Front main - why?

[JerEazy]

I have now had 2 front main seals go out on me on my 1990 BMW 325i M20B25

First time MAY have been my fault from poor install. Kinda half assed it and rushed through. 2nd time no way. Took my time, used a new housing, got seal removal and install tools and was incredibly methodical with it. Smoke test after came back perfect. Car drove great for maybe 4 months. Then all of a sudden I’m getting this stumble. Then the car won’t start. Smoke test reveals Front main is leaking again.

these cars don’t have a PCV system to speak of. Just a vent hose from valve cover to intake. And that is new and clean. I can’t think of another reason why.

I read somewhere something like too heavy a weight of oil can cause pressure to increase? Seems unlikely.

Need some thoughts.

[82eye]

I have now had 2 front main seals go out on me on my 1990 BMW 325i M20B25

I can’t think of another reason why.

could simply be poor quality seals. you may also have groove wear on the seal journal that interferes and leaks. a little blowby might also be pressurizing the crankcase.

I read somewhere something like too heavy a weight of oil can cause pressure to increase? Seems unlikely.

it calls for 20w50 which is thick enough it's hard to find.

[roguetoaster]

Not starting and a leaking seal have nothing to do with each other, unless it's just bathing the crank sensor in hot oil, or the leak has ruined the crank damper and clocked the trigger wheel.

I second poor quality seals, or more likely there is damage on your crank snout.

You should do a compression and leakdown test to see what's what.

[JerEazy]

Not starting and a leaking seal have nothing to do with each other, unless it's just bathing the crank sensor in hot oil, or the leak has ruined the crank damper and clocked the trigger wheel.

I second poor quality seals, or more likely there is damage on your crank snout.

You should do a compression and leakdown test to see what's what.

I would assume a bad seal and a big vac leak would be a problem and cause a no start issue. Am I wrong there? It’s the only place putting out smoke on a test. Car literally went from running, to barely running, to no start.

everything else tested fine - it’s why I ran the smoke test.

[JerEazy]

could simply be poor quality seals. you may also have groove wear on the seal journal that interferes and leaks. a little blowby might also be pressurizing the crankcase.




it calls for 20w50 which is thick enough it's hard to find.

I used elring last time and run 20w50

[82eye]

I used elring last time and run 20w50

still leaves the other 2. i second doing a compression and leakdown test.

[JerEazy]

Compression test done and all within a few PSI of each other. Don’t have the tool for a leak down - but could go get one. But I don’t think that’s causing my no start. Been in and out of this motor - and she ran like an absolute top before this seal went. So it is my focus now. Also just had a mechanic give it a once over while having final steps to A/C solutions kit installed. Regarding running it has:

NOS IAC
remanned AFM from BavRestoration
new fuel injectors
new plugs, wires, coil, cap, rotor
new FPR
new fuel pump
new fuel filter
valve job done with new gasket
Tested and confirmed TPS
150 miles on timing belt and tensioner and related components
full fresh tank of gas

Could I have a clogged oil drain tube (or whatever the real name is for the bitch tube). I’ve never removed or checked it.

[82eye]

is it a crank / no start or no crank?
how bad is the seal leak ? drip or gusher?

the leak and no start may not be related. gawd i hope they are not related ...

[digger]

The initial stumble and then no start is not due to whatever small leak exists at the seal, the engines are not that sensitive to small vacuum leaks

you need to treat this a no start scenario and ignore the seal for the moment

check for spark, then fuel .....

[JerEazy]

The initial stumble and then no start is not due to whatever small leak exists at the seal, the engines are not that sensitive to small vacuum leaks

you need to treat this a no start scenario and ignore the seal for the moment

check for spark, then fuel .....

I have confirmed fuel. Was the first thing I checked because it felt like it ran out of gas. Will confirm spark tomorrow AM.

I was reviewing the video of the smoke test from when I found the leak. It’s not small. If you ignore the blue fluid (coolant from pulling hose) there’s a chunk of the seal and looks like a chunk of the cover itself. Will disassemble further tomorrow along with spark test.

[digger]

one way to test the vacuum leak hypothesis is to cap the valve cover vent hose fitting at the throttle body then it wont matter if there is a vacuum leak to crankcase

In 100% stock form engine should still "run" even with the oil cap loose or dipstick not 100% seated which is a small leak, ask me how i know it just wont run very well. if the seal is effectively blown out to the extent it is missing i would be surprised if it was enough to cause a complete no start

[JerEazy]

one way to test the vacuum leak hypothesis is to cap the valve cover vent hose fitting at the throttle body then it wont matter if there is a vacuum leak to crankcase

In 100% stock form engine should still "run" even with the oil cap loose or dipstick not 100% seated which is a small leak, ask me how i know it just wont run very well. if the seal is effectively blown out to the extent it is missing i would be surprised if it was enough to cause a complete no start

Doesn’t the tube from the intake go to the crankcase too?

Mine would stumble and almost fall off with oil cap removed. Would get a little “lope” with dipstick out.

I ordered replacement seals and will disassemble the rest today along with testing spark and compression once again.

[JerEazy]

Got the front cover and harmonic off. Something went or was bad. The spring/metal inside the seal came out, wrapped around the crank nose, marred the back of the balancer and the nose. If replaced I’m assuming it’ll just go again? Did a video short doing my best to show the nose. Attached is picture of the back of the harmonic. And it was a B to get off because the metal had wrapped into it.

https://youtube.com/shorts/03Oprh6nFgs?si=hVnr_TL4Tb4jyWbs

[digger]

Doesn’t the tube from the intake go to the crankcase too?

Mine would stumble and almost fall off with oil cap removed. Would get a little “lope” with dipstick out.

I ordered replacement seals and will disassemble the rest today along with testing spark and compression once again.

that tube doesn't go to to the actual runners of the intake, it is a secondary path to connect the crank case to the valve cover

[digger]

Got the front cover and harmonic off. Something went or was bad. The spring/metal inside the seal came out, wrapped around the crank nose, marred the back of the balancer and the nose. If replaced I’m assuming it’ll just go again? Did a video short doing my best to show the nose. Attached is picture of the back of the harmonic. And it was a B to get off because the metal had wrapped into it.

https://youtube.com/shorts/03Oprh6nF...nr_TL4Tb4jyWbs

how did the front face of that step/shoulder get marred? The crank gear hard bolted to that shoulder