inner roter kits

[jockey1989]

i have a lifan 125 start in any gear i wanna no if its worth puttin a inner rother kit in it i have only heard bad things about them??? cheers

 

[SnItChY]

IRK Install SnItChY Tech Tip - Putfile.com

watch my vid i recon there alright

 

[xb80]

lol u cant put iner rotor kit on 125cc the clutch runs were the lightend oil slinger goes so u cant put light slinger on so if u install a roter kit the crank will snap off.

 

[ducar.r.spec]

xb80 ur rong
if its a start any gear engine then he can install and irk and lightened oil sling

 

[1fifty1wheel]

you can, just make sure you install a lightened slinger aswell like xb80 said. the crank will snap, maybe not straight away but it will.

 

[1fifty1wheel]

ignore the red circle, pic was used for another topic

thats the left over spline in the center

 

[jockey1989]

cheers mi mate had one in his 140 n it keep on crackin hiz case

 

[Custom]

You do not need a lightened slinger to run an IRK. The crank drives the gearbox from only ONE side, if cranks were going to snap that is what would cause them to snap, not the lack of lightened slinger. Clutch drops, hard riding and lack of maintanance are what snaps cranks

 

[ducar.r.spec]

actually custom i snapped a crank and i had irk with clutch on other side
and i look after my engines

 

[Custom]

I dont doubt that you do but in theory that setup would make it harder to snap the crank. Which side snapped off?

 

[1fifty1wheel]

You do not need a lightened slinger to run an IRK. The crank drives the gearbox from only ONE side, if cranks were going to snap that is what would cause them to snap, not the lack of lightened slinger. Clutch drops, hard riding and lack of maintanance are what snaps cranks

speak to most reputable mechanics and you'll get a different answer, i'm no mechanic but have seen it many times. and guarantee its not due to riding style.
i haven't seen a crank snap in that position when a lightened slinger is fitted along with an IRK to date.

 

[liljohn_92]

im with custom on this cuz ive had an irk in my n start only for about 5 months and it still goes hard

every1 says its guna snap my crank wtf mine aint snapped and i hardly maintain it either it just gets flogged and it still goes

so theres proof you dont have to lighten both sides of the crank

liljohn

 

[kaneo]

Yeah i ran an irk in my 140 for over a year, flat out every weekend without the lightened slinger and it was fine. I think they are too user unfriendly with the slinger in as well. They stall easily, lock up the rear on down changes into corners, and kick the back high on jumps by returning to idle too quickly. Just like hitting the rear brake. I actually put some long bolts with heavy washers in the rotors two puller threads to make it heavier for jumping. The benifits of the rotor i was after was the adjustable timing not the lighter weight.

 

[Cactus Jack]

Yes kaneo and custom are right ...... it's got everything to do with harmonic buzz causing metal fatigue and crank failure ..... anyone who claims that heavy flywheels at either end of the crank somehow "twist" or "shear" the ends off has both hands on their knob big time ....

Anyone who believes the heavy flywheel "shear" theory should try to explain why the ends of the crank don't shear off on stock motors if you rev the bike and drop the clutch ..... According to their "theory" ... when the engine revs drop suddenly on a clutch drop OR when the engine is revving high then gets stalled instantly on rear wheel lock up under braking .... the flywheel side would shear off in next to no time at all ........ Ha Ha Ha Ha ........

The cranks aren't breaking due to "power" either ...... that's for dead certain ..... IF they WERE .... then they'd shear off in between the right hand side crank bearing and the primary drive gear ....... Even the most crap made crank would support tons and tons of weight off the ends ........

Look at bigger 4 cylinder bikes that put up to 200 hp thru the ends of their cranks ..... when you think about that ....... 20 HP is frig all force on a crank ..... The TRUE answer is that unchecked high frequency vibrations weaken the metal via cyclic loading fatigue (rotating bending stress) ....... to the point that it can no longer handle the loads it was designed to cope with .......

Harmonic buzz aka critical resonant frequency sets itself up at certain points throughout the rev range .... and IF the revs are held for any length of time in the critical frequency zone ....... the metal fatigues and fails .......

The above scenario is more likely to happen in motard or road race engines where sustained high revs are reached and maintained ..... So the complete crank assembly needs to be balanced to operate smoothly at those rpm's .......

ATI - The Dangers of Power Pulleys & Understanding the Harmonic Damper

An exerpt taken from another link :

High-Frequency

[High-frequency vibrations are evident in buzzing and a numbing effect on the feet and fingers of crew members. High-frequency vibrations are caused by an out-of-balance condition or a high-speed, moving part that has been torqued incorrectly. The balancing of high-speed parts is very important. Any build-up of dirt, grease, or fluid on or inside such a part (drive shafting for example) causes a high-frequency vibration. This type vibration is more dangerous than a lateral or vertical one because it causes crystallization of metal, which weakens it. This vibration must be corrected before the equipment can be operated.]

 

[kaneo]

Well put cactus. They did a thing on mythbusters about resanence. Was pretty cool the damage it can cause to things.

 

[1fifty1wheel]

cactus, could you then explain the reason i've seen three snap in the same spot, with the same mod, and none without an irk/slinger or with both?
curious.......

 

[liljohn_92]

cuz ur a retard :O haha jks man

 

[1fifty1wheel]

good on ya, that was worth it.

 

[Cactus Jack]

cactus, could you then explain the reason i've seen three snap in the same spot, with the same mod, and none without an irk/slinger or with both?
curious.......

Well you've heard from others that they ran an IRK with the stock slinger and their engine ran reliably ... with no problems ...

What were the engines you're talking about used for ? Dirt or tar ? .......

As I stated , it's got EVERYTHING to do with the harmonic balance of the engine being upset .... Incidentally when people do a mod to an engine they usually somehow assume that they now have a "racing" engine and flog the guts out of it ....... so the way the engine is used and treated ALSO changes along with the modification ...... It's easy to blame the breakage on the modification and NOT the way it's being treated ......

Fitting an IRK .... ALSO removes the rev limiter that was put there by the factory to prevent the engine from being revved into the crank breakage zone ...... it's like removing the safety pin from a hand grenade ... then wondering why it "grenaded" on you ....

Stock engines are balanced to suit STOCK usage and treatment ........ IF you are going to rev an engine to higher than stock revs ..... you'd better get the crank assembly re balanced to operate at those rpms .... that's a no brainer .......... On top of that , people alter compression and piston weight by fitting a bore kit WITHOUT getting everything rebalanced ....... then they wonder why things break .....

IF you start wringing a long stroke engine out and holding the revs ..... you are going to break something ..... Honda knows that only too well ..... that's why THEIR genuine racing engines have short strokes ......... ie F1 cars .... CRF150R .... 66 MM BORE X 43.7 MM STROKE ..... THINK about WHY they've used a shorter stroke ...... and WHY manufactures fit rev limiters ...... and you'll answer your own question ......

 

[Cactus Jack]

Another factor I forgot to mention is (as kaneo stated) ... the TIMING can be easily altered when an IRK is fitted ...... that means that IF the person fitting the IRK isn't a skilled engine tuner who knows how to use a timing light .... then they can set the ignition to too advanced and detonate the hell out of the crank ....

As stated in the ATI link .... people THINK that steel is solid and rigid but it's NOT .... it flexes , twists and rebounds .... IF you get a pen , piece of metal rod or something and sit it on top of a cup to simulate a crank shaft (the edges of the cup where it sits represent the main bearings) .... then push up and down on it with your finger to simulate a piston pushing on a crank .. you'll see that the ends move up and down ....... That flexing happens in a running engine only on a microscopic scale but it happens none the less .....

The crank counterweights are weighted to minimise that flexing so the bob weights have to be over balanced opposite the piston and rod to cancel out the bending force that the combined piston and rod weight puts out when they stop dead then reverse direction ...... but the stock balance "factor" only works within the stock rev range ..... if the crank revs higher than stock the piston and rod goes up and down faster and therefore gains more weight / mass via inertia so the higher the revs ....... the less counter active force the counterweights have in relationship to the added reciprocating weight increased via inertia ...... so the ends of the crank start flexing up and down (bouncing) like crazy and since the crank is rotating fast .... the flywheel or sling get sent into spiral orbit ... They get flung out off their axis then get pulled back but they don't stop at the central axis point , they go past it to the other side equally then return like a pendulum ..... that sets up a resonant frequency and when it hits a critical pitch .... the metal crystallizes and cracks and it can fail at a far lower load or stress than it can normally handle .... Detonation greatly amplifies crank flexing ......

You can clearly see that the metal from the end of the crank inside the pic of 1fifty1wheels slinger "appears" to be brittle .... and that's typical of crystallized metal ... IF it had sheared off it would be smooth and there'd be spiral twist marks but there are none .......

In short , the end of the crank fails like a piece of coat hanger wire that's been flexed back and forth rapidly until it fatigues and breaks ........

Lightening the flywheel CAN cause vibrations to be transmitted across the crank to the other side ..... heavy weight tends to dampen out and control vibrations ( put a bare barbell bar between 2 supports ... dong it in the middle repeatedly with a lump of wood and watch it vibrate like crazy .... then add heavy weights to each end and repeat the test ..... the heavier the weights ... the lower the vibration .....)

Years ago in the US a circle track car driver was injured when a stock iron harmonic balancer exploded so everyone started replacing their balancers with light weight alloy hubs ........ then after that there was a spate of busted cranks ..... that's when they first learnt about the destructive effects of harmonic vibrations and started to fit special explosion proof steel balancers ....

As far as horizontal chinese engines go , it's run an IRK ..... run the risk of crank failure .....

As I've stated on other forums ..... you'd have to assume that Lifan has done dynamic balance testing on the new 150's crank and altered the balance factor to get them to survive at their peak rpm limit with the outer rotor and no oil sling ........

I found a link on Kohler racing engines where they showed that they over balanced the cranks in their modified engines to reduce the loading that the reciprocating weight put on the crank as the engine revved higher .....