[95chevy406]

Raps light when idleing and goes away when rpm goes up.tore motor apart and have gouges in main bearings and some are chrome looking and others look like bronze or had a bronze coat that looks to be wearing off.also had no oil pressure after motor was warm.motor is a 72 400 bored 406 that had new pistons and bearings when i got ut.

[hcompton]

Originally Posted by 95chevy406

Raps light when idleing and goes away when rpm goes up.tore motor apart and have gouges in main bearings and some are chrome looking and others look like bronze or had a bronze coat that looks to be wearing off.also had no oil pressure after motor was warm.motor is a 72 400 bored 406 that had new pistons and bearings when i got ut.

Does it have arp rod bots? Were the rods resized or are the big ends round now. Sounds like it used up the bearings bronze is the base metal the bearing material is grey like zinc colored.

High rpm engine? It may have just had cheap bearings with a little too much clearence. High rpm engine can beat them up pretty quick if the clearence is off either way.

[95chevy406]

Originally Posted by hcompton

Does it have arp rod bots? Were the rods resized or are the big ends round now. Sounds like it used up the bearings bronze is the base metal the bearing material is grey like zinc colored.

High rpm engine? It may have just had cheap bearings with a little too much clearence. High rpm engine can beat them up pretty quick if the clearence is off either way.

I bought the motor the way it is.i was thinking they put new bearings in and didnt prime it before they started it.its not a high rev motor.wont see more then 5500-5800 rpm

[hcompton]

Originally Posted by 95chevy406

I bought the motor the way it is.i was thinking they put new bearings in and didnt prime it before they started it.its not a high rev motor.wont see more then 5500-5800 rpm

Could be From lack of prime or a few other reasons. Many times top and bottom being worn can be from low idle rpm and big cam or just bad clearences to begin with.

[95chevy406]

The bearings fit kinda loose in the rods.my other motor they kinda fit in snug

[hcompton]

Do you have a bore guage to measure the inside of the big end without the bearings inside but the bolts tight.

Maybe even a caliper will work if your real careful and try it several times to make sure you get a good number. I got a feeling the rod bolts were changed without rod resizing. I bet the top to bottom number is different than the side to side number.

How does the crank look.

[95chevy406]

Originally Posted by hcompton

Do you have a bore guage to measure the inside of the big end without the bearings inside but the bolts tight.

Maybe even a caliper will work if your real careful and try it several times to make sure you get a good number. I got a feeling the rod bolts were changed without rod resizing. I bet the top to bottom number is different than the side to side number.

How does the crank look.

I dont have anything to measure them with.if i need the big ends resized how would bearings be?

[95chevy406]

The crank still looks like it was just polished with no grooves at all in the mains and rods and they are arp studs

[cobalt327]

Detonation might have beat the bearings to the point the oil clearances are shot. Would cause knock and low pressure.

Sometimes "budget" rebuilds will mean the crank was simply polished, not turned to the next undersize. Have the crank measured for straightness, journal roundness/taper and diameter as well as checking the rod big ends to see if they need sized. Replace bearings all the way around to whatever size the crank ends up being.

If the rods need sized, replace the rod bolts w/ARP hardware before resizing for insurance.

[95chevy406]

The guy was running vortech heads.i have a set of 64cc 87 350 heads shaved .040 with ss valves and steam holes drilled.with the pistons and heads i have the compression will be around 10.9:1

[hcompton]

Its usally pretty cheap to have the rods resized and straighten at the machine shop maybe best to take them in and see if that was the problem.

Also do the bearings have an .010 or .020 on the back of them. They may also say std. If they are stock rod bearings and the rods are larger than stock the bearings will fit loose. They should have no gaps in between the beraing with the cap on and on the pin. If there is any space they are the wrong size.

They also can get weak when they wear oit and not fit as well. Best to get everything mearsured out.

[95chevy406]

The main and rods are .010 clevite bearings

[95chevy406]

Crank was turned .010 on rods and mains and the big ends were honed out.are regular .010 undersize bearings good or do i need ones for the honeing done

[cobalt327]

Originally Posted by 95chevy406

Crank was turned .010 on rods and mains and the big ends were honed out.are regular .010 undersize bearings good or do i need ones for the honeing done

No special bearings are needed. The honing that was done put the big end back to stock specs. The way it's done is a small amount is removed from the parting surfaces, then the big end is reassembled and honed back to stock spec. So when all's said and done you have a stock spec rod big end.

[BigEd36]

Originally Posted by cobalt327

No special bearings are needed. The honing that was done put the big end back to stock specs. The way it's done is a small amount is removed from the parting surfaces, then the big end is reassembled and honed back to stock spec. So when all's said and done you have a stock spec rod big end.

How much does re-sizing shorten the rods center to center length? If the mating surfaces are both cut some that will increase the "in the hole" distance of the pistons.