# 65 389 Rear main seal leaking



## Scott06 (May 6, 2020)

i just got my 65 convert drivable two years ago… i did a back yard overhaul ( rings bearing valve job…) in the early 90s car has mostly been sitting for last 30 years started occasionally, kept it running, sat for 8 years without starting in early 2000 s…

Ok the more i have driven it the more the rear seal has been leaking.. tried a wagner adjustable pvc valve to no avail. Does have some blow by for sure ( compression is 175 psi…) but now the clutch slips due to oil…

i hate to pull the engine just to replace the rope seal with the two piece BOP seal Because when my kids get out of college in a few years i will do a correct rebuild…

before i pull it for resealing Anything else i should look at? I saw a post about some one saying they had leaks after switch to synthetic. Any chance i should switch from the conventional Driven I’m using back to Rotella i used previously? While the rear seal wasnt bad at that point i wasn’t driving it and hitting full throttle etc…

might be grabbing at straws …thanks


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## geeteeohguy (Feb 2, 2008)

Pulling the engine to replace the rear main is the only way to do it right, IMO, and is actually not too bad if the car does not have AC. I can get one out in 45 minutes.

Get the thing out and on a stand upside down and you can remove the main caps and lift the crank up about 1/2" to roll the old seal out. Your seal leaks because they dry out from sitting, and when finally started up, the crank 'grabs' the dry seal and turns it into a 'cat-turd'. The pre 1985 or so rope seals did better (asbestos) but the post '85 cotton ones not so much. I have used several BOP 2 piece seals with 100% success. Make sure the striations on the crank journal do NOT contact the lip of the seal where it rides. At least not with sharp hash marks. You can also use a Best Gasket square 'rope' seal and they get good reviews. I pulled the 400 out of my '67 in 2011 for just this reason. While I was at it, I took the opportunity to reseal the other gaskets (not the head gaskets, though) and replace all the core plugs. I had rebuilt the engine in 1988 and it was getting seepy. 12 years later, all still leak free and good. Also, with the engine out, it's a great time to clean and detail the engine bay and frame, etc.
This is a weekend job. Do NOT rush, DO get help pulling the engine and putting it back in, DO borrow or buy a levelling bar so you can pull the engine and trans as a unit, and DO remove the shifter before you do, or loosen it and get it out of the tunnel hole. 

If it were me, I would do a cylinder leakdown test, and if the leakdown was 20% or more, I would overhaul the engine properly and be done with it. I did that in 2019 with the small block in a Corvette I have.....195 psi in every cylinder, but 30-35% leakdown and blowby like a train.
I have been using Rotella in all my flat tappet vehicles since 2002 with zero issues.


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## Scott06 (May 6, 2020)

geeteeohguy said:


> Pulling the engine to replace the rear main is the only way to do it right, IMO, and is actually not too bad if the car does not have AC. I can get one out in 45 minutes.
> 
> Get the thing out and on a stand upside down and you can remove the main caps and lift the crank up about 1/2" to roll the old seal out. Your seal leaks because they dry out from sitting, and when finally started up, the crank 'grabs' the dry seal and turns it into a 'cat-turd'. The pre 1985 or so rope seals did better (asbestos) but the post '85 cotton ones not so much. I have used several BOP 2 piece seals with 100% success. Make sure the striations on the crank journal do NOT contact the lip of the seal where it rides. At least not with sharp hash marks. You can also use a Best Gasket square 'rope' seal and they get good reviews. I pulled the 400 out of my '67 in 2011 for just this reason. While I was at it, I took the opportunity to reseal the other gaskets (not the head gaskets, though) and replace all the core plugs. I had rebuilt the engine in 1988 and it was getting seepy. 12 years later, all still leak free and good. Also, with the engine out, it's a great time to clean and detail the engine bay and frame, etc.
> This is a weekend job. Do NOT rush, DO get help pulling the engine and putting it back in, DO borrow or buy a levelling bar so you can pull the engine and trans as a unit, and DO remove the shifter
> ...


thanks for your comments, and agree the engine needs a bore and proper rebuild. As I stated above i have two in college so proper overhaul and being done with it are a few years down the road… 

ive also had good luck with rotella just not sure if it will leak less, reality tells me it wont


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## PontiacJim (Dec 29, 2012)

Scott06 said:


> thanks for your comments, and agree the engine needs a bore and proper rebuild. As I stated above i have two in college so proper overhaul and being done with it are a few years down the road…
> 
> ive also had good luck with rotella just not sure if it will leak less, reality tells me it wont


As *geeteeohguy* pointed out, no easy fix based on your information - the seal has gone bad. The Driven and Rotella are both conventional oils, so changing won't do anything.

If you feel brave and want to chance it, you can try one of the stop leak products and hope that slows the leak. OR, park it and wait until the kids are out of college.


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## AZTempest (Jun 11, 2019)

Think of it this way. Why not try some of the snake oils? You got nothing to lose as you know it needs to be pulled anyway. If it stops or even slows the leak you can still have some fun with it and pull it when you're ready.


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## RMTZ67 (Mar 12, 2011)

If it has a lot of miles, maybe 30w and snug up the pan bolts a touch.


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## armyadarkness (Dec 7, 2020)

My vote is the Band-Aid method, just rip it off and get it over with!

Just like headers or a trans swap, it's very easy to procrastinate and put it off forever, and then you find that you spent more time worrying about it and looking for cheats, then it would take to just do it.


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## Scott06 (May 6, 2020)

armyadarkness said:


> My vote is the Band-Aid method, just rip it off and get it over with!
> 
> Just like headers or a trans swap, it's very easy to procrastinate and put it off forever, and then you find that you spent more time worrying about it and looking for cheats, then it would take to just do it.


Its not procrastination- The question was is there anything else I should look at before doing the seal. In my younger days I would tear into stuff then find out I had either diagnosed it wrong or there were other contributing factors... seeing the number of folks here who have done rear seals only to still have it leaking I wanted to pick peoples brains.

I didn't think about the seal drying out and getting bunched up but that is a very real possibility given the 30 year gap between rebuilding this and actually driving it. 

Thanks


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## Scott06 (May 6, 2020)

geeteeohguy said:


> Pulling the engine to replace the rear main is the only way to do it right, IMO, and is actually not too bad if the car does not have AC. I can get one out in 45 minutes.
> 
> Get the thing out and on a stand upside down and you can remove the main caps and lift the crank up about 1/2" to roll the old seal out. Your seal leaks because they dry out from sitting, and when finally started up, the crank 'grabs' the dry seal and turns it into a 'cat-turd'. The pre 1985 or so rope seals did better (asbestos) but the post '85 cotton ones not so much. I have used several BOP 2 piece seals with 100% success. Make sure the striations on the crank journal do NOT contact the lip of the seal where it rides. At least not with sharp hash marks. You can also use a Best Gasket square 'rope' seal and they get good reviews. I pulled the 400 out of my '67 in 2011 for just this reason. While I was at it, I took the opportunity to reseal the other gaskets (not the head gaskets, though) and replace all the core plugs. I had rebuilt the engine in 1988 and it was getting seepy. 12 years later, all still leak free and good. Also, with the engine out, it's a great time to clean and detail the engine bay and frame, etc.
> This is a weekend job. Do NOT rush, DO get help pulling the engine and putting it back in, DO borrow or buy a levelling bar so you can pull the engine and trans as a unit, and DO remove the shifter before you do, or loosen it and get it out of the tunnel hole.
> ...


I also had concerns on the crank serrations. Paul Spotts had recommended the BOP two piece as well ...

By sharp hash marks - define sharp. This is a stock 65 389 crank do I need to sand them down or anything? 

Also is there a leakdown percentage that it just wont make a difference what seal I am running? Its a stock bore block that I did a drill hone and can still see some cross hatch on. 

Given it has sat and generally run rich (now fixed) I did try to de carbonize the rings with Mercruiser Power Tune but not much carbon came out the tail pipe. 

Thanks


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## armyadarkness (Dec 7, 2020)

Scott06 said:


> Its not procrastination- The question was is there anything else I should look at before doing the seal. In my younger days I would tear into stuff then find out I had either diagnosed it wrong or there were other contributing factors... seeing the number of folks here who have done rear seals only to still have it leaking I wanted to pick peoples brains.
> 
> I didn't think about the seal drying out and getting bunched up but that is a very real possibility given the 30 year gap between rebuilding this and actually driving it.
> 
> Thanks


For the record, I wasnt insinuating that you _were_ procrastinating


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## 67ventwindow (Mar 3, 2020)

geeteeohguy said:


> Your seal leaks because they dry out from sitting, and when finally started up, the crank 'grabs' the dry seal and turns it into a 'cat-turd'.


 I am not doubting your diagnosis. It just seems to me it would be more like the present the racoon left me on my saddle after he ate one of my best laying chickens.


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## Scott06 (May 6, 2020)

armyadarkness said:


> For the record, I wasnt insinuating that you _were_ procrastinating


Didn't take it that way


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## Baaad65 (Aug 29, 2019)

Scott06 said:


> Didn't take it that way


I did 🤣


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## armyadarkness (Dec 7, 2020)

Baaad65 said:


> I did 🤣


You take it EVERY way!


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## geeteeohguy (Feb 2, 2008)

Scott06 said:


> I also had concerns on the crank serrations. Paul Spotts had recommended the BOP two piece as well ...
> 
> By sharp hash marks - define sharp. This is a stock 65 389 crank do I need to sand them down or anything?
> 
> ...


This is telling. You likely washed the cylinder walls with the rich running and wore out the rings in a hurry. Leakdown will tell you. If you are over 20-25%, you will have issues. My old Chevy was 30-35% leakdown but didn't leak oil out the gaskets.....it blew it out of the oil filler tube and breather. No oil past the rear main

Depending on where you are, labor-wise, you are not much more into it by freshening up the lower end properly and being done with it. If it's tired with blowby and you are predicating this on your kids, just keep putting oil in it. Waste of time to do all that labor on a worn out engine. 
As for plans, I have two standing offers to friends to help get two classic cars running so their kids can drive them to High School. Kid number one is now 35, married with kids and is a math teacher on Maui, and kid number two is now 33 and has a family of her own. Car number one was used as a chicken coop for 15 years and sold, and car number two is still inoperable and in pieces. 

You only live once, and time can get away from you.


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## PontiacJim (Dec 29, 2012)

Scott06 said:


> I also had concerns on the crank serrations. Paul Spotts had recommended the BOP two piece as well ...
> 
> By sharp hash marks - define sharp. This is a stock 65 389 crank do I need to sand them down or anything?
> 
> ...


The serration issue was with the new reproduction cranks which had very rough/raised serrations. You should not hav an issue with the stock crank as after all these years they are smoothed out.

You want to off set the seals where they butt so they do not line up with the block/main cap. You also want to add a few punch/stake marks in the seal area under the seal so it grabs the seal and keeps it from rotating. The instructions will also point out where to add sealant. Put oil on the seal once you are ready to drop in the crank and main cap as you don't want to crank it up dry.

The Viton seal can be hit or miss - it may not leak, it may leak. Often, the Best brand graphite rope type seal seems to favor a better chance of not leaking. I used the 2-piece seal without issue on my last 400 build, so I had no problems, while others seem to. 

Youe next concern will be the rear pan seal. Some of the cork seals are not as factory if going with a cork seal - they are thinner. You want some crush on that seal. So be aware of this as a potential oil leak after assembly. 

Also, get the oil pan corner reinforcements when you do the pan. Pontiac added these in later years to help hold the pan down better at the rear and prevent oil seepage.


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## Baaad65 (Aug 29, 2019)

Scott06 said:


> thanks for your comments, and agree the engine needs a bore and proper rebuild. As I stated above i have two in college so proper overhaul and being done with it are a few years down the road…
> 
> ive also had good luck with rotella just not sure if it will leak less, reality tells me it wont


I get that, I waited 30 years for this car but when the last tuition payment on the last kid was paid I finally could start looking, 30K a year X 2 kids X 4 years especially when they're in at the same time for 2 years buys a lot of car. You're being responsible because when you open up the motor it's always more than you think and then you get the "while I'm in here" disease.


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## Scott06 (May 6, 2020)

Sorry for dropping off the thread- been busy at work Thanks all for the tips will follow up with how it goes.

Any recommendations on the clutch supplier? I have the 10.4" ten spline ...


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## O52 (Jan 27, 2019)

LUK clutch is a good replacement if not used on the track


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## geeteeohguy (Feb 2, 2008)

LUK is excellent. Also, I got a Zoom 'street strip' basic clutch kit from Rock Auto for $108 in 2019. Included all the parts. Same exact kit was $216 from Summit and Jegs. 

It's been smooth and light to the pedal for the past 3 years in my old Corvette. 

I installed a few LUK's and they always had a very, very light pedal but never slipped or chattered. A pleasure to drive.


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## lust4speed (Jul 5, 2019)

Here is a crank just unboxed from Butler. Notice that the serrations have been polished down and while there are notches, the tops have been flattened and won't dig into the seal. 









Personally I rate the ability of seals to be leak free as follows: One piece BOP, two piece BOP, Teflon/Graphite seal, and finally the replacement seals in the engine gasket kits coming in dead last. The one-piece BOP has two lips and the two-piece BOP has one lip and while the parting line of the one-piece is at the very top, the two-piece has the separations at or close to the parting line of the cap. After several years I might see a little residue or a drop trying to form with the BOP but nothing hitting the ground. The Teflon/Graphite seal will start to weep after a few years and might leave a drop or two of oil on the cement overnight. The replacement rope seal usually starts marking its territory after six months or less.


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## jmd55 (Oct 30, 2021)

i know this might sound gaff but i put a 66 389 in my 66gto it is all org low miles been sitting at least 10 years i did oil pump new pan timing chain and all freeze plugs did not even think of rear main started leaking after a few hundred miles put 1 qt Lucus oil stop leak it must have swelled the seal back up now dry as a bone


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## Scott06 (May 6, 2020)

jmd55 said:


> i know this might sound gaff but i put a 66 389 in my 66gto it is all org low miles been sitting at least 10 years i did oil pump new pan timing chain and all freeze plugs did not even think of rear main started leaking after a few hundred miles put 1 qt Lucus oil stop leak it must have swelled the seal back up now dry as a bone


i may try that as i did have good luck using their power steering stop leak with good success .


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