Cryogenic treatment for crank, rods 2

[Rink]

Hi all,

Engine- Flat four, air cooled, was 1588cc - soon to be 1883cc, head/valve work, twin plug ignition, split-lobe cam, etc.

Service- Dedicated, lightweight autocross car.

Hoping to achieve 35-40% power increase but mostly a higher and wider torque band. I have been advised to cryo treat the crank and rods. My questions are about the order in which this should be done. Should shot peening be employed and if so, where in the sequence? Is this the correct order? -

1. Crank magneflux & inspect
2. Grind (if necessary)
3. Remove/clean/replace passageway plugs
4. Balance
5. Cryo treat

1. Rod inspect/straighten
2. Rebush small end
3. Balance
4. Cryo treat

Any other components that will benefit from the cryogenic treatment?

Rink

 

[patprimmer]

You might want to cut and shut then ream the big end to size to ensure optimum bearing crush.

Shot peening definitely works, cryo is in the sounds very space age, but no conclusive evidence that it really helps catagory.

You can improve the crank by masking the journals and shot peening the fillet radii.

If it is an air cooled VW with OEM crank, every one I saw had a rolled fillet radii, so it is already about as good as it gets. Extra counterweights are the way to improved crank durability on an air cooled VW.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[MechanicalChef]

It depends on the alloy of the steel. Some tool steels require a sub zero quench to harden the steel properly. You will see it somewhat more common in knife-circles. Is it worth the trouble for your application, probably not.

 

[evelrod]

The 'hot setup' in vintage racing circles is cryo treating brake rotors. Seems to not cause any problems that I have seen, but then neither have my non cryo rotors.

Hey, it's your bucks. I've managed to break just about every part that can be broken over the years, even one of the fancy Cosworth rods that had been cryogenically treated!

Rod

 

[Tmoose]

Are you modifying stock rods, like these?

http://www.dansperformanceparts.com/buggy/epc/98-0154-B-1.gif

Rod failures can be fatigue cracks or distorted big-ends killing the rod bearings.
There was a time (1970s) when the rods fit loosely on the bolts, and tricks (shims and rubber hammer blows) were used during assembly to reduce binding, which was the result of the road and cap being severely misaligned or shifted. Even Free turning was still no guarantee the big end bore was still round. Everybody else used Snug fitting bolts provide good rod.cap alignment.
New or used Rods should be magnafluxed (wet method) with the bolts out and seats deburred, and rods shotpeened with steel shot to Almen 0.012 or so, then rebuilt with new bolts.

crank mods - for years it was claimed counterweighted cranks help the cases survive at higher than stock (low)rpm. I believe it.
check here -

http://www.geneberg.com/section.php?SectionID=12

 

[patprimmer]

I never had a rod failure with a properly prepared stock VW rod.

I had lots of centre main bearing webs pound out with stock cranks at anything over 5000 rpm.

I never had a centre main pound out after I switched to fully counterweighted cranks. I ran these to 7000 rpm.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[5secondracing]

Cryo seems to work really well. We do most all of our engine components including turbos(huge gains on turbo life!!!) It is kind of a stress reliever like shot peening. I think it would be a little redundant to do both. I have learned that things do move a little during cryo. It is a good idea to do all your magnafluxing first(to make sure you are not wasting money on cryo) then cryo before you finish grind as well as resizing. This gives you the most accurate parts in the end. Cryo also makes most materials easier to grind or machine.

 

[macquari]

5secondracing is right about the stress relieving.
I am currently grinding an RB26 Nissan crank which is to be nitrided.The heat treatment company uses cryo to stress relieve some shafts before normal stress relieving as it reduces the amount of distortion when the shaft is heat stress relieved.When the shaft came back it had .005"tir at No4 main when rollered on No 1&7 mains and .007"tir when set up to snout and seal in grinder,other shafts have had up to .015"tir when not cryo'd.
The shaft has now been ground to -.20mm and stroke deviation corrected and will be nitrided next week and ground to finish size,if the heat treater is right there should be little or no further distortion.

 

[Ataloss]

Secondracing,
What parts of the turbo are you cryo-treating? What parts are/were you failing? Is this done for both the ferrous parts and the aluminum parts?
Just curious.
Thanks,
Bob

 

[Rink]

Okay, thanks for input.

I have revised the order in which the processes should be done:

1. Crank magneflux & inspect
2. Cryo treat
3. Grind (if necessary)
4. Remove/clean/replace passageway plugs
5. Balance

1. Rod inspect/straighten
2. Cryo treat
2. Rebush small end, 'trim'/hone big end
4. Balance

With regard to cryogenic treatment of steel engine parts I guess the following would benefit as well- Rocker arms, rocker shafts, valves, and maybe pushrods (?).

I too would like to hear more about cryogenic treatment of aluminum components.

Now, how hard is it going to be to find a place that can do this work? As an aside, I have a local machine shop that does cryo treating. They heat to 100*C then dip into liquid nitrogen, multiple cycles. Does this meet the "standard." Or, said another way, what questions do I ask to insure that a given shop knows what they are doing?

Thanks for the input from all of you!

Rink

 

[5secondracing]

Rink,

I am far from an authority on cryo. I will try to get my guy on here to explain in some more detail. Cryo works equally well on ferrous and non ferrous with the exception of some stainless steels.

All components of the turbos are treated.

The process you spoke of is not the way my guys do it and just for reference your not supposed to induce liquid nitrogen to bare metal until deep cryo is reached at -180F.

It is a 72 hour process they take the parts down to -280F at 1 degree per minute. Once in deep cryo it is left there for at least 24 hours depending on the cross section. Parts over 3 inches thick go over 36 hours etc, the parts are then returned to room temp at 1 degree per minute, then heated to the same temp + as it went - at the same rate of 1 degree per minute and held for at least 12 hours and more depending on cross section. This is the proper process in a nutshell. It is timely and somewhat costly.

 

[Tmoose]

1. Inspect big end width/straightness/length , and big end size and roundness. If the BE is more than about 0.005 out of round or the slightest bit worn, or if the bearing insert spun it is probably best to start with another rod.
1AA. inspect bolt fit, cap fit and perpendicularity,
1A. rough balance
1B. remove bolts and magnaflux
1D. deburr and smooth rod and cap bolt seats
2. Cryo treat if you really want to
3. Shot peen to almen .012 with 230 cast steel shot
4. Resize big ends using new bolts, and taking minimal matarial off the parting faces using cap grinding equipment that cuts the parting face flat, not wedged. BE bore specs should be less than 0.0002 inch taper or out of round excluding a band about 6 mm aon each side of the parting face, which can be several 0.0001 larger, kind of lemon shaped. Not many rebuilders are likely to be able to achieve that.
4. Rebush small end using boring equipment that references the finished BE bore to bore the bushing parallel to the BE bore and at a particular rod length. Multiple setups may be necessary to get all the bushings to "clean" at a consistent length. You may have to allow rod length +/- 0.002 inch to get the bushings to "clean" at the proper size.
4. Balance

 

[patprimmer]

I very much agree with Tmoose, but would add to his point 2 if you really want to and have a lot of money to spend on something that gives no improvement that has not been conclusively measured by properly controlled scientific method testing by an independent respected authority.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Lou Scannon]

Well, now that everything's out in the open, just what evidence is there from the cryo boosters? How about an explanation for the supposedly favorable structural transformation in terms of a specific alloy composition, time temperature history, and phase diagram?

 

[Rink]

Hi all,

I like the way this discussion is going. I just used Google Scholar and, using the search term "cryogenic treatment of crankshaft," got 96 hits. Some of those are books, some papers and some are patents.

Using other search terms, I see a lot of references to Cryogenic treatment of tool steels. However, going back to my original problem, I have no idea what kind of steel Porsche would have used to forge my 1958 manufactured crankshaft (?).

I would be most interested in comments from those willing to persue published works on this topic.

Rink

 

[GregLocock]

I had a quick punt around the web yesterday for cryo. There are undoubtedly some benefits for some properties of some steels if certain procedures are used. A factor of 2 on tool life was mentioned in one paper.

BUT

conrods aren't made out of tool steel.
An improvement in hardness, or toughness, (for example) may do nothing for the life of the rod
the benefits depend on the procedure.




Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[Ataloss]

5secondracing wrote: 'All components of the turbos are treated.'


How has this produced huge gains in turbo life? Increased bearing life? Fewer wheel failures? Fewer oil or exhaust leaks?