Blown Engine.......What do you think happened?

[dirtbandit]

Engine was just freshened, had 28 laps on it when it blew. 406 SBC 23*, dart little m block, callies stealth crank, crower h beams. Blew at end of straight. Rods on 2nd throw of crank are both broke. The breaks are just below the wrist pins and right above big end of rod. Pulled the pan and found the both rod caps and large ends. One large end had no bolts broken off in it and the other had both of the bolts broken off in the large end. We could turn the broken bolts in the threads with out fingers. Found one complete undamaged rod bolt in the pan (along with a ton of other debris). The motor was turning 8k rpm prior to letting go. Oil pressure was 60lbs/28lbs at idle when hot.

Is it likely that the engine builder did not get the rod bolts torqued by what I am describing?(I have had another problem with this guy putting the wrong dome pistons in the wrong hole causing it to scatter a valve.)

[rubbinsracin]

what was the temp about at when you lost it? was the motor broke in before you started racing it?

[stockcar5]

better double check your rods. crower doesnt show and h beam for a sbc.

[dirtbandit]

Temp was 180 when it went. The engine was run one night easy to break in. The rods must be carrillo then, its been a while since we bought them.

[parrot69777]

Not sure if you can tell....but what did the rod bearings look like on the two rods? Entirely possible the bolts could have been torqued but started to stretch and it wasn't caught. Could have been torqued to the wrong specs as well.

Would almost bet the rods were scat or eagle. I don't think I have ever seen a carrillo break like that.....usually just severly bent.

[rubbinsracin]

sounds like an engine builder that got a phone call or had someone show up at the shop while he was torquing bolts.

[dirtbandit]

Threads were good. The bolt found in the oil pan went right into either hole and did not have excessive play. Threads in both rods were good. The rods were definately not scat or eagle. And they were not aluminum rods. The bearing were not there and there was alot of bearing material in the pan along with some piston skirt material, some cast iron and the pieces of the rods.

I guess now we will take it back to the builder and see what if anything he is willing to do.................. My other motor is already another shop being looked at.

Thank you for all the responses!!!!!

[hpontap]

Hate to say it without seeing everything for myself but, it does sound like atleast 1 rod bolt was not torqued right. Usually a quality rod like Carillo, Crower, Lunati etc with their bolts and torqued right, Ive seen the rods break and the caps still be on the rods.
All it would take is for the one rod to let go and the other in the same journal at that rpm is sure to be damaged also.

[fast_crew]

Are the big ends of the rods burned or blued? Usually a brg problem is the cause for broken rods.

[dirtbandit]

The big end on the rod that had no bolts in it did not show any burning or blueing. The one that had one bolt missing and the other broken off showed a sign of some burning but very little.

[gadirtracer]

Rod bolts are not to be torqued! Way too many variables to just say a sbc 3/8" or 7/16" rod bolt is to be torqued to "X" number of foot pounds. Material, heat treatment, lubrication(type, amount, & distribution) of threads/bottom of bolt/nut, etc.....
They are to be stretched to a set point of maximum clamping force. A quality bolt manufacture will supply the correct amount of stretch required and a quality race engine builder knows this!

[lovinlatemodels]

Make sure that the rod bearing were placed in correctly if they were H bearing. And you said it's been awhile since you bought them what awhile how many laps are on the rods.

[merc123]

Is the oil pressure kinda light? Mine runs 60 at idle and 80-100 at race speeds.

[gadirtracer]

Engine was just freshened, had 28 laps on it when it blew. 406 SBC 23*, dart little m block, callies stealth crank, crower h beams. Blew at end of straight. Rods on 2nd throw of crank are both broke. The breaks are just below the wrist pins and right above big end of rod. Pulled the pan and found the both rod caps and large ends. One large end had no bolts broken off in it and the other had both of the bolts broken off in the large end. We could turn the broken bolts in the threads with out fingers. Found one complete undamaged rod bolt in the pan (along with a ton of other debris). The motor was turning 8k rpm prior to letting go. Oil pressure was 60lbs/28lbs at idle when hot.

Is it likely that the engine builder did not get the rod bolts torqued by what I am describing?(I have had another problem with this guy putting the wrong dome pistons in the wrong hole causing it to scatter a valve.)

Yep, seen that b4! Use a stretch gauge and this won't happen again!

[bushracing67]

Is the oil pressure kinda light? Mine runs 60 at idle and 80-100 at race speeds.

why in the hell would you have 100# oil pressure ? how do you keep rear main seals in it ? you never need anything over 80, and i normally never run anything over 70.... 30# hot at idle after a race is fine