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1931 Chrysler CD8 replacing frost plugs

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I pulled the 5 frost plugs from my '31 Chysler CD8 engine in order to clean out the 90 years of scale, rust  etc. Took out about 2 cups of crap. The frost plugs are the simple convex disk type and go into a 1/8" seat in block I understand normal process is to set them in as a snug fit and tap them with a pall pean hammer to swell them for a tight fit. I set all 5 in yesterday and also put some gasket sealant in the seat before installing plugs. Tapped center for a slight depression. When I filled cooling system today, one of the larger plugs at rear of block popped out. Obviously was not in tight enough. 2 questions; does any one use gasket seal in installing these or should they go in dry? Secondly, how does one know how much of a depression you need to make in order to ensure they are tight enough not to leak or pop out? Can one use too much force to depress them? I realize an experienced mechanic would find this a piece of cake, but not something I have ever tried. BTW, the seats were cleaned, appear no pitting or excessive corrosion etc.  Thanks. 

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Sounds like you installed them correctly. Had to be really loose to pop out with almost no pressure. Are you sure you have the correct size? Many Chrysler plugs are sized by the 32nd of an inch.

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Posted (edited)

Yes, you can damage the block and blow out the lands the plug sits in.......been there, done that. Use brass plugs, steel require more force, and rot out. I would fill the block with evapo rust, straight, and let it soak for a while. Also, when the block gets hot it expands, so be sure they are installed tight,  or when you climb a hill they will pop out from the heat expanding the block.......don’t ask how I know.

Edited by edinmass (see edit history)
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Usually it ends up with 1/8" to 3/16" dimple in the centre of the depression. The depression might typically cover over 50% of the plug. I use a hard setting sealant, 'Stag', but only because my father always used it. Some Welsh plugs have given me a hard time, recently, and I have taken to buying over-size brass plugs, and carefully turning them down to an accurate fit on the lathe. (They are easily friction held against a three jaw chuck with a tail-stock centre). They can be installed without sealant, but I have not tried it myself. Such a pain in the a....   if they leak on start-up. I suspect you are not dishing them quite deeply enough.

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Also be sure the surface area on the block where the plugs fit is clean and smooth.  I used a power washer to clean out my block, inserting the nozzle in the various plug openings and blasting away.  An amazing amount of crud washed out.  I had the block on an engine stand and rotated it during the clean out.

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I have used brass and steel in "domed" expansion plugs.  Have never used any kind of sealant and never had one leak or pop out.  The secret is have the right size, have the seat clean and set the plug with one hit only.  With "welch" plugs I have used an appropiate sized socket and one hit only.

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I am always afraid to smack them hard enough to seal.

Have had problems more than once.

 

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Thanks for all the advice folks, brass plugs not available as near as I can determine, so we gave the steel ones some additional hammering along with gasket seal, seem to be tight now, filled with coolant, no leaks there. But now have a different problem related to wrong head gasket (see topic in Chrysler general discussion forum). Oh well, still having fun! 

 

Greg, the car is as seen in my Avatar, a '31 Chrysler CD8 Roadster 2014 rough barnfind. Especially rare, this is only known surviving CD8 Roadster built in Canada about May 1931, serial # 9820125 (range is 9820001 to 9820199). Chrysler built 199 CD8 vehicles (first and second series) in Canada in 1931 including all models, Sedans, Coupes, Convertibles and Roadsters. Although Roadsters comprised about 6% of all US production of CD8's, being a colder climate in Canada, and in middle of depression, estimates are that as few as 3% of production here were Roadsters (or 5-10 first series Roadsters) (Chrysler Heritage has no Canadian production records). So a Roadster survival rate of <10% would suggest my car is only one left.

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Thanks for sharing the info. I would like to find a CD8. I located a touring car here in SoCal but with the help of forum members here, I found it was grossly over priced. I am flexible on model, I like closed sedans as well. 

Greg

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