fitting a 140cc head on a 125...

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Peter1230

Peter1230

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Hey guys,

Just wondering if a lifan 140cc block/head with piston will bolt on to a lifan 125cc engine.. or will i need an adapter.. can someone point me in the right direction.

Thanks
 
you need to no the stroke of the crank on you 125 is it 55.5mm 57mm i think most 140cc crake stokes are 57mm and 59mm i no the xy140cc is 57mm so if you were to use an xy140cc bore your piston with sit to far in the bore and thats no good for you comp just buy a bigbore kit off ebay i have 1 for sale second hand $100 if you in melbourne s/e subs
NEW 146CC TB BIG BORE KIT FITS JIALING 125CC YX 140CC - eBay Other Makes, Bike Parts, Motorcycle Parts, Accessories, Cars, Bikes, Boats. (end time 17-Feb-09 16:21:50 AEDST)
 
The piston won't go as it has a 14mm gudgeon pin in a 140 and only a 13mm gudgeon pin in the 125.
 
Lifan 140's have a 15 mm gudgeon pin , Lifan 120/125/127/138's all have a 14 mm pin ... I bought a TB 150 cc ceramic BBK to suit the Lifan 140 and it has a 57 mm piston with a 13 mm pin ... but in the kit there's a bronze bush that goes into the small end of the rod to adapt the 13 mm pin to 15 mm rod bore ...
 
yep...and the orig. barrel of the 140 is too long and heavy as fukk....so better get a bbk from t-bot or akunar or so
 
The head off the 125 will be better to run than a 140 head since it has a smaller chamber and will give more compression ... The 140 head has a big squish band around the outside whereas the 125 BVH head doesn't ...

The best thing to do would be to either buy a (P I153 57MM 14#) TB 57 mm ceramic bore kit with a 14 mm pin piston and cylinder that's the proper height to suit a Lifan 125 OR buy an Akunar set up as the mountain says ... Stick a TBW300A cam in while you're at it and a 26 mm carb ...


Either way , it's better to run the 125 head but just be careful of how you kick start the engine since it'll have more compression ...

While we're at it we might as well ... Hack , slice , and chop thru the BSHP figures that are getting thrown around on forums ... The FACTS are ... that you can't make any more genuine HP than the carb venturi will flow at atmospheric pressure ... Way too many people are making exaggerated claims when it's physically impossible to make what they're claiming with the given carb size that they're running on the engine ... They'll have you believing that each of the $10 notes they own are worth $15 ... $5 more than your own $10 notes and every other $10 note you've ever seen in your life ... IF you let them ...

If you check thru the chart below , (ACCORDING TO IT) you'll see that you need a carb with a 32 mm bore thru the slide (venturi) to make 20 hp ... just like the the carb the CRF150R's have as stock to allow them to make their 20 HP ... A MOLKT is only good for a genuine 10 HP ... A genuine VM-26 mm Mikuni OR 26 mm OKO is only good for 12 genuine HP ... A 28 mm OKO is only good for a genuine 14 HP etc etc ... And the chart is quite accurate when you start looking at production bike HP figures and compare it with the carb sizes they are running ...

http://www.classichonda50saustralia.com.au/uploads/techinfo/images//CarbSelectionChart.jpg
 
and once you get too big a carbie, it starts dying when you open it wide on the takeoff...isnt that why those xr200's had twin carbs? airspeed drops too much....
 
Yes , you're spot on ... You can get better response by using a cammed throttle or an accelerator pump carb ... But in a nutshell , it's best to pick a sensibly sized carb ... A 26 mm round bore carb will work OK with a BVH ... but a 24 mm carb will be more responsive on the bottom end ...
 
interesting advice from dhz when i went to go get my new pipe the other day..."dont bother with the big bore kit, just do the cams"

makes sense...whats 10-15cc gonna give me? but replacing the piston maybe...

and avoiding making a sale...wow.

what got me was taking the restriction from my old posties intake...had to rejet to a 0.8 i think. all it did was take my mileage down by 80 km a tank. then when i went back to origional...it stayed like that:confused: weird....
 
What cams did they recommend ?
 
Last edited:
headsmess said:
interesting advice from dhz when i went to go get my new pipe the other day..."dont bother with the big bore kit, just do the cams"

makes sense...whats 10-15cc gonna give me? but replacing the piston maybe...

and avoiding making a sale...wow.

what got me was taking the restriction from my old posties intake...had to rejet to a 0.8 i think. all it did was take my mileage down by 80 km a tank. then when i went back to origional...it stayed like that:confused: weird....
Click to expand...

mmm..got my doubts...a BBK don't put so much strain on the engine as a agressive cam does...so if you want power over reliability...get both :p:p
 
he didnt...he just said change the cams...
ended up buying them off him today anyway...
(was that a trick question?)
not really much choice is there? unless you grind them yourself. or pay someone.
(this just gave me an idea...)

better make a difference, or ima gunna shrug...
im leaving the bigbore til last if i even bother...

main issue i got is my clutch:eek: one minute it slips, one minute it grabs. dodgy linkage set up. too many pivots and not enough movement. (like 1mm in the end)do some mods and make it a bit more direct. seriously, its the worst clutch ive come across... no feel to it at all.
adjust it, try it, fine...walk away, come back...stuffed. etc etc. lifan ip52. should take a pic of the before and after when its(hopefully) fixed. not good when youre on the road. always thinking "will it slip this time or stall?"
 
hey, srry to bring up a old thread but wood it work the other way, a 140cc barrel on a 125cc head, or jst easyer to buy a 146 big bore kit?? and i have a 54mm bore and stroke wood a 57mm kit work
 
You're better off to buy the 146 kit ... it'll make your engine into a 138 ... ( 57 mm bore x 54 mm stroke = 137.79 cc) ... As long as your 125 engine has a big valve head with the 2 bolt valve adjustment covers ... the cylinder stud pattern should fit ... But you could also buy a high compression piston kit from Akunar and have your stock cylinder bored to suit by a machine shop ...

You're better off to run the 125's BVH since the combustion chamber doesn't have the big compression reducing quench ring that the 140 heads have ... PLUS ... You can run a TBW0300A cam which is heaps bigger than the cams sold on ebay ... OR you can run a Z-40 cam ... You need to run high lift springs as well ...
 
A comparison pic between a Z-40 / R-20 / and stock Lifan cam ... All Honda type cams which fit Lifan 120/125/127/138 BVH heads ...

Z40R20STOCKCAM.jpg


Dratv Z-40 cam ...

BCIZ-40CAM.jpg


Lifan 140/150 ... Loncin 120 type long cam ... (AHP long type race cam) ...

AHP257Lift73mmlongcam.jpg
 
Cactus Jack said:
You're better off to buy the 146 kit ... it'll make your engine into a 138 ... ( 57 mm bore x 54 mm stroke = 137.79 cc) ... As long as your 125 engine has a big valve head with the 2 bolt valve adjustment covers ... the cylinder stud pattern should fit ... But you could also buy a high compression piston kit from Akunar and have your stock cylinder bored to suit by a machine shop ...

You're better off to run the 125's BVH since the combustion chamber doesn't have the big compression reducing quench ring that the 140 heads have ... PLUS ... You can run a TBW0300A cam which is heaps bigger than the cams sold on ebay ... OR you can run a Z-40 cam ... You need to run high lift springs as well ...
Click to expand...

hey, thanks but how can i tell if my heads a BVH? it doesnt have the two bolt valve covers, is there any other way to tell?? btw its a zongshen
 
Only by pulling the head off and checking the valve sizes ... But I think the Zongshens only have the CRF50 stud spacings so you're most likely out of luck with one of those Lifan BBK's ... It looks like an Akunar piston kit and bore job for you !!!!!!
 
um, the only other thing ive noticed with BVH heads, be they a lifan or ducar, is a little triangle symbol on the fins , plug side, top fin, near intake port.

havent seen the symbol on any normal/e22 style heads.
 
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