Plug, Cup, Crankshaft Oil Galley, for 90~95 ZR-1 LT5. Sold individually, Eight (8) Expansion - Cup Plugs are required for the LT5 crankshaft, including plug at rear of crankshaft.  This part is most typically replaced only at the rear of the crankshaft, located just forward of the pilot bearing. 

NOTE: Refer to the GM Service Manual for correct installation depth.

There is an LT5 special tool made to install this plug to the correct depth.  If one is not available, follow the below listed guidelines for installation.

• Plug should be driven from the inside bottom of the plug, not from the rim of the cup.
• If a sealant is not used, lubricating the plug & hole with oil or grease before insertion minimizes scoring/galling and resulting leaks.
• Plug should be driven squarely into the hole.
• A bottoming shoulder on the installation tool controls the depth of insertion and plug alignment.
• The radius on the end of the installation tool should not interfere with the radius on the inside bottom of the cup - it should be large enough to provide adequate clearance.  A clearance chamfer works as well.

The following is a test performed by a friend & fellow ZR-1 enthusiast/expert, who also is an engineer. 

Test design & execution by Phil Wasinger.

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.