rod growth rate

liquidesnake2 said:

"As soon as you hit 7,000 rpm, even just once, the damage is done, and it's only a matter of time (much sooner rather than later) when the engine will need a replacement crankshaft."

why will the engine need a new crank can the needle bearing not take high rpm or just vibration from an unbalanced crank?

Click to expand...

because he is silly and he likes this argument if you arent careful, this thread will go off tangent, running for another twenty five pages or so...


8k is fine... sure theyll blow up!

they blow up anyway! you said it, they are CHEAP

doesnt matter what you do they blow up!

look at this forum board!

full of people with engines that are BLOWING UP!

(never had a crank issue myself...and i was always over 7k... oh, the days of being legal... never had any reason to ever look at the crank itself... though i once found one with a nasty crack in the conrod. brand new...)


what it winds down to, is these things are so cheap, that any modifications made that approach "normality" usually cause spontaneous destruction within several minutes... they seriously are NOT WORTH IT! oh, they can take some serious abuse,and handy for getting around on but they dont take surgery too well!

then again... you dont need it for transport, youre just having some fun...



GO FOR IT.

seriously


just personally, i would rather be mucking around with other types of engines if all-out performance was my intention

`The connecting rod big end bearing doesn't hold up at anything over 5,000 rpm, which has consistently been the case with all of my engines (5 of which were band new, but used the caged needle roller bearing in the big end). The crowded needle roller big end bearing is much more durable, but it is even less tolerant of high rpm because of the extra friction caused by needle rollers rubbing directly against each other. If revving the rings out of the engine, expect the crowded needle roller big end to weld the needle rollers together in short time. The caged needle roller bearing will last a little longer, maybe by a few minutes, but the end result will be the same, as the needle rollers get pounded to death. If engine is operated between 3,000 and 4,500 rpm, (with the occasional 10 short burst to 5,000 rpm), you can expect to get in excess of 5,000 miles out of a bottom end when using a Jaguar CDI.
If you hit 6,000 rpm, expect the big end bearing to last less than 300 kilometers (220 miles) before all the needle rollers have ejected themselves out of the exhaust port, if you keep riding through the horrendous noise:

http://motorizedbikeforum.the-talk.net/t298-connecting-rod-bearing-failure-analysis-chinese-bicycle-engine















Damaged (big end) caged needle roller connecting rod bearing
















New (big end) caged needle roller connecting rod bearing













Dimensional differences between new and damaged needle roller


















New vs damaged caged needle roller bearing








66cc connecting rod dimensions








Caged vs Crowded needle roller assembly












This photo shows the differences in design evolution of connecting rods installed in Chinese bicycle engines.
The rod on the far left is the most modern design and in step with a typical Japanese design.

My this has been fun reading.You guy's really let people get to you.Life is too dam short!Mmmmmmmmmmmmmmmmmmmmmmm

Fly

yup. we sure do

life would be boring if we all agreed to agree

note the last post full of pics...only uses ONE example... now, to blame ONE failure on ANYTHING is erroneous.

it could be just ONE roller in the bearing, slightly under or over size that caused the failure.

it could have been brinelling of the ID of the rod.

it could have been brinelling of the crank pin.

it could have been a faulty cage allowing one or more needles to "skew".

it could have been a lack of metallurgical treatment.

it could have been an inbuilt stress on one part.

it could have been a chunk of swarth from the factory!

given the price and the QC given to these engines... anything and everything is possible. (like 8000 rpm+ without major instantaneous failure...)


repeat the experiment, with a MINIMUM sample of ten engines, PROVE that they ALWAYS fail in the same spot, for the same reasons... this means a complete teardown and measure of EVERYTHING, followed by the destructive tests...


otherwise its just like me saying ALL 66cc engines are JUNK cus the only ONE i ever bought was exactly that... an alloy anchor.

(they are though!)

HeadSmess said:

note the last post full of pics...only uses ONE example... now, to blame ONE failure on ANYTHING is erroneous.

it could be just ONE roller in the bearing, slightly under or over size that caused the failure.

it could have been brinelling of the ID of the rod.

it could have been brinelling of the crank pin.

it could have been a faulty cage allowing one or more needles to "skew".

it could have been a lack of metallurgical treatment.

it could have been an inbuilt stress on one part.

it could have been a chunk of swarth from the factory!

Click to expand...

My experience shows that the failures all occurred in the same part of the engine, with a repeatable level of consistency, being 600 kilometers (375 miles) using low rpm in the 3,500 range. If the engine was revved higher, life expectancy would be reduced to 300 kilometers (190 miles). In every case the engine was fitted with the standard CDI.
Once the Jaguar CDI was fitted to the ignition system, the premature big end connecting rod bearing failures were reduce to zero, and max safe engine rpm could lifted to 4,500, with short burst rpm being lifted to 5,000. If the engine was operated over 5,000 rpm on a continual basis, big end connecting rod bearing life would be dramatically reduced.

HeadSmess said:

repeat the experiment, with a MINIMUM sample of ten engines, PROVE that they ALWAYS fail in the same spot, for the same reasons... this means a complete teardown and measure of EVERYTHING, followed by the destructive tests...

Click to expand...

does component failure in the same location over a sample of 7 engines count as an indication that the standard CDI was causing detonation that hammered out the connecting rod big end bearing, considering that installation of the Jaguar CDI completely stopped these failures; extending the life of a partly damaged connecting rod big end bearing to 3,000 kilometers (1875 miles), where it would have otherwise failed at 600 kilometers (375 miles).

My experience has shown that there is nothing inherently wrong with the caged connecting rod big end bearing.
My experience with this issue has shown a strong correlation between the standard CDI causing nothing but big end connecting rod bearing failures.
My experience has also shown that the crowded needle roller big end connecting rod bearing is bullet proof, compared to the caged needle roller big end connecting rod bearing.

With an engine fitted with a crowded needle roller big end connecting rod bearing and a Jaguar CDI, you can reliably expect the cylinder bore to wear out before the big end connecting rod bearing fails, so long as the engine is operated below 5,000 rpm.

I typically get 4,000 kilometers (2,500 miles) out of a cylinder, and my last engine had the bottom end giving 10,000 kilometers (6,000 miles) of service life with the Jaguar CDI.
To say that i am enthusiastic about the Jaguar CDI is an understatement, because it gives me the one thing that i want: "dependable engine reliability"

ARRRRRGH!!!! too many pictures! loading, loading, loading...note to self...never click on this page again!

meh, phooey! here i am with out ever having suffered any con rod bearings, therefore ALL 66cc engines are junk if they need all this careful treatment to last anymore than ten revolutions without suffering severe post traumatic stress. maybe im being a parrot, but never had an issue with bearings in 48cc engines... nor in the one (1) 66cc i had the misfortune of receiving, though that never cleared the 3km mark, let alone the 300km mark...

(i shall point out that that is the only crank ive also received with crowded rollers on the big end, albeit irrelevant. shame i had to drill the end of it out for some bizarre reason so i couldnt do a test in a 48 with it. um. uh. to get the pinion off...)

this forum should be full of posts of shattered bearings, if they fail at 600 km at 3500 rpm... id expect it to be happening every few seconds, at the rate these engines are sold...

seven engines is pretty good innings, but all youre telling me is that something YOU did caused YOUR engines to fail prematurely(in a spectacularly individual display of nonconformity), and rather than alter the way you USE your engines...you altered your engines to suit you.... which is fair enough i guess

surely you cant be the only person capable of turning bearings to dust not just once, but again and again and again and again and again and again and...again?

thats outside of racing circles, of course.

and running twice as much oil as i feel safe using...curiouser and curiouser, as a fictional character once commented.




meh...wheres that icon again?



something to while away the wee hours

im only jealous, because try as hard as i can,i dont get no good pics of catastrophic bearing failures !

I still haven't had a bearing go bad in these things. all my engines spin a lot faster than fabian says will destroy them in a minute flat yet I ran 1400 miles on my last engine (which failed because titanium makes a terrible wrist pin) and am up to 500 on my current one

25:1 oil/fuel ratio is not a factor because every 2-stroke that i own, and have owned (be it lawn mower, chainsaw, whipper snipper (weed wacker), motorbike, has been run on 25:1; without negative effect.

The only change that gave a dramatic increase in big end connecting rod bearing life has been the installation of the Jaguar CDI, of which the Jaguar CDI doesn't produce any meaningful power increase over the standard CDI; verified by doing instantaneous back to back tests between the two CDI's, but whatever the Jaguar CDI is doing, it is preventing premature big end bearing failure.

Surprisingly, i have "NEVER" had a connecting rod small end bearing fail, despite many people reporting failure of this part. In fact, the small end bearing in my current engine has been in two previous engines, of which i estimate that the needle bearing has around 20,000 kilometers on it (12,500 miles) and when my current engine needs the bottom end refurbished, i intend to put that small end bearing into the new engine, just to see how long it will last.

I,m new to these engines, but not to racing two strokes.We had 100cc kart racing engine that ran 20000 rpm.
Just about every 100 cc KT100S pistion port engine runs 14000 to 15000 depending on the pipe.What I wonder
is, with these china engines is the heat treat of the rods & pins?

What type of alloy there making there rods & so from.We used cage bearing in the top & lower ends with little
to no problems.The ole Mc engines used what you guys call crowded neddle bearing lower ends, but they only tuned
12000 rpm.

I see no reason these things should have these problems.It could also be clearance but from the pic,s they don't
seem to but getting hot.It looks like soft metal.If I had a old rod My next trip to Okie City, I can check the rock well
hardness & tell you real quick, if indeed I,m right.

Just my two cents from a new guy
Fly

I would be most interested to find out what the Rockwell hardness of the connecting rod and pin and needle rollers.

Having said that, the newer crowded roller bearing design is bullet proof from my experience, albeit using the Jaguar CDI.
I have not run the crowded roller bearing design with the standard CDI, so i can't make critical comment on that arrangement.

Treated with respect that a $100 engine deserves, these Chinese 2-stroke engines are surprisingly reliable, for what they are.