Titanium wrist pin verdict

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mew905

mew905

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So upon chatting with some guys in the Facebook group Motorized Bicycle Gallery, someone has tried the titanium wrist pin, and with disastrous results. Apparently the piston wore through it rather quickly, and when the motor heats up, the aluminum expands at 4x the rate the titanium does! That means mean your motor is toasty warm and ready to go, that pin is barely holding on. Apparently the wobble got so bad the piston caught a transfer and ripped a good chunk of the wall off (he provided pictures).

So the verdict: as good as it may sound, do not use the titanium wrist pin or risk catastrophic damage to your engine. Sorry Juice Moto, looks like we gotta lighten up our pistons another way (Reeds, balance, true and bearings are your only options to reduce vibrations, sadly, reeds will have the biggest effect making your sweet spot much longer and higher up in the range, balance will have a good effect but only move your sweet spot, does not make it longer. Truing is tricky and possibly give you minor results, giving you a smoother bike throughout the whole RPM range, and bearings will give you the most insignificant results, again through the whole range. Moped pistons weigh more than our pistons, bushings weigh slightly less, and the only other option is material removal from either the piston or the wrist pin.
 
mew905

mew905

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the images of the damage resulting from using the titanium wrist pin. If memory serves, it was only a week into use.


 
Kioshk

Kioshk

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Oct 21, 2012
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Curious: despite the expansion diff., what bearing did they use? Juice's site sez:

"We highly reccomend using our bronze bushing with this product because that is where we tested it the most. The hardened steel pins in wrist pins could potentially damage the od of this lightweight pin. The use of our bronze bushing prevents this and still allows you to maintain the same top end assembly weight. "
 
mew905

mew905

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That's actually a good question, the bushing works by using an oil film instead of a series of rollers to allow freedom of motion. I was looking into those aluminum bushings too, I wanted to try them as a combo but after seeing this... I dont think there's much hope for the pin
 
biknut

biknut

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Sep 28, 2010
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mew905 said:
So upon chatting with some guys in the Facebook group Motorized Bicycle Gallery, someone has tried the titanium wrist pin, and with disastrous results. Apparently the piston wore through it rather quickly, and when the motor heats up, the aluminum expands at 4x the rate the titanium does! That means mean your motor is toasty warm and ready to go, that pin is barely holding on. Apparently the wobble got so bad the piston caught a transfer and ripped a good chunk of the wall off (he provided pictures).

So the verdict: as good as it may sound, do not use the titanium wrist pin or risk catastrophic damage to your engine. Sorry Juice Moto, looks like we gotta lighten up our pistons another way (Reeds, balance, true and bearings are your only options to reduce vibrations, sadly, reeds will have the biggest effect making your sweet spot much longer and higher up in the range, balance will have a good effect but only move your sweet spot, does not make it longer. Truing is tricky and possibly give you minor results, giving you a smoother bike throughout the whole RPM range, and bearings will give you the most insignificant results, again through the whole range. Moped pistons weigh more than our pistons, bushings weigh slightly less, and the only other option is material removal from either the piston or the wrist pin.
Click to expand...
I'm not buying this explanation. The stock wrist pins are hardened steel. A titanium wrist pin won't have that much different of an expansion rate.

The wrist pin doesn't keep the piston straight in the cylinder, the piston skirt does.

In the past a lot of engines came with bushings in the small end of the rod, and people said they wore out fast.
 
mew905

mew905

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Titanium has a thermal coefficient of linear expansion of 8.3 um per K,
Steel is 13.0
Aluminum is 22. So i was a bit off, aluminum expands almost 3x as fast and steel expands about 60% faster. I do plan on running one myself in a cautionary, experimental bike, but until its proven itself to me i dont think my mood toward it will change. It looks like the piston caught the transfer port but it could have been something else coming through it on the pistons descent and getting caught. He did say he got 7 rev-happy tanks out of it. Idk how long ago this was or if hes done a full inspection (maybe the big end bearing blew up?) but a catastrophic failure with an excessively worn down wrist pin doesnt look good for it
 
mapbike

mapbike

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Mar 14, 2010
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I ran the Titanium pin and run the juice moto Aluminum Bushing on the pin, the Aluminum bushing failed and ruined the wrist pin but It looked to me like the Titanium pin would have done ok possibly if I had used a bronze bushing, I did the whole thing as an experiment just to see if the Aluminum bushing on the Titanium pin would hold up, It didn't....

Another thing I noticed was that it made very little difference in the amount of vibes than engine generated, It made a slight difference but if the crank is severely untrue lightening the top end will not balance the engine.

Map
 
D

dmb

Active Member
Dec 4, 2010
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a bridge and piston coating, roller pin bearing might have saved that motor. i like that your willing to try stuff. case induction stopped the use of piston distorting holes in the skirts and giant intake ports, always a sticky issue. dennis
 
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mew905

mew905

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mapbike said:
I ran the Titanium pin and run the juice moto Aluminum Bushing on the pin, the Aluminum bushing failed and ruined the wrist pin but It looked to me like the Titanium pin would have done ok possibly if I had used a bronze bushing, I did the whole thing as an experiment just to see if the Aluminum bushing on the Titanium pin would hold up, It didn't....

Another thing I noticed was that it made very little difference in the amount of vibes than engine generated, It made a slight difference but if the crank is severely untrue lightening the top end will not balance the engine.

Map
Click to expand...
Map, are you the origin of these images? I'm just trying to determine if the failure pictured was due to the aluminum bushing, or if it's a warning about me wanting to try the aluminum bushing.
 
mapbike

mapbike

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Mar 14, 2010
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mew905 said:
Map, are you the origin of these images? I'm just trying to determine if the failure pictured was due to the aluminum bushing, or if it's a warning about me wanting to try the aluminum bushing.
Click to expand...
The pix in this thread are not mine, I have takenn some pix of my personal failure with the titanium pin and aluminum bushing, 27th aluminum bushing is what failed and caused the serious damage to my titanium pin, as others have thought I also think that the titanium pin may work out ok when used with a bronze bushing but it has been showed to fail multiple times when being used with a needle bearing and in my case also with an aluminum bushing.

My personal recommendation would be forget the titanium pin all together and hust use the hardened steel pin with a high quality needle bearing, it's the bezt and most reliable way to go.

there is nothing to gain by going with a titanium pin and a bronze bushing and the pin will not hold up with a needle bearing runni g on it.

map
 
F

Flyman

Member
Nov 28, 2014
259
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Vian Oklahoma
Funny reading this.Years back a titanium connecting rod came on
the market for racing kart engine.A friend & customer of mine bought
one for his BM 130.With in 4 laps it locked up.We pulled it down & the
lower needle cage & rod had fuzed together.I never ever saw any engine
do that.

There was a engine builder there Dan Lamello who was one of the best
BM engine guy I know of.I went & showed him it.He said, ya seen that
before & I don't know why, but they don't work.I never tried another after
that.
Fly
 
mapbike

mapbike

Well-Known Member
Mar 14, 2010
5,502
109
63
Central Area of Texas
Flyman said:
Funny reading this.Years back a titanium connecting rod came on
the market for racing kart engine.A friend & customer of mine bought
one for his BM 130.With in 4 laps it locked up.We pulled it down & the
lower needle cage & rod had fuzed together.I never ever saw any engine
do that.

There was a engine builder there Dan Lamello who was one of the best
BM engine guy I know of.I went & showed him it.He said, ya seen that
before & I don't know why, but they don't work.I never tried another after
that.
Fly
Click to expand...
Yep Titanium is a bad idea for pins and rods.... found that out the hard way.. made me feel like a fool kinda but hey ya never know till ya try right..? LOL
 
F

Flyman

Member
Nov 28, 2014
259
3
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Vian Oklahoma
I tell something that does work.We used to get thin wall tool steel wrist pins.
I for got who made them back then.I wish I still had a 2000 degree oven
as I could make them.Why is it I,m thinking like this?Heck that's why I retired (wink).

I need to quit reading this stuff, Ha Ha!

Fly
 
mapbike

mapbike

Well-Known Member
Mar 14, 2010
5,502
109
63
Central Area of Texas
Flyman said:
I tell something that does work.We used to get thin wall tool steel wrist pins.
I for got who made them back then.I wish I still had a 2000 degree oven
as I could make them.Why is it I,m thinking like this?Heck that's why I retired (wink).

I need to quit reading this stuff, Ha Ha!

Fly
Click to expand...
LOL.......!

It's just part of this addiction we share, just have to come to grips at some point that once you get this bug, there really isnt a lasting cure, it get in your blood and stays.

My wife has two ceramic kilns left over from her business back in the day when all the ceramic dust collectors were such a big deal, I cant remember how hot those kilns get but I know they get purdy dang hot, puttin a wrist pin in one would be kinda funny though since theyre big enough to probably put 5-6 whole china girl engines in all at once..LOL! but it would still be ok if the kilns get hot enough.

I've thought about making me a small forge like the one seen in this link at some point to do some simple redneck heat treating.

http://youtu.be/uIRTcmR6sSk

Map
 
F

Flyman

Member
Nov 28, 2014
259
3
18
Vian Oklahoma
Well the problem is this.If a guy was to make one from A2 tool steel, you
need to whole it at 2000 degrees for a good hour then air cool.Then take it back
up to 1400 for another 20 min,s to stabilized it, before grinding it.That why
a good heat treat oven is needed.

Fly
 
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