Can you turn a rod journal 20 under?

[SS_Sean]

As the title says. My rod journals were already 10 under and I'll need to take them to 20 under because of a wiped bearing. Thanks

 

[gossamer]

My crank is turned .020 /.020 now. It's been in the 11's on pump gas. No problems here. I'm sure you'll get all kinds of opinions on this one...

 

[chasmat2316]

Some will say no ,but mine has been 10 mains & 20 on the rods for ever

 

[Jeff40]

It would not bother me to install a .020 crank in my wifes GN or a customers.Have run .040 in sbc circle track stuff for years with no crank problems.
Jeff

 

[SS_Sean]

Sounds like a silly question, I know....020 on BBC/SBC stuff is no problem. I just don't know how much material there is on the 3.8 cranks. Thanks.

 

[chasmat2316]

Sounds like a silly question, I know....020 on BBC/SBC stuff is no problem. I just don't know how much material there is on the 3.8 cranks. Thanks.

Some people off set grind 3.8 cranks down to 2.20 BBC rod size.

 

[87GNSteve]

I would assess the cost how much is the grind going to cost?
Then see if I could find a STD STD crank on the boards from someone....
You might see one at a low price.

 

[Grumpy]

Melissa's GN/Mazda motor has a 20/20 crank in it .. Its only gone 9.94 @ 138 in street trim. Ya its a DRIVER

 

[fc227]

I ran a 30/30 crank for years. That was in the olds and at the time it was running low 14's.

 

[Just a Six??]

30-20 here for years & no problems.

 

[turbofabricator]

I'll explain this technically for you. The strength of a crankshaft is in the fillets. The thickness of a rod/main journal has little to do with overall strength. The journal fillet is the weakest part of a crankshaft. With the hydraulically rolled fillets on a stock turbo crank, if you grind the journal down to the surface of the fillet "gutter", you still haven't lost any strength in the fillet area. In fact, you are doing your bearings a favor. It reduces bearing speeds (and we all know that a 8,000 rpm Buick V6's NEED to reduce bearing speeds )
Now with that said, if the car is going to make over 600 hp, then I would suggest a forged steel crank. Cheap insurance these days.

 

[chasmat2316]

Turbofab hit it right on the head, cast or steel you have to make sure you don't grind into the fillet when you cut the crank.

 

[CTX-SLPR]

Massive revival here but wanted to fold it in with most recent mentioning of BBC rod journals.

I'm building an LSR motor and am likely to be destroking to 3.0L. Can I take a stock 2.66in stroke 3.0L crank and turn it down to BBC rod journals of 2.20in and run narrowed BBC rods safely? I don't want to do this if I don't have to but so far my search for a forged 2.66 forged crank is coming up empty and I'd like the reduced bearing speed and cheaper rod options from the BBC.

Thanks,

 

[dr_frankenstein]

i wouldnt ever turn a buick crank down to chevy journals. forged or not.

the crank has split pins. when turned down to that size, your massivly reducing the amount of material left in the crank pin itself. it will fail at this point. there is a reason you rarely ever find BMS or after market crank made this way. it will fail.

 

[Mike E]

Massive revival here but wanted to fold it in with most recent mentioning of BBC rod journals.

I'm building an LSR motor and am likely to be destroking to 3.0L. Can I take a stock 2.66in stroke 3.0L crank and turn it down to BBC rod journals of 2.20in and run narrowed BBC rods safely? I don't want to do this if I don't have to but so far my search for a forged 2.66 forged crank is coming up empty and I'd like the reduced bearing speed and cheaper rod options from the BBC.

Thanks,

I think the strength of the even fire v6 crank is determined by the cross section created by the overlap of the two rod journals. See the pic below, but a 2.66" stroke with a 2.2" rod pin has more cross sectional area than a 3.4 stroke with a 2.25 rod pin. I don't know what your power goals are, but you could go all the way down to a 2.1" pin with that stroke and have the same cross section as a stock 3.8 crank.

The only issues you may find is that you'll cut through whatever hardening the crank surface has if any. Also, you have to be very careful of the oil feeds to the rod bearings.

 

[750H.P.V6]

Mike,

You meant even fire not odd fire correct?

Neal

 

[Mike E]

Yes. Thanks for catching it.

 

[SCOOBY DOO]

20/30 here. Times are in sig.

 

[87GN_70GS]

The rod fillets are at 0.025" under. So 0.020" is the limit for keeping them intact, if you go 0.030" you'll be into the fillets.