Rotating seals are under the same conditions, except maximum rpm, no matter where they are used. Heat and rpm up to 4000 are still the same, when using the same oil. So having knowledge of experience, whether SBC, Corvairs, Mustangs or Challengers should not be discounted, just because you don't want hear about experience from other engines. I was really providing real life experience from other engines that related the SBC experience I read about. But if that is the way you want to push away experience. I get the hint. You don't need my experience. BYe, Bye, again.

rp930 · Jun 17, 2023

Im qui

Georgia68 said:
Rotating seals are under the same conditions, except maximum rpm, no matter where they are used. Heat and rpm up to 4000 are still the same, when using the same oil. So having knowledge of experience, whether SBC, Corvairs, Mustangs or Challengers should not be discounted, just because you don't want hear about experience from other engines. I was really providing real life experience from other engines that related the SBC experience I read about. But if that is the way you want to push away experience. I get the hint. You don't need my experience. BYe, Bye, again.

I’m quite sure Felpro has sold thousands of Viton seals. I’m not sure what the Corvair guys are having issues with. I’m sorry if it offended you. I have around 50 years experience myself. Porsche has been using fluorocarbon rear main seals for decades.

If I had to add a bottle of Bar’s Leak every 5000 miles to keep a rear main seal from leaking I would seriously rethink my process or parts selection.

BillK · Jun 17, 2023

69banana said:
I get a little oil running down the outside of the scattershield

If its on the outside of the bellhousing I doubt that it is the rear main seal. I have seen oil come from all the way at the front of an engine and get blown around to the back. Try the die and see what you find. Is it a Big Block or Small Block ?

69banana · Jun 17, 2023

It's a small block. I took it for a 15 minute 10 mile drive today. When I got back there was a drop of oil coming from the back bottom of the oil pan and a slight oil stain by the bell housing bolt above the starter area in the back of the bell housing. I checked again about an hour later and there was oil weeping around a lower passenger side bell housing bolt in the back of the bell housing. I would love for it not to be the rear main seal but I suspect it is leaking into the bell housing and weeping out some of the bolts. Once I add dye I can look up top but if it is like last time I won't see any dye until after I pull the trans and bell housing off.

BillK · Jun 18, 2023

I cant imagine it weeping out from the bolts. Is there a weep hole at the bottom of the bellhousing ? Is it dripping from there ? Do you have the short 3/8" bolt in the front to block the hole that goes into the fuel pump pushrod area ? I guess the Dart block has that hole. Oil will drip out of there and run down the passenger side oil pan rail to the back.

69banana · Jun 18, 2023

I do have a bolt up front near the fuel pump and have not noticed any oil up front.

Next time I drive it I'll clean it and take pictures as best I can but it's all on the passenger side. Looking with a UV light but no dye the highest point I can see any oil is the back of the bell housing near the bolt right below the dowel. It's around the bolt and spreading down around the starter bubble in back. There are hairline oil lines in the creases around the starter bubble. The first lower bolt below the starter has oil around it and running down the back of the bell housing so to me it looks like oil is coming out where the bolt is and running down the back bottom of the housing. There is also some oil on the bottom of the starter just outside where it goes into the bell housing. The only other place I see oil is a drip at the back center of the oil pan that either drips down the scatter shield or the back of the oil pan. It varies and is either one or the other.

SoCal805 · Jun 18, 2023

because of engine rotation direction, the oil gets "slung" towards the PS of BH so it then drips down that side which is likely why the starter area is showing oil. Current symptoms to me indicate an RMS leak but given the job it is to replace a 2-piece RMS, it is prudent to use il dye to confirm source of leak as oil will always migrate to the lowest point but it could have started top, front, etc of motor. Before adding dye, then driving, clean existing oil off as best you can.

My C10 motor, 6 cyl, has same symptom but the drip has not hit the point of me pulling the trigger to replace the RMS so currently just using a pan under motor when I park in driveway. I absolutely hate leaks and will be forced to replace my 2=piece but having a successful outcome can be a 50-50 thing. I will buy the Felpro offset version if I do it.

BillDini · Jun 18, 2023

I have the exact same problem with my 350. I did find a leak around the front and real pan seals which required careful shaping on the front and rear seal areas of the replacement pan. After two days of not leaking it started again. Looking carefully up I do not think the rear seal or the cam plugs are leaking. Driving me insane. I am really starting to think these one piece Felpro oil pan gaskets are junk. I see oil on the starter bottom, passenger side frame and on the TH350 tranny cover.

Another rear main seal leak?

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