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Discussion Starter #1
Hey all

I have kind of blown up this site the last few weeks, for that I apologize.

I have my rebuilt 350 on the stand and have been running it. After a while of run time, it developed a leak from the rear main seal. (Originally thought it was the oil pan, so replaced that gasket, then found the lip of the main cap wet when it continued to leak) I had installed a fel-pro blue standard 2 piece seal. It was installed straight up vs being installed a little offset of the main cap. Used a thin smear of rtv black on the cap.

After the leak started, I dropped the pan and main cap, removed the old seal, and replaced with a new fel-pro with the offset lip made for worn crank shafts. This time I clocked it 3/8" as per the instructions and again used a thin smear of rtv black on the main cap and a coating of oil on the seal surface. Finger tightened then torqued down an hour later.

And it's still leaking!!!!

I really don't know what to make of it. I can't tell if oil is making it passed the actual lip of the seal or maybe working it's way around and through the main cap. When I reseated the cap, I could tell the lip was in contact with the crank. So now I'm at a total loss and getting really tired of pulling this darn oil pan...

Any suggestions? I don't want to put a leaking engine in a freshly painted and undercoated car...
It's not a gushing leak, but will make a dime sized drop on the concrete after 15 minutes idling.

Thanks
Joe
 

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Maybe I’m misunderstanding but I put a little rtv in the cap and in the block on the lip the seal sits on. Then offset the seam and leave the seal ends dry. Only time I had a leak was putting sealer on the seal end.
 

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Discussion Starter #4
Maybe I’m misunderstanding but I put a little rtv in the cap and in the block on the lip the seal sits on. Then offset the seam and leave the seal ends dry. Only time I had a leak was putting sealer on the seal end.
You're saying the notch the seal rides in? I ha e always heard to never put sealer in there??

Are you sure you have the seal in facing the correct way?
Yes, it is facing the correct way. I have put them in backwards before, it was very obvious o_O
 

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I just took a look at my Chevy FSM.
As you were installing the seal half into the block portion, did you use a rear main seal installation tool (positioned between the crankshaft and the seal seat in the block)?
The manual states that your supposed to use this tool while installing the upper seal... using the tool as a "shoehorn" to protect the seal bead from the sharp corner of the seal seat surface on the block.

The manual also states to use this installation tool when installing the seal into the main cap, using the tool as a shoehorn while feeding the seal into the cap.

The manual does state that you put the RTV sealer on the "cap to block" surface... and not on the seal itself (as you had done).

I'm not sure if this info will be useful... but posted just in case it might help.
 

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Discussion Starter #6
I just took a look at my Chevy FSM.
As you were installing the seal half into the block portion, did you use a rear main seal installation tool (positioned between the crankshaft and the seal seat in the block)?
The manual states that your supposed to use this tool while installing the upper seal... using the tool as a "shoehorn" to protect the seal bead from the sharp corner of the seal seat surface on the block.

The manual also states to use this installation tool when installing the seal into the main cap, using the tool as a shoehorn while feeding the seal into the cap.

The manual does state that you put the RTV sealer on the "cap to block" surface... and not on the seal itself (as you had done).

I'm not sure if this info will be useful... but posted just in case it might help.
I did use the white installation shoehorn when installing the second seal on upper half.
I did get sealer between the two edged of the seal the first time around, second seal I did not use rtv on the seal itselfe.
 

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not sure if this will help, but my dad installed just changed his leaky 327 chevy small block with one from a resto shop that was thicker than the stock replacement from fel-pro. no more leaks. i will try to find out what brand it was.

maybe just try to check out different brand dimensions..? i saw them side-by-side and there clearly was a difference.

-Rusty
 

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when you put the RTV on the cap and seal, don't let it setup before you install and torque the cap down, when you let it setup first it makes the cap not sit all the way tight to the block, as it is a precision machined fit, when you install and torque it down before it sets up you are squeezing out any excess RTV and letting the cap fit like it needs to
 

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Discussion Starter #9
when you put the RTV on the cap and seal, don't let it setup before you install and torque the cap down, when you let it setup first it makes the cap not sit all the way tight to the block, as it is a precision machined fit, when you install and torque it down before it sets up you are squeezing out any excess RTV and letting the cap fit like it needs to
Thanks for the suggestion. I did torque it down right away the first time (when all the seams were lined up) but only tapped it set with the hammer handle the second time, then let the RTV set up. I think you might be on to something there. I will be sure to not wait this next time around.

Next question would be, since this seal is so new, do I go get another new one, or re-use this one. My gut tells me to just go get another one...
 

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Discussion Starter #10
not sure if this will help, but my dad installed just changed his leaky 327 chevy small block with one from a resto shop that was thicker than the stock replacement from fel-pro. no more leaks. i will try to find out what brand it was.

maybe just try to check out different brand dimensions..? i saw them side-by-side and there clearly was a difference.

-Rusty
My local parts store only had the one seal in stock so I didn't even think about that. I'll run into town to Oreillys or autozone and compare side by side. Good idea! I definitely want the offset lip though.
 

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Sort of unrelated, but I’ll throw it out there. Out racing truck has a 383”, spins lots of rpm. It ALWAYS leaked out the rear main, pretty typical, until we put a Scat aftermarket crank in it.
It cured the rear main seal leak, seems odd. But, when it was torn apart with the previous factory crank, it also was pretty hard on main bearings. The Scat crank has been in there for 4 years, haven’t torn it apart recently.
 

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I like the idea of the offset seal, and I also like the idea of an oversize seal. Dumb question, but did you check the surface where the seal rides on the crank? There are no ridges or issues with that, right? I had a 283 that I couldn't get to seal and realized that it was the surface on the crank, not the seal or method of installation. It had a ridge where the seal rides, and would prematurely wear out any new seal I tried.
 

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I went over to the website and found that I can afford to buy them a dozen at a time.They list them as costing $0.00 + FREE shipping. :giggle:
 

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Discussion Starter #17
I like the idea of the offset seal, and I also like the idea of an oversize seal. Dumb question, but did you check the surface where the seal rides on the crank? There are no ridges or issues with that, right? I had a 283 that I couldn't get to seal and realized that it was the surface on the crank, not the seal or method of installation. It had a ridge where the seal rides, and would prematurely wear out any new seal I tried.
I thought about that and saw there was some old pitting on the original seal area that didn't come out when polished. That's why I went with the offset. I will be trying to tackle this today along with some other house projects. So I won't know if of success till at least monday.
 

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Discussion Starter #18
Just pulled the pan, pump and main cap off. It definitely looks as though oil is making it's way passed the seal. I compared the seal half with no tension to the half still in the block and there didnt seem to be much tension being applied to the crank.
About to head into town to compare with others at the parts store.
 

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Discussion Starter #19
So after 4 parts stores that only have the 2 seals I have already tried, the last parts store guy asked if the block had been align honed.

It was.

There is a Felpro 2912 that's supposedly for align honed 350's and this might be the issue.

I have to order it since its non stock all over town...

Ho hum
 

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just got back from my dad's. oversized one he used is FEL-PRO part # P2900 on a 327.

not sure if this is one you had. gotta go put the kids to bed!

-Rusty
 
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