Crank to flexplate bolts backing out.. sbc

This is the second time it has happened, everything else stays tight. Why harmonics or vibration only affect those 6 bolts is throwing us for a loop. We thought we fixed the problem by loctiting them the last time but i guess thats not the case. 4.165x3.500 sbc 6-71 at 10% over.

 

drill and wire them to be safe

 

a lot of times if you have a crack in your crankshaft this happens.Dave

 

Running a damper?

 

Crank bolts backing off

We had this issue until we went to 1/2 inch crank bolts, red locktite, and torqued then to 140LBS.

also on some converters you are able to get in and tighten up the bolts without having to pull the trans, some you may have to unbolt the converter from the flex plate and move it into the trans pump to make room, We also had to make a wrench to get the job done, after a few times they will take a set.

Good luck

Butch

 

No damper.

We are getting some crank flex, 2-3-4 mains are trying to delaminate the layers, going to a softer single layer babbit now.

 

Your problem most likely isn't bearing related ------at 10% od on the blower you aren't making alot of HP either --- is this a forged or billet crank ?

 

How are the convertor to flexplate bolts holding up?

 

As John Hart said, drill and safety wire the bolts. The direction of which chevys run is clockwise (looking at crank) the rear of the crank (converter side) turns counter clockwise.This puts the bolts in a loosening situation.Wire them,DAVE

 

I won't argue about the merits of wire--- but I will say you shouldn't have to be doing it ----

 

you have some wrong hormonics going on to cause this look into it further..Dave

 

I ran blown SBC for a long time never had a bearing or flywheel problem ran with and with out balancers billet and STOCK forged cranks sounds like you have something bad going on balance issue or cracked crank

 

What kind of flex plate? If it is powder coated, sand/grind the coating off on both sides in the area of the crank hub. Maybe not your problem, but have heard of multiple instances of this happening with powder coated flexplates.

 

I wonder if there is too much ignition timing, was it tuned on dyno?

 

timing would do it..because the detonation.. but I would look for a crack in the crank..just remember things come loose for a reason.dave

 

This will definitely cause it however you should not be having bearing problems. Our blown sbc is at 45 pounds of boost, 34 degrees timing and shifting at 9000 with no bearing issues. It didn't shift once and went to 9916 rpm @55 lbs and we did have bearing issues on the mains. 34 degrees timing was probably a bit much for that!

 

normally to much timing on a SBC and you push the head gaskets out on the front or rear......but the bearings still look as new lol