Loncin 125

[LOWLYF]

Hey Guys

Im pretty new to the pit bike thing, i got a 125 pitty 4 free it just needed a little clean up and its got a 125cc loncin motor in it. The guy i got it off never did any maintinance on this bike so with a good clean it came up pretty good.

Saying that i think it could do with new rings and service(prob needs valve clearances checked) then i wanna start jumping it so i want a bit more power.
I cant find much on these motors, some say ok some say bucket of s#*t but i dont really wanna go spent $300 - $400 on a new motor when it cost me nothing. So could anyone suggest some mods to do and possibly a link to where i can get the engine parts from.

I tried to search but i cant get the search page to work.

Thanks

Nick

 

[headsmess]

yeah, i have one of these, so far the best mod i made to it was to use a race cam from pitster pro on ebay. bolt straight in, but do need one mod first...take off the end bearing and theres a oil slinger thing next to the exhaust lobe that has to be removed...it interferes with the exhaust rocker, causing it to not run. if you get one. 110 bucks with the new springs.

other than that theres not much you can do besides maybe a hi comp piston. dhz has oine, not sure how high it raises the compression though. (its a 13mm gudgeon /wrist pin)
im going a different direction anyway. akunar and a bore out, and modify a big valve head to suit the stud pattern.

left stock standard, they are pretty reliable, if a little gutless...

two threads to read throughhttp://www.miniriders.com.au/tech-talk/23022-strange-engine-number-so-called-lifan.html

andhttp://www.miniriders.com.au/tech-talk/23105-lifan-140cc-1p55fmj-cam-sprocket.html

search tab...right click,open in new window/tab

 

[Cactus Jack]

The "oil slinger" thing you're talking about is the anti kick back sprag ... (one way bearing) ... When the engine tries to go backwards in the event of a kick back ... the tab on it opens the exhaust valve just enough to let the pressure escape ... Stock Loncin 120 cams have one on them so it's strange how it caused problems for you unless it was bigger in diameter on the race cam than the stock one ...

Did you buy a Lifan 140 cam ? ie 73~74 mm long , has a smaller sprocket end bearing than the Lifan 120/Honda type cams and the cam sprocket bolt flange is pressed on ... The 140 cam is made to suit a Lifan big valve head not a Loncin small valve head even though everything else is the same dimension ... that's why you copped the problem you had ...

One mod you can do to most "Race" cams is to fit a small end bearing that is sealed on one side ... What that does is boosts the oil volume and flow to the cam lobes to minimise the risk of them burning and wearing too quick from the added load of higher lift and race spring tensions ...

I've got a few cams (2 x TBW0300's / 1 x Sachs madass / and 2 cams from Pitster Pro) but they haven't got the sealed bearing ... I just bought a Lifan 120 ~ 138 race cam off 4332g and it's got the sealed small end bearing ... The TB cams have a lot more nose duration than any of the others ... but for dirt you want more bottom end and midrange torque anyway ...

Yeah the Loncin 120's have small restrictive ports so they have strong pull down low then drop off quick after the midrange ... A ported 110 has less bottom end but comes on stronger up top and revs a lot harder ... even with the stock cam ... 110 cams are shorter than the 120 cams (68~69 mm vs 74 mm) and they don't have the anti kick back sprag or the plate between the rocker shafts ...

It's best to not go too big in the carb on a small valve head ... I fitted a Genuine 22 mm Keihin (24 mm outlet bore and a 22 mm oval venturi ) with a #38 pilot and a #105 main on Davos ported 110 and it was super responsive and went fast enough for the brakes to barely stop it on tar with the front 12 " wheel skidding ... Davo was supposed to keep bringing it back for gradual additional tweaking and fine tuning but he didn't ... he gave some guy a go and got hounded to swap it for a CR125 plus cash ... so he sold the bike to him within a few weeks without bringing it back to me ... that pissed me off after doing all the porting , carb and pipe modding hand work ... He used the excuse that he was building a better bike with Lifan big valve engine ... so I did that for him too and he sold THAT for profit as well ... which REALLY pissed me off ... NO more freebies for him ...

 

[headsmess]

i dunno, i just got the cams from pitster pro(aka dhz)

and yeah, they bolted in fine with only that little problem..

i guessed it was a kick back thing cause it only goes one way, but no, i didnt have one on the original cams... basically a mil of the rocker sits on it...theres a flat spot on it somewhere that is lower than the base circle,( that just happened to be where i weas setting the clearance) but the rest of the thing is higher, then has a big lobe on it...who knows anymore? i threw it away months ago...

lengthwise, theyre exactly the same as the stockers, and as a ducar 125 head as well. no problems there.

just looking at the ducar cams, and the lift appears to be the same, duration is definitely different...though im not about to measure anything.... just washed my hands

and damn those entreprenaural bastards that get mates to do things with no compensation... keep the NO FREEBIES moto within reach at all times... but ill keep that porting stuff in mind wheres my dremel? i dunno, maybe i get good engines, but i havent found much in the way of dags and casting flash in any of my ports yet... but still, a tidy up and enlargen could be the ticket i have a feeling one of my new 140s has had some work done to it...

 

[Fiddy@norway]

Porting is the way to go if you want more power, I ride a Loncin 110cc and a friend of mine rides a 125cc loncin, when we first got our bikes the 125cc would pull away from my 110cc with ease, so I purchased a better carb, a high comp piston and did some minor adjustments here and there, after these mods the 125cc still pulled away from my 110cc...

I was frustrated that my fat friend was faster than me, so I got interessted in doing my own porting, and with the guidance from Cactusjack here I did what I consider a mild to medium portjob, then my 110cc absolutely destroyed my friends 125cc!!!

my friend was of course pissed that I finally was faster than him, so a few months ago, when he was replacing his rings, I guided him through a very mild portjob on his bike, the result was that our bikes our almost even on the straights, my 110cc will hit harder in the midrange and rev much higher, while the 125cc still has more bottom end and will sign of earlier, but if we opened up the ports some more, the 125 would probably be a killer....

there is power to be found and it's not expensive either...

 

[Cactus Jack]

The 125's longer stroke is why it drops off earlier up top ... that's because the piston has to accelerate faster than it does in a short stroke engine ... As a result the expanding gasses have a more rapidly diminishing effect on driving the piston ... When the piston speed reaches a certain point , it's going as fast or faster than the rate of gas expansion ... so slowing the piston down with a shorter stroke actually increases peak HP ... As proven by the CRF150R's 21 HP stock with a 42.7 mm stroke ... If they had a longer stroke they'd be junk that blows up all the time ...

Engine manufacturers know that only too well ... that's why they go to multi cylinders ... a certain bore x stroke combo gives the greatest efficiency , the broadest power curve plus the highest peak power coupled with the highest reliability and dependability ... so the answer to building a bigger engine is to bank that known combo together rather than go to a bigger bore and stroke ...


It sounds like you did a good job on your ports mate ... The best way to advance your skills and knowledge are to port a head in stages then reassemble the engine each time to stop watch test the bike around a set course ... Then compare the lap times against your previous tests (including when the bike was bone stock) ... That's how I learnt and is how all the drag racers learnt ...

It's great to see you've put the info to good use ... then passed some of it on ... The main aim behind porting Davo's head , intake and pipe was to teach him how to do it and show him first hand how to assemble and tune his bikes so that he didn't keep hassling me all the time ... but he just can't get it ... He STILL can't adjust valves properly or tune carbs let alone do any other mods ... He's 42 and claimed he knew how to work on engines ... yeah ... 2 strokes which a kid can assemble ...

 

[Fiddy@norway]

Well I owe you for feeding me with info that broke that whole porting "mystery" into something understandable, the pics and long sections of info you sent me really motivated, I will get some better tools and have a go at the 110cc again when my Lifan 150 powered bike is up and running (My damn knee has slowed everything down) and I will take a more aggressive go at the head of that 110cc semi-auto engine I have laying around...

but anyways LOWLYF: If you just want power you really should look into doing some porting first, if you plan on hitting big jumps, throw some money into better suspension first.

 

[headsmess]

two strokes that a kid blinfolded can assemble... porting them is another matter entirely though...

reminds me of a cox .049 i was given...ran like shit...turned out one of the transfer ports hadnt been machined in. now theres a simple engine that will run both ways... occasionally while its running at full tilt...and you dont even notice. needed a bigger flywheel.

i still wanna see this knee, fiddy please? pretty please?

 

[Cactus Jack]

Yeah you need a special die grinder with a 90 degree angled head to get at the transfer ports from inside the bore ... I've done a few two strokes ...

Yeah ... Where's the gory knee pics ... I found this pic in a search ...

Staph Infection! on Flickr - Photo Sharing!

This link says it lives in your nose ... Ya' didn't pick ya' nose then scratch ya' knee without washing ya' hands did 'ya Fiddy@Norway ? ... LOL ...

Staph Infection Symptoms - Medical Symptoms Pages

 

[headsmess]

here we go, off topic again...

sorry lowlyf(love that name) this is sorta for cactus...

first ones interesting, cause its by crower, who obviously is one of the head honchos in drag racing cam design...who hasnt heard of crower cams?

Inside Bruce Crower’s Six-Stroke Engine: AutoWeek Magazine

and the one i wanted to find cause it was the one i read about ages ago...and its by an aussie(though im sure we all know about ralph sarichs orbital engine)and it was in a bike

DucCutters: "Beare Head" 6 Stroke (Beare Technology)...now if it was a doh crankshaft, maybe, just maybe... its how i always envisioned it to be...

cant find any decent pics, but can find a lot of references to the "6 stroke" idea...of varying degrees of success...

and then, theres a model one been made here...Model Engine News, April 2004

and finally, rcv, who have made a succesful business on alternative valve designs, mainly in the model engine department(and the 110 "cub" motor they have shown is not available, damit, they never took it beyond a 50cc prototype...RCV Engines Ltd Home Page

yeah yeah, alternative engines, and where are they now? stick to the otto cycle...though! the toyota prius runs an atkinson cycle(toyota prickus)

 

[Cactus Jack]

Ha ha ... yes we HAVE side tracked a bit ... but from reading what we've said Nick should have gotten a fair idea of what mods he can do to his engine ie port the head , match the intake manifold and exhaust ... fit a bigger than stock carb (depending on what he's already got) ... a 22 mm Keihin or Mikuni carb would work the best ... What carb are you running Fiddy@norway ? ... Davo claims he tried a "25" Mikuni which IS actually a 22 Mikuni ... and he said it went great everywhere but I never got a chance to verify what he says ...

Nick can buy a stock bore high compression piston and race cam which will really boost power ... but as F@N has stated ... the head porting is really where it's at with Loncins since they only have small ports ... GPX Jialings have bigger ports as stock (25 mm) ... and Lifan BVH engines have a 26/27 mm intake port ... As we stated ... you can go to a certain size in the carb and porting without losing bottom end grunt ... same goes for cams ... Akunars A-2 grinds are good all 'rounders ... for dirt riding you want good throttle response ,and good down low down pulling power with a decent midrange ...

Akunar cams ...

AKUNAR MOTORCYCLE CAMSHAFTS

Pistons ... looks like you have to hone the stock 52.40 bore 10 thou (.010") bigger .,..

AKUNAR PRO PISTONS

 

[Fiddy@norway]

I run a oval bore "26mm" mikuni, compared to the stock PZ16 carb, it's a huge difference. it let's the engine revv much higher and is easy to dial in, they are cheap too.
but I haven't tried a genuine round-bore carb on it, I'm guessing it should be a noticable difference, look around on ebay for a good deal, but remember, don't get greedy, bigger carb doesn't always mean more power, go to big and you end up with a pig that bogs everytime you crack the throttle.

 

[headsmess]

sorry to be a stick in the mud, but my loncin came with a carbie thats more what youd expect to see on a 50... 20mm maybe smaller, i havent measured it, but it is tiny. so i went and got a mikuni(fake?) that i think is a 26mm. any way, its almost twice the size. and the only difference it really made was to double the fuel i use. ie, i went from about 50km/l to about 25-30km/l. ok, i did gain about 4km/h on the top speed, but still...not happy, jan...and that 4km is downhill. still pulls about the same on the flat...100km.... still, pretty fast on 10 inch wheels and no, its not running rich either

yeah, when this damn piston comes from akunar...do they usually take more than a week? im getting pissed off... things from china on ebay are faster than this... and at the amount i spent on postage, id expect it to be here already...grrrr...any way, when it gets here i shall be doing some porting and leave the bvh conversion on the back burner... despite the so called financial crisis, my engineer mates just gotten a hell of a lot of work(something to do with ordering stuff from japan, thats got a 6 week waiting period, but orders are accumulated and only sent once a month) so if id started this say, a fortnight ago, no problems.... i really do hate to disturb people that are working on paid jobs, for what might be a pointless excercise... otherwise i might get impatiently patient and go the file method...

in fact, the loncin was pulling better as it was than the lifan 140 i just put in the bike...but i havent tuned it yet, so...and the flywheel pickup isnt quite where it should be, due to a previous owner and a snapped chain... and everyones out of stock for the new stator plate, arent they? typical....

so i have two bikes that are now basically unrideable...dont ask about the three punctures in a week on my other one....2 while going and hassling dhz for parts...


*goes and sulks and gets drunk*