D2 Fuel Pump O-Ring Installation

[Delta KJ]

I am getting diesel in the engine oil on my D2 4U so I removed the fuel pump and the transfer pump to re-seal them. My problem is installing the o-ring in the fuel pump on the governor housing side. My parts book shows that the pump uses the same o-ring to seal the pump at the filter housing and the governor housing; 8B4967 and I bought the o-rings directly from CAT. The rear o-ring fits over a plug that is retained in the pump housing with a retainer fastener to the pump housing with a stud and nut. I can't get the o-ring into the housing! I greased the o-ring but it appears that the OD is too large. Are there any tricks to installing this o-ring or do I put a smaller o-ring in its place?2012-05-09_07-34-26_94.jpg

[Old Magnet]

Dimensions should check out the same as a #318 trade size o-ring.

[Delta KJ]

I checked the CAT o-ring against the 318 o-ring and they are the same; It wasn't that I questioned Old Magnet's information but rather found a reference to the 318 ring in another thread and compared the two earlier this morning.
Should I put the o-ring into the pump housing first and then force the plug into the seated o-ring? I tried that already using quite a bit of force without luck. I was afraid to apply more force for fear of cutting the inner wall of the o-ring. Does warming or cooling the o-ring help with the installation?

[ol Grump]

Could that require the use of a tool similar to what's needed to assemble Cat's Duo Cone seals? Without that tool, trying to get those seals into a bore is near to impossible.

http://abravo41.angelfire.com/