How far can you grind a BMS crank ?

[jjvites]

What is an acceptable undersize for a 3.590 BMS crank? What power level can these handle once ground down?

Thanks,
Marty

 

[750H.P.V6]

Marty,

It's a pretty open ended question. I guess my question to you is how far undersize is it and what happened to it to get it to where it's at? For instance if someone starved the engine on oil and blackened the bearings then turned the crank 40/40 to clean it up I'd tell you to pass. If you can give a bit more info it would help.

Neal

What is an acceptable undersize for a 3.590 BMS crank? What power level can these handle once ground down?

Thanks,
Marty

 

[jjvites]

Neal,
Nice to hear from you. The reason for the question is because I am looking for stage 2 parts to build a shortblock and want to know what has worked for the buick cranks. For example the buick power source book says that a stage block shouldn't be used beyon 4.020. Yet racers here have shown that many in the buick community have gone to as much as 4.090 with good results. I understand that the figure given by the powersource book had a certain HP level in mind or maybe it was because these motors were used in a long duration races. But for short duration 1/4 mile racing a much larger bore might be O.K. So yes you are right that a cranks history is more important then how much is removed but that is not always obvious on a reworked crank So like all parts whether they are buick or ford there has to be some working limit. These being forged material that h.p. limit should be high.
I guess if a consesus opinion was that a 20/20 was the safe limit then I would not look for anything beyond that. Just learning.

Thanks,
Marty

 

[750H.P.V6]

Marty,

I agree that I wouldn't be interested in a crank that was turned more the 20/20. Not to say thet it wouldn't be usable past thet point but I don't know where you can get rod bearings if it's a wide journal crank. As far as the Power Source statement about 4.020" being the limit on bore size I would tell you the there wasn't a headgasket available at the time the book was written with a flame ring dia. larger than 4.020".

Neal

Neal,
Nice to hear from you. The reason for the question is because I am looking for stage 2 parts to build a shortblock and want to know what has worked for the buick cranks. For example the buick power source book says that a stage block shouldn't be used beyon 4.020. Yet racers here have shown that many in the buick community have gone to as much as 4.090 with good results. I understand that the figure given by the powersource book had a certain HP level in mind or maybe it was because these motors were used in a long duration races but for short duration 1/4 mile racing a much larger bore might be O.K. So yes you are right that a cranks history is more important then how much is removed but that is not always obvious on a reworked crank So like all parts whether they are buick or ford there has to be some working limit. Also bearing availability is consideration.
I guess if a consesus opinion was that a 20/20 was O.K. then I would not look for anything beyond that. Just learning.

Thanks,
Marty

 

[EightSecV6]

I prefer F-M brgs on a steel crank but they are not available under .010 King make a wide journal rod bearing all the way down to .040. I have used them with GREAT success, they are not listed as a performance bearing but the tech guy at King said it is EXACTLY the same as their race bearings for other engines.
As far as the bore, I wouldn't be afraid of a 4.060 bore,after that you want to be very sure on wall thickness.

 

[jjvites]

Thanks Guys and a Merry Christmas to you all.
Great info.

 

[robbyc]

turned cranks

remember that the problem aside from the avalibility of bearings is having a correct radius as well as the problem with when grind you can break through the hardness on the crank as depending on the type of hardining process used it only extends .020 to .030 into the steel so you can have it rehardned or what is called tufftried or tennifer there are places that do this process having a smaller diameter bearing is not bad to a point it does reduce surface area but the benefit is reduced bearing speed thanks i hope this helps robby

 

[John Mason]

On my N/A Super Stock motor I turn the rod journals down to 2.100 (sbc size) with no problems at all. The bore on one of my motors is 4.080, the other 4.060. Leave at 7500 rpm, shift at 8800, through the lights at 9400.

 

[REDS HOT AIR]

Leave at 7500 rpm, shift at 8800, through the lights at 9400.

sweet ...I bet that sounds good

 

[NEARING]

On my N/A Super Stock motor I turn the rod journals down to 2.100 (sbc size) with no problems at all. The bore on one of my motors is 4.080, the other 4.060. Leave at 7500 rpm, shift at 8800, through the lights at 9400.

Could you post a vid of that?