Most effective mods - Lifan 140

[numroe]

Okay an old topic, but I'm looking for a summary.

I am keen to learn more ... What I want is a moderate power (acceleration) increase (like 10 to 15%) over a reasonably broad RPM range, from my new Lifan 140 with the engine still being able to last for 50 to 70 hrs of riding (mostly full throttle or full brakes) using 98 fuel, clean unifilters, fresh good oil every 4 to 6 hrs, and my magnetic oil drain plug. I don't mind spending on good results. After 70 hrs of serious fun, I'd happily get a new engine.

With no case split (limit on time investment in the mods), key variables appear to be:
* Good jetting, air filter and decent carb.
* Hour meter for maintenance timing.
* lightened flywheel (IRK) and/or slinger. Balancing issues??
* Coil and CDI. Quality.
* Polish ports and intake.
* plug type? Better than the NGK-CR7HSA.
* Camshaft+springs (I need to ride my bike more before picking a cam). Akunar?
* Compression ratio increase (Akunar domed piston).

So what's the priority ordering of these mods plus anything I've missed?

Re cam and compression/piston: I am not sure of the type of cam I'll need (lift, duration and curve). Ideally I'd have a "top end" cam so the mid pulls thru into a good top end, but that means using sustained RPM a lot (it'll never be too powerful but shorter engine life). I could instead go for a bottom end cam, since the mid RPMs already pull good, and the bottom feels weak and boost the compression ratio with a new piston.

Re IRK. I'd like to conservatively play with ignition timing. I believe I can hear pinging and reasonably early. I always use 98 fuel. But the crank vibration and fatigue issue due to the crank ends weight loss does concern me. I believe I want less spinning engine mass since I am after bike acceleration and not just fixed RPM HP.

 

[numroe]

I got an email from Runuka at Akunar.com. Very helpful guy! Based on his input I am currently thinking of going for:

Either the A1 or A2 bottom/mid 6.7mm lift cam. Plus springs.
Better coil and plug.
Probably keep both crank weights installed.
The 8.5mm dome hi-comp piston (with thinner alum gaskets to match deck height).
Polish my ports and intake.

My goal would be to have a motor which is very snappy/torquey anywhere in the bottom to mid revs. Of course not a high revving high peak HP engine, but a good torque spread of usable power. Avoiding the issues with high RPMs. I just need to ride my bike more and be sure on jetting before picking a cam curve.

 

[Cactus Jack]

I'd start by getting a decent sized exhaust pipe to allow the 140 to breathe the best that it can ....... THEN a bigger carb (26 mm for the best all around power) .

Read what Mick Mackeral engine Tuna ... ....... says in this thread .... it's brilliant advice .... he knows what he's talking about ....... I've found precisely the same thing from years of experience modifying XR75's . TT500's and XL 350's ... Get that exhaust gas flowing as well as the intake flowing ... and any engine will come to life ..... even with a bone stock cam ......

http://www.miniriders.com.au/forum/mini-chat/12446-can-you-tell.html

Also , doing a high velocity port job and 3 angle valve job as described in the porting thread will further help you achieve what you want ... The modifications are designed to increase bottom end power and pull right throughout the rev range ........ If you don't rev your engine higher than stock it will last as long as any stocker since they are set up to live that way ......

I lighten my rocker arms to further reduce the possibility of valve float ...... it's an age old mod that was done to race XR's and has proven to be 100 % effective and reliable .......

As to the IRK and lightened slinger ........ you'd have to ask someone who has been running one on a 140 for an extended period of time to see if they can honestly tell you that they've been super reliable ........ but they ALSO have to tell you of every other mod they've done and how they've used the motor to get a reasonably accurate idea ........

 

[Cactus Jack]

Did you quiz Akunar on his views as far as IRK's are concerned ???? The A-2 .. 6.7 mm lift cam sounds good ..... but they have no anti kick back mech ......

 

[Dreadful]

Durant has been running this cam it's the goods...in fact all our trickery has come Akuna

They are on the GAS ...ask him about thier 180 scooter lol.

But yeah you are already on the money ...this is close to the build me and Durant did to the MSO Elite they are giving away in the hood .

Cam , dome piston ,cdi,and a bit of porting trickery ....and yeah make sure ya header is big enough to let it breath....

oh yeah the oko 26mm d slide carb with the clear bowl is also worth askin Akuna about.

But yeah tough ,torquey ,RIDEABLE motor ..... you won't be dissapointed and sound like you'll have no trouble makin the mods .... let us know how ya go.

 

[damann33]

currently I am working on my 140cc. I have ordered a z40 cam, new springs rockers, etc. Using the stock piston I will put the assembled head on and check clearences. Afterwards, if its all good (should be) I will get the head ported out by AHP, I wanted to get it done by mack but shipping is alot of money. I also might get the flywheel lightened a bit, and if I figure out a way to install an akunar piston w/o clearence issues or timming issues, then I will buy a hc piston. These friggin 140's are a pain in the ass to mod. If you use that piston from akunar, ur valves will probably hit, and you cant lower the cylinder to match the deck height on the akunar piston by much. The base gasket is .5mm thick, remove that and use glue, your piston will now be about 1.3mm down in the cylinder, and the head valves might not clear the piston. If you can run the piston lower in the cylinder (what im trying to figure out) then you could install a bigger head gasket, if clearence is an issue, or even use a dremel to the piston dome where the vlaves make contact. There is a lot of shit u needa look into, everyday I am doing reaserch to find out exactly what to do. I think I may just get the head ported, using the normal size valves, and use the stock piston, just to get things done quicker and then wait for the BBK to come out.

 

[numroe]

Thanks Cactus. I read Mack's posting too.

32mm exhaust is std. 41mm muffler exit is std. Same pipe as on the pitster pro 08 I presume. A 26mm OKO carb (flat slide round I believe) on the way.

Been riding with a 24mm Mikuni round as an interim solution. Stock main jet is marked 97.5 (keihin numbers?). Got a 95.5 in there at present. Stock 97.5 probably better. Pilot = 17.5, screw (air?) seems best at 1.75 turns (if I remember right), fiddled with screw in 1/8th increments and sure makes a diff. Needle clip in stock posn = one up (leaner) from middle. Runs terrible with the needle in any other position. Raised float level a tiny bit because is was bogging on heavy flat jump landings which seemed to fix it - impressed myself . Basically all stock in the Mikuni 24mm seems best apart from the float level. First day out I had too much oil on my filter.

Now prefer wait for the OKO26 and fiddle with that with good air (uni)filter. Also put a new rear tyre on today for next weekend. A Pirelli Scorpion MX 12-80/100 which looks like a little meat hook.

Valves adjusted after about 5 minutes of running. Intake manifold hand sanded with 120 to 400 and I verified inlet ends line up. Done about 3 hrs total now. I've also dropped a Fuelstar TM-VC $35 thingy in the 140 fuel tank (does magic on my KX450F) and I'll remove the TM-VC later to see what diff it makes - after it has coated my valve seats with tin.

My Lifan 140 runs pretty good considering this hot+humid weather. I just want it to be a bit more intimidating without killing it too soon. The lightened oil slinger sure helps the top end wind out faster. I'd love to keep that spinning weight off, but if I go for the A1 (bottom end) cam then I am sure I'll need the spinning mass to prevent stalling with the HC piston. I use a 15:39 final gearing, since it easily pulls 2nd gear in the slowest of turns (maybe a click flick at times) and does not run out of legs so early in 4th. 15:41 was a joke in 1st gear - blip and shut the throttle and I almost got whip-lash. If the engine feels great, I might hunt around for a new 1st gear cog, split the case, and make the final gearing taller again.

So my plan in summary: The OKO26 and good air filter is next. Then jetting. Inclined to try get a nice fat low+mid torque curve via the A1 or A2 Akunar 6.7mm lift cam, hi comp piston and probably keep the crank weights installed. If I check valve/rocker and valve/piston clearance then I hope she'll pump out the action for many hours. It's a hobby for me, and I'd like to be able to race it against big bikes at club meetings in winter.

Re IRK and Akunar, he just implied that I run the risk. Just like you said!

Dreadful: Really - the Akunar A2 6.7 lift cam and the 8.5mm dome piston is the norm for you guys? Cool! You tried the A1 cam? As mentioned I need to ride my machine more before I work out where I want to patch up the torque curve the most. With only 3 effectively useful gears and riding on large mini and small MX tracks I need some rev range. You use Akunar's CDI too - what's the diff and price?

btw: Where is Mack's workshop?

 

[numroe]

These friggin 140's are a pain in the ass to mod. If you use that piston from akunar, ur valves will probably hit, and you cant lower the cylinder to match the deck height on the akunar piston by much. The base gasket is .5mm thick, remove that and use glue, your piston will now be about 1.3mm down in the cylinder, and the head valves might not clear the piston. If you can run the piston lower in the cylinder (what im trying to figure out) then you could install a bigger head gasket, if clearence is an issue, or even use a dremel to the piston dome where the vlaves make contact. There is a lot of shit u needa look into, everyday I am doing reaserch to find out exactly what to do. I think I may just get the head ported, using the normal size valves, and use the stock piston, just to get things done quicker and then wait for the BBK to come out.

Big bore kit eh ... from who and when?

Re the 8.5mm dome HC piston from Akunar: I am not sure what probs your z40 cam creates, but what I think Akunar told me is that:
a) we can remove the 0.5mm base gasket entirely and use a glue.
b) put in a thinner (0.5mm alum) head gasket ($5) to get more compression back.
I assume it does not matter much (or at all) where the head/cylinder join is relative to the top of the piston. The join is up in the chamber, no more detonation risk surely. According to Akunar's advice, I assume the Akunar 6.7mm lift series of cams wont push the std Lifan valves into the 8.5mm dome HC piston (but I'll have to check that and adjust via gaskets).

Time and patience permitting I think I might do mine in stages. eg.
1) OKO26 + unifilter.
1b) New coil + CDI.
2) Akunar A1 (bottom) or A2 (mid) cam + springs. Port polishing.
3) then lastly an Akunar HC piston.
Before step 3, I suppose I could thin out the head gasket with the stock piston still in there for a mild compression increase and try that. I can also try with and without the flywheel weights - but with the A1 cam plus a higher compression I cannot see myself going without the stock flywheel and slinger weights, since I'd be stall too much I think. I don't mind difficult starting and kick back. I wear real boots and know how to kick it. But stalling aint ever fun.

Advice/warnings anyone?

 

[themountain]

I think you are spot on....OKO26+Uni filter..good way to do...
BUT: Don´t buy akunar cams!!!

I like Rakuna ...he`s a hell of a guy and their other stuff is decend ,but the cams suck BIG TIME!! ...its the material and the bearings !!
Get a racecam from AHP!!...some here will say that this ones are from akunar too, but thats not true...I spoke about this with mark(the owner) and he said they got a lot of stuff from Akunar, but no cams, because they had issues!!

 

[numroe]

I think you are spot on....OKO26+Uni filter..good way to do...
BUT: Don´t buy akunar cams!!!

I like Rakuna ...he`s a hell of a guy and their other stuff is decend ,but the cams suck BIG TIME!! ...its the material and the bearings !!
Get a racecam from AHP!!...some here will say that this ones are from akunar too, but thats not true...I spoke about this with mark(the owner) and he said they got a lot of stuff from Akunar, but no cams, because they had issues!!

Hmm interesting. Thanks. How long ago was that? Maybe fixed in the product now. Maybe not an issue below certain RPM and/or with adequate oil flow. You mean the cam lobe surfaces or bearing surfaces?

Dependent on the outcome (torque spread) with the carb, I am very tempted to give an A1 or A2 cam a go in any case. I assume an AHP "race cam" is a top end cam. I want to keep the revs below stock design limits. At AUD55 per cam, and being a quick job to replace, and not over revving valves etc, I'm not panicking.

Appreciate your feedback! Keen to hear more details.

 

[Cactus Jack]

Well dude it sounds like you've well and truly got your act together ..... The Fuelstar tin catalyst device is a smart idea to keep detonation in check ..... I know people who use worked 11.5 to 1 compression Chev V8's on the street running on low octane unleaded without any problems ...... tin is the best anti knock agent / octane booster and upper cylinder lubricant ..... even better than lead ..... If you eliminate the possibility of detonation ..... you've solved most of the problems ... You'll know if the Fuelstar is working because the piston crown will have frig all carbon on it ...... carbon glow is the high compression engines worst enemy .......

Knock sensors only work AFTER they sense knock ...... you don't want the engine to knock in the first place ...... you're smart to run a fuelstar in the 450F ...... for that very reason ...... Most of the people blowing 4 stroke MX engines up are doing so because they are following the factory advice and not running an upper cylinder lubricant and anti knock additive in the fuel ... I posted that in a Thumpertalk thread where people were talking about suing Honda because they lost desert race championships (after winning every race in the past) due to rapid valve seat recession and they quicky deleted the entire thread . A cheezed off Honda representative got on there arguing with me after I said that manufacturers are deliberately building engines that they know will have problems running on pure straight unleaded and he denied it saying it was ludicrous to suggest that Honda would deliberately reduce an engines' reliability ..... but he had no answer when I mentioned that Honda had removed oil slings and alloy flywheels from the previously super reliable XR75's and ran the cams on the bare alloy head without bearings ...... instead of in a bullet proof stand alone iron cam tower like they previously had . The later engines ran heaps hotter .... needing larger finning but the cams still stuffed up taking the head out with them whereas with the earlier set up you could easily simply replace the cam tower OR get it machined and bushed ... thats IF you ever did have problem due to your own reassembly stuff up. On the later model '77 and up heads ..... half the journals were DIE CAST into the head and were extremely costly to get welded up and machined .... and because of the journal location it took a special machine to do redo them after welding ....

If your engine is running well without problems with just the lightened slinger and you like the throttle response plus the way it pulls and grips .... I'd leave it that way and do all the other mods ...... I can tell you from experience that higher compression will greatly boost bottom end torque and punch ..... but it tends to act as a rev limiter with a given cam ... The cam and compression go together hand in hand ..

Incidentally I've also read on numerous posts where people say the Akunar cams are junk ...... but they never actually stated WHY like mountain has .......

 

[themountain]

You mean the cam lobe surfaces or bearing surfaces? .

Its the bearings...they are mostly noname....ahp uses NTN

I want to keep the revs below stock design limits.

Why want you do that?? the 140 is decend down low...it sucks when you try to rev about 8000 rpm...so a cam with a higher output feature and stronger valve springs will do the trick

 

[Cactus Jack]

Why want you do that?? the 140 is decend down low...it sucks when you try to rev about 8000 rpm...so a cam with a higher output feature and stronger valve springs will do the trick

LOL ....... Yes mountain is right ........ you need a cam that allows the engine to punch hard in the mid to upper revs and you use the BEST rev limiter there is on this planet ........ Your brain and your right hand !!!!!!!

Many drag race engines will blow up instantly in the hands of an amateur .... they'll rev hard enough to destroy even the best available race parts ...... so they use either driver skill and throttle restraint or rev limiting tachometers etc ...... in top fuel they started using every imaginable computer controlled electronic device so that any idiot could sit their butt in a car and compete but that was quickly outlawed ...... otherwise it would have gotten to the point where they had monkeys sitting in the cock pit with some rich wanker controlling the car by radio control ....

That's also why pit bike engine manufactures fit rev limited / conservative advance CDI boxes to stock engines .... you can safely rev an engine high as long as it's pulling a load and NOT detonating ...... Free revving , peak revving under under light loading and on down shifting can grenade a motor quick smart ......

You can always pick out a bad rider racing around a track ..... they'll be peak revving the engine out unnecessarily and holding every gear for too long whereas the smarter guy (who is usually miles ahead of them) will be using the torque and power curve to the best advantage (short shifting at peak torque) and also trying to save his motor by only using the minimum necessary revs at any given time ..... .

James "Bubba" Stewart and Ricky Carmichael did it quite well .......

 

[numroe]

Why want you do that?? the 140 is decend down low...it sucks when you try to rev about 8000 rpm...so a cam with a higher output feature and stronger valve springs will do the trick

tm, I cannot answer/comment on it yet (ie. why I'd consider boosting bottom or middle instead of top end). I need to try the bigger (and substantially different) carb and generally learn the current power spread better, then decide where in the RPM range I want to boost it to try and give me the lowest lap times and most fun.

For sure though, I believe that if the engine can presently run safely on 91 octane fuel, and I am prepared to put nothing in it but 98, then I have to be able to safely gain some efficiency over the whole range via a basic compression increase. With the fuelstar gizmo I can push it a bit further too. If the raised compression gives me an effective rev limiter then no probs, that'd be good.

Hey I put my OKO26 on tonight. Interesting in a few ways besides the slide shape. Needs the longer/higher manifold so the bowl clears the cylinder fins. The OKO26 has a much large carb intake and better looking. Very different carb throats and manifolds too:
Mikuni: 24mm round carb. 28mm carb exit. 28mm manifold entry, 25.2 manifold exit, 25.0mm port entry.
OKO: 26mm round, 26.5mm carb exit, manifold 25.0 all the way, 25.0mm port entry.
On the OKO, I trimmed and sanded the rubber join piece to smooth out the sudden drop from 26.5 to 25mm. Still ugly though.

btw: OKO26 (my) stock jetting: Main = K102, Slow = K37, needle clip = middle, air screw = 1+1/8th out.

Comments welcome!

 

[themountain]

For sure though, I believe that if the engine can presently run safely on 91 octane fuel, and I am prepared to put nothing in it but 98, then I have to be able to safely gain some efficiency over the whole range via a basic compression increase. With the fuelstar gizmo I can push it a bit further too. If the raised compression gives me an effective rev limiter then no probs, that'd be good.!

well ...the fuel is in a 140er not an issue...there is no that high compression piston around , that you will have problems with it! ....and by the way a raised compression doesen´t give a rev limit...mostly it´s the other way round ...the valvefloat and weak springs acting more like one!

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

 

[Cactus Jack]

Engines will rev until dynamic cylinder pressure hits a peak ...... the super high pressure then acts as a brake to limit the engine speed ......

Increasing cam duration works to raise the rpm limit by delaying the onset of peak dynamic cylinder pressure ........

Hi dome pistons aren't as good as some people might think .....

I gave damann good sound advice when I told him to use a 120 chambered head and the stock height piston ......


Engine Compression Ratio - Tech - Popular Hot Rodding Magazine

 

[themountain]

Nice read!!...your the man ,cactus!!

 

[numroe]

Yes Cactus, nice read thanks. Maybe some heatshield material between the cylinder and carb would be wise in the warmer months. I know domed pistons are ugly, but in a 2 valved engined with ugly side mounted sparky and funny shaped chamber - what else to do to raise the comp? I think a comp ratio to at least suit 98 fuel is just too inviting/easy.

I never got to ride this weekend and test the OKO26. Transport problems, and probably too wet in any case.

My plan remains the same though.
1) Test + jet the OKO26. Pick the Akunar A1 or A2 cam.
2) Install cam+springs, with better coil and CDI. Maximise compression via less gasket thickness. Re-test.
3) Install the Akunar 8.5mm domed HC piston.

Themountain, The A3 (top end) Akunar cam is still outta the question in terms of what I want. I don't see the point in trying to rev out a 2 valve stroker engine with an old fashion chamber design and weak crank. Anyone in a disagreement rage, just stop your dreaming. It'll never be an efficient revver. Take a look inside a modern 250F engine and see the diffs in design alone. You are right the Lifan 140 bottom end power is "already decent". That is the bottom is not flat, but it's no way strong compared to the mid. I agree the top signs off early at present. Every fast MX 4-stroke engine needs a good transition from bottom end into the midrange. So I first have to ride the bike as is, and have a guess pick at the A1 or A2 cam. Probably I will buy+try both. I don't want peak power. I want a stronger engine for quicker laps around MX and SX tracks.

btw: The OKO26 with manifold is 300g lighter than the Mikuni 24. Bonus!

 

[themountain]

well ,numroe, the 140 is limited through his head design and his stock cam....nothing to do with its stroke.....for tight minitracks/SX ...ok ,the lowend cam make sense...depends on which wheelsetup you have 12/10 or 12/14 ??...traction is everything!!

 

[numroe]

well ,numroe, the 140 is limited through his head design and his stock cam....nothing to do with its stroke.....for tight minitracks/SX ...ok ,the lowend cam make sense...depends on which wheelsetup you have 12/10 or 12/14 ??...traction is everything!!

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.