Crank .030 undersize
Thread Starter
Teching In
Joined: Jun 2019
Posts: 24
Likes: 1
Crank .030 undersize Hey All,
I just purchased a crank for my lq4 that's been cut .030 under on the mains. I'm being told by several sources that .030 is too big of a cut to run in this engine. I was going to run a 50 shot on the motor. Would you feel confident running this crank or should I be looking for a new one? Thanks!
I just purchased a crank for my lq4 that's been cut .030 under on the mains. I'm being told by several sources that .030 is too big of a cut to run in this engine. I was going to run a 50 shot on the motor. Would you feel confident running this crank or should I be looking for a new one? Thanks!
R0TBox70,
Please read this link it directly addresses most of your questions.
Crank Grinding Many Service Technicians Still Cling to Myth
I suspect .030 under concern is based on obsolete information from the 1940's & 1950's when more Babbitt material was required to make a bigger & weaker bearing for an under crank. Today's bearing are made differently.
Back in,the 1960's & 1970's offset grinding as much as 1/4 inch, that's .250 was accepted for many cranks to build a stroker motor. Cutting .030 typically reduces strength by about 4 percent. In an extreme applications that might be a concern like a 1,500 whp twin turbo build with a stock LS Crank. Probably not much of a concern for the typical NA engine build with a small 50 shot of spray.
With that said the undercut and polish work needs to be sport on otherwise a stress riser can be introduced. I've seen stock LS cranks for $125 in the last month so it might be just as cost-effective to find another crank. I've also seen them for three times that.
Most importantly make sure your dealing with a qualified machinist and engine builder.
Best regards
Please read this link it directly addresses most of your questions.
Crank Grinding Many Service Technicians Still Cling to Myth
I suspect .030 under concern is based on obsolete information from the 1940's & 1950's when more Babbitt material was required to make a bigger & weaker bearing for an under crank. Today's bearing are made differently.
Back in,the 1960's & 1970's offset grinding as much as 1/4 inch, that's .250 was accepted for many cranks to build a stroker motor. Cutting .030 typically reduces strength by about 4 percent. In an extreme applications that might be a concern like a 1,500 whp twin turbo build with a stock LS Crank. Probably not much of a concern for the typical NA engine build with a small 50 shot of spray.
With that said the undercut and polish work needs to be sport on otherwise a stress riser can be introduced. I've seen stock LS cranks for $125 in the last month so it might be just as cost-effective to find another crank. I've also seen them for three times that.
Most importantly make sure your dealing with a qualified machinist and engine builder.
Best regards
TECH Addict
Joined: Dec 2017
Posts: 2,177
Likes: 968
Strength reduction, or bearing thickness, is a minimal concern.
What I'd worry about more is, the hardening is only skin-deep. Only the surface gets hardened completely. Can't tell you haw deep it goes, but it's not real far. Taking off too much can get down to the softer metal underneath, in which case, it will wear a good bit faster.
Personally I'd recommend getting another one as well, and chalk up the cost of this one to the dumab$$ tax. Hopefully it wasn't too much of an installment payment...
What I'd worry about more is, the hardening is only skin-deep. Only the surface gets hardened completely. Can't tell you haw deep it goes, but it's not real far. Taking off too much can get down to the softer metal underneath, in which case, it will wear a good bit faster.
Personally I'd recommend getting another one as well, and chalk up the cost of this one to the dumab$$ tax. Hopefully it wasn't too much of an installment payment...
On The Tree
Joined: Sep 2016
Posts: 103
Likes: 18
Strength reduction, or bearing thickness, is a minimal concern.
What I'd worry about more is, the hardening is only skin-deep. Only the surface gets hardened completely. Can't tell you haw deep it goes, but it's not real far. Taking off too much can get down to the softer metal underneath, in which case, it will wear a good bit faster.
Personally I'd recommend getting another one as well, and chalk up the cost of this one to the dumab$$ tax. Hopefully it wasn't too much of an installment payment...
What I'd worry about more is, the hardening is only skin-deep. Only the surface gets hardened completely. Can't tell you haw deep it goes, but it's not real far. Taking off too much can get down to the softer metal underneath, in which case, it will wear a good bit faster.
Personally I'd recommend getting another one as well, and chalk up the cost of this one to the dumab$$ tax. Hopefully it wasn't too much of an installment payment...
