TFX 96 Rear Main Will Not Stop Leaking

I have a TFX 96 with approx. 20 runs on it. Second event of this year the number 5 rod exited the block in a dramatic fashion. Block was repaired at BAE (2 windows, thrust main cap replaced). Crank showed no damage and was cleared OK by the local crank guy. Made two passes at an event after reassembly with no issues. The following weekend we made one pass and I noticed an abnormal amount of smoke in the cockpit from the instant I left the starting line. I noticed oil behind the car in the shutdown area. We confirmed the rear main was leaking so we dropped the pan and replaced the rear main seal.

Spinning the motor over after replacement revealed that the rear main was still leaking. A fairly steady drip appears to be coming from the center of the bottom seal.

Only routine maintenance (leak test, check a couple rod bearings, etc) done between the first and second events.

1. Any ideas what could be causing this?

2. What is the groove that is cut into the number 5 main cap in between the bearing and the rear seal?

Thanks,
Tony

 

The groove is for the oil slinger on the crank to sit in. This prevents oil under pressure firing straight at the seal surface.

 

check tunnel in block is round and straight(straight edge in main tunnel with feeler gauges)
get crank checked for runout in seal area(may have been ground with runout)
check seal area in block has not over crushing seal upon assembly(if block has been tunnel bored with caps having material removed)
check when fitting rear cap that drain holes are not blocked with silicone or similar(do not use to much sealer when fitting sump or rear cap)

 

Rear main seal leak

When the centre cap was replaced the block was line bored, the groove that the rear main seal runs in needs to be re-machined, if this isn't done the block side of the groove in the centre isn't as deep as the sides and the cap and makes the seal egg shaped and it leaks, you can try shimming behind the seal on each side of the cap and block a couple of thou may give you a quick fix at the track, it is easy to check when the motors apart and it doesn't take much to make it leak.