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Discussion Starter · #1 ·
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.
 

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Discussion Starter · #2 ·
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
 

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Discussion Starter · #4 ·
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?
 

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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.
 

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Discussion Starter · #7 ·
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
 

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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.
 

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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.
 

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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.
This depends on how far out of spec the rods is and whether material was removed from both the rod and cap or just the cap. So to answer you, it could be anywhere from several thousandths down to a tenth or two. I feel that checking/correcting bend and twist is as important. Problem is, some shops either don't or can't do this.

I would like to say using an aftermarket forging will cure all the problems associated w/resizing rods. But in this imperfect world we live in, even new rods can be out of spec, so they should be thoroughly inspected before use.
 

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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
That is too much compression. For pump gas and iron heads about 9.5:1 will be on the safe side. You really need to measure the chambers of those heads. You cannot figure compression ratio without knowing piston head volume and cylinder head chamber volume. If your heads were 76cc chambers and you milled .040 from them you probably have about 67 cc chambers. With a 7cc flattop pistons and .015 head gasket you would have about 9.792. You might have to use 89 or 93 octane gas depends on how your timing is setup. If you have a motor with 18cc dished pistons and using those heads your compression would be about 8.760. Factory pistons with the same heads and gasket would be 8.443 compresssion ratio.
 
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