Reconditioning titanium rods
 

I'm looking for a place that specializes in reconditioning titanium rods as I have a used set of pankl titanium rods that I want to send out. Does anyone know of a shop that does this?

Any normal auto machine shop can do this.

I think it is more of a specialty with respect to the rehardening of titanium parts with the brief research that I did.. The shot penning process for these tit rods may be different.

If anybody has reconditioned Pankl or vintage 935 rods, would be interested who you used.

Ask Pankl?

What I meant was any auto machine shop that does PORSCHE can handle this job. Try Walt Watson, Competition Engineering.

Pankl is a good idea.

I used Walt at CE for my last engine machine work but some parts (e.g. Reconditioning forged rockers) need a specialty shop. I think reconditioning used titanium parts may fit in that category but could be wrong. I'll ask Pankl, Crower and other Porsche machine shops and see what they say.

If any of you have experience with reconditioning titanium rods that have been timed out, let me know.

Did you ask Walt? I think you will be surprised at the answer.

Depends what Rod you have. If they are early 935/962 they use a titanium bolt, washer and nut. I would hate to know what those bolts cost today. The last time we recon'ed a set of these I think the bolts were over $ 130.00 ea. Pin bushings are unavailable and will have to be made.

If the rods are late GT3 then they use a bolt only but this is special also. They are not cheap either. Bushings are available if you use Aluminum Nickel.

Be careful as some production shops will cut corners and you may end up with 6 rods of different lengths and piston deck heights all over the place. The rods have to be handled with care at all times. It would be good to know the time on them if possible. Make sure they are checked for straightness as older used rods are known to bend.

I agree with you Neil.

I have late GT3 rods that have about 25!hour of racing or more on them. I am looking to make them as reliable as possible so looking to take them to the right place.

I am not sure what you mean by re-hardening Titanium ?

6AL4V which is the most common material used for Ti Rods is most likely used in an annealed condition.

To Re-anneal would involve temperature of around 785 degC and this would almost certainly cause some distortion and processing in this manner would IMHO be a mistake.

A 'Time Expired' rod could have it's fatigue life extended by shot peening if the process is carried out correctly but to assume you can peen these rods using either the same media or the same Almen Levels as 4340 Rods may also be a mistake.

There is a huge amount of published data on the influence of shot peening on the fatigue life of 6AL4V and there are many conflicting results.

In general terms when Ti is media blasted 'dry' there is always an explosion risk and whilst the use of a stainless steel media and carefully controlled conditions should eliminate this risk a basic knowledge is required.

More recently Ti is being peened using a Ceramic Media and 'wet' conditions.

The manner in which a 200% coverage of the surface, which is a typical requirement., is obtained can also be important.

If the treatment is carried out incorrectly then fatigue life can be reduced rather than enhanced.

I would suggest that the best approach is to find a contractor with experience of these materials and that has documented procedures backed up by fatigue testing.

The Metal Improvements Company in the UK certainly has this capability and they have a methodology that, I believe, is FAA/CAA Approved.

They are now part of the Curtiss-Wright Surface Technologies Group and their Headquarters in the USA is in Paramus NJ.

We have treated 'old' GT3 Rods successfully in the UK but generally only use them in 2.0 litre engines.

In other words, Chris is saying to send them to the scrap pile. 😂 ;)

Not at all - if the process is correctly managed the results will be excellent - I would just spend some time looking for a Company with experience which is why I suggested Curtiss Wright as a good contact. :)

Thank you Chris. That is the information I was looking for. I thought it might be a specialized process to shot peen these rods.

The first thing you need to ascertain is if the big end needs to be resized. It can be that at 25hrs just the gudgeon pin bushing need to be delt with.

regards

We have done several sets of GT-3 Pankl rods and the small ends are usually good, given the relatively low hours these are typically taken out of service.

Big ends, however need to be resized with all new fasteners. :)

Why do people think it is safe to re-use the GT3 rods when they have reached the end of their service life? Is there a body of experience to suggest that they are removed too soon?

1. Hours are not a very good indicator of fatigue life, unless it is hours of defined usage (25 hours on a couple of specific tracks). Otherwise, it is time for Rainflow counting and the Palmgrin-Miner rule, which requires more data collection than just the four over-rev ranges.

2. The large load reversals cause most of the damage. That is why there are the four over-rev ranges counted in the vehicle. Staying below those lofty RPMs causes MUCH less fatigue damage.

3. Re-annealing and/or shot peening does very little to restore fatigue life. It is like putting the smoke detector in after the house has burned down.

4. Re-sizing takes away material from the rod cap, making it even thinner. Is that safe on a highly weight optimized rod like the GT3?

The thing with the GT3 rod is that, because it is a high reving stroker, it needed bigger bolts, but there was no way to make the big end larger to accommodate them. No room relative to the case.

That being the case, if you are building something less that 3.4 liters, I wonder if you would be better off with a custom titanium rod, even if it is cut from annealed plate, rather than forged. It will have a much more reasonable fatigue life, due to more material in the right places, of course with a weight penalty.

There is a lot of emphasis placed upon the need and use of titanium in engines. There is even more put into the fear of titanium. Most is all part of the mythology that has been place against the use of this material.

Yes it has to be respected and handled carefully and everything said so far is correct, but it is not as fragile as most make it out to be.

We service some 962/962C engines that have rebuilt rods many times over still giving good service. Sure these engines are not pushed as hard as they were back when raced professionally, but so far we have not had one failure.

Lately, GT3 rods are becoming more common to use. Unless we see some obvious damage, we rebuild these and do not allow fear to be the only determining factor if they should be used.

Neil,

In the early days of the production of Alpha-Beta Titanium Alloys there was significant variability in the fatigue behaviour of alloys such a 6AL4V.

When I was doing my Post-Doc work we used to fatigue test and qualify these materials, on a cast-by-cast basis, for the Uk's 'Under-Water Weapons Research Establishment' with materials made in Birmingham by IMI and used in the manufacture of some quite advanced Torpedos. Some batches were good but others could be quite poor.

In modern terms most manufacturers now quote K threshold stress intensity factors that should effectively allow a rod to be designed for 'Infinite Life'. Manufacturing inconsistencies have also been virtually eliminated.

I would agree that only a lack of detailed testing results cause the continuing 'fear factor' to be maintained.

Chris,

Well said.

nh

This was more of a question directed to Steve Weiner and the specific case of timed out GT3 rod reuse. The question is: "Has that been 100 percent successful?"

There is no question that Ti is a suitable material for rods. Both the older 935 rods and the current Corvette rods have no defined service life, but when a pretty reputable OEM says that their GT3 rod has a very limited life, I am wondering why people think it is OK to ignore that. Is it too conservative, or just a case of no data/small sample size?

Also just FYI, the material variability in just about any Ti alloy is much more tightly controlled by plasma arc vacumn remelting nowadays.

I do agree that '40 hours' is a poor way to define fatigue life and may be a better means of analysis could be provided using modern data loggers.

I do tend to believe that the 40 hours life is simply because there is no real data to hand.

I would suggest using Inverse Power Law - Weibull Models to allow more realistic accelerated testing if budgets were available.

The use of shot peening for the enhancement of fatigue life has been well established for many years as has the use re-peening to restore and improve fatigue life to the levels of that found in new parts.

Much of the early published work was carried out using steel components but there is a reasonable body of work to also show re-peening Titanium does re-establish the compressive residual surface stresses that can be lost due to stress relaxation.

I would agree that if surface or sub-surface defects have already initiated there would be little or no point in using this technique.

Interesting discussion and have a follow up question. With the Pankl rods, I'm getting the used titanium bolts and assume that I can't reuse those. If my assumption is not correct or if one or more of the bolts can be checked for possible future use, let me know your thoughts.

If not, the question becomes whether I should purchase new titanium bolts (which are about $75 per bolt) or whether I should just replace with ARP steel bolts of equivalent. It seems that some argue that titanium bolts may not be strong enough in a high HP air cooled application since typically the pistons are heavier than those used in the GT3 motor. I'm trying to lighten the reciprocating mass on the engine as much as reasonably possible so would like to know the options on that. Thanks.

I'm sure there are different viewpoints on this, too, but would be interested in what you all are doing and if you've seen or heard of failures with titanium bolts.

Rod Bolts are always designed to ensure that they are never subjected to fatigue loading and thefroe should never fail.

When correctly tightend the preload introduced really mans that the bolt only needs to withstand the static load applied.

It is possible that rod bolts do fail in fatigue but this is normally associated with them having been incorreclty tightened.

If the preload is insufficient the bolt will be subjected to fatigue loading and in my view failures would be much more common due to the stochastic nature of fatigue process.

I do here comments aboyt Ti Rod Bolts galling in service but this also seems to imply that there is insufficient preload.

As an annealed 6AL4V has a tensile strength of around 160ksi it would seem that Ti Rod Bolts need to be larger diameter than steel bolts.

SPS have recently introduced TITAN 180 Bolts which are 180 ksi.

The early GT3 rods seemed to us a 'though' bolt with brass washers and a Ti Nut but later rods seem to have the bolts screw directly into the rod.

The early rods seem to be use once parts which suggest that they are preloaded beyond thier yield point.

I would consider using a steel bolt but this probably means the rod will need to be re-sized.

Lots of confusion here. The easiest and most effective way to lighten the masses going round and round and up and down are the rods as they go in both motions.

Late GT3 rods take a bolt only and are steel. ARP make these but these are a custom size and not sold through the ARP outlets.

I don't think there was a Ti bolt for any of the GT3 rods. The early rods used a bolt, washer and not but these were super-ceded with just a bolt only.

Ti bolts were used in earlier race engines only.

recondition ti rods
 

Rich Jascic in Blairstown N.J. 201-362-8163 has rebuilt many Pankl Ti rods for Peter Dawe who stocks the Ti small end bushings.Ciao Fred

The 2001 GT3 R used a Ti throughbolt, hardened Ti washer, and Ti nut. This bolt also aligns the caps together. There is a large diameter near the center of the bolt that fits tightly in the rod and cap to align them. The bolt should turn freely, but the clearance is small. ARP can make a steel replacement, but it is not off the shelf.

The bolt is the least of your worries. You are running rods that are probably near the end of their fatigue life. That was more concerning to me, and I evaluated the same rods for my project. Ultimately, I decided to buy aftermarket Ti rods. Same 6Al-4V, but from billet instead of die forged, with steel bolts. The thing is, there is really no point in buzzing a 3.4L engine to 8500. The intake valve area is just not there for it. I'm going to be happy with 7800 or so. For that reason the lesser rods were OK with me. They are a little beefier (and heavier), but they won't be timing out any time soon.