Crank Junk??
 

Ok I know opinions on this are mixed but is there a consensus answer on what to do with a crank with a spun rod bearing. This is a crank that has come out of an engine I bought for my project all was looking good untill I got to my last rod when I removed it the bearing had been ground down like tin foil hence the crank obviously needs re-sizing on the rod journals, all the mains look in very good shape with no obvious wear not had chance to measure them yet though to confirm. Assuming the mains are good how do I proceed? Scrap crank and find good used one? Magnaflux - Re grind and re-harden ?proper method for re hardening??

Crank is 83 3.0

Steve

Steve,

Hard to tell unless you measure the journals.

The standard procedure is to have the rod journals reground undersize and use undersize bearings to compensate. The old Tenifer process is gone, as a bath in molten cyanide was part of the process with its obvious environmental and workplace safety implications. There are rehardening processes available but these are claimed to be not as good.

Conventional wisdom is just to skip the hassle and locate a STD/STD used crank.

...and if you need a std/std crankshaft for a 3.0 they are around....I have one extra for example....

Dennis

Hi Dennis are you hanging onto your spare or is it for sale? is so can you PM me a price.

Regards Steve

John,

Tenifer tretaments are alive and well and are still available. To some extent they have been re-branded.

Turftriding in UK and Melonite in the USA.

Bodycote in Germany still offer the Tenifer Process and Burlington Enginnering in the USA are leaders in Melonite.

http://www.burlingtoneng.com/melonite.html

Tandler Precision in Germany who manufacture quite a few Porsche Ring & Pinions also use Tuftriding/Melonite.

All of these processes use Salt bath Hardening and they are classified as ferritic nitrocarburising.

The surface chemistry of all three types is identical as is the hardening mechanisms.

Chris

Would you be happy to use a crank in one of your engines that has been reground and re hardened by turftriding correctly done?

My local machine shop offers tuftriding but advised me to check on the suitability of the crank material with porsche or the owners club etc first

Thanks Steve

Steve,

We have been Tiftriding cranks for years and the process is relatively material tolerant. It is 'nitriding' that is much more material intolerant.

As Porsche Tenifer treated the cranks originally then you can be confident that Tufrtiding and Melonite treaments are fine. I did dig out the composition a couple of years ago and had no real concerns.

We are just thinking about building a short stroke 2.8 using a 66mm stroke 'S' crank and this will be reground and Tuftrided and I will still sleep at night.

If you crank machinist isn't happy you could try Rob Walker Performance Engineering in Oxford.

Rob has ground and re-hardened several 911 cranks for us and also debungs and rebungs and then micropolishes.

I must say that it isn't particulalry cheap to carry out all this work and from time to time it is possible to find good used cranks for a similar cost.

Looks like im stuffed anyway, just had the crank at the machine shop and its worn .2mm so will need to go more than .25 and I dont think .5 shells are available anymore?

They couldnt find them in there catalogue

They did say they may be able to cross referance to another suitable bearing on there database, is this a bad idea?

Steve

Steve, 0.50 rod bearings are cheap and plentiful. Search here for 901-103-141-60-OEM, Pelican sells them for $12.25 for the set.

Hi john

This is an SC crank but after having a better look it seems pelican does have them

930-103-148-60 ROD BEARING SHELL $23.00

Whats the price for? A single shell or pair? ie one journal ??

Steve