The Stovebolt Site Forums The Shop Area Engine Shop Chevy 235 Rear Main and Balancer Leaking Oil

Hi all. I have a 1949 5 window Chevy pickup with a 235 engine out of a 1954 Chevy Belaire and four speed transmission. The engine has developed a pretty significant oil leak at the rear of the engine and a small leak at the front seal. I'm assuming both seals need to be replaced. Can the seals be replaced with the engine in the truck or will the engine have to be removed? I've seen the write-up on the main page on replacing the rear main seal with the engine in the truck, but I've been told it's not good to loosen all of the bolts on the crank. Looking for advice on this one.

If the engine has to come out, I think I might as well have the engine gone through and rebuilt. If I have to go with this option, I'll be looking for someone in the southern middle Tennessee area to do it for me. I'm not comfortable enough with my mechanical abilities to tackle that job.

Photo of truck attached. Sorry for the Indian motorcycles photo-bombing the truck.

Thanks,
Darrell

I don't see any Exxon Valdez oil slick flowing towards your motorcycles in your pic.
If it were me, and the leaks are not extreme, I'd keep driving it until I was ready to rebuild the engine. Just check the oil every time you put gas in it.
It can be a miserable job replacing either on of those seals while the engine is in the truck. You may be able to do that, but then you have to put the oil pan back on and hope that it doesn't leak. They can be a bear too.
I am able to do all of these things successfully, but I am telling you with reverence, I would rather not.

If you could find a newer 235 with the 848 head and have it rebuilt. Then swap it out over the winter 👍👍

If you swap out for a newer 235 or 261 there are 54 owners on this site that would love to get that old engine. That particular engine is peculiar to the 54-55.1 series 235. 53 and earlier had babbitt bearings and 55.2 and newer had a different waterpump and engine mount set-up.

Lol. That was a photo a few years ago before it started leaking bad. It leaves a pretty good puddle now and a stream down the driveway when it's moving. I haven't driven it in a while due to the leak. Anyone know of a reputable person in the southern middle Tennessee area that could do the rebuild? I think I'm at that point. Would love to tackle it myself, but I'm just not comfortable enough with my limited knowledge.

Just asking᠁ are you developing crankcase pressure?and might a PCV system help?

Chuck

I don't know.

Stop up the 2 slits in the valve cover with tape. Blow compressed air into the oil fill and see if it comes out of the draft tube.

Hanks custodian bring's up a good point. Do you have the original valve covers that are vented at the top rear of the valve covers?

If someone has swapped valve covers to the newer "closed" not vented , you should have ( if you do not already ) a vented oil fill cap on your valve cover. Otherwise it may be possible that you are creating positive crankcase pressure and maybe it's pushing the oil out the seals.

Dusty, you are spot-on.

Another possibility to consider, the rear main may not be leaking very much. A small leak there is almost expected, however a major contributor to the leak could be the side cover or the tappet cover gasket. I replaced the rear main gasket on my ‘51 this spring while adjusting main and rod bearing clearances. Now it appears to be leaking like a screen door when in fact it’s the side cover gasket. The lower left side corner is a prime suspect. The engine sits at an angle and oil pools in that corner, leaking and looking exactly like a rear main leak. Same goes for the rear of the tappet cover.

The only way I’ve found to be sure is to pressure wash the engine really well, go for a drive and when checking for leaks pay particular attention to the area just above the starter. Any oil there is from one of the aforementioned gaskets.

Good Luck

RonR

I believe it is the original valve cover. I also have a vented oil filler cap.

Thanks. I guess that's what I need to do is pressure wash the engine and get all the gunk off and then see if I can see where it is coming from.

If it's leaking as badly as you say so as to leave a trail down the driveway I'd look somewhere besides the rear-main seal. They don't usually leak that much, whereas a ruptured oil-filter hose or cracked fitting will leak a lot.

It's a steady drip coming off the bell housing about every three seconds when the truck is running. I don't know if that's considered a lot or not. My next idea is to do what the above suggested and see if I can pressure wash the engine and see if I can get a better idea where it's coming from. It's hard to tell now with so much oily matter and grease on the engine and frame.

That is a lot. Once it is clean, that should be fairly easy to track down.

It does sound more like a hose or a fitting at that rate.

I remember a dye we used to add to motor oil that turned it bright red- - - -made spotting a fresh leak really easy. I don't have any idea where to find that stuff these days! There was also a dye that showed up neon green under black light.
Jerry

Do a search for "UV dye leak detector" and most FLAPS carry it. We use it regularly.

My 235 drips at the timing chain cover and rear main seal. Not enough that I have to add oil between change. My solution was to put a black mat under the truck! Don't see the leaks any longer!

If you replace the front main-seal, check the sealing surface carefully for a groove made by the lip seal. It there is one get a speedy sleeve by whatever name. Several are available. Much cheaper from the bearing houses than from NAPA or other FLAPS.

Changing the rear main is a whole weekend's work that can even result in changing the main-bearing shims if you're anal about such things. I ended up installing all new bearings, rods and mains, and the two seals on my now retired 235 truck engine. Don't start this in November unless you have a well-heated shop or live in the south. Don't ask how I know.

All the above was the result of chasing a rear main leaking into the clutch. I cut back the clearance on the rear main to stem the leak and decided to change them all. Engine was much quieter afterward.