How to spot a VHPD Crank??

[Bob Corb]

I've bought a crank which I was told is a VHPD item. I'm about to tear my std 1.8 apart to rebuild as a VHPD but whilst playing in the garage a few minutes ago I spotted the words "std crank" scribbled on the corner of the box which the crank came in which has got me worried.

 

The story is that it came out of a std VHPD engine which Lotus rebuilt to Elise race spec which includes a billet crank. I'm hoping that the reference to standard on the box means std VHPD and not bog std 1.8?? It has the part no LEF10092 in the forging but I'm not sure if that helps as I guess they press the VHPD cranks using the same tools. Can anyone help??

 

Cheers

 

BC

[Rob Walker]

Hi Bob,

 

I was told that only the very early VHPD cranks were hardened . They were the standard 1.8 cast cranks that were tuftrided in attempt to improve durablity, the later VHPD cranks were standard 1.8. The Caterham sales spec said that the VHPD had a nitro carburised crank, this puzzles me as its not possible to nitride a cast crank. Give PTP a ring with the part no.

 

I would stick with your standard crank you won`t have any trouble unless you go above 200 bhp and 8000rpm.

 

Rob

[Bob Corb]

I'm not too worried about the durability aspect as I use the car mostly on the road anyway. Its just that I paid good money for the crank... PTPs web site advertises the VHPD crank as using different material and costing £483.. it must be different somehow?

 

I'll speak to PTP tomorrow but they aren't usually very good at detailed enquiries like this. I dont think they have a lot of technical know-how really?? Who actually builds the VHPD engines that PTP sell?? Do Minister build them all or just for Caterham..

[tom7]

Bob,

Make sure you ask for Neil Butler or Frank Swanston, I'm not sure there is a K series question they can't answer.

 

Tom

[V7 SLR]

Extract from an article I have regarding surface hardening techniques, aimed at crank manufacture:

 

It is obviously quite easy to confuse nitrocarburising and carbonitriding but they are very different processes.

I would be happy to share it with anyone. Email me direct.

 

Worcs L7 club joint AO.//Membership No. 4379//Azure Blue SLR No. 0077//Se7ens List Tours

 

[R2D2]

Nitro carburising is not the same process as nitriding and could be applied to virtually all "standard" cranks without any real concern. Nitro carburising is commonly called Tuftriding

 

What the improvement in fatigue life would result is difficult to estimate but it's not a bad insurance policy and isn't too expensive to have done.

 

I just looked at the PTP Website which states the following:

 

"Based upon the standard 'K' Series design, a new casting material and machining process is specified by PTP to give 17% more strength.

 

The crankshaft is most commonly used on the 190Ps VHPD engine with recommendation being used on engines producing up to 200Ps"

 

I am always interested in these new but completely unspecified materials that always give great improvements. I would also like to know how the machining process gives more strength.

 

Do you think that the material has better tensile strength or fatigue strength?

 

I also looked at the billet steel crank details and again they don't specify any particular steel or heat treatment.

 

I would certainly prefer to know what I was getting for my money.

 

 

 

 

 

Edited by - chris flavell on 20 Jan 2003 11:06:43

[oilyhands]

I'm sceptical on the improved material bit, but I think they use a better rolled fillet radius to improve strength. Generally Tufftriding can be applied to any ferrous material, nitriding however can only be applied to specific nitriding steels. Billet steel cranks are normally EN40B or newer equivalents and are nitrided as a standard operation.

 

Oily

[oilyhands]

I'm sceptical on the improved material bit, but I think they use a better rolled fillet radius to improve strength. Generally Tufftriding can be applied to any ferrous material, nitriding however can only be applied to specific nitriding steels. Billet steel cranks are normally EN40B or newer equivalents and are nitrided as a standard operation.

 

Oily

[AMMO]

Chris

 

I have had stainless valves made for many years which are tuftrided. I understood this to be a very shallow anti-scuff treatment. On the valves it is black and makes the stems resistant to wear. I don't think it actually makes the component stronger. I may be mistaken. There may even be different types of tuftriding for all I know.

 

I've also had EN40B cranks made that were nitrided that looked quite normal. The webs did have a kind of greyish look but the journals were polished as you would expect. The journals are probably finsh ground and polished after nitriding as there would probably be some distortion during heat treatment.

 

As for identifying what Bob has, I've seen old guys take a file to the web of a crank to see how hard the material is. A modern day version might be having it hardness tested. Would that tell you anything? 60 Rockwell C seems to ring a bell.

 

 

AMMO

[Peter Carmichael]

Isn't it funny that Powertrain Projects Limited and Powertrain Limited can't agree on whether the K-series crank is forged or cast...

 

The "K" Series engine has its roots in the 1980’s when it won government funding from politicians renowned for their dislike of state support for the manufacturing industry. The elegance of its design, with one set of bolts clamping the whole engine together, is still considered to be world class in many respects.

 

 

K Series 1.1l, 1.4l & 1.6l engine

The major components of the unit – the four "Cs" – are largely produced in-house. Castings for the cylinder block and cylinder head are made from raw aluminium billets using the LPS (Low-Pressure Sand) process in the Foundry. The transformation of these raw castings into machined components also takes place on-site in East Works. Forged blanks are bought in as the starting point for crankshafts and camshafts. Precision turning, grinding and finishing transforms these blanks into the heart and soul of the engine. Following these parts through the assembly process is not as easy as you might think. There are two assembly tracks running side-by-side. One of these does a subterranean "U" turn half way through. Between and around the lines are sub-assembly loops for manifolds and cylinder heads obscuring the overall pattern.

---

[Bob Corb]

Right.

 

Basically this crank has come from a Minister VHPD engine that was being upgraded to race spec billet crank - thats the story.

 

PTP say that other parties are involved in the production of their own "VHPD" motors hence the confusion. A lot of other suppliers alledgely dont fit the 8002 type crank.

 

The way to spot a true VHPD crank is the marking for the gradings, early 8002 cranks have scribed numbers/letters. Later 8002 cranks are stamped with a single punch type number, production cranks are stamped by an automated pinstamp machine (Dot matrix printer type font).

 

Frank Swanstons comments on nitrocarbusing was that this can lead to porousity in the material due to carbon being displaced near the surface around the bearing surfaces, not good....

 

Therefore I think I have a std 1.8 crank. Its now for sale for £100 ono or swap for one new Omega VHPD piston.

 

Mail to rcorbishley@cosworth-technology.co.uk or call 07899 878313.

 

Thanks for all your help.

 

BC

[oilyhands]

Ammo,

 

Tufftriding creates a thin skin of harder material all over a component and as a result the fatigue life of the component is improved. I dont think it makes it stronger, just improves longevity a little.

 

K series valves are routinely Tufftrided out of the factory.

 

Cant say I've noticed any problems with porosity near the surface on any Tufftrided cranks or other comnponents.

Usually any bearing surfaces that have undegone Nitriding or Tufftriding are polished since the material grows a little. Some cranks are induction hardened rather than undergoing immersion treatments, this can be more closely controlled and can be localised.

 

Oily

[R2D2]

 

Tuftriding can be applied to all materials that use iron as the base material.

 

For valves it would give good scuff resistance but it is common to Tuftride cast iron or carbon steel cranks such as the old EN16T Mini cranks.

 

Tuftriding does produce a residual surface compressive stress that is good for fatigue resistance.

 

Tuftriding is a process more accurately known as Ferritic Nitrocarburising and is carried out at about 570 deg C.

 

Tuftriding leaves a "white layer" on the surcace of the component and this should be left in place.

 

Nitriding is quite a different process and does rely on specific type of steel.

 

The most common nitriding steels are EN40B or EN41 but 40B is the most suitable for cranks.

 

Nitriding steels tend to have a relatively high percentage of aluminium. This produces aluminium nitrides in the surface of the component when heated in a suitable environment.

 

These aluminium nitrides are very hard, very strong and produce very good wear resistance and because they also generate very high residual compressive stresses have a very positive effect on fatigue life.

 

Nitriding, if carried out correctly doesn't really produce and distortion. The basic process route should be:

 

1. Rough machine

 

2. Harden and temper to a 'T' condition to give good parent material properties.

 

3. Stabalise at 575 - 590 deg C for 12-24 hours to remove all residual stresses and eliminte

subsequent distortion.

 

4. Finish machine leaving a grinding allowance on journals. This is to remove the White Layer that is

produced by nitriding. (Different to the white layer formed by Tuftriding)

 

5. Nitride component

 

6. Finish grind to remove white layer.

 

The white layer in nitriding is high in Iron nitrides, tends to be brittle, can flake away from the surface (spall) and unlike the white layer in Tuftriding must be removed.

 

The poor performance of Iron nitirde is why non-nitriding steels shouldn't be used for this process.

The iron nitride produced would give poor surface properties and not really produce any residual surface compression.

 

I wouldn't do Rockwell Hardness Tests on surface treated parts. Rockwell C uses a 150kg load and a diamond indenter. This would punch through the nitrided casing and may cause damage.

 

A Vickers hardness machine and a light load would be much better.

 

I think that the first "Rover" crank to made from SG Iron and fillet rolled was the Metro Turbo. This was very successful and according to some of the guys at Longbridge this crank gave better fatigue life than the old EN40B nitrided Cooper S crank.

 

I am surprised that carbon will diffuse out of the surface of a steel/iron component at 570 deg C, even on an SG Iron Crank where there is some free carbon hanging around.

 

Both nitriding and Turftriding do leave a little surface porosity but to a very limited depth which should have no impact on fatigue crack initiation, it may be that this surface condition does help by grabbing hold of an oil film and helping with some degree of mechanical adsorption.

 

I would be very interested in any information concerning carbon loss from the surface of Tuftrided parts.

 

[Peter Carmichael]

Nitrided cranks are rather more than polished to finish them. They have to be remounted on the girnding machinery and given a final grind. The material swells considerably.

 

Tufftriding just needs any residual scale from the process to be polished away.

 

Both processes will stress-relieve the material skin, improving fatigue life.

[Lawrence_Z]

In an attempt to assist Bob in his decisiion making, it should be remembered that Caterham Parts supply all the parts for cars, including all the engine parts used by Minister.

If there is a different crank in a vhpd then surely such an item will be available from Dartford. Last time I checked it was only the steel cranks for R500 that were listed.

Lawrence

[R2D2]

 

Typical growth for nitrided surfaces are 0.005mm for a case depth of 0.25mm or 0.01mm for a case depth of 0.5mm.

 

Tuftriding only produces surface layers around 0.01mm to 0.02mm and doesn't really produce any real growth.

 

Both process introduce significant compressive stresses into the surface of the crank. Stress releiving isn't really part of the equation.