ugly rod bearings

We run a wetsump BBC pretty hard with a 14-71 kobelco. Made lots of good laps at 34psi and 8800rpm. At the last race 1/8th mile we sped the blower up to 37%(40 psi) and the car really picked up to the 330 but the track turned to $hit after that and it shook hard and spun from 330 on for 6 passes in a row. We crossed the finish line at 9200 with a 4.56 gear and a 34.5 tire. We had lots of timing pulled out trying to calm it down but it was going straight and covered everbody by .3 so we just kept running it that way.
Won the race but the rod bearings and fwd side of the thrust are beat up. We use a V series hemi rod bearing and the outer 25% on both sides of the upper half is shiny and smashed with flaking on the edges that ends up in the oil filter. The thrust shows a few little spots of copper flaking off.
The tuneup was a little leaner than normal but still had some cad on the plugs. No signs of detonation anywhere.
I thought it might be an oils system issue but the pressure is good. .00375-.004 rod clearance. Mains look perfect.
Any ideas?
Thanks,
Mike

 

Any signs of the pistons contacting the heads? How thick are your head gaskets? How far down the hole are the pistons?

If the bearings are mashed it had to be something other than a happy motor.
If it wasn't contact, just about had to be detonation. May not be quite as evident on the plugs in the 1/8th because you didn't have time to build as much heat.

Troy.

 

tire shake

 

Hmmmm... Good thought... I could see where shake would affect the thrust and mains but rod bearings? Not sure on that.

 

it can get the rod bearing also...some weard hormonics going through the motor..Dave
www.myspace.com/daveloweswr

 

You're likely running it too hard for the wet sump system. We had the same problems a few years ago, and changing to a dry sump seemed to make it go away. Not sure what the exact cause was; maybe not enough pressure down the track, not enough reservoir of oil (at high rpm's a lot of oil gets trapped in the top of the motor), or even lack of oil when the chutes come out.

 

Also, what weight of oil are you running? We found that pure 70 wt made our bearings look really bad, changed to 60 wt and everything was fine. I would stay away from 20-50 or any other multi grade oil.

 

thats exactly what i thought this morning when i seen this post because of what he had said about thrust bearing tire shake plays hell on a crankshaft

 

we run 60wt redline with solid 80-100 psi through the run. It was a weird high speed/rpm shake. Broke both wheelie bars without them touching the ground,killed the crank trigger and broke the door off the hinges. It had to be putting some freaky loads on the engine. I always figure bad shake will result in an aborted pass but the car would go straight everytime.

 

Mike, tire shake does some wild $hit to a motor. Harmonics are outrageous in shake, as you know.

 

Lots of great ideas in previous posts. A few thought starters on causes of vibrations and rod bearings. Water in a tire. Did the shake move the timing pointer giving you inaccurate timing from where you think it is. It is hard to evaluate the bearings with several runs on them. I would want to pull them after one run and see what they look like. Especially if you run the risk of knocking the rods out of it. Was the corrected altitude at this time better than you normally run. Depending on the compression ratio maybe it doesn't normally hurt bearings but this day it did detonate. What do the wrist pins look like? Are they free or going out or round? How many runs on the rods? Many rod brands go out of round up to .005 after even 5 runs. Some people resize the rods then and they are OK until 20+ runs. I do also concur with the first post. Is the wet sump running out of oil. A half and then 3/4 pass should show a marked change if this is happening. Of course a cross fire in the ignition may not knock the burst panel out but cause a "vibration". It would be great to hear the final cause at some point. Good luck

 

Tire shake

We had brg problems after tire shake. We thouight that to oil was cavatating. The shake starts way before you feel it. The vibration will cause the oil to stand still. (An airplane problem from prop shake)

Just my op.