Crankshaft

[SCOOBY DOO]

PACECARTA is one of the best in the business. He's correct about crank flex at a certain HP being seen in bearing wear. The first engine I had cracked a cylinder all the way to the top of the deck...and the block had to be scrapped. On tear down the bearings still looked new. I wasn't making enuf HP to flex the crank and the engine saw zero KR. Fuel system is up to snuff in my car...and I record each run. On a build I have everything magnafluxed. An option for you is to sell your crank...and put the money towards something better. Just a thot.

Keep in mind that crank in your engine is 30 years old and has had a miliion heating/cooling cycles...and how much KR might it have endured before you owned it. Lots to think about.

 

[marleyskater420]

Possible dumb question.

Is there any heat treatments, cryogenic treatments, or coatings that can enhance the strength of the stock crank?

I suppose if there is, it may cost about the same as an imported forged crank.

I hate buying & using Chinese products!

There are no dumb questions. So NEVER think that, or let that get in your head and prevent you from asking a question and learning something new. If you are ever concerned about what it may look like on the forum, please shoot me a PM and if I cannot answer the question, I will point you in the direction of someone that can...but it is frustrating the amount of customers that I've had in the short time I've been in business that tell me that they're afraid to post questions on the board for fear of getting flamed/yelled at/made fun of....that is total bullshit that they should have to worry about stuff like that...this place didn't used to be like that...

Anyway, to answer your question- yes, there are ways to enhance the strength of a stock crank.

There are heat treating facilities all over the USA that could heat treat the stock crank and add some strength to it, but when you factor the cost to ship your crank there and back, plus the heat treating cost, you are basically at the price of an affordable forged crank, so it is a bit of a moot point. BUT, there are ways to make it stronger.

Now, I do not know the specific heat treating processes that you would have to get done. That is something you would have to talk to Fabro Cater about.

On a related note- you can also take a crank that has been cut to 30/30 or 20/20 and make it just as strong as it was when it was new. I'm sure if you ask most people they wouldn't be able to tell you why a 30/30 crank is no good, besides it has been cut down.. Well when a crank is originally heat treated, only the top layers of the crank receive this heat treating, otherwise the whole crank would become brittle. So only the top, let's say, .060 or so receives the heat treating.

So when you cut a crank to 30/30 you are effectively cutting in half the heat treating, which is where the strength comes from...so you just cut the strength in half, basically.

If you were to send that crank off to get heat treated, the crank would have the same strength as it did originally (assuming of course the heat treatment was done to all the same specs as stock) and you would have a 30/30 crank with just as much strength as an un-cut crank.

This was what I was driving at asking the question can the crank be reconditioned to the "zero time" state. Probably not a big market, if any, for this kind of service. The other piece would be detecting defects/inclusions. If I am not mistaken, magnaflux will only find defects that extend to the surface. To find casting defects below the surface x-ray or maybe ultrasonic inspection would have to be used. That's probably the biggest drawback to the casting. It would be good to be able to reuse the stock crank, but not if it cannot be reasonably evaluated/reconditioned.

Thanks to everyone for the feedback so far.

Yes, it is possible. Please see my response above.

Why would you even think about reusing 30 year old crank technology? The modern day cranks have current metallurgy vs 30 year old metallurgy. Sounds like you're looking for a reason to use a OEM crank.

I was speaking with Tom Lieb (owner) of Scat at PRI, says that he buys metal from the US and ships it to China for the cranks as the Chinese metal is not as good as US. He has the cranks made in China and ships them back to the US to be finished. He lives 6 months in China and 6 months in the US.

This past PRI, Eagle had a Buick V6 3.625 stroker crank on display.

Like what Nick stated, your block will thank you by having a less flexing crank.

Like the saying goes...."spend once, cry once"

Billy T.
gnxtc2@aol.com

I'm glad you made that comment about SCAT. When I spoke with Tom (on the phone, I wasn't at PRI) he really emphasized SCAT's heat treating processes for their billet cranks, and where they source their metals from.

I don't know if people think all metal is the same, but it isn't. In fact the best steel is actually from Japan-i forget the name of the city- but that is where you will see things like the world's top chefs have their knives made from, or uber-high-end cutlery/blades/etc.

Being as that metal costs a lot, and isn't fiscally viable for usage in a large scale marketplace like aftermarket crankshafts, SCAT went to the next best option-USA steel.

There is a reason why certain Chinese cranks cost $400 and why others cost $700. A Chinese crank isn't always a "Chinese" crank. You need to ask yourself- Who designed the crankshaft? What were their qualifications? Where was the steel sourced from? What heat treating processes do they use (and how many) on this crank? What are the production tolerances that they adhere to?

I could have a connecting rod made from 1 Chinese manufacturer and it is made to a .05" tolerance (you would be shocked to find out that there are Buick vendors that use connecting rods that are produced to this tolerance....) and another Chinese manufacturer that produces connecting rods made to .00003" tolerances. Quite the difference in quality, wouldn't you agree? I am giving you this example to show that just because something is Chinese doesn't mean it "Chinese" as some people have come to interpret it.

I don't have a problem replacing the crank when it is time for a rebuild, just looking to confirm it makes sense for my intended purpose. I don't want to chuck a good part, if it is still good and can perform its intended purpose. I appreciate what you posted about Scat, because I prefer to spend my money on US made products. I'm not a zealot over it, because it is getting to be impossible, but being made in the USA is always a factor, and it looks like Scat has a mostly made in the USA product which is a plus in today's world.

The intended use would be a street car, that probably sees 50 or so 1/4 mile passes a year. My guess on HP would be in the 550 range at the crank max. I don't think I am going to add a role bar, and I don't plan to start racing. I mainly like to tinker and run the car at test and tune.

Using a rough guideline of what Pacecarta and Scooby posted, a good condition stock crank can handle that power for what seems like quite a while. Part of that equation though is being able to tell what a good stock crank is, and it is a gamble to some degree. I've seen the posts where others have really pushed the stock parts, and my guess is more have grenaded the stock stuff and you don't always hear about it.

I actually like doing the investigation part like I am doing now, and appreciate people chiming in with their experience.

I think Scoobydoo and Pacecarta are trying to emphasize the point that just because the stock crank could, in theory, handle the power, by the time you get it heat treated/micropolished/whatever you would like to do to add strength to it, that the cost-benefit ratio is simply not there. The cost for a brand new forged crank would be not much more money, and it would provide so much more piece of mind. The cost of your rotating assembly and risking it being thrown apart by a stock crank just giving up at 30+yrs of operation just isn't worth the risk. As you have seen in this thread, stock cranks can hold high HP for some time, but they'll blow up (but there have been lucky people who have never had that happen to them-but are you going to take the chance that you're one of the FEW lucky people?), or they blow at much much lower levels...you just never know.

I hope some of this helped answer your questions. If you are looking for a crankshaft, we did just have a Christmas Day special of $510 for a brand new SCAT crank. Although the sale is over, I will extend the offer to you if it would help you keep your build within your budget (since I am assuming this build is budget-minded, hence why you are inquiring about reusing the stock crank?) and still provide you with a quality piece for your engine.

 

[gnxtc2]

Usually a competent shop that cuts cranks for performance use, will have them nitrated after machining. Nitrating increases the journal size on the cranks.

I have frozen (cryogenics) cranks and blocks. I will tell you this, after freezing all the tolerances changed. The bores distorted, mains moved, journals swelled....basically had to reaching every thing.

Biggest thing with manufacturers is that they have stuff made over seas and finished here. The labor and not having to deal with EPA regulations is much cheaper over seas. The finishing tolerances is much better here.

Billy T.
gnxtc2@aol.com

 

[Nigel]

There are no dumb questions. So NEVER think that, or let that get in your head and prevent you from asking a question and learning something new. If you are ever concerned about what it may look like on the forum, please shoot me a PM and if I cannot answer the question, I will point you in the direction of someone that can...but it is frustrating the amount of customers that I've had in the short time I've been in business that tell me that they're afraid to post questions on the board for fear of getting flamed/yelled at/made fun of....that is total bullshit that they should have to worry about stuff like that...this place didn't used to be like that...

Anyway, to answer your question- yes, there are ways to enhance the strength of a stock crank.

There are heat treating facilities all over the USA that could heat treat the stock crank and add some strength to it, but when you factor the cost to ship your crank there and back, plus the heat treating cost, you are basically at the price of an affordable forged crank, so it is a bit of a moot point. BUT, there are ways to make it stronger.

Now, I do not know the specific heat treating processes that you would have to get done. That is something you would have to talk to Fabro Cater about.

On a related note- you can also take a crank that has been cut to 30/30 or 20/20 and make it just as strong as it was when it was new. I'm sure if you ask most people they wouldn't be able to tell you why a 30/30 crank is no good, besides it has been cut down.. Well when a crank is originally heat treated, only the top layers of the crank receive this heat treating, otherwise the whole crank would become brittle. So only the top, let's say, .060 or so receives the heat treating.

So when you cut a crank to 30/30 you are effectively cutting in half the heat treating, which is where the strength comes from...so you just cut the strength in half, basically.

If you were to send that crank off to get heat treated, the crank would have the same strength as it did originally (assuming of course the heat treatment was done to all the same specs as stock) and you would have a 30/30 crank with just as much strength as an un-cut crank.



Yes, it is possible. Please see my response above.



I'm glad you made that comment about SCAT. When I spoke with Tom (on the phone, I wasn't at PRI) he really emphasized SCAT's heat treating processes for their billet cranks, and where they source their metals from.

I don't know if people think all metal is the same, but it isn't. In fact the best steel is actually from Japan-i forget the name of the city- but that is where you will see things like the world's top chefs have their knives made from, or uber-high-end cutlery/blades/etc.

Being as that metal costs a lot, and isn't fiscally viable for usage in a large scale marketplace like aftermarket crankshafts, SCAT went to the next best option-USA steel.

There is a reason why certain Chinese cranks cost $400 and why others cost $700. A Chinese crank isn't always a "Chinese" crank. You need to ask yourself- Who designed the crankshaft? What were their qualifications? Where was the steel sourced from? What heat treating processes do they use (and how many) on this crank? What are the production tolerances that they adhere to?

I could have a connecting rod made from 1 Chinese manufacturer and it is made to a .05" tolerance (you would be shocked to find out that there are Buick vendors that use connecting rods that are produced to this tolerance....) and another Chinese manufacturer that produces connecting rods made to .00003" tolerances. Quite the difference in quality, wouldn't you agree? I am giving you this example to show that just because something is Chinese doesn't mean it "Chinese" as some people have come to interpret it.



I think Scoobydoo and Pacecarta are trying to emphasize the point that just because the stock crank could, in theory, handle the power, by the time you get it heat treated/micropolished/whatever you would like to do to add strength to it, that the cost-benefit ratio is simply not there. The cost for a brand new forged crank would be not much more money, and it would provide so much more piece of mind. The cost of your rotating assembly and risking it being thrown apart by a stock crank just giving up at 30+yrs of operation just isn't worth the risk. As you have seen in this thread, stock cranks can hold high HP for some time, but they'll blow up (but there have been lucky people who have never had that happen to them-but are you going to take the chance that you're one of the FEW lucky people?), or they blow at much much lower levels...you just never know.

I hope some of this helped answer your questions. If you are looking for a crankshaft, we did just have a Christmas Day special of $510 for a brand new SCAT crank. Although the sale is over, I will extend the offer to you if it would help you keep your build within your budget (since I am assuming this build is budget-minded, hence why you are inquiring about reusing the stock crank?) and still provide you with a quality piece for your engine.

Thanks for the reply. I am currently planning ahead, I am thinking I am good for another year or so of driving. Budget is always a concern, but not the main reason I was thinking about reusing the stock crank. If, and that's the big if being discussed here, if the stock crank could handle the power reliably I already have parts that fit, don't leak oil, have good clearances, make good oil pressure, and so on. When the time comes I am more than likely going to replace the crank.

A couple of key takeaways so far from the discussion.

Crankshaft life/capability/flex, block life/capability/flex. These items are not mutually exclusive. As mentioned by a number of guys in this thread, the crank may not fail, but the crank flexing will cause premature bearing wear, and possible block failure. Exact cutoff point for this not known exactly, but 600HP range is beginning to push.

From a general point of view (just applying some basic principles to the crank) the point of failure on a crankshaft is most likely going to be at the journal fillet. This is the point with the highest stress concentration factor. With a defect free crank, it will fail after x cycles. The problem is the material and the manufacturing processes produce parts that will have some level of defects. So long as the defects are small enough, and do not cause significant financial harm to the manufacturer, they are acceptable. The purpose of the rolled fillet is to reduce the stress concentration and increase the cyclic life of the crank in order to mitigate failure.

From a cyclic standpoint, so long as the strain from each cycle stays in the elastic deformation range, the part can withstand a significant number of cycles, would probably outlive us. Once the strain gets into plastic deformation(which it certainly will when pushing the limit of the part), each cycle does a certain amount of damage. The life of the part will be governed by adding up the amount of damage, and once the fatigue life is reached, the part will begin to fail.

Defects in the material in the life limiting feature will have varying results, but will shorten the life. Think of a small inclusion/ bubble just below the surface in the fillet, this would have a significant effect on life. A defect at the center of the shaft, or in a counter weight would have virtually zero impact, unless it was very large, which would then mean the manufacturer was making junk if something this large escaped.

 

[SCOOBY DOO]

Okay, I always have my rotating assembly balanced. Will that take some stress off the crankshaft from a balance/vibration standpoint?

 

[Nigel]

Okay, I always have my rotating assembly balanced. Will that take some stress off the crankshaft from a balance/vibration standpoint?

I would like to hear some expert response, but from a general standpoint yes.

 

[PSID6]

I would like to hear some expert response, but from a general standpoint yes.

After having balanced numerous rotating assemblies over my lifetime. The Buick V6 never ceases to amaze me as to the amount of power these crankshafts can take. Anyhow the stock pieces in a rotating assembly vary quite alarmingly from each piston and rod assembly. The life expectancy of a factory crank and can only be expected to increase after a proper balance job. After drilling on the counterweights to bring a stock crank into balance it makes you wonder how these things make it to the corner store.

 

[ILikeSix]

I recently had a motor professionally built, the guy is not a 3.8 specialist by any means but he has built a few. For my modest power goals (smallish right now turbo respoonse and 500-550 CHP) the stock crank was deemed sufficient. If I had seen this thread before the build tho I certainly would have wanted to spend the $500ish on a new forged piece. Anyway the reason I chimed in is because something he said to me, he said we're running out of good rebuildable stock 3.8 cranks, even with a good source for his pieces he had to magnaflux 3 cranks before he found an acceptable one.

AJ in OC