ok with all the other questions i asked this might have got lost if i get my stock crank redone will this work or do I have to get a new one tight tight budget
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ok with all the other questions i asked this might have got lost if i get my stock crank redone will this work or do I have to get a new one tight tight budget
Yes a reground stock crank is fine, what is it ? steel or cast ? If it is either material get it crack tested before regrinding.
New cast steel cranks are less than $200.Quote:
Originally Posted by maineevent
They would also have the radiused edged journals and radiused oil holes so they would be stronger. I dont know what it costs you to regrind a crank in your area, but if the difference is less than $50.00 to $70.00 I would be gunning for the new crank.
:HMMM: Now here is the other thing that will offset all that, you may have to get everything rebalanced with the new crank.:CRY:
:eek: So your expenses are starting to stack up, so choose carefully after doing some thorough research. :HMMM: That seems to be the thing with components.....brainpower is free :LOL: You just have to figure out what components you want and how much it is going to cost to make it all work.
Mike brings up a valid point about the rebalancing, but remember, you'll have to rebalance anyway if the new pistons are much different in weight from the stockers.
The $200 cranks are probably typical porous Chinese castings. I would feel more confident with an older American ground crank. I personally have a cast iron crank turned .020 under in my truck and it is holding up just fine to over 400 ftlbs of torque. It only costs about $90 to have a crank turned. The crank grinders radiused the jornals and chamfered the oil holes as well.
eagle has a steel crank for 140 at a part store out here but turn my cranks like 70
Guess what??Quote:
Originally Posted by 76GMC1500
Scat,Eagle,etc. are all made in China.
If you are buying a crank under $800 other than a factory steel it's made in China.
Also don't worry to much about we have a crank made in China in a 700+hp dirt burner.
Night after night at 7,500+ rpm's.
Yes,it is made from4340 steel.
Our back -up truck that pulls the race car around has a 496 BBC and it has a cast steel crank in it.
30k miles later and still working great.
Erik is right. And I wonder how many bicycle part fillers are in any 4340 purchased from China.
I require material certs on all critical machinery components at work; why settle for less on our own stuff? No need to answer, but the point is you would be amazed at what variations in quality you can get in materials. 4340 is definitely on that list as well.
What you want to know in general is;
1) Composition ranges and tolerances
2) Processing methods and temperatures
3) Inspection procedure for detecting flaw size and tolerances
4) Stress strain curve (tensile test) on material drop
That's part of why real racing cranks cost real $ ................
Kitz
so i 'll get mine reground then
[QUOTE=maineevent]so i 'll get mine reground then[/QUOTE
:) Sounds good are your new pistons the same weight as the ones you have in there? :cool:
Oh and when you get it reground ask the machinist if he can leave a little radius at the edge of the journals and to smooth off the oil holes that go through the crank. It all helps. Then when you get that crank back take the time to clean out the oil holes with a small pipe cleaner brush and check to make sure no grit is left in the oil holes.
As we all know steel is a blend or mix of different metals.Quote:
Originally Posted by kitz
If I remember right both the Scat and Eagle are made in China but machined here in the US.
I have seen a 540 BBC with a Scat crank go over 1,000 on the dyno with two stages of n20.
[QUOTE=southerner]This is very good advice.Quote:
Originally Posted by maineevent
I would feel fine using a Chinese steel crank. Steel is easy to cast and get good results with, but iron is kind of finicky. Hidden porosity can lead to a severely weakened crank. Most cast cranks are nodular iron, not steel.
A 10/10 regrind is fairly standard for a first rebuild of a motor, meaning the rod and main journals are both ground down by a mere 0.010" to make sure the rebuild is based on round journals instead of slightly egg shaped due to wear. Above you see that even a 0.020" grind is OK. In bygone years there was a danger that maybe by 0.030" any surface treatment would be removed, but machinists have told me that doesn't matter anymore so I don't know where to draw the line for an unusable crank, but for sure if it only takes a 10/10 regrind that should be as good as new.
Don Shillady
Retired Scientist/teen rodder
chinese cranks 4130 and 4340 more than 30+ of them in evey thing from 4.250 to 4.750 stroke in big block chevys street.strip. pull truck. air boat.sand drags. and more chinese H beam rods than i care to think of .yep it is all junk???? well they still sell the stuff ?and the Best cranks do fail. i have only see one crank crack 4130 but it did not fail it was in a customer 548 that went to 8000 all the time in a chevy 4 wheel drive full size pickup hill climber and have had gm steel cranks .040 rod and .030 mains that had a very hard life and is still good ? there is not one thing bad with gm cast cranks built many big block with them for mild builds that went to 6500 all the time getting a good grind job is the big thing . and oil clearances and damping the harmoncis. this will keep the crank happy .round here to turn a crank is about $80. looking for the cheap job is not the best .i will pay more to get back some thing thats is right
ok I'll make sure to tell the machinist to do those extras I'm know the pistons are going to be different then the stock cause im going with the dished keith blacks 5.7 rods just having trouble getting them in a kit already