Wrist pin / gudgeon pin lightening

splatt said:

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

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Looking at the two in front of me, the T140 pin is 1/16 bigger in diameter than the 850 Norton pin, however, they are actually shorter, so I wasn't really being fair in my initial comparison.
Nevertheless, my basic thought still stands, the Triumph pin is a lot lighter, and that is largely due to the internal taper removing a lot of material.
Interestingly, they are also both incredibly rough inside, with lots of (to me) clear opportunity for stress points to start. The fact that this doesn't happen, again leads me to conclude that there is a large excess of strength in these items.
So I still think there is plenty of very safe scope to play with here. This is probably how the aftermarket manufacturers save weight, better machining means more material can be removed whilst not compromising strength.
But I'll reserve judgement until I've let a more qualified machinist have a good look at them.
It seems to me that there is also a lot of excess material on the sides of Norton pistons, around the wrist pin area, this could easily be removed, saving weight and effectively turning the piston into a slipper piston.

acotrel said:

Are the JS pins titanium ?

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No they are not.

650 /trident pins ,don't have any t140 bits,carbide tool in the lathe and finished of with the die grinder clamped to the tool post to remove any machine marks, like you said the insides are vey roughly bored and it should be very easy to improve

splatt said:

650 /trident pins ,don't have any t140 bits,carbide tool in the lathe and finished of with the die grinder clamped to the tool post to remove any machine marks, like you said the insides are vey roughly bored and it should be very easy to improve

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Have you successfully ground / machined the inside of wrist pins previously splat? An earlier poster pointed out this may cause issues by removing the treated surface. If you've tried and tested this already, it would be good to know!

acotrel said:

Are the JS pins titanium ?

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As Fast Eddie pointed out, no. The are steel, 9310 probably, but could be another alloy. Jim has them DLC coated so he can run them in the steel Carrillo rods with no bushings, thus allowing him to have a lighter small end. Race car guys have been successfully running steel pins with DLC coatings in steel rods with no bushings for some time now, and Jim's kit also seems to work well with them.

Ken

I can't positively id this tapered pin but from Ken's list it must be a powermax as it weighs in at 61 gr. The taper is quite smooth through the bore. The telephoto lens distorted the image a bit as in reality the wrist pins are longer than what they appear to be here compared to the diameter. Telephoto lens distort distance. The taper goes more than a 3rd the way in on each end. The stock pins weigh 68 grams so only a 1/4 oz difference (7gr.) Still, a 1/4 oz is a 1/4 oz. I also weighed a set from another engine which weighed in at 71 gr. so depending on the year or date of manufacture the stock pins vary a bit. These are 750 pins. An 850 stock pin I weighed was 78 gr.



On a side note, I was looking at my wore out steel side stand bush the other day and noticed the wrist pins looked about the same diameter. Sure as hell it fit perfectly. Holy crap the id also fit the bolt perfectly too so I hacked off a section of a bad one with a zip disc and trimmed it to length on the lathe. I was able to start in the center between the inner and outer hardened surfaces and work the piece down to length that way. Problem I had was when I went to install it the bolt was too thick, I must have slid the wrong bolt into it when I first fluked on this idea. Without any hard cutting tools I had to hog the inside bore out with an abrasive bit I had that was the proper size and it was a job (for such a little thing). My side stand is nice and slick now with no wobble. I realize the stand bore and the bolt will be the things that wear now instead of the wrist pin bushing but I hate ordering this stuff, paying for shipping and waiting. I guess I could heat it up and cool it slowly to soften it up or cut some grooves in it and add a grease nipple to the side stand but for now it's back on the bike.

Here's a shot of the progress. The old bushing is on the right. The other 2 are the old wrist pin cut in 2. Hang on to those old wrist pins boys, this was a quick fix.

Fast Eddie said:

splatt said:

650 /trident pins ,don't have any t140 bits,carbide tool in the lathe and finished of with the die grinder clamped to the tool post to remove any machine marks, like you said the insides are vey roughly bored and it should be very easy to improve

Click to expand...

Have you successfully ground / machined the inside of wrist pins previously splat? An earlier poster pointed out this may cause issues by removing the treated surface. If you've tried and tested this already, it would be good to know!

Click to expand...

Not on a Norton but 4cyl club car, it was hard going but they didn't fail, but if they can be purchased I probably wouldn't go through the hassel, Maybe I'm to lazy now

Can anybody confirm that the taper bored pin in Rennie's photo is supplied by Powermax ?