Mikkh's WPB 125 CRF 70 framed build

[mikkh]

Are the pipe mounts and pipe angle from the head same on the CRF style and KLX style motors? I´m asking because I bought big bore exhaust system meant for KLX style, it looks like i need to bend the pipe a little to fit my lifan.

 

[my67xr]

Yeah they are different styles and angles.
The Crf port engines have a long flange tube and 6mm sud's.
The KLX port's have a short flange tube and 8mm stud's and a different angle too.

So to use a KLX port exhaust you'll need to either cut the end off and weld a CRF flange pipe and flange plate onto it at the angle you need.

Or you can buy an adapter pipe/tube and fit it between the head and pipe.

Adapter pipe and stud's
NCC Pipe Adapter

Here's a pic of one fitted (borrowed from PM)

TBolt US also mention sometime's you can get away with using 2 or 3 copper crush gasket's to make up the gap.
https://tboltusa.com/store/tech.php?pID=85/Exhaust+Pipe+Adapters

 

[mikkh]

Nah I just used my old header pipe although it´s rusty. Didn´t want to risk bending it because I might go the KLX style engine route in the future.

Little bit of offtopic: I´m thinking about building 10/12 wheeled A swingarm type pitbike with Elka rear shock. Is it even worth thinking? Or the H swingarm beats the A swingarm without any questions? Could somebody recommend me hubs and spokes for 10/12 setup (thinking about using them for SM pro wheels)?

 

[gottagetacheaperhobby]

Are you planning on racing it? Thats probably the only reason I would be building a bike with that wheel combo, pretty useless on trails..

 

[mikkh]

I´m not planning to race my pitbikes (maybe some visits to local tracks, but thats it). 10 inch rear is fun for whelies. And the other setup would be based on crf 50 frame.

 

[my67xr]

There are quite a few around using the H type rear swingarm
I have a CRF50 based 140cc 12/10 with a H swinger, i reckon that'll be a lot of fun to muck around on.

 

[mikkh]

Only air filter, clutch cable, oil cooler and rear brake to go. Then it´s finished:applaudit: .

About the crf50 style build I´m planning I have aluminium A type extended swingarm, that´s why I even considered the A style swinger.

 

[mikkh]

Did a test ride today. The engine backfires and pops alot. Something to do with electrics system. At some moments it revved good and didnt pop at all. Finally the spark got lost. The engine felt very slow and weak.

The kick back was massive. It even blew off the carby two times.

 

[my67xr]

Might pay to check your stator reading's again, check it hasn't shorted out the winding's.
But my guess is that the cdi may have cooked ?

Have you double checked how many degree's before tdc the cdi is firing?

 

[mikkh]

tested again it had spark and after few minutes it was lost again. Now I need to find out where my other CDI is . The clutch seems weird too like it´s slipping. (Z160HO clutch and lifan wavy washer; should I try it with Z160HO countershaft, I have one laying around. Or i could just buy a 5 plate clutch.

 

[mikkh]

Got it running. The clutch is definately slipping. What could cause it? Btw 5 plate clutch is on the way.

 

[my67xr]

The clutch cover must be too close to the basket still,
there mustn't be enough room for the clutch pusher (#8) to retract into the cover and it's still hard against the clutch bearing

 

[mikkh]

Grounded the clutch cover for more clearance and it seems to be working well. Couldn´t start it though beacuse of the broken woodruff key. It took the magneto with it. Lapped the new magneto with valve grinding paste to be sure it fits. I will try to find suitable washer for woodruff key (cut it myself).

 

[mikkh]

Well the carb is too rich (porting and Z40 should cure that :action-smiley-033: ). And the clutch seemed like slipping again (or the carby problem, doesnt want to pick up revs, seems like no power; when engine was cold worked excellent).

 

[gottagetacheaperhobby]

Have you played around with your jetting at all? Plenty of tutorials on here..

 

[mikkh]

Haven´t played around with jetting beacuse I´m planning to use ported and milled yx140 head with stiffer springs and correct squish band and z40 cam. The head that´s currently on is from a lifan 120. Got the z40 for lifan head, need 6902 bearing for the cam end to fit in the yx head and then I´ll try it out.

 

[mikkh]

Full teardown of the engine coming in the next few weeks :boom: .
Does anybody know what gear to use to convert primary clutched crank to secondary ? Is there some part from big jap manufacturers. I was thinking about welding the cast basket and primary gear together (will add pictures sometime to clarify the idea). Will the cast hold up welding? Tried to weld it with mig, it developed cracks with too fast cooldown.

 

[mikkh]

Any ideas on the primary gear coversion. Might buy a daytona 150 crank afterall. Would it fit?

 

[my67xr]

Why would you want to weld the primary gear to the basket ?
You can buy a billet basket kit with the gear being part of it
frizione made in italy

I don't know if the crank's will interchange
But there was a stroker crankshaft available for the Daytona 150's
MOTOSYKO - the mini-bike specialists. Daytona 160cc race crank 85808

Are you going to try and strengthen the r/h case on the lifan ?
They are made with melted down coke can's i'm sure


Engine case's for the primary clutched engine's will need to be case bored for the bigger o/d on the skirt of the cylinder too

Imo save yourself the headache's, sell the lifan 150 engine and cut your losses, then buy a Daytona engine

 

[mikkh]

I could get the daytona 150 crank for cheap which has 58.7 stroke. Is the cylinder height 78mm on both lifan 150 and daytona 150?

The welding idea was for the primary clutched engines not lifan 150 (for making the daytona style primary gear, couldn´t find it anywhere, but there should be one included with daytona clutch). Basically I have numerous primary clutch cranks laying around in excellent condition and I would like to have an use for them. And the primary clutched engines I have fit lifan 150 cylinder no problem. One thought was to use lifan/zs 150/155 clutch + lifan 150 crank and side cover. It would kick through the trans.

Are the zs and lifan clutch basket kickstart gears different?

The clutch baskets, both lifan 150 and z155 have lots of play on them (move left and right on the mainshaft not left and right wobble). Thinking about curing it with using washers underneath the wavy washer.

Havent thought about the strengthening but these cases can be welded with good results.

Where is the fuel tank rubber grommet supposed to go on the crf70 ?