Kicked a rods again

Kicked a rod again

Theres a bit of a back story here so bare with me, I'm crewing on a roots blown hemi funny car we had a really good year last year and on the last run the mag drive cam loose and we spun number 2 rod bearing this was the only run all year where any of the bearing showed any sign of detination. A track promotor wanted us to run a match race a few weeks later so we made the terrible decision to buy a second hand rotating assembly to run for that weekend. On the second run (1/8th mile) we kicked out number 2 rod on closer inspection we found that the crank had been repaired and chromed and a piece of chrome was missing from number 2 journal the bearing was folded up and black like it had no oil, all other bearings looked brand new, last weekend we went out with a new (to us) short we bought from a racer we know it was his spare engine and had only used it 1 weekend for a qualifier and 1st round then it went back in the trailer we did 1 launch 300' checked the bearing all looked good next day 1st run was fine second run number 2 rod broken again, also on this run the intake pushrod cup came out not burned or anything looks like it just fell out, the intake valve is bent and we backfired the supercharger. The bearing in the oil pan still looked like new and measured up fine egts show number 2 is always middle of the pack we are seeing no signs of being lean or detinating on data, plugs or bearings. The tune up and all part above the head gasket have stayed the same, am I missing something here or is this the biggest coincidence ever??

 

Ok I'm going to try to get the ball rolling a bit here
I guess the biggest question I have is does this sound like parts failure from using second hand parts or is it tune up related?
Is it possible that the pushrod went first and the backfire caused our latest broken rod?
Should we be looking at our torque wrench being out of adjustment?
If its tune up why is the first sign of trouble a broken rod, after every race I pull all the rods out, measure the bearing, measure the journal for out of round and check pin fit and ring lands, is there something in our maintenance that were not doing / doing wrong?

Looking for any ideas no matter how left field as this is getting old real quick!!!

 

Where are the rods Breaking?
No damage to the pushrod cup would have me think damage occurred first rod, then valve. The pushrod IMO would have walked out from the added clearance from a stuck open valve.

 

The rods have broken about 2/3 of the way up 1 - 1 1/2 inches below the little end most of the beam has been intact and the big end is in a few pieces, also the rod bolts have been in the oil pan and don't have any thread material from the rod on them i.e the threads didn't pull out.

 

We put the first spun bearing down to the ignition timing advancing when the mag drive had come loose although that should make it retard if anything, we have always run between 28 and 30 degrees with early brad FUEL heads, Pro mag 20 and between 11 and 11.5:1 compression. I will go back and check our TDC mark to make sure the timing is where I think it is and have a good look at the cap to see if there is any reason that it could be advancing on that cylinder.

Could we have a problem with the mag / points box causing it to fire on 1 cylinder before it should?

If we are running too much timing shouldn't we be seeing it in the bearing or the ring lands before it breaks the rod?

As far as plug readings number 2 looked no hotter than the others if anything 5 and 6 have been our 2 hotter cylinders.

I have had 2 experienced nitro tuners look over everything with me and they both said it doesn't look tune up related and their very surprised that it broke the rod. Both also said never ever use second hand rods again so we are fitting a set of new GRP rods with shorter rods in the front 2 holes, I just want to cover all bases before we run it again, I'd feel pretty dumb if we broke another one!

 

I would check the piston to head clearance on #2 again just to make sure it's not a mechanical issue. Also, how hard are turning the motor? Rods can stretch .060" at 8000 rpm with a big piston.
Joe

 

I made new plug wire before the last race we change them every year and the coil wire twice a year, I'll ad that to my list of things to have a close look at to see if the insulation is still ok.
We're not using a crank trigger at the moment is this something that we should look into?

 

I assembled 1 and 6 when I first put this latest short together to check piston to head and piston to valve clearances and we had over .100 for all clearances, the exact measurements are written down with the car I'll double check on the weekend when I go down there. Perhaps I should have checked all 8.
Shift light is set at 8000 which turns into 8500-8600 by the time its actually shifted and about the same through the lights.

 

With a nitro combo I would always check all 8. Any small differences would effect the tune up.

 

I've put a lot of shorts together for a nitro funny car and we have always run different compression heights on all cylinders, this car is just an alcohol bracket car, I eye balled all the rods they looked the same length and the pistons were all the same so I assumed that they would be the same on all cylinders as long as the decks were the same which is why I measured one on each bank, but you know what the say about assumeing! I'll ad that to my list of things to check the height of the other 7 to make sure they are all the same.

 

The first 2 bearing shell looked like they had been staved of oil, the journals 1st time round was black about 90 degrees around what would be the bottom of the journal at tdc, the second journal looked fine except for the chunk of chrome missing from it. Hard to tell when the 1st bearing spun but the second time it broke the rod well into the breaking area which sounds to me like the bearing had gone first.
The most recent one the bearing shell surface and the journal looked like new we had changed blocks and crank also gone from an oberg filter to a system 1 the only thing that stayed the same was the pump which is a Pluger pump, as fait would have it the data logger never recorded the last run but all others have shown 80psi at idle then over 100psi on the run with Lucas 70wt, are there any other signs that we have an oiling problem I should be looking for?

Is there any chance that the intake pushrod has gone first held the valve open and the backfire has somehow caused the rod failure and I'm looking at 3 unrelated incidents????

 

A question - M or V rod bearings
Another question - rod bolt torque and with what lube on the threads (bolt and the rod itself)

 

We normally use 'V' bearings, when we bought the 2nd hand rotating assembly it has 'M's in it already so we left them in and ran them. I'm thinking we might switch to 'M's to try to pick up on what its doing a little earlier.

We have been torquing the bolts up to the specs on the paperwork we got with the rods, it's all in a book with the car but from memory we ran Brooks B2 with 85ft lbs Brooks 88 with 80ft lbs and the latest ones were Venolia V2 with 95 ft lbs we use Lucas assembly lube on the bolts and white grease on the bearings.

 

M Bearings are a hand grenade with a 3 run fuse - if you make any power at all they will disenegrate. Tire shake - to much timing - to much power - ka boom fast. 1500 hp - Ok anything above that junk em - They start disenegrating at the first pass - and if you are not carefull you will miss the signs - they start flaking the tin coating off - thats the bearing falling apart inside. ONLY use V bearings - they are forgiving and never fall apart. I know this from MANY failures - this info cost me many many thousands of dollars - don't take it lightly - I guarantee its a fact.
All rod manfacturers state clearly - only use straight 30 wt oil on the rod bolts and the rod threads - there was a deal years ago about the color of the washer and 10Lbs less torque on a certain color - thats pretty old stuff - however I believe you are under torqing the bolts as well as using the wrong lube to. 95 to 100 lbs with straight 30 wt oil. Anytime you find the bolts in the pan with no rod attached to em - well you know where I am going with that - they backed out for a reason.

 

Wow thanks for the info on the M bearings sounds like you saved us a lot more heartache, I'm planning to get the torque wrench calibrated/ replaced, 100lbs sounds tight will we need to upgrade the bolts? GRP rods 7/16 arp bolts?

 

Bearing

When you say "M" and "V" bearings what do you mean? May be a silly question, but... ?