Titanium Rod Bolts

[D Miller]

I am interested in learning about Porsche's use of titanium con-rod bolts in the early 911engines, up to 1973.

1) Which engines utilise these bolts?

2) Are they 'single use' like the standard bolts, or can they be reused?

3) What sizes were available (and what are the applicable part numbers)?

4) Are they still available?

5) Are they considered reliable?

Any and all information appreciated, TIA.

Duncan

[chris_seven]

Duncan,

I would find it surprising that Porsche used a Titanium Bolt for a connecting rod particularly pre 1973 as this was very early in the development life of Alpha-Beta Titanium alloys.

A typical Ti bolt material of the period would have been made from 6Al4V which would have had a maximum tensile strength of about 160 000psi but very poor notch sensitivity.

Modern high performance steel fasteners are readily available at 220 000psi and advanced materials can be as strong as 300 000psi.

ARP claim that their 6Al4V fasteners are rated for 180 000 psi but this would mean that the material would have to prestrained prior to heat treatment and I believe their ductility would be very poor.

There are much better Ti alloys to use for 180 000psi fasteners but again they will all have limited notch sensitivity and relatively poor ductility due to the manufacturing techniques needed to obtain this level of strength.

The old Porsche 'use once' fasteners were simply not strong enough to give enough preload needed to avoid fatigue failure without permanently deforming hence the instruction to replace them once used.

Modern steel ARP fasteners should be reusable even at the low end of their spec which is the ARP2000 material.

If you tried to use a lower strength Ti alloy (160 000 psi) fastener in this manner you would find that the yield strain and the fracture strain would be too close together to be reliable and that some bolts would fail during tightening as they would have very little remaining work hardening capacity.

When you add to this the ability of Ti to gall I think it is a most unsuitable con rod bolt material.

[mike curnow]

I think I have some Ti rod bolts do not know what year. Also did 906 Ti rods use steel bolts, or Ti bolts?

[JohnT]

That begets an interesting question. A reliable source told me that Most of the Factory 906's used Pauter TI rods after Porsche observed their superiority in Vasek Polak engines. This left the Porsche TI rods only for customer engines........

So which 906 rods used which bolts?

johnt

[davep]

Are the bolts themselves titanium, or are they just special bolts for titanium rods.
At one time I had some, and traded them for other parts more useful to me.

[chris_seven]

Even at 180 000psi the strength of the fastener would only be the same as a cap screw in terms of preload capacity. - about 4000kg per bolt I would guess.

An ARP 2000 would be closer to 5000kg per bolt.

Its elastic deformation would be about double that of a steel fastener and it would have to be nitrided or treated in some other way to stop it from sticking to the rod.

Mike- if you have Ti rod bolts can you determine how they were treated to stop galling. It may be worth a quick check with a magnet.

[Flieger]

The 917 engine (912) used Titanium case through-bolts, If I remember Fere correctly. Thinner diameter, too, because of the spherical washers. The power take off to the clutch was also Titanium on the later models.

I believe the Can-Am cars used Titanium uprights, so does that mean the center-lock hub was Titanium as well? They were using it for springs and other pieces.

[jcge]

Mezger indicates the use of Ti rods and Ti rod bolts in the 917 in his paper to the IME in 1972. With respect to coating..... "Porsche uses a surface treatment called
'Tiduran' to improve the sliding characteristics. Tiduran means a normally two-hours treatment in a cyanogen bath at 800°C"

[chris_seven]

Tiduran - Titanium Nitride about 0.002" deep - classic for anti-galling. Probably would now be carried out with a plasma technique to replace the Cyanide Bath.

[Mr9146]

I have a setof Ti rod bolts sitting in a box on the roof of our engine room.

They will never see use as their history is unknown...

However, it's interesting to note that they came along with a pile of parts from a privateer long-stroke ST motor.