Most effective mods - Lifan 140

[Cactus Jack]

Rev limit: Personally I don't mind a longish stroke on a 2 valve engine which is never going to be ideal for fast gas in/out over the entire bore. On the Lifan 140, my line of thought is: Long stroke means higher piston speeds, with the cheap crank = risk. Especially if I put on a heavier HC piston.

Yes traction indeed. Pirelli Scorpion rear tyre. Rim locks and proper pressures both ends. My wheels are 12/14. For racing big bikes in club races I am considering a 14/17 setup - which I know would make me a traitor. But hey gotta do what I gotta do.

Yes I'm with you as far as the long stroke engines go ........ long stroke motors rise to a strong mid range then drop off quickly up top whereas a short stroke motor has a broader more linear power range coupled with a higher max rev .......

That's because the piston accelerates too fast for the expanding combustion pressure to keep up as the revs increase plus inertia of the reciprocating parts reaches a high level quicker , putting up a resistance to slow the motor down ..........

Knowing that means that fitting a heavier than stock piston is not such a bright idea (puts engine out of balance) ..... plus the increased crank flex over stock will cause it to fail quicker

Also the fact that the piston will be down the bore = stupidity (read about the quench area in the detonation link) ....... especially with higher compression the engine will detonate and that will flex the crap out of the crank ......

Hemi heads were designed to work with a centrally located spark plug for a good even burn ...... you'd also need a "flame trough" thru the piston dome to get decent flame travel since the plug is in the wrong position on a BVH .....

The BEST way to raise the compression of a 140 at the moment would be to use a smaller chambered 120 BVH and the stock piston with a thinner copper head gasket ..... OR weld up the head to reduce the chamber size and shape the piston dome to suit ......

 

[numroe]

The BEST way to raise the compression of a 140 at the moment would be to use a smaller chambered 120 BVH and the stock piston with a thinner copper head gasket ..... OR weld up the head to reduce the chamber size and shape the piston dome to suit ......

Hmm, tempting to abort the HC piston - if the engine performs nicely after step (2) - which will hopefully also include a minor compression ratio increase via the head gasket thinning.

Other options like welding up chamber space, or shaving the head base or whatever don't seem appealing compared with a new head or whole new engine - like the Lifan 150 - which will hopefully have better options for comp ratio increasing.

 

[themountain]

...- like the Lifan 150 - which will hopefully have better options for comp ratio increasing.

sorry to disapoint you but the Lifan 150 will have the same head design

I will bet after step 2 your engine will fly...maybe a bit headwork and thats it ...have fun!!

 

[Cactus Jack]

Yes , I was going to say the exact same thing as mountain ...... When they make the capacity bigger , they also usually lower the compression to protect the kick starter gears from poor kick starting technique so as to avoid a barrage of complaints ...

People are better off to wait until someone produces a high compression piston for the 140's that has the correct pin height and dome shape .....

Here's a pic of a prepared XR75 hi dome stroker big bore piston showing what they've done to match it to the combustion chamber to improve the quench area , unshroud the spark plug (flame trough) and improve flame travel (flat part on top) ...... the piston would also benefit from further hand finishing to remove all sharp edges ..... then be polished and glass bead blasted to achieve the proper surface texture ........ a heat resistant coating would be even better still .........

Pic of Lifan 120/125/127/138 combustion chamber :

http://us.st11.yimg.com/us.st.yimg.com/I/dratv_1985_317987702

Pic of Lifan 140 combustion chamber showing larger quench ring (care of Mack) :

 

[numroe]

Well this morning, I ordered the A1 (6.7mm) cam + springs + CDI + coil + 0.5mm alum head gasket.

Without pre-test riding it, but decided to take a punt on the A1 cam because I can remember the power curve reasonably well with the Mikuni 24mm. It'll be interesting. I'll probably put the heavy slinger back on so I can exploit the bottom end more. It should hook up nicely out of turns, slingshot up jump ramps, and with some clutch action I should be able to chuck boulders out the back on demand.

Actually I went up and down the street quickly to test the OKO26. Just a quick warm up (garage and in 1st) then pinned it in second to let it wind out to about 3/4 revs. It felt pretty damn good straight away. Pulled smooth.

btw: check out my air intake snorkle and repositioned air filter.
http://www.miniriders.com.au/forum/tech-talk/15882-air-intake-snorkle.html#post149431

 

[numroe]

And you are a bit large on the mainjet and a bit small on the pilot...I would recommend 48pilot/100Main !!

Keihin #48 slow jet in an OKO26 ??

I have the stock jets in my OKO26 at present. ie. #102 main and #37 slow. Needle clip in the middle.

btw: #42 is the slow jet in my FCR40 on my KX450F-06. Not sure if that means anything though. 450 main is a #175.

To play with I have mains #100, #102 and #105. Slows: #36, #37, #38 and #40.

You done some time with the OKO26? I'm guessing I'll have to spend some time getting it right with the stock cam and then again with the new cam.

 

[numroe]

Anyone tried one of these ready made bolt on Lifan 140 heads?
SAFB Mini Parts

 

[numroe]

To play with I have mains #100, #102 and #105. Slows: #36, #37, #38 and #40.

I think my OKO26 is working great.

Air filter = 75x100mm genuine unifilter foam POD direct onto carb.
Air screw = 1.75
Slow jet = #38 (stock was #37)
Main = #100 (stock was #102).
Needle pos = middle.
Float level raised "a tad".
Inlet mainfold: Ports lined up. Hand sanded inside to 240 grit.

No bogging on flat jump landings. It is possible to m ake the engine bog on a throttle snap open at extreme times, so some care is needed, but it's almost idiot proof. Just very sensitive to air filter cleanliness (no water on it!).

I raised the float level as bit of a random change when I got a big confused (due to air filter state changing during jetting). Once I fix the air filter and the jets, it ran so well I just left the float level where I put it.

I am away for most of March. Hope my new ignition and cam arrives soon!

 

[themountain]

here we go!!...but I still think you are too small on the Pilot, though!!

 

[numroe]

here we go!!...but I still think you are too small on the Pilot, though!!

Well next time out, I can (and shall) try larger size on the pilot. I have in the kit a #40 and something huge like a #47.

I started on #37 (after I did the main and float) and it ran pretty good. I flipped a coin and tried a #36. It was for sure too lean. Hesitation and some popping on decel. I tried a #38 and it felt great. A deep exhaust note and torquey off the bottom. The #38 felt so good I assumed your advice for a #48 was a mistype or something.

Comparing main jets at WOT, interesting how this OKO/Keihin carb pulls more petrol through the main than the mikuni 24mm. I mean running equiv well with 38 thou (K100) on the OKO26 versus 41 thou (M97.5) on the Mikuni 24m.

 

[themountain]

The #38 felt so good I assumed your advice for a #48 was a mistype or something.QUOTE]


well it depends all to temperature you know...we got winter here..more cold, more fuel!!
But even so you should put the #40 inside and the throttle snapping issue, you talked about, is over !!

 

[numroe]

sorry to disappoint you but the Lifan 150 will have the same head design I will bet after step 2 your engine will fly...maybe a bit headwork and thats it ...have fun!!

themountain, Just checking, will the Lifan 150 have the same head design as the 140, including accepting the same cam part? If yes then I wont mind trying a few diff cams in the 140, since I can re-use the healthy cams when I get a 150 at a later date.

On the topic of the 150, do you know anything about it's gear ratios? My Lifan140 has ratios 3.182/1.706/1.238/0.916, and I am hoping that 1st gear in the 150 will be much taller to bridge that massive gap to 2nd. I understand that Lifan (or their suppliers) wouldn't give a rats about ideal ratios for MX usage/customers. But I can always hope.

update: Bugger: According to Macka in his post here Anyone seen the new Lifan 150 yet? - Planet Minis Forum I am out of luck and the granny gear is still with us. So I'll to live with a 3 speed. I calced the ratios between the ratios, and the Lifan 140/150 have a .74 drop between 2,3,4 but a massive 0.54 drop from 2 to 1st. So 1st is totally useless unless I like to climb 45 deg hills. The YX150 is not so bad: 4 to 3 = 0.77 drop. 3 to 2 = 0.7 and 2 to 1st = 0.59. Nothing like a MX box (rarely drop more than 0.8) but the YX is better. With a wide RPM spread of engine torque the YW150 ratios might be ok.

 

[numroe]

My Lifan 140 rips now. Akunar A1 6.7mm lift cam. Akunar valves and springs. At a rough guess I'd say at least 25% more torque in the bottom and mid range. The mid rev torque is just unreal. Top end torque is still respectable. The old torque curve would have a hump in the mid revs. Now I have a very healthy bottom, better mid, and the top still works (if needed).

Rest of the setup: Stock piston (dremelled for intake valve). OKO26 flat slide carb (K102 main, K38 slow, needle 1 clip rich than middle). 60mm "snorkle" to unifilter under seat. Alum slinger. Stock flywheel. Akunar ignition coil. Mobil 8000 fuel. In comparison, the stock Lifan cam looks to have about 4mm lift and 2/3rds the duration on each lobe. Yep that much difference.

In good traction conditions, I actually find myself rolling open the throttle, not because I fear bogging the engine, but because I have torque on tap and can break free the rear wheel (nice Pirelli Scorpion MX tyre) almost when ever I want. At wide open it generally just digs trenches. I am not talking about top end down the straights or road racing HP. I am talking about torque for shitty condition MX tracks etc. So much fun! The "fun cam"!

I bent the stock intake valve on first assembly. So got some Akunar valves, then put it together again with a 1.5mm deep arc dremeled in the piston crown. Also the compression feels better now with the Akunar valves compared with stockers. The seat fit (seal) looked better (by eye) with the Akunar valves than with the stockers.

The engine is notably louder in the exhaust and the intake throaty sound. The throttle response is superb and crisp. My KX450F never bogs and is very crisp on the throttle, and no kidding my Lifan 140 is probably as good with response. For a AUD250 engine with AUD100 in options, plus a AUD100 carb, this freaks me out. It's unreal because with such control of rear wheel output, there is heaps more room for error in terms of corner entry speed, lean and line.

Now I need stiffer clutch springs. My clutch has only done about 15hrs and I dont fan it that often. But now when shifting if I accidentally open the throttle before the clutch has grabbed, then it NEVER grabs. On the first few occurrences, I thought I'd missed an up shift when I opened the throttle, but I was in the higher gear, just clutch slipping. I have ample cable slack.

I want to try taller gearing again. Started with 15:41. Now have 15:39. Want to try 15:38 so I can use 2nd more. In 2nd today the rear wheel rips anything up too easily. 1st gear is of course a joke.

It's great NOT having the decomp mech on the new cam! Now I can ALWAYS find TDC and starting is far less butcherous. With a firm correct kick and tiny throttle roll on, it starts real easy and never kicks back. Love it.

Not yet inspected the engine oil or mag drain plug. That'll be interesting. As will be checking the valve clearances. Valves set at 004 each or just looser. Update: Mag drain plug had a minor "iron affro", and the oil was full of dark clutch material but otherwise good oil.

It's also great not needing to rev the long stroke engine hard. This must help with lubrication. But for sure it'll die one day with a bang. The output just seems over the top for a 140cc china engine. I would guess the crank, or the rocker arms or the timing chain will jump. Lots more valve train load (felt by hand and heard with the ear). But so good now I wont care if I just got a few more hrs out of it. The drive chain stretched so much in 90 mins of riding that I had to move my axle back 8mm in the swingarm to reset the chain slack.

PS. Yes I can touch type.
PPS. This web site is some much responsive these days. Thanks! New cam in the server??

 

[themountain]

Right on ..imagine the engine now with a bigger piston. ...on the gearing I am running 15/37 at the moment and its a beast in Third....who needs first gear anyway hahahaha!!
Clutchsprings and plates will go now frequently..hehe...try EBC springs for the ATC 110(Partnr. CSK22 )and honda plates!!

 

[numroe]

Right on ..imagine the engine now with a bigger piston. ...on the gearing I am running 15/37 at the moment and its a beast in Third....who needs first gear anyway hahahaha!!
Clutchsprings and plates will go now frequently..hehe...try EBC springs for the ATC 110(Partnr. CSK22 )and honda plates!!

Cool. Thanks for the advice re the clutch! Those parts drop straight in ?

15:37. Why not ... 15:39 vs 15:37 is 0.054 difference in ratio. 2nd to 3rd is a difference of 0.73. What was I thinking?! 37T rear it is.

Yeah I wish I could remove 1st gear. Useless spinning mass.

A hi-comp piston would be lovely. But to be honest, despite crank issues or whatever, as is now, it's more grunt than I generally need in this chassis on wooped out and rutted tracks. Even for short take off jumps it's GOOD fun now.

Next time I am feeling cashed up, I'd love to put an Ohlins shock in the rear.

I need a better front tyre. The Kenda Millville aint good enough and sometimes I am not sure what to expect. Cannot get the M403 in a 14" front, so tempted to try a Pirelli Scorp MX on the front too.

Hey tell me about the timing chain: eg. How do I check, adjust and maintain it? The bigger cam must put double or more load on it.

 

[themountain]

Next time I am feeling cashed up, I'd love to put an Ohlins shock in the rear.

Hey tell me about the timing chain: eg. How do I check, adjust and maintain it? The bigger cam must put double or more load on it.

Öhlins ???..are you running motard?? Öhlins don´t have a decend dirtshock yet.....damn shame
the chain isnt a´big issue...check frequently if it not too tight...slack get out with the auto tensioner
If you feel you have to change it get a reforced Takegawa..they ain´t much expesier but tuff as nails!!

 

[numroe]

Öhlins ???..are you running motard??

No, I just believe they don't make anything of poor quality.

About the clutch plates: You said Honda parts. Do you mean both sets of plates or just the ones with fiber? Also which current model CRF has the compatible clutch?

 

[tubes380]

im pretty sure the atx110 springs will fit and so will the fibres and bring the clutch up to spec with the motor

 

[themountain]

everything from the little ATV's (90+110) is useble...you can get a whole kit from EBC too !!But you can use only the fibre's the steelplates are too thick! Caution ...the springs from the atv's are so stiff that my son can barely pull the lever...so I use only two of them !

 

[Stubsy]

well thanks numroe i think you have sold me. will be sending of an order this week for the cam and springs etc. cant wait