Small drip at new rear main seal- have it replaced, or wait?

['41 Fat Bottom Girl]

I have 90 miles or so on my newly rebuilt flathead 6.

Inspection shows a small leak at the engine rear main seal, not huge- but after cleaning the area a few times, I get a drip down the back of the oil pan every few days with the car sitting (it's sitting while I am in the process of replacing the tranny rear seal).

I can see it is coming from the rear main seal, it is not at the oil pan gasket.

Back in the '70s I rebuilt a flathead 8 for '40s wood boat and another flathead 6 for my '39 Oldsmobile with these old type packing main seals and don't recall any leaks after putting those engines together. 

The question- is it likely this will "run-in" with more engine hours and stop leaking, or should I get it back to the shop right now to have a new rear main seal installed?

Recommendations?

Thanx!

 

 

[Plymouthy Adams]

these mains will leak and many do just that.....they are a constant bother at times.....how annoying is the leak and to what degree are you loosing oil?  If you wish this to be correct by the shop that built it?   IF so, yes now is the time to return it as it is still as new at 90 miles...

[plymouthcranbrook]

I noticed a leak on my 52 shortly after I bought it 18 years ago and did worry mostly about getting oil on the clutch disc.  But the leak was small(never enough to show on the stick) and eventually I decided to heck with it and put a drip pan under the car.  Don’t regret that choice at all

[keithb7]

I have two leakers over here....Seems to be par for the course with these rear seals. With tranny out, it may still be challenging to remove upper seal retainer bolts. They are in between the flywheel and block. Although I have not done so, I was thinking maybe a person could unbolt the flywheel. It won't be able to exit out of the bell housing unless housing is removed. Somehow push the flywheel aside up in there. Access the seal, change it and reinstall everything. Could it be done this way? Anyone able to confirm?

 

I suppose other option is to remove the engine, put it on a stand and roll it over.

 

Oil leaks are annoying. Especially after you've done all that work to rebuild an engine.

 

I tore into a rear seal to learn, last fall. First time I was in there, is seen here:

 

 

Edited September 20, 2020 by keithb7

[Andydodge]

Keith.......good video.......the "leather" seal you refer to is more than likely a rope seal which was the standard seal in the late 30's/40's..........there are 2 other types of seal than I am aware of, both are neoprene/rubber  d may or not fit.........BUT the more interesting thing I found from your video is that your engine does not appear to have either of the right & left "cap gaskets" as described in my 36-42 Workshop Manual.............there were at least 2 types of these side gaskets, they fit either side of that oil slinger and essentially fill the small gap that occurs between the block and main cap when its bolted down..........

..............when I decided to renew the rear main seal on the 41 Plymouth I had I assumed that it had a rope seal...............as it should have had...........I had on hand a complete Best brand gasket set to suit a 230 which had a pair of neoprene seals plus a pair of 2 different side gaskets..........when I opened up the rear main in the car I found that a previous owner had installed a neoprene seal BUT NO side gaskets which would have left a gap of maybe 50 thou or so........so thats mainly why it leaked..........I installed the pair of side gaskets that fitted and the leak basically stopped..........the moral of this story is not to assume that what SHOULD be there IS indeed there...........lol............for me, apart from the need for a new rope seal I would also install some side gaskets at the very least.............regards, Andy Douglas     

[knuckleharley]

Can't add anything to the advise you have already received,but man alive,that is a pretty car!

[DJK]

17 hours ago, keithb7 said:

I have two leakers over here....Seems to be par for the course with these rear seals. With tranny out, it may still be challenging to remove upper seal retainer bolts. They are in between the flywheel and block. Although I have not done so, I was thinking maybe a person could unbolt the flywheel. It won't be able to exit out of the bell housing unless housing is removed. Somehow push the flywheel aside up in there. Access the seal, change it and reinstall everything. Could it be done this way? Anyone able to confirm?

 

I suppose other option is to remove the engine, put it on a stand and roll it over.

 

Oil leaks are annoying. Especially after you've done all that work to rebuild an engine.

 

I tore into a rear seal to learn, last fall. First time I was in there, is seen here:

 

 

On my 52 Cranbrook I was able to remove the flywheel with some persuasion, went back in much easier after grinding away a small amount of material on the bell housing. And mine still leaks, have to add a few ounces at each fill up, it's annoying.

[greg g]

I believe that the ones that don't leak are the animally.  I had my previous engines crank turned, spray welded and turned to spec. Still leaked. Since alot of folks lived and drove on dirt roads, oil leaks functioned as dust control. As well as when combined with dust became the world's most effective chassis undercoating.

Edited September 21, 2020 by greg g

['41 Fat Bottom Girl]

Great comments.

Going back to Plymouthy's suggestion, I guess I need to find out how much is leaking. It sounds like that is going to be the determining factor in either getting it replaced, or if minor, keep using my drip pan.

After I get my tranny rear seal squared away, I will have the car on the road again and get a better idea of the amount leaking, probably in the next week or so. I did notice more in the drip pan overnight after driving, compared to the car just sitting.

So, in the meantime, I will let the machine shop know of the leak and what I am doing to quantify it.

I will try to get a volume of the leak over a day or several days of driving, and then see what you folks on the Forum think.

After this $5K plus rebuild and getting everything back together I sure hope I don't have to tear everything down and pull the motor again and haul it back to the machine shop. Good times!

Stay safe, all.

And thanx!

 

 

[plymouthcranbrook]

I expect mine only leaks while running and maybe a short time after parking. I do occasionally run it in the garage just cause if I haven’t had a chance to drive it for a couple of weeks. Still only a small amount

[Jerry Roberts]

1 hour ago, plymouthcranbrook said:

I expect mine only leaks while running and maybe a short time after parking.

 That makes sense as the oil level is below the seal when the engine isn't running . 

[JBNeal]

when it comes to oil leaks, I recall my '89 Dakota with the 2.5L 5spd...the valve cover leaked enough to be noticed around the perimeter and down the block a little, no matter how many times I updated the gasket + sealant, but I assumed the bulk of the oil leak was going out of the tailpipe, as the dipstick would read one quart low right around every 4000 miles, just when I needed to change the oil + filter...I took a step back, looked at the mess being made vs. the time required to make the mess go away, decided after 5 yrs of fiddling with it one long Saturday afternoon a year to focus my efforts elsewhere...fast forward 20 years later, I rebuilt the hydraulics on my John Deere 425, and after 20 hours of operation, I noticed that hydraulic oil was seeping out of the pump input shaft; after 50 hours, so much dust had attached to that area, that the oil seepage was hardly noticeable; after 300 hours, the fluid level is still at the upper mark on the dipstick, with another 200 hours before fluid + filter change is required.

 

I recently relayed this story to a friend who wondered if her car was having a serious problem, after I told her that her car didn't smell like it was in distress...I elaborated that I had been around mechanics who seemed dismissive of problems at first, but after years of acquiring similar experience, I know why those guys knew when to fix things and when to leave things alone...it comes in handy on occasion

[knuckleharley]

21 hours ago, '41 Fat Bottom Girl said:

Great comments.

Going back to Plymouthy's suggestion, I guess I need to find out how much is leaking. It sounds like that is going to be the determining factor in either getting it replaced, or if minor, keep using my drip pan.

After I get my tranny rear seal squared away, I will have the car on the road again and get a better idea of the amount leaking, probably in the next week or so. I did notice more in the drip pan overnight after driving, compared to the car just sitting.

So, in the meantime, I will let the machine shop know of the leak and what I am doing to quantify it.

I will try to get a volume of the leak over a day or several days of driving, and then see what you folks on the Forum think.

After this $5K plus rebuild and getting everything back together I sure hope I don't have to tear everything down and pull the motor again and haul it back to the machine shop. Good times!

Stay safe, all.

And thanx!

 

 

What engine does the car have,and what,if any,are the modifications? This has nothing to do with the oil leak problem. I am just curious.

If it is a flat 6,especially a modified flat 6,do you have any videos with sound of the engine running and the car taking off?

The more I look at your car,the more I am thinking of painting my 42 biz coupe yellow instead of baby blue,and I LOVE baby blue.

[Sniper]

oil leaks irritate me, to the point that I will spend inordinate amounts of time fixing them.  But that is me.

['41 Fat Bottom Girl]

Hi, Knuckleharley,

I decided to rebuild the original L head 217.8 cu. in. engine instead of dropping something else in. It would have been fun to put a crate in her too, and I thought about it- but she runs so nice with the old flattie and three speed I decided to go that way (the decision was made even easier after I costed out the changes to the front suspension, steering, tranny, rear end, etc etc)

I have another car that's a go-fast to play with, so old bubble butt remains just a cruiser.

So, no surprises on the exhaust sound- the one glass pack is pretty quiet!

Thanx for the compliment on the car. Good luck with the '42. Send photo when you paint. Have fun with it!

 

Sniper, I am with you on that... I also have a difficult time letting a leak go on. I usually try to fix 'em. When I get a better idea of the severity of the leak, I'll get back to the Forum to see what you guys think.

 

Regards to all. 

[knuckleharley]

22 minutes ago, '41 Fat Bottom Girl said:

Hi, Knuckleharley,

I decided to rebuild the original L head 217.8 cu. in. engine instead of dropping something else in. It would have been fun to put a crate in her too, and I thought about it- but she runs so nice with the old flattie and three speed I decided to go that way (the decision was made even easier after I costed out the changes to the front suspension, steering, tranny, rear end, etc etc)

I have another car that's a go-fast to play with, so old bubble butt remains just a cruiser.

So, no surprises on the exhaust sound- the one glass pack is pretty quiet!

Thanx for the compliment on the car. Good luck with the '42. Send photo when you paint. Have fun with it!

 

Sniper, I am with you on that... I also have a difficult time letting a leak go on. I usually try to fix 'em. When I get a better idea of the severity of the leak, I'll get back to the Forum to see what you guys think.

 

Regards to all. 

Glad to hear it. I am a hot rodder at heart,but there just aren't that many original cars left around anymore,and it seems like a shame to make obvious changes to one that is still all-original.

BTW,if you feel the need for more power later,230 flat 6's are still semi-easy to find,and they are the same size outside as the engine you have now,and have a lot more power and  internal parts are easier to find.

My all-original 33 Dodge 4dr came to me with an engine that needed everything,so I plan on just rebuilding a 55 Plymouth 230 to put in it because no modifications need to be made,and the next owner won't have any problems putting the 218 back in it if he wants.

I have a Edgy finned aluminum head for it,and a 3x1 intake. Looking for cast iron headers,but if I can't find any I will just used tube headers. I plan on leaving the body,interior and running gear on it in "as bought" condition, and enjoy driving a car that looks like something you could have bought for 50 bucks out of somebody's back yard in the 60's. Other than surface rust on non-original front fenders,the car is virtually rust-free.

Who would think it would ever be possible to buy an original rust-free car from the 30's in a city named "Cold Water,Michigan"?

This was the type of car I dreamed of finding when I was a teen and 50 bucks was a lot of money. Well,I would rather have a coupe than a 4dr,but you get the idea. Something I could afford to buy to fix and drive.

 

 

Edited September 22, 2020 by knuckleharley

[keithb7]

2 hours ago, knuckleharley said:

 

If you feel the need for more power later,230 flat 6's are still semi-easy to find,and they are the same size outside as the engine you have now,and have a lot more power and  internal parts are easier to find.

 I plan on leaving the body,interior and running gear on it in "as bought" condition, and enjoy driving a car that looks like something you could have bought for 50 bucks out of somebody's back yard in the 60's.

This was the type of car I dreamed of finding when I was a teen and 50 bucks was a lot of money. Well,I would rather have a coupe than a 4dr,but you get the idea. Something I could afford to buy to fix and drive.

 

 

 

I'm on the same page here. A 1938 Sedan, mostly stock. Driver, that looks like to just came off the farm. Currently has a 1954 228 CI  25" long Canadian engine in it. It runs just fine. However I could use a little more torque. The steep hills here with the 4.11 in 3rd gear, 1:1, the engine manages, but barely. Ain't nothin left up a steep hill. With no run-up to gain momentum, the throttle mashed I get 30 -35 mph. And fuel burn on that long hill? Oh boy yes, considerable, as the throttle is wide open and the engine is burdened down pretty good.

 

I have my sights set on a 1949 251 CI Chrysler engine. 25" as well. I'd rebuild it to stock specs. Bore it over as needed. It should net a considerable power improvement in my little 2800 lb 1938 sedan. It should fly up the hills around here.

 

Edited September 22, 2020 by keithb7

[James_Douglas]

My 251 leaks and drives me nuts. It leaked from new. I have changed the seal three times. I asked Best Gasket what is the shaft range the seal is designed for and they said they do not have that. ???

 

The crankshaft I have when I put it in was checked at the crankshaft shop. It was NOS at the time.

 

One of my engines for the '49 convertible was rebuilt in 1963 by Automotive Engineering. It sat from 1968 to 2013. When I ran it it almost did not leak at all.

 

I have a NOS MOPAR rear seal that was made by Victor. It is built completely different from the one Best sells. The seal surface of it is three or four times as wide and it has a Vulcanized material over the rubber.

 

I think the Best modern seals do not work well. 

 

The next engine I build, I am going back to the rope seal. I think the larger seal too shaft area will provide a better seal.

 

My 2 cents worth.

 

James

 

Edited September 23, 2020 by James_Douglas

[knuckleharley]

11 hours ago, keithb7 said:

 

I'm on the same page here. A 1938 Sedan, mostly stock. Driver, that looks like to just came off the farm. Currently has a 1954 228 CI  25" long Canadian engine in it. It runs just fine. However I could use a little more torque. The steep hills here with the 4.11 in 3rd gear, 1:1, the engine manages, but barely. Ain't nothin left up a steep hill. With no run-up to gain momentum, the throttle mashed I get 30 -35 mph. And fuel burn on that long hill? Oh boy yes, considerable, as the throttle is wide open and the engine is burdened down pretty good.

 

I have my sights set on a 1949 251 CI Chrysler engine. 25" as well. I'd rebuild it to stock specs. Bore it over as needed. It should net a considerable power improvement in my little 2800 lb 1938 sedan. It should fly up the hills around here.

 

My first car was a 1938 Chrysler 4dr sedan. Bought it for 20 bucks from money I made as a laborer that summer working for a crew digging septic tanks and drain lines with shovels. Found it in a backyard about 60 miles from home after hitchhiking there to visit friends. The owner inherited it from his aunt who bought it new,and the engine was stuck.

 

My father hated old cars so he refused to tow it home for me. I got an older cousin to do that,and once home he helped me get the engine freed up,and damned if it didn't run so quiet you couldn't hear it running while watching the fan turn.

 

Body had surface rust and the steering box seemed worn,but other than that it was damn near perfect. Plans were to get it painted,new tires,etc,etc,etc from money earned working summers so I could have a car to drive when I turned 16. My father had already told me I wouldn't be allowed to borrow his car,and we lived in a VERY rural area. The closest female under 40 that wasn't related to me lived almost 10 miles away,the closest movie was 26 miles away,and there weren't even any telephones in the tiny community we lived in. Had to drive 7 miles to find a pay phone.

 

Came home from school one day to discover somebody had stopped and offered my father 100 bucks for the Chrysler,so he sold it and kept the money. "My house,my yard,my money."

 

He did the same thing the next summer with a 40 Ford I bought using money  I had earned from being a deck hand on a shrimp boat all summer,but he sold that one for scrap.

 

Still,I have fond memories of driving that old Chrysler over the sand dunes and dirt roads where  I lived before it was sold.

Edited September 23, 2020 by knuckleharley

[Booger]

3 hours ago, knuckleharley said:

My first car was a 1938 Chrysler 4dr sedan. Bought it for 20 bucks from money I made as a laborer that summer working for a crew digging septic tanks and drain lines with shovels. Found it in a backyard about 60 miles from home after hitchhiking there to visit friends. The owner inherited it from his aunt who bought it new,and the engine was stuck.

 

My father hated old cars so he refused to tow it home for me. I got an older cousin to do that,and once home he helped me get the engine freed up,and damned if it didn't run so quiet you couldn't hear it running while watching the fan turn.

 

Body had surface rust and the steering box seemed worn,but other than that it was damn near perfect. Plans were to get it painted,new tires,etc,etc,etc from money earned working summers so I could have a car to drive when I turned 16. My father had already told me I wouldn't be allowed to borrow his car,and we lived in a VERY rural area. The closest female under 40 that wasn't related to me lived almost 10 miles away,the closest movie was 26 miles away,and there weren't even any telephones in the tiny community we lived in. Had to drive 7 miles to find a pay phone.

 

Came home from school one day to discover somebody had stopped and offered my father 100 bucks for the Chrysler,so he sold it and kept the money. "My house,my yard,my money."

 

He did the same thing the next summer with a 40 Ford I bought using money  I had earned from being a deck hand on a shrimp boat all summer,but he sold that one for scrap.

 

Still,I have fond memories of driving that old Chrysler over the sand dunes and dirt roads where  I lived before it was sold.

That is a tremendous story. Damn

['41 Fat Bottom Girl]

Obviously, integrity and character won out for you. Good man.

['41 Fat Bottom Girl]

Car is back together after a tranny seal adventure, and my Redline MT90 tranny oil arriving today so will be back on the road soon.

To measure the amount of leak at the engine rear main over time, I went to the store and bought some large maxi pads. Wired one up right under the rear main and will see if I am successful in trapping oil. 

BTW...

1) Despite your grin, I am not looking at this as a long-term fix.

2) I was tempted to tell the clerk they were for my Fat Bottom Girl... and then wait a few seconds before telling her that's my car's name. The initial reaction probably would have been interesting...

 

I will drive it for a while and see how much oil I collect over a short time.

Thanx!

  

[keithb7]

Looks like a viable long term fix for many of us suffering the same! Lol. 

[knuckleharley]

2 hours ago, '41 Fat Bottom Girl said:

Car is back together after a tranny seal adventure, and my Redline MT90 tranny oil arriving today so will be back on the road soon.

To measure the amount of leak at the engine rear main over time, I went to the store and bought some large maxi pads. Wired one up right under the rear main and will see if I am successful in trapping oil. 

BTW...

1) Despite your grin, I am not looking at this as a long-term fix.

2) I was tempted to tell the clerk they were for my Fat Bottom Girl... and then wait a few seconds before telling her that's my car's name. The initial reaction probably would have been interesting...

 

I will drive it for a while and see how much oil I collect over a short time.

Thanx!

  

When I do this by lying to a local clerk and telling her MY car is named "Fat Bottom Girl",I am going to tell her it was your fault for putting that into my sick,twisted mind,and making me jealous that *I* didn't think of it.

['41 Fat Bottom Girl]

To answer the question on my my newly rebuilt engine "...how much is it leaking?"

Here was my procedure:

1) Removed the absorbent Maxi Pad with the oil it soaked up after 123 miles of driving- a mix of freeway and around-town. 

2) Used a balance with oiled pad on one end and fresh unsoiled pad on other. Added a sufficient volume of oil to the fresh pad to balance with the pad removed from the car, and the volume found to be .713 fluid ounces.

This shows (providing the leak remains the same over time) that the rear main seal will be leaking 17 ounces  of oil before a 3,000 mile oil and filter change- more than half a quart.

To me, that seems to be too large a rear main seal leak for a freshly rebuilt engine with only 244 miles on it.

This is worse than the rear main leak I had when I pulled the engine at 90,562 miles to have it rebuilt. 

My experience has been that leaks don't lessen with time, either.

 

Looks like I am going to be pulling the engine out of the car again (grrrr...)and taking it back to the shop that rebuilt it. They aren't equipped to do it in the car, they will want it pulled.

Waddya think?

Thanx, all.

Good Times. Que sera, sera.