Build a race motor

[Linc]

OK I want to build a race motor from scratch I have a 125 but need a max displacment of 115.5cc and to de-bore/stroke the 125 is proving very hard to get parts.

Budget is far from unlimited but I am willing to pay for some serious power; this thing will be raced at the highest level and I firmly believe one of these motors could show up the Jap and Italian powered machines we will be up against.

So seeing I can start with any motor what do you suggest?, 3 valve?....2 valve big head? I don't know.......Do any of you guys build motors?.

Linc

 

[noidea]

If 115cc is your limit then ide get one of those 110cc motors and go from there. I think they are zongshens?

Whats the motor youve got atm? Im looking for a lifan 125 if thats what youve got and interested in offloading it to boost ur budget, email me; [email protected] or private message...

 

[Linc]

Yeah the 110 is an obvious choice as a starting point but which one?; at the same time if I'm going to bore something out for max displacment it really doesn't matter if I start with a 90 as long as I end up with a good strong motor.

I dont think my 125 is a Lifan and I can't sell it ATM anyway.

 

[noidea]

no probs ;-)

 

[No-Fear]

what class are u racing in that needs 115cc max?
just wondering

 

[Linc]

It's going in to a kids race quad. The class is dominated by 90cc CVT 2st's but allows for 115.5cc (110+5%) 4st. Some of these guys plow big money into little johnys race quad one model is $8kUS ! and this is for kids.

All I can work out for now is that I need to start with a motor that has a 69mm tall cylinder???? I think what I'm aiming for is a 50.5mm bore x 57mm stroke torque monster but as I said I dont know where to start. Of course then I want to make sure the one I get has a strong clutch and g'box.

????????

 

[minidirt]

bloody hell, serious stuff.
I'd be thinking you'd want to start with a three valve 110, not sure of brand.
bigger higher compression piston, for 115cc, light port work, 26mm carby with port matched intake, large oil cooler, as it's going to be working hard, maybe advance ignition a bit.
but even then i have to say i think it would be lucjky to be with a trick 90 two stroke, what kind of power output do they have?

 

[Linc]

Thanks for the advice.

Yeah the thing will have to work pretty hard but the 2st quads have a heavier chassis and run a CVT auto transmission. That evens things up a bit and thats the whole point, I think this set-up will give the 2st's a good shake-up

The 3 valve 110 sounds good; I also want to check out a 54 x 54 and see if they have a 69mm cylinder height; if so I can get a 52mm hi-comp. That will see me at 114.7cc.

I'm checking out some motors today so I will take my tape measure and my limited knowledge and see what I can come up with.

Linc

 

[Mack]

I think a 3 valve 110 has great potential if budget isn't an issue.

 

[Linc]

Ohhh.....Ahhhhh.

Jialing JH152FMH
49.5 x 52.4
107cc
4Sp all up g'box
start in any gear

 

[Linc]

So I've started measuring things up.......no wonder people say these things liven up with a port matched inlet manifold.

22mm carbie....into
22mm inlet manifold with a big lip on one side.....
21mm manifold outlet that is not round or properly lining up with head.....
26mm manifold gasket.....
25mm inlet port that tapers (machined) down 1mm....

This is all before we even get to the inlet ports......ugly. And back out a 18mm exhaust port that is not round.

Linc

 

[noidea]

Yep, your right. The attention to detail is very low... good news really if your into diy mods.

Shape isnt a major concern, just make sure all joins flow nicely and you get a better finish. Let us know how it goes!

 

[Linc]

OK.....better.

26mm Carbie......into
26mm inlet manifold with slight lip
26mm smooth bore (lightly sanded) inlet tract
26mm manifold outlet

still into....

25mm inlet port that tapers (machined) down 1mm meaning it's really a 23mm inlet port.

The carb is a pretty impressive unit, as I said its a 26mm with an oval bore. I dont know if it's a chinese copy or not but it has Mikuni and japan stamped all over it. It may be too big but the price was right. I'll see how we go.

Linc

 

[Linc]

The good the bad and the ugly

Well the quad had it's first outing; mixed results but overall not too bad.

First race we found that the rear brake was dragging and was near impossible to roll after the race. Second Race, disconnected rear brake (only use front), muffler fell off after one lap......sounded cool.

How did it perform?; well against the 2-strokes it didn't do well out of the gate but 3/4 down the straight you could clearly see the we had a speed advantage, just got to encourage the boy too rev the thing out.........4th place. Best result ever for this kid.

Need a bit (alot) more torque, top end is great, suspension too soft; small things to sort out, will do before next race.

Linc

 

[Poppy]

PB for him and a lot of fun. As long as they go home tired and happy it's all worth it.

 

[Linc]

"tired and happy" is a gross understatment......that makes me "tired and happy" too.

 

[Linc]

Hmmmmm.......ProCircuit

 

[hinzey]

Hi dude that thing looks mean wher you race at also if dont mind asking how much it cost you ,i got a yamaha blaster 200cc 2stroke and getting one of the cheapo china atv's whith the same engine as thumpsters to ride bush so i dont have to worry bout dumpin the thing if i get coaught as campared to the blaster

 

[mad man]

ah har. Yes that is one fine looking bike there. Nice air your son got there. 4th pretty impressive. What are you doint to the quad next? it looks pretty good also the exhaust looks top notch. how much it cost? you'r son must be one happy lad. Why not race 2 wheels?

 

[eichkay]

Thats a cool little 4 banger quad.. Should check out the import section on www.planetminis.com , alot of the guys on there know an awful lot about these little motors.

If you want to get serious with the motor get a Innor Rotor Kit , that will lighten up the rotating mass on the igntion side. Or shave some weight and dont forget the oil sligher but dont get the IRK nd shave the oil slinger..

The T4 exhaust are a good exhaust, I found a aftermarket CDI does wonders for the maping on the ignition and gives some good plug on power gains..