Ive been collecting parts to put a 350 (0.030 over) 4 bolt main into my Firebird...Ive got a cast crank from the local Napa and its ground 0.030 under on both the main and rod journals...Would that weaken the crank enough to cause a problem?

 

Don't know what you paid for it, but I'd take it back. You can buy 350 cast cranks on ebay for as little as 100.00 + shipping brand new. Woha I just seen you're in Alaska, might be a differant story. I'd still look into it though.

 

It depends what your intent is. Crank journals are fairly thick, removing .030 shouldn't hurt anything on a mild/stock engine. If you're building a high power engine, then maybe better to rethink things.

 

Usually you can get away with .010 and have no worries, but .030, I would'nt even consider it for a stock rebuild.

 

i would take it back and request a .010 crank (unless your in a hurry to get the motor back together. best of luck, tom

 

Listen, we taken .250 off of the mains in certain situations and .060 off the rod journals and not even thought anything about it. GM is not going to make anything close to margin in this area.

 

Well, the plans look like this so far

355 4bolt block
L-31 Vortec Heads screw in rocker arm studs w/guide plates, 1.5 roller tip rockers.
xe268 COMP Cam
Edel. Performer Intake
625 cfm Carb...

Just your typical 300ish horse engine

I think Ill just go with the 0.030 under crank and see what happens. 0.030" isnt really all that much material.

Was just curious what others had to say about it.

Thanks for the input, and if she frags on me, ill let ya's know

 

I wouldn't use it, unless you absolutely have to. Turning a crank down that far decreases the fillet radius, or something like that. The tapered area between the journal and the counterweight, see how it curves instead of being a sharp corner? For as cheap as 350 cranks are, and as much of a pain as it would be to fix it if one gave you problems, IMO it's not worth it.

 

He's had enough "don't use it" responses, so when she goes, it was'nt cause he was'nt warned.

 

It depends on how it's ground undersize, if the grinder left a little .030 radius in the corners it will be fine, you can take a crank .125-.250 under if a big 1/8" radius in maintained on the journals.

 

If 10/10 cranks weren't readily available and very cheap, I'd say that it might be worth it to take your chances, but with 10/10 cranks everywhere you look, why take the gamble? I paid about $110 for my 10/10 crank at Advance Auto a few years ago.

 

I would not use it... the surface hardening only goes about that deep, and that much grinding may have exposed unhardened metal. You could have it re-treated, but that costs as much as or more than a less sodomized crank.

Also, think of it this way: either that crank has had a really long service life, and has been turned and used twice before, in which case it has..... how many miles left in it before it breaks? Or, somebody's motor blew up spectacularly around it, and to clean up the mess, it had to be cut that far. In either case, is it worth the risk? Do you want either of those things in your new motor? I think not, but of course that's just MHO.

 

It's not going to break! All you people with no experience with underground cranks please get off the soap box.
Thank you.

It will be fine unless your crank has some other problem.

 

Just be sure to tell him that when he's re-doing the engine, again, for the sake of saving money and time-at that time, hell maybe you could reimburse him as well if your SO sure there won't be a problem. Why use inferior parts-ESPECIALLY the crank, when other options are available? And knowing NAPA they probably did'nt give the crank away to begin with. This is'nt like a rocker arm or head gasket, we're talkin the whole motor will have to be torn down AGAIN, reboiled to get all the metal shavings out of it, plus chancing the cylinders, rods, block, valves, heads, etc...when it let's go. Why even take a chance like that, when another week or two for shipping or even another $100 will put yet another "questionable part" to bed. Sometimes skimping is'nt always good, I know some guys can run junk parts and never have a problem one, but I'll bet at least 90% of us are'nt that lucky. Hey, Frozen Firebird, buy a lottery ticket the day you install your crank, see if it's your "lucky" day or not.

 

LOL ya make a good point IHI...Im not in a real rush to get the engine together, and I dont think I can swap the crank at Napa, I got the crank about 2 or 3 years ago and dont have the reciept.

But I guess ill hold off with the crank for now, ive got all winter, and see what comes my way...Besides its only $100 bucks or so...But ill have to get it locally due to the fact that I get BENT OVER for shipping to Alaska.

Thanks again for all the input.

 

030 cranks are fine. those journals are fairly thick, and shaving .030 off won't cause problems. my brother has .030 crank in his fairly potent 400, and has noproblems for 30k plus miles. the local machine shop shaves that far regularly, and has never had any problems.

 

I met one of your fellow Alaskins at Nationals this year, his name was Jay Hunison, races a red 66 Mustang. After we got wind of someone coming all the way from Alaska to Cordova, IL. to race, we had to go meet their group. Super nice people, but, but told us the whole car was built from parts ordered straight from Summit or Jegs. He was telling us that there is'nt a real "speed shop" up in that area, so you kinda gotta do what you can do. I don't know what they get to ship to your area, but it must be pretty bad.
The Alaskin crew shipped all the stuff down in a container 66 Stang, and 3 jr. dragsters, plus all necessities, 3 months prior the event, and said it cost him $3300 1 way to have that done-now there's some dedication to racing.

 

Feel free to tell us your qualifications and where you earned your mechanical engineering degree from, and how many metalurgy classes you aced or how many winston cup cars you build motors for.

 

Go back to nethirdgen.org.

Have fun on the non-tech pages.

 

Man, I gotta come back to this site more often....I didn't realize how many perfectionist built engines here.


All I really say on this matter (someone did make a mention to it...those who know, will be able to read the above posts and pick up on this), is those of you who are concerned about taking .030 off a crank, should ask your fathers how they got more cubes...back in the day.

Anyone ever heard of an "offeset ground crank"?


Ever wonder how much was taken off one?

Hmmn.

For those that think taking .030...heck, even more, off a crank is going to hurt it...I'm guessing you think the crank is paper thin?

 

Thank you. I was going to mention offset grinding, but I figured there was no point in arguing with these guys.

Also, in the last Hot Rod (yeah I know, racing magazines...), I read about grinding the crank down to a 1.888" rod journal size, to accomadate Acura rod bearings. Aparently, this reduces the amount of friction. AND, it requires grinding the crank MORE than the standard 0.010".

 

I still would have to ask, how the crank in question came around to needing .030" taken off of it.

There's a world of difference between taking a new, or at least low-mileage, crank and turning it down to make a race car; and takign a worn-out stock crank with who knows how many hundreds of thousands of miles on it, and trying to make a street car that you expect to run a hundred thousand more miles. Cranks don't last forever, especially cast ones, as we all know. I've broken a few myself. I did my share of offset-grinding steel cranks back in the day, but there's better ways of getting that result now, with less risk.

I would not take a crank of unknown origin with that much maintenance having been required over its (apparently) long and industrious lifetime, and sink my money into building a motor around it that I expected to last a long time. The potential downside far outweighs the cost of trading it in.

I feel the same way sometimes about arguing... we all have opinions, they're all just that, in the end the car owner has to make the decision; just because some magazine wrote an article about some curious and intersting combination, or somebody's brother-in-law's cousin's roommate's boyfriend's co-worker says he met somebody at the track once that says he saw a stock cast crank 350 go 10,000 RPM with small journal rods every week all season long, doesn't mean that it's a good thing to do to my car or your car for running on the street and depending onto get to work in the morning.

 

You're a class act through and through. You even have to criticize me in other non-related threads.

You still haven't attempted to explain why your opinion is any more valid than anybody elses.

Most of us don't seem to be saying that you can't do it... only that for the sake of a lousy $150, why even take the chance?