Roller Bearing Failure Survey Thread

We've got some people floating around in here with some good intelligence and good advise.

BoltsMissing makes a good point - i was going to mention the same thing as i cannot afford to be off the road - mostly, you get what you pay for and generally reliability cost money.
A long time ago, (back in the early days of my driving years) i needed to see a mechanic to get my car fixed.
This guy had a reputation for being an excellent mechanic but he was pricey.
I needed my car to be reliable so naturally i wanted it fixed properly.
When he added up the repair costs, i was taken aback by the price.
Calmy mentioning that i didn't have enough money for the repairs and needed a cheaper option, he also calmy mentioned "if you don't have the money to fix your car with the best quality parts and competent repair work, you should not be even thinking about driving your car on the road, as my saftey is important to me".

I had to think about his comment.

Basically he was saying, "if you want to drive an unsafe car with sub standard parts and labour, that's your own stupidity, but doing so risks my life if the parts fail on your car and the result is an accident where you crash into my car, you could either injur or kill me - you shouldn't be driving on the road if not having the money to do the job properly.

You get what you pay for - a cheap chinese engine kit is built to a price - don't complain about low quality parts if paying a ridiculously low prices and don't complain if the result is an accident where the engine fails from over revving and low quality parts.
Personally, i would much rather pay $700 or $800 for an engine kit and have total reliability. Since i cannot get such an engine, i must operate the motor in a speed range where it gives good reliability, such as keeping the revs low.

Quote BoltsMissing:
So, we have Kit A @ $500 and Kit F at $300
We know Kit A is Quality +++
and Kit F is Quality ---
All 6 kits are from the exact same "blueprint" of the HT.

You as the consumer on a budget and time restarints, meaning you cannot afford to be off the road, which kit will you settle for ?

The $300 or the $500, when you already know to get a $300 kit up to specs. it will end up costing $500 anyway,
only thing is you have to DIY.
 
I'll say again what i've said before

Get yourself a SickBikeParts Jackshaft kit, it's more than just being able to use gears.

The kit allows the bike to make reasonable speed whilst keeping engine revs low - in ways this kit could and may very well save you from injury or worse.

The Jackshaft kit in my opinion is a saftey requirement.

Fabian
 
How many RPMs are we talking here to grenade an engine? over 5000? 6000? I run mine down moderate hills but it doesn't go much faster than WOT on flat and level ground. I keep comparing these to string trimmer engines, but I guess they're not put together that well. Jackshafts are not legal here in South Carolina, but most cops wouldn't know it.
 
I must be careful in my response as i don't have a tachometer fitted to my motorised bicycle.
Really, i shouldn't be even giving an answer as it may be a wildy inaccurate appraisal of engine rpm used on my bike.
Having said that, and please, take my answer with a grain of salt, as i'm making an assumption (based on noise and vibration) that my average rpm's would not exceed 2500 and maximum rpms would not exceed 3500 rpm in top gear at a self imposed speed limit of 50 kilometers per hour.

By the numbers (and i haven't worked it out) you could very well prove me wrong by going back through my gear ratios.
I'm using a SickBikeParts jackshaft shifter (shift) kit and the numbers are as follows: engine output sprocket size - 10 tooth connecting with a 17 tooth sprocket powering the input side of the jackshaft.
From there the jackshaft has an 11 tooth sprocket on the output side driving the crank chainwheel of 48 teeth.
This chainwheel is directly connected to a 36 tooth chainwheel powering the rear cassette which is a Shimano 11-32T (11 tooth top gear sprocket and a 32 tooth hill climbing sprocket).
My mountain bike uses the industry standard 26 inch mountain bike tyres (from memory the circumfrence works out to be 2073mm).

There are more people in here with better brains than i have and i'm sure they can do some quick mental arithmetic to work out my engines rpm's in 250 rpm increments.

My engine starts to noticibly vibrate at just above 52 kilometers per hour (the speed i stay below) in top gear and the vibration zone i stay below regardless of gears or speed.
I run the engine down to 35 kilometers per hour in top gear before shifting gears.

In first gear (32 tooth cassette) sprocket and with a heavy trailer load, the bike speed falls to 8 kilometers per hour before i have to input pedal power to keep the engine running.

It would be interesting for someone with mental aptitude to give me the numbers my engine is turning through various speeds, both top gear and 1st gear.

Cheers Fabian
 
Just adding a bit of refinement.


A very quick tutorial on 2-stroke engines and their reciprocating load bearing requirements.
- Any reciprocating engine will have two load transfer points to the connecting rod, either using plain metal shell bearings or roller bearings.

2 strokes only have one load bearing surface, the bottom. The top does not share the load.

Those little needle rollers have a speed rating. If exceeding the speed rating the needle rollers will try and keep spinning whilst the connecting rod is trying to reverse their rotation. Naturally the connecting rod will drag the needle roller cage around on the crankshaft pin and at some pint the needle roller will stop spinning and momentarilly be dragged accross the pins surface whilst stationary.

The needle rollers actually have Very little maximum speed rating. What limits the rotation is the bearing cage. It is the needles that much accelerated and decellerate the cage. When the cage becomes to heavy for the needles to overcome its inertia, it makes the needles start forward thrusting, which is called "skidding"

A really easy way to increase your bearings redline failure limit is to

A) make sure your wrist pin has the correct tolerance. When you drop it in a cool piston, it should fall through on its own weight. If it does not, get some lapping compound and a second wrist pin and Lap it out a bit.

B) Not as easy to do, remove the thrust washers from the crank end of the con rod, and instead use thrust washers at the piston end to shim and align the rod. Doing this allows an increase of 1500 RPMs to your bearings redline limit.


I'm currently working on a developing a blueprint schedule for these motors, I have lots of little tricks like this but, dont know the exact specs of everything yet.
 
I am looking forward to your blueprint schedule.

A noteworthy point - excluding the transfer of pressure from piston to piston pin, from memory, the connecting rod has two ends, which also happen to have two bearings; you can follow the logic with two load transfer points.

Fabian
 
Ah.... I thought you meant the bearing itself had 2 load bearing points, as in top and bottom.


A 4 stroke engine has top and bottom load bearing points, as the cylinder is both pressurized and relieved, but a 2 stroke has only downward pressure on the con rod bearings.



As soon as my motor is delivered i can start working on the actual specs of the motor... :-/
 
For Fabian and anyone else interested in jackshafts....

I have both a speedometer and a SenDec tachometer and worked out the math in a spreadsheet. I like to ride my 80/66 cc generic Nantong engine in the high 3000 and low 4000 rpm range. Here are some speeds in American miles per hour when the engine spins at 4200 rpm and the jackshaft has the 11 tooth sprocket on a 26-inch wheel frame.

1st gear: 15.3 mph
2nd gear: 17.8 mph
3rd gear: 20.4 mph
4th gear: 23.8 mph
5th gear: 28.5 mph

I have read where a motorbicycle builder quoted 7300 rpm as the redline these engines. I have gone over 33 mph with my bike, but I feel most comfortable riding at 25 - 27 mph all day long. The engine is not straining in the low 4000 rpm range. I weigh 245 pounds; I don't see how lighter guys could strain the engine at all in these gears and that rpm. I completed a 102-mile ride today. I may go out again tomorrow.

And I know my engine has needle roller bearings lubed by synthetic oil.

MikeJ
 
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would a piston moving at 20 feet per second and then changing direction almost immediately at 20 feet per second be exerting a serious reverse loading on the bearing face.

I agree with you that combustion pressure would be the greater stress factor when piston, rod and crankshaft pin are moving downwards, both bearing surfaces are experiencing compressive stress on the upper bearing face, though when completing a power cycle to start another, the upwards motion and sunsequent reversal of piston motion would see a reversal of stress, 180 degrees to the combustion cycle and depending on how hard the engine is over revved, those stresses could be more than gentle.

Looking forward to your blueprint specs on the motor - please take a hi-res photo tutorial on the strip down and reassembly process whilst your at it.

Cheers again

Fabian
 
You forget though, in a 2 stroke motor you already have ignition (depending on a setup) at 20-30* before TDC. And not only that, it is fighting against 125-185 static PSI ( again I dont know the actual specs for this motor yet) and up to 750 volatile PSI through actual combustion

The piston is never actually rising into a free float. Neither are the rings, the rings are also staying on their bottom seat.... unless you have ring flutter, which might be a possibility on these motors because from what I see the rings look Fat!



Also, another point I might add... if I'm able to build this motor properly we should be seeing mean piston speed of about 40 feet/sec.

Fab, how intimately do you know this motor? can you get me the bore, stroke, con rod length for this motor? Also, the radial ring depth?
 
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