Crankshaft Material Choice

[akatheman]

I'm Looking into billet choices for a crank shaft and was wondering what everyone thought the ultimate material would be? A titanium mayby 6-4? Or something less exotic and standard like a "clean" steel? Going to have rebuilds about once a year (25000 miles) Not all racing. a mixture of drag autocross and street. Looking for the lightest wieght assembly possible that will not cause signifigant durability problems. Stroke 3.465 Max Rev 8k. Fully counterweighted. Internally balanced 4 cylinder.

 

[GregLocock]

No, titanium is not the material of choice - it isn't stiff enough. Or, more accurately, for a given geometry you'd get such an increase in performance by going for the right steel that you'd go for the steel one.

My guess is that forged steel crank is the best solution that is easily available (sorry, I don't know about what grade of steel).

What do F1 cars use?



Cheers

Greg Locock

 

[icrman]

4340 forged steel seems to be the best choice. I suppose
something like 4130M would do also. I have worked alot with 6Al 4V, I would think that with the proper cross section it would work as well as the steel and have a better fatique resistance. I think the cost would be way prohibitive though. I am quessing in the area of $10,000. US. vs $1000. or less for the steel unit. Aircraft quality titanium is very expensive, and then there is the higher cost of machining it. It can not be machined as fast as steel can be.

 

[patprimmer]

icrman

I agree 4340 cranks work great in serious racing with American V8's like NASCAR, Australian V8 Super Cars, All forms of Drag Racing like Pro Stock where Standard production block dimensions are employed. Where special dimensions are allowed, billet rather than forged cranks are used. I think the preferred steel for billet cranks is ES or EN 46, but I am guessing from a hazy memory. I don't know the actual composition for the grade.



While they may not be F1, they still have high budgets and employ some very high technology.

Re titanium, you say given proper cross section, but room is mostly the limiting factor, and if a 4340 steel crank already is at optimum dimension for strength, the titanium crank will fall short re strength.

I can enquire into grades of steel used for billet cranks in Top Fuel cars if you like.



Regards
pat pprimmer@acay.com.au
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.

 

[DVE]

Hello,
Some of F1 engines use a steel grade from Aubert & Duval and the code name is something like GKHYW.
A Famous F1 crankshaft manufacturer is Chambon in France.
DVE

 

[tbuelna]

akatheman:

If cost is no object, 4340 VAR is the material of choice for a billet crank. 4340 VAR is an electric arc vacuum remelt chrome-moly alloy steel of very high quality and purity. This is the material used for all 4 stroke racing cranks, including F1. Roller bearing cranks, like 2 stroke GP bikes, are typically made frome a case hardenable alloy steel like 8620.

4340 can be hot forged to produce an optimum material grain structure, if you're willing to pay a huge amount of money for forging dies. Also, a hot forged crank should be 100% machined on all surfaces to remove any surface imperfections/contamination from the forging process.

After rough machining, the 4340 crank can be stress relieved and gas nitrided to harden the journal surfaces and then finish ground and balanced. Nitriding is the preferred surface hardening treatment because it does not require a quench and the distortion that would result from quenching.

6Al-4V Ti would be a poor choice for a crankshaft because it has a low modulus of elasticity, would be difficult to produce a hardened journal surface on, and would have a very limited fatigue life.

Regards,
Terry

 

[Tmoose]

Titanium has earned a reputation for not getting along with other metals. Special coatings are required on light-duty bearings like rod side faces.

http://www.timet.com/fab-p34.htm

PREVENTION OF GALLING
Galling not only causes excessive wear on titanium but may also result in accelerated corrosion through fretting action. Simple lubrication, using graphite or molybdenum disulfide, is often sufficient to overcome galling. It is, therefore, possible to use titanium for moving parts or for parts in sliding contact with itself or other metals with light to moderate loads. Heavier loads, on the other hand, require hardened titanium surfaces. "

 

[swall]

For a steel beyond 4340, you could go to 300M or Aermet 100. Prices are beyond 4340 as well.

 

[royceso]

top fuel cranks are made of 9320 steel.

 

[bobqzzi04]

What kind of engine? If it is an imported engine with a factory forged steel crank it may well serve. My general experience is that quality for quality a forged crank is superior.