Crankshaft Cup Plug Test

[Jagdpanzer]

The question of how much faith we should have in our press in crankshaft cup plugs has been bugging me for awhile. I looked around but could not find any engineering information on the mechanical properties of cup plug pressure holding capabilities so I conducted the following pressure test to find out.

Here is the test fixture I turned out on the lathe from 4140 chrome molly steel material to use with the hydraulic shop press:



A 22mm tall sidewall cup plug supplied by Jerry's Gaskets pressed in the 22mm bore of the test fixture with Loctite 620 applied according to FSM instructions:



Set up on the shop press and pumped up to 300 psi test pressure:



Jerry's plug laughed at 300 psi for two hours so I switched to a 1000 psi pressure gauge and pumped it up to the to the full 1000 psi. Amazingly it still held!!.




Loctite 620 is some tough stuff. Take a look at force it took to press the plug out afterwards:



Conclusion: Anyone using Jerry's 22mm tall wall cup plugs properly installed can be fully confident those plugs are in to stay.

Up next is the Dorman 555-119 cup plug which cross references over to the GM 10067639 OEM plug

[LGAFF]

Awesome research!

[A26B]

Most impressive! Excellent engineering Phil. Very ingenious device to conduct the test.

[mgbrv8]

Nice work excellent execution

David Hertrick

[QB93Z]

Good work Jerry!

Jim

[Scrrem]

Great test Phil! I know I will sleep better at night.
Rich

[A26B]

Originally Posted by QB93Z

Good work Jerry!

Jim

I didn't do anything! Phil did it all.

[Hib Halverson]

I don't understand what prompted this research?

Has there been instances of the crank plugs "blowing" out?

[Scrrem]

Originally Posted by Hib Halverson

I don't understand what prompted this research?

Has there been instances of the crank plugs "blowing" out?

Yes Hib, I recently did a 380 stroker build with an offset ground crank. After the griding process, the crank was heat treated and I was unaware that the plugs had not been replaced. The heat treating process took all the tension out of the plug side wall. When my motor was fired up for the first time I blew out a rear plug with 60 psi of oil pressure. Phil assisted me in replace all the crank shaft plugs. This test was just to satisfy his natrual engineering curiosity on what kind of pressure that the plugs would stand up to.
Rich

[GOLDCYLON]

Originally Posted by Scrrem

Yes Hib, I recently did a 380 stroker build with an offset ground crank. After the griding process, the crank was heat treated and I was unaware that the plugs had not been replaced. The heat treating process took all the tension out of the plug side wall. When my motor was fired up for the first time I blew out a rear plug with 60 psi of oil pressure. Phil assisted me in replace all the crank shaft plugs. This test was just to satisfy his natrual engineering curiosity on what kind of pressure that the plugs would stand up to.
Rich

Same thing happened to me after 10 mins of run time on the "First" 380. Solution is to weld the plugs in which is what was done. I suggest that is the way forward. I also shared that bit of info to the entire readership YEARS.....ago. For those that dont know the crank has two types of plugs. threaded and Expansion plug style. It they were all threaded we would not have this issue. However I suggested welding the plugs like Kevin Pietro suggested (Who built my motor) but it looks like Phil also has a way forward. Your mileage may vary