died on the dyno. your veiws please

[LJ851]

thats the trouble with modifying engines i guess.

This is true. Some people would say i am cynical and nontrusting of other peoples work but in reality i think my attention to detail is a little stronger than others. When i send a rod out to get the big end resized to xxx for some crazy reason i expect it to come back xxx, not xxx in one dimension and .0015 inches off in another dimension!

This sounds silly but it happens all the time , even with competent, high end machine shops. Always check the work you have done for you, it will save you tears later on.

Assembling an engine doesn't sound like a big deal but building one where you know every single important aspect of it and are 99.9 percent sure it will produce the power and not fail is a whole 'nother animal. This is from experience, i have built several non stock high performance engines a year for the last 10 years or so.

[329jay]

def not. this is a ground crank. i even had it checked and polished but some were big some werent. id like to think matey did the damage and it wasnt something i did but at the end of the day im just going to have to sort it out when i can. thats the trouble with modifying engines i guess.

[nando]

is it possible some debris stuck behind that bearing is what caused it to be tighter than the rest?

I remember mine being right in the middle of the tolerance range.

[329jay]

when i was putting it together i had alot of drive to finish as i wanted to see what it was like. i spent money i didnt have to finish it. right now im totally not interested in it. i already have a new crank and bearings so ill put it back together one day, just dont know when.

[LJ851]

Thats pretty tight. On your future engine builds, it's generally best on a performance engine to run the high side of the rod bearing spec if possible.

What are your plans for the car now? Rebuild this engine or go another direction?

[329jay]

hmm What was the clearance you measured on the offending journal? Detonation is very hard on rod bearings, do any of the other rod bearings show contact?

Also, the dyno is harder on an engine than real life but the stress can be minimized. Did he put the car in neutral as the dyno coasted down after pulls or leave it in gear and let the engine come down with the dyno?





.

going from memery the clearance is .0020 to .0055. my bearings were between .0025 and .0050. the tight one was obviously .0025. all other bearings still look fine. i didnt notice if he was coasting down in gear or not.

[LJ851]

Sounds like the engine wasn't properly broken in.

Whaaat?

Rod bearings don't break in.

[Mlarsen]

Sounds like the engine wasn't properly broken in.

[LJ851]

^ Once the bearing contacts the journal it's all over. After that, yes the bearing starts getting hammered on and will eventually vacate the journal area completely.

Sustained high RPM, no load (coast down) is hard on bearings as well.
So is sustained high load at low RPMs. Both of these situations can be created on the dyno and can contribute to rod bearing stress.

[329jay]

a drag racer i spoke to recons its what can happen on a high power motor with loads of nitro. the bearing is the softest bit so under load the bearing flattens out. the bearing starts to squash out of the side and into the crank creating heat to further kill it. he sugested that while timing it the dyno guy went a bit too far and the bearing with the tightest tolerance got wiped out. i like this theary. also this would explain the loss of power with every run he did

[LJ851]

hmm What was the clearance you measured on the offending journal? Detonation is very hard on rod bearings, do any of the other rod bearings show contact?

Also, the dyno is harder on an engine than real life but the stress can be minimized. Did he put the car in neutral as the dyno coasted down after pulls or leave it in gear and let the engine come down with the dyno?





.

[329jay]

Have you disassembled your oil pump? Did you check your rods big ends and rod journals for roundness/taper when you built the motor? Are all the oil pump drive parts doing their jobs? How long did it take to build oil pressure when you first started it after the build?

havent taken the pump apart yet. but i actually drove this away from the dyno (for a couple of miles) and it still had oil pressure. i primed the oil by hand when i was building it.
and no i didnt check the journals for roundness

this car had been on a dyno once it had been run in just to check afr's. it had been on a trackday and it had done 5 runs down the strip (15sec dead). it had done about 2000 miles. i would say if it was a build problem it would have let go alot sooner. it let go after 4 hours on this guys dyno.

[329jay]

Dumb question, but you did use assembly lube on all bearings and parts that are touched by other moving parts? That'
s gotta be bad part/ assembly/ starvation. what do the valves look like in that cylinder? If it was a timing problem, there would have to be another piston with damage no?

yeah assembly lube used. valves look ok although ive only looked at them not actually checked them. id agree about the timing damageing more pistons with only one thought. this was the tightest bearing so would have had less oil as a cushion. this was the weakest link.

[LJ851]

Have you disassembled your oil pump? Did you check your rods big ends and rod journals for roundness/taper when you built the motor? Are all the oil pump drive parts doing their jobs? How long did it take to build oil pressure when you first started it after the build?

[10Toes]

1-2mm will definitely lead to head/piston contact. An engine designed with a good quench area (like an M20B25) doesn't leave a lot of room between the piston crown and combustion chamber. 5-6mm? that's like a 1960s inline-4 with flattop pistons..

lol