Needle Bearing on Wrist pin Loose?

[Flapdoodle]

When I first saw the upper caged roller bearing sliding back and forth, what came to mind was they just stuck it in the hole intended for a bronze bushing and gave it no further thought. In other words, it was NOT engineered. They just wanted to claim the engine is all roller bearing.

As to the comment that a spring retained could not be trusted with the heat, piano wire is tempered about 1200 degrees F (I have done that numerous times). It takes almost red heat to anneal it. There would be no piston left before that happened. The little G shaped retainers for the wrist pin are similar alloy.

There would be little worry of the retainer coming off either if properly designed, but I do prefer my original suggestion of brass tubing. It looks more professional.

I have a mental picture of a million+ Chinese bike riders scratching their heads and cursing.

Has anyone in here considered a repository of fixes for these engineering snafus?

 

[arceeguy]

When I first saw the upper caged roller bearing sliding back and forth, what came to mind was they just stuck it in the hole intended for a bronze bushing and gave it no further thought. In other words, it was NOT engineered. They just wanted to claim the engine is all roller bearing......

Of course it's engineered. The needle bearing diameter has to precisely take up the clearance between the rod and the wrist pin. The small end of a connecting rod on a bushed engine is smaller in diameter than a needle bearing type, so no - they didn't slap on a bearing just to say it has one. I'm sure that the floating bearing cage was also considered by the engineers, and was determined not to be a issue. There are many HT engines with thousands of miles on them, with no brass spacers, wavy washers, or piano wire retainers. As hobbyists, we like to tinker and modify things - sometimes unnecessarily. I can't say with any certainty whether adding those wavy washers has done any good for the reliability of my bikes.

 

[Russntustin]

I dunno....
But a bearing that can slide half way off just don't seem bueno.
This is how i cut the brass spacers. (photo)
I aint got no spesh-e-all tools.
The tubing crushed too much just cutting with the cutter. Found a socket that fit the tubing real close-like and that worked. Wheeee!

 

[Flapdoodle]

The first thing I noticed when I slid the wrist pin out of the piston was that it was wearing more on one side, likely due to the bearing cage preferring one side of the pin. The engine only has 160 miles on it.
If allowed to continue it will wear the conrod small end like the below drawing.



I consider this a major design flaw.

 

[Mountainman]

second thoughts ???

The tubing crushed too much just cutting with the cutter.
Wheeee!

second thoughts regarding tubing used

unless it is a snug fit -- no play what so ever

may cause failure faster than all get out

reason being -- think about the high rpms

that's some serious pounding going on when that THING is running

if you also have some questions regarding life span of said made spacers

a good engine mechanic should be able to answer

whether or not that THING will hold up ?

my guess -- guess is (tube spacers) will pound out in time

maybe before that time (total failure) small pieces into working engine ?

not trying to bum you out -- just someTHING to think about

ride that THING

 

[Russntustin]

I aint bummed......
Think of a bearing that is supposed to take the full load of that con rod at these two stroke RPM's, but that bearing is hanging half way out of said con rod.
I've seen and experienced small bearings that have slipped half way out of high speed wheels on an axle...(load on half of the bearing) Twernt goood.
The brass spacers probably don't even way a gram.
Oh I dunno....we'll see.
Jeepers...I don't wanna argue...just thought I might help someone who thinks the same way.

 

[Flapdoodle]

Well said. Thanks.

 

[Mountainman]

just sharing our thoughts

Jeepers...I don't wanna argue...just thought I might help someone who thinks the same way.

no me either
many of us just sharing our thoughts
and all of us hoping for the best outcome

nice long -- many rides on that motor bike THING

 

[Flapdoodle]

I finally got around to making my spacers. I used 3/8" nylon compression fittings for plumbing use on plastic lines. The finished thickness is .090 each for .180 total.

The width of the cage is .500", width of the conrod small end is .390, however it is not a flat surface. It is sort of scalloped with the narrowest area measuring .290".

The needle length is .360. This means that when the cage slides, 1/2 of the needles length is indeed outside the rod's bearing surface. Perhaps even more depending on where you measure it.

Even if this effort does not increase the life of my HT, the peace of mind is worth a lot to me.

~Flap

 

[Flapdoodle]

Nylon wristpin spacers.