Wrist pin / gudgeon pin lightening

I know that gudgeon pin is the correct name, but I'll use 'wrist pins' here so as not to perplex our American cousins....

Norton wrist pins are just plain bored (and not even centrally on mine!) whereas Triumph wrist pins have a taper bored into them and although they're bigger, they're lighter.

I can't see any reason to not replicate a similar taper in the Norton pins, and thus help lighten the loads on the conrods a little.

Has anyone done this? Any thoughts to share? Am I missing something obvious?

Rgds,
FE.

Norton pistons used to have taper wall pins. If you look at older OEM pistons from the early 60s and replacement pistons from the same era you will see they had taper-wall pins that were thin on the ends and thicker in the middle.

After a certain date Norton piston manufacturers in the U.K. dropped the taper wall and went to heavier straight wall. The exception was the Hepolite PowerMax racing pistons, which kept the taperwall pins.

You need to research how a pin is made before you or anyone alters it. A through-hardened pin should be save to grind, if a case hardened pin was ground I would wonder about the line where the case hardening is ground through being the starting point for a crack. The only people who could give good advice on this would be those who actually manufacture pistons and pins.

Fast Eddie said:

I know that gudgeon pin is the correct name, but I'll use 'wrist pins' here so as not to perplex our American cousins....

Norton wrist pins are just plain bored (and not even centrally on mine!) whereas Triumph wrist pins have a taper bored into them and although they're bigger, they're lighter.
I can't see any reason to not replicate a similar taper in the Norton pins, and thus help lighten the loads on the conrods a little.
Has anyone done this? Any thoughts to share? Am I missing something obvious?
Rgds, FE.

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Gudgeon pin became wrist pin in the Japanese language as there is no way of translation in the Nipponese language – there is also a species of freshwater fish called a Gudgeon ……..GOK how you explain that to any Japanese visitors coming to the UK ;
http://www.fish-uk.com/species_gudgeon.htm

It is possible to taper your existing gudgeon pin but as it is already hardened you will have to have it internal bore grinded, or you could just use, if they will fit, the gudgeon pin from the Hepolite PowerMax racing pistons as Beng mentions.

Would the weight saving really be worth the benefit or the risk? I wouldn't think so somehow.

daveparry said:

Would the weight saving really be worth the benefit or the risk? I wouldn't think so somehow.

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When did you last see a pin fail in a motorbike? I never have.
When did you last see a conrod fail? I've lost count!
So, on balance, I think there is very low risk in creating a pin failure and every chance of reducing stresses on the conrod. So it seems worth looking into to me.
Rgds,
FE.

You could well be right Freddie but I just think that the weight saved would be negligible when compared to the weight of the pistons and rings?

daveparry said:

Would the weight saving really be worth the benefit or the risk? I wouldn't think so somehow.

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FWIW, the weights I've recorded for Commando pins over the years are below:

Powermax 750 - 61 gr.
Stock 750 - 72 gr.
Late Stock 850 (Same size as 750 pin, just slightly thicker wall) - 78.8 gr.
Custom pin by Western Pin (no longer in business) for JE pistons in 52100 tool steel .100" wall - 51.8 gr.
Custom pin by western pin for JE pistons in 52100 tool steel .125" wall - 61.6 gr.
Custom pin by Western Pin for JE pistons in 52100 tool steel .100" wall taper bored - 51 gr.
Venolia piston pin - 68 gr.
Forgedtrue piston pin - 79 gr.
Omega piston pin - 81.5 gr.
Cosworth piston pin -69 gr.
GPM piston pin 55 gr.
JE short stroke piston pin (.750" diameter, made by Western Pin) - 72 gr.
JE short stroke piston pin (.748" diameter, made by Western Pin) - 68 gr.
Omega short stroke piston pin (.750" diameter) - 84 gr.
Titanium pin for short stroke JE pistons (.748" diameter) - 43.6 gr.

I used to have the pins for my JE Norton pistons made by Western Pin. Since they went out of business, I've had them made by PPPC in North Carolina. I haven't weighed them, but they are the same material and dimensions as from Western Pin, so the weight should be very close to 61.6 gr.

If you want an education in all the different materials and treatments you can get with custom made pins, ceck out the web site at http://www.pppcenter.com

More than you ever needed to know?

Ken

Who is the supplier of the titanium pins ? 30g off the little end of both rods - you would feel that.

What is the shear strength of Titanium compared to hardened tool steel?
cheers
wakeup

wakeup said:

What is the shear strength of Titanium compared to hardened tool steel?
cheers
wakeup

Click to expand...

Here you go....

Comparison of Grade 5 & 8 Steel vs 7075 Aluminum vs Grade 5 Titanium

Grade 5 Alloy Steel (commonly used on automobiles for lug nut and lug bolt applications)
Yield Strength: 92,000psi
Ultimate Tensile Strength: 120,000psi
Shear Strength: 72,000psi
Density: .284 lb/in^3

Grade 8 Alloy Steel (used for lug nuts and lug bolts in high strength applications):
Yield Strength: 130,000 psi
Ultimate Tensile Strength: 150,000psi
Shear Strength: 90,000psi
Density: .284 lb/in^3

7075 Aluminum (used on various automobiles for lug nut and lug bolt applications):
Yield Strength: 73,000psi
Ultimate Tensile Strength: 83,000psi
Shear Strength: 48,000psi
Density: .102 lb/in^3

Grade 5 6AL-4V Titanium (Tikore's preferred material):
Yield Strength: 128,000psi
Ultimate Tensile Strength: 138,000psi
Shear Strength: 79,800psi
Density: .160 lb/in^3

The shear strength is comparable, and about 43% lighter. All you need to convert to titanium is deep pockets!

Slick

Thanks for the Gudgeon term origins. Never seen one this side of the pond. We have huge problems with zebra mussells , european gobys , rusty crayfish. Kill everyone I encounter as suggested by fishing regs. guide. As for Nortons, interesting but stock goodly and if anyone wants to pursue this to lighten reciprocating weight, get to it. :idea:

acotrel said:

Who is the supplier of the titanium pins ? 30g off the little end of both rods - you would feel that.

Click to expand...

They were made by an ex-Boeing engineer who was responsible for the design of titanium parts for their aircraft. After he retired, he worked part-time designing and having manufactured custom items for motorsports folks. He happened to have a set of leftover 19 mm pins the right length for the JE pistons I was having made. I ordered some short stroke pistons for me in 78.5 mm bore to take advantage of the AHRMA rules at the time that allowed .060" overbore for 750 twins. The pistons were .280" shorter deck height than standard short stroke pistons to go with some long Crower Titanium rods I had. The standard short stroke pin is .750" in diameter, so it was pretty easy to have JE make this batch for the .748" (19 mm) titanium pins. I never used them, and I think I'll eventually try to sell them as a package. Not sure if there's really any demand out there for that sort of combo.

The guy that made them is no longer in business, but if you want custom titanium pins, PPPC will make them, but they are quite a bit more expensive than the 9310 steel ones I buy from them. They are Casidiam coated ( a DLC coating), and PPPC recommend using hardened steel washers with them to prevent problems from the circlips.

Ken

Yes I read the site Ken and saw the part about using hardened steel washers to protect the titanium pins against the circlips.
That seems sub optimal to me, replacing 1 part with three, seems there'd be a greater chance of play / fret occurring.
Perhaps replacing the circlips with PTFE buttons would be more sensible, no need for washers or circlips then.
It's all a little bit more involved than my first thoughts of simply grinding a taper into the ID of the stock pin!
Rgds,
FE.

That's good about the Ti shear strength. If you are contemplating Ti conrods and gudgeon pins, use some form of bush in the conrod. Ti rubbing on Ti welds together.
Why would you use Ti conrods, when the standard rods are fine?? Also several national debts (yours not ours) cheaper.
cheers
wakeup

Just check a auto parts supplyer , one of the old ones . Some have stuff on the shelves dateing back to the Arc. Like Daimler V8 ones - Turner Design , maybe. . . . perhaps . . .
they used the rods in the Repco Brabhams . standard 8 shells in the T100R , etc . . . if they speak english , leave a sample if they wont loose it , so he can look when its a bit quiter .

I use a few titanium bolts on my Seeley. It is really difficult to get on size when machining it. I believe Porsche use a lot of titanium internals, I might look there. One of our guys used a titanium inlet valve with a 1/4 inch stem in a very fast G50, however I believe that is fraught with danger. Lighter gudgeon pins are a very attractive idea.
I've noticed that if a bracket gets loose on a titanium stud there is a dramatic reduction in size where impact has occured, so clearances might be critical for titanium gudgeon pins.

wakeup said:

...Why would you use Ti conrods, when the standard rods are fine??...wakeup

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For a street bike, I probably wouldn't. For the race bikes I was building, titanium's high specific strength allows a lighter rod for given design strength than steel or aluminum. That's why you see Ti rods in F1 and Motogp engines. Ti has its own design peculiarities, as do other metals, but they are well understood now by motorsports manufacturers. In general, I would go with stock rods for street Commandos, Carrillo steel rods for most race engines, with Ti rods if the application seems to benefit from them.

What I'd really like to see are metal matrix rods using one of the aluminum/silicon carbide or other high strength matrix aluminum alloys, but I don't see anyone offering that. The cost of the material and the expense of diamond cutting tools to make them seems too much of a hurdle at this time.

Ken

acotrel said:

I use a few titanium bolts on my Seeley. It is really difficult to get on size when machining it. I believe Porsche use a lot of titanium internals, I might look there. One of our guys used a titanium inlet valve with a 1/4 inch stem in a very fast G50, however I believe that is fraught with danger. Lighter gudgeon pins are a very attractive idea.
I've noticed that if a bracket gets loose on a titanium stud there is a dramatic reduction in size where impact has occured, so clearances might be critical for titanium gudgeon pins.

Click to expand...

Titanium valves are a pretty common application now in race engines. I've used Ti valves in my Wood Rotax race bike for years with no issues. They do require a compatible valve seat material. Mine are a beryllium copper alloy, but the common nickel aluminum bronze alloys also work very well.

Titanium gudgeon pins do require a suitable coating because of the materials tendency to gall against other metals. Various molybdenum based coatings have been used successfully for Ti parts, including gudgeon pins, but the current standard seems to be one of the DLC (diamond like carbon) coatings. The pins Jim includes in his JS Engineering long rod/light piston kits have DLC coatings. Their only drawback seems to be that you have to be careful in handling them. Any scratches in the coating can lead to drastic failure.

Ken

Are the JS pins titanium ?

Right back at the start you said the Triumph pins were bigger but lighter,I thought that's strange they are both 11/16'' pins, but yes the Triumph pin is about 0.0013'' bigger so it would lend itself very well to repairing any tired rods or piston problems, as some one was trying to do in another post