Lighter wrist pin problems in china girl 66

[Wolfshoes]

My two motorbikes stopped running within a week of each other from engine problems. On engine removal and examination it appeared the vibration reducing lighter thinner titanium piston supporting wrist pins have crushed and one has broken. The engines were running with stock compression and heads.

Pistons, piston rings and jugs are also broken but I suspect as a effect rather than the cause of the wrist pins being crushed. This crushing created enough of a distortion that it was probably the cause of a gradual loss of engine power and erratic performance over the 3 or 4 summers the engines were used. When this breakage happens, after many hours of engine use, whether or not it is best to replace the engine and not repair, I don't know. The wrist pins were after market parts from Juice. One was installed in a Grubee, the other in a Gasbike'

 

[gary55]

That's some messed up looking wrist pins. Were the bikes road close to equal amounts? Just curious because of two different engine types producing the same after marker component failure so close in time to one another. I've caught some in time where the wrist pin was showing signs of fatigue on stock pins, and repaired others with bearing failure, but never seen one nearly sheared in half. Might be hard to get the bottom end thoroughly cleaned without splitting the case with that much displaced material in it. I would be replacing the engines.

 

[crassius]

haven't seen those in several years - old threads here may mention them and the failures they caused

as a repair shop, I rarely replace a top end since the cost of my labor can make the job almost the same price as a new motor - also, it is hard to detect all the fine debris that may have gotten into the bottom end bearings

a new motor is about $100, so as a hobbyist you may be able to fix one for half that in parts and see how it goes

for my own machines, I always go for the new motor just because I'm too old to bother with fixing motors that are essentially disposable

 

[Street Ryderz]

My two motorbikes stopped running within a week of each other from engine problems. On engine removal and examination it appeared the vibration reducing lighter thinner titanium piston supporting wrist pins have crushed and one has broken. The engines were running with stock compression and heads.

View attachment 78278

Pistons, piston rings and jugs are also broken but I suspect as a effect rather than the cause of the wrist pins being crushed. This crushing created enough of a distortion that it was probably the cause of a gradual loss of engine power and erratic performance over the 3 or 4 summers the engines were used. When this breakage happens, after many hours of engine use, whether or not it is best to replace the engine and not repair, I don't know. The wrist pins were after market parts from Juice. One was installed in a Grubee, the other in a Gasbike'

What I see as to cause is that the bearing seized grabing the pin and wore the ends for quite some time!And one wasn't centered very well,It may have been the titanium expanded to much and helped lock it in the bearing or the bearing just locked on to it but etheir way did you not hear the clanking of misfited parts?

 

[Crisco]

It may have been the titanium expanded to much and helped lock it in the bearing or the bearing just locked on to it but etheir way did you not hear the clanking of misfited parts?

Ti has a way lower thermal expansion rate compared to alloys, and a similar rate to the stainless that would be in the needle bearings. A bit unlikely that a foreign body caused the same incident twice... Maybe just a crapola alloy that isn't actually titanium..??

 

[crassius]

can't recall all the discussion at the time, but I'm thinking problem was said to be the roller bearing, and using a brass bushing might help

 

[FurryOnTheInside]

Yes Crassius is recalling correctly, if I am, the solution was said to be use of a bronze bushing instead of a bearing.


"The surfaces of titanium and of all commercially produced alloys of titanium have relatively poor wear resistance. In particular, titanium surfaces in contact with each other or with other metals readily gall under conditions of sliding contact or fretting. ..."
That's the first result on Goggle for the search "titanium wear"

 

[butre]

titanium wrist pins has always been a half-baked idea. that's part of why I ran them, it's a fun engineering challenge.

I had originally stated that oilite bronze was ideal but on later inspection found they go oblong under the stress causing premature failure. on the bright side, the failure isn't catastrophic unless you're running a very very tight squish band. I've since used both a mild steel bushing and an AMPCO 18 bushing with no such effects, but the mild steel bushing wore through the titanium far too quickly, though still slower than the hardened steel needle bearing.

of course, now I'm back to using steel wrist pins with steel bushings. not because I got tired of the titanium, but because 10mm wasn't big enough anymore.

if you can't get your hands on ampco 18 in reasonable quantities it's roughly equivalent to the more generic CA954, which is readily available from in small quantities from any metal supply store. ampco 18 is a proprietary alloy that you've gotta order from ampco in bulk quantities but it's the good stuff