Thread: will a reground stock crank work

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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.

Originally Posted by maineevent

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

New cast steel cranks are less than $200.

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.

Now here is the other thing that will offset all that, you may have to get everything rebalanced with the new crank.

So your expenses are starting to stack up, so choose carefully after doing some thorough research. That seems to be the thing with components.....brainpower is free 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

Originally Posted by 76GMC1500

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.

Guess what??
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?

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.

Originally Posted by kitz

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

As we all know steel is a blend or mix of different metals.
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]

Originally Posted by 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?

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.

This is very good advice.

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