Crankshaft Cup Plug Test
 

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:

http://i540.photobucket.com/albums/g...psfmlxpalt.jpg

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:

http://i540.photobucket.com/albums/g...psywvjbj8h.jpg

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

http://i540.photobucket.com/albums/g...psarefxlal.jpg

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!!.

http://i540.photobucket.com/albums/g...psjdujqq96.jpg
http://i540.photobucket.com/albums/g...psnacyzave.jpg

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

http://i540.photobucket.com/albums/g...psaedjn26u.jpg

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

Re: Crankshaft Cup Plug Test
 

Awesome research!

Re: Crankshaft Cup Plug Test
 

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

Re: Crankshaft Cup Plug Test
 

Nice work excellent execution

David Hertrick

Re: Crankshaft Cup Plug Test
 

Good work Jerry!

Jim

Re: Crankshaft Cup Plug Test
 

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

Re: Crankshaft Cup Plug Test
 

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

Re: Crankshaft Cup Plug Test
 

I don't understand what prompted this research?

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

Re: Crankshaft Cup Plug Test
 

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

Re: Crankshaft Cup Plug Test
 

In view of the GM plug being NLA, I started researching a suitable replacement to stock. In the course of that research, I found no "engineering standard" for drive/cup plug specifications, wall thickness, height, cup diameter, interference fit, etc. I ended up sourcing cup plugs from the UK in a 22mm size. Apart from a "seat of the pants" feel for the drive fit, I was still concerned about the performance of the plug in service, especially considering the critical service it performs.

Prompted by Screm's experience and Phil Wasinger's involvement in Screm's engine build, Phil undertook a comparative analysis test between 3 different plugs, the 22mm plug I sourced from the UK, the OEM GM plug and a Dorman SAE size plug. All three of those plugs differed in wall thickness, cup diameter & cup height. The objective being confirmation of the 22mm plug, especially since the GM plug is NLA.

Phil's work confirmed the 22mm plug suitability for the intended application.

I hope this sheds some light on the importance of the test results.