The Stovebolt Site Forums The Shop Area Engine Shop coolant leak between engine and transmission

I have a very small leak (little drip) between the back of the 216 engine and the transmission on my 1946 Chevy pickup. I cant see where it is coming from. Do I need to pull the engine to find it? Any help would be great.

Yes- - - -there is a big freeze plug at the back of the block that gets rust holes and the only way it can be changed is by removing the bell housing. The engine needs to come out, then the clutch cover and flywheel is next. Change ALL the freeze plugs while you're at it. If one is rusted out the others are well on the way to more leaks.
Jerry

Scott I can't remember on the 216 but there is a coolant plug on the back side of the 235 that will leak and if it does the water will run down as you mentioned. I believe (emphasize the word "believe") the 216 is the same. To fix this you'll need to remove the transmission, clutch, flywheel and separate the bell housing from the engine. Not a fun chore. Here is an image of the 235 plug...goes right in to the water jacket of the engine block at the rear.

Sorry, Jerry...I went out to get Scott a picture.

What Jerry and Jon said. The 216 has that plug on the rear of the engine. This one is about ready to start leaking. I replaced all of them.

The only commercially available plugs that size are made of steel. With a little creative metal butchery it's possible to duplicate it in brass. It will last a lot longer and won't rust out. Ditto for the same size plug at the front of the engine. About 4 plugs can be made from a sheet this size:

www.ebay.com/itm/202786233683?

Jerry

Thank you guys for the input. I havent pulled an engine before but it should be interesting. Anything else you might recommend while I do it?

You will learn about the innards of the old girl. Maybe see something else that needs attention too 👍👍

Give it a good cleanout /flush. Decades of crud, rust scale, etc.

Before you pull the engine, do a thorough cooling system flush with evap-o-rust or phosphoric acid to loosen up the crud in the bottom of the water jacket. There's usually an inch or more of debris at the bottom and it can be as hard as concrete. If you don't want to contaminate the radiator, loop the upper and lower radiator hoses together and circulate the flush through the engine a few minutes at a time to keep it warm.
Jerry

Scott if you've never pulled an engine before, my suggestion would be to try to find a GM shop manual and carefully and slowly follow their instructions. Among other things, you'll need to remove the hood, the radiator, the radiator support piece, the transmission & linkage (and there are certain ways to do this), disconnect the battery and carefully remove anything connecting the engine to the frame and the wiring to the starter, coil, etc. Then you'll need to attach a heavy chain or engine lift chain to the cylinder head and say a prayer. I usually pray constantly while doing this even after having removed scads of engines over the past 60 years. Yes...it will be interesting and educational. Good luck!

What Jon said.
The shop manual actually recommends pulling the engine and transmission in a single piece. The connecting points on the head shown in the shop manual are probably located to balance the engine and transmission as a unit. Alternatively, you could use an engine leveler device, which would allow you to adjust the angle as it comes out, reducing the chance that it smacks something important on the way.
A helper is a good idea, along with that prayer that Jon mentioned.
Good luck. You'll find it an interesting exercise, and it might give you an opportunity to fix other things that need addressing, like completing the flush that Jerry recommends by removing all the casting plugs and sticking a pressure washer wand in the jacket to get the rest of the crud loose.

Getting a 4 speed out of the truck attached to the engine can be a bit of a challenge, even with the shift lever removed. Pulling the top cover creates a bit more vertical clearance. A 3 speed and engine assembly comes out together pretty easily.
Jerry

Soooooo....

..... if you're going to separate the trans from the engine *anyway* ...

.... and separating the trans *before* attempting to remove the engine makes that procedure easier ... (which it does, from my own limited experience) ...


.... ergo per ea facta ... does it not then follow that removing the transmission before you remove the engine is the better COA?

Jus axin'

And another thing ... Jerry, for those of us who haven't been machinists since Moses was a Mess Cook, would you explain a little more about *how* to make freeze plugs from sheet brass? How do you concave them? Diameters? Make a perfect circle???

Please?

I second John’s question.

Don

Edit: Does a holesaw have anything to do with it? 3/32 thick, I can see that lasting forever.

1. Measure the diameter of the hole in the block with the step in it for the plug to seat against.
2. Cut a disc from 3/32" thick brass sheet slightly larger than the OD.
3. Turn a template on the lathe with a slight dome in it the size of the stepped hole.
4. Find a big 3/4" drive socket slightly larger than the disc, and use a hammer or a hydraulic press to put the dome into the blank plug- - - -about 1/4" deflection is plenty.
5. Use a disc sander to adjust the OD of the plug until it's a close slip fit into the hole.
6. Use a piece of flat steel plate and a BFH to expand the plug into the hole- - - -use a little Permatex Super 300 to assure a coolant-tight seal between the plug and the block.

The next time the plug needs to be changed, your grandkids can deal with it!
Jerry

Could a bigger ball peen hammer substitute for the lathe-turned template?

A mule pulling a one-bottom sodbuster plow could substitute for a 4 wheel drive John Deere tractor, but it wouldn't be my first choice. A piece of hard maple and a wood lathe would be another option to make the forming die if you don't have access to a metal lathe. A male and female die set for forming the convex plug could be made that way, also.
Jerry

Or you could just install a standard preformed steel freeze plug knowing that it will likely never rust out in your lifetime.

Yep, The first one lasted 70 plus years.

Want to bet the quality of the replacement part is the same as what they made 70 years ago? How about points, condensers, fuel pumps, water pumps, voltage regulators, or brake linings?
Jerry

I'm not taking that bet Jerry, but do you have half of those 70 years left? (I likely don't.) Sometimes you just have to settle for good enough. Sad state of affairs on replacement part quality, but it's what we have to deal with.
But on the other hand, a steel disk is pretty hard to mess up.

That's a bet I won't take- - - - -Some of the guys who have worked for me could screw up a steel ball bearing with a feather duster.
Jerry

I think I've known one or two of those guys as well.

Let my 53 chevy with 216 and 3 speed set all winter and the clutch disc would not disengage due to a coolant leak from the same freeze plug you are talking about leaking and resulting in coolant making its way onto the flywheel and clutch plate area. Another good reason for you to pull the engine and replace all freeze plugs.

True. But as Brother Roache says, "If you don't have a dog, you hunt with the cat."

On the topic of corrosion of steels…
Most machine shops (like ours) will have an in house phosphate or kemplate tank to add corrosion resistance to steels and may be willing to throw a few plugs in with a batch if you’re nice to them. Much of the downhole components we make have higher hardness/ corrosion resistance requirements and are sent to a local metal treater for carburizing, induction hardening or liquid/gas nitriding as required. Check if you have a similar facility near you.

https://www.thermexmetal.com/services

Summer before last I bought a set of bronze soft plugs for a 235. Trouble is I don't remember where I bought them; anyhow, they existed just over a year ago.

If you, the original poster, were willing to do a little shee-tmetal work on the toe board, you could pull the trans, clutch, flywheel and bellhousing and access the soft plug after a little sheet-metal surgery. But by that time you're just a hood, front motor mount, some wire, hoses, exhaust flange bolts and a radiator away from pulling the engine. Oh, and the gauge connectors. I replaced a leaking cam plug that way one time. Didn't have to cut anything though.

On separating the engine and trans for engine removal: I have only done it that way but the older I get the harder it is to wrestle that SM420 even on a jack. Next time I think I'll try that the one-unit approach. I'll have to open the shop man-door to get the extra three feet though so I wouldn't do it in the dead of winter. We're expecting 20 below end of the week.

An 8 foot 4 X 4 post across both windowsills with the doors open gives you room to manipulate a cable come-along to remove and reinstall a SM 420 without crawling around on the floor and trying to balance the transmission case on a jack. Just bolt a chain to a couple of top cover bolts and hang the transmission on the chain. I've actually done that when replacing transmissions and/or clutches on conventional cab 18 wheelers with transmissions weighing several hundred pounds.
Jerry