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Supermot Mini-Pit (CRF50 rep)

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binge
Emo Kiddy



Joined: 02 Jul 2004
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PostPosted: 13:48 - 31 May 2011    Post subject: Supermot Mini-Pit (CRF50 rep) Reply with quote

After running the mid-size pit bikes for the past two years.
I not only fancy a change to something a little smaller, and more "fun".
I also want to get my girlfriend out on track too, starting on some of the smaller tracks like Caxton.

Another benefit of this bike, (If I'm allowed), will be to chuck it in the back of the car when I got to watch the racing at Brands hatch, to get around the circuit. Especially when they are racing the GP Circuit.


So here's what I've got so far:

I started out by building a 125cc engine, out of 3 different types/makes of engine. But the result is a very fast 125.

The bottom end is from a Masai Road legal. Which uses the YX140 crank cases, but with a conventional 1N234 gearbox, rather than the all up boxes in the YX engines.

The Barrel and piston are from a Lifan 125 Primary clutch engine. Known for having big oil ways and a bulletproof bore.

The head is a Gen 3 YX140, big valve head. Fitted with a high lift Z40 cam, and an exhaust valve Mod.
The mod is to use the Inlet valve, from a 125 small valve head, as the Exhaust valve in the YX140 big valve head.
The valve is the same size, but the stem is 1mm longer, giving higher lift, and a longer exhaust valve duration.

Mikuni VM24 carb, which has been bored out to 26mm on the upper half of the venturi. So at low throttle, it'll have the VM24 response for the smaller cc. But at full whack, it'll have the airflow of a VM26.

And a 28mm underslung Stainless Powerpipe from OORacing.


The engine set up I have, is the same as what they used to run in the LCRRC 125 league. They can produce up to 17bhp at the wheel if set up right. Cool
So it'll knock the socks off a YX140 in standard trim.

Bit ruff in the picture as it's only placed together to make sure the oil ways line up etc.

https://a1.sphotos.ak.fbcdn.net/hphotos-ak-ash4/226996_10150196421310606_506045605_6927448_4431713_n.jpg


The shock I will be using is a Fastace BS58RC. It's only got a 250lb spring on it. But it's a nitrogen charged shock, so it doesnt rely entirely on the spring for the compression.
It's fully adjustable, and very light weight.

https://a1.sphotos.ak.fbcdn.net/hphotos-ak-snc6/228340_10150194473415606_506045605_6916720_8007622_n.jpg


The forks are from a small pit bike. I dont know exactly what they are off, but I think it's something like a Demon X Minipit, or a Stomp Juicebox.
Either way, they are nice and short, but have good internals.
I've pre-loaded the springs, and put thicker oil in them to give them a more SM feel. But to be honest, suspension set up isnt vital on a mini pit. They aren't the best at SM. But a hell of a lot of fun! Very Happy

https://a3.sphotos.ak.fbcdn.net/hphotos-ak-snc6/227256_10150194361820606_506045605_6916183_6205864_n.jpg


My wheels are scooter items. I will be running two AP50 front wheels.
They are 10", 2.5" wide, and run tubeless.
My Grandad has made up a sprocket carrier for me, with a 3rd bearing support in it, machined the wheels to take bigger bearings, and fit the sprocket carrier on. What a legend!

https://a8.sphotos.ak.fbcdn.net/hphotos-ak-snc6/226987_10150190671505606_506045605_6884923_7927196_n.jpg

https://a6.sphotos.ak.fbcdn.net/hphotos-ak-ash4/251714_10150203299905606_506045605_6990826_460345_n.jpg


And the frame I am running, is an RCF50 frame.
It's basically a Chinese replica of a Honda CRF50 frame. So it's proper CRF50 size too.

https://a8.sphotos.ak.fbcdn.net/hphotos-ak-snc6/246633_10150205141495606_506045605_7012303_5896356_n.jpg


I'm waiting on some more parts to arrive. But it'll be running Pro-taper SE bars, Proflex plastics in Red and white. And I have had some stock Honda CRF50 graphics made up by a guy I know with a plotter.


Will update with more pictures when bits arrive.




Ben
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Damon
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Joined: 24 Aug 2007
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PostPosted: 15:25 - 31 May 2011    Post subject: Reply with quote

What a fun little project Smile

Keep us updated
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Gazdaman
I did a trackday!!!



Joined: 12 Aug 2004
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PostPosted: 18:42 - 31 May 2011    Post subject: Reply with quote

Agreed, very cool project.

Gaz
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binge
Emo Kiddy



Joined: 02 Jul 2004
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PostPosted: 20:49 - 31 May 2011    Post subject: Reply with quote

Couple more pictures for you guys.
Today I got the motor fitted. Bit of petrol, and an exhaust without an end can.
It started up first kick, on a carb which is jetted for my YX160. Laughing

So that big valve, gas-flowed cylinder head, really must be making it a petrol thirsty engine.

It revs up, and right out very nicely too. So well impressed with my own engine building there.

https://a5.sphotos.ak.fbcdn.net/hphotos-ak-snc6/253745_10150206125135606_506045605_7022970_5478757_n.jpg

https://a6.sphotos.ak.fbcdn.net/hphotos-ak-snc6/255144_10150206125470606_506045605_7022974_4259296_n.jpg


And just for comparison, this is it along side a Supermoto CRF70 based bike, which isnt all that tall anyway. Just shows how small the mini is.
Bearing in mind it still needs tyres and a seat, which will add about another 9 or 10 inch to the seat height.

https://a2.sphotos.ak.fbcdn.net/hphotos-ak-snc6/250884_10150206125670606_506045605_7022976_4769724_n.jpg
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neatbik
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Joined: 27 Jun 2007
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PostPosted: 21:41 - 31 May 2011    Post subject: Reply with quote

Awesome, and i want one.
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Stalk
Brolly Dolly



Joined: 26 Dec 2005
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PostPosted: 22:45 - 31 May 2011    Post subject: Re: Supermot Mini-Pit (CRF50 rep) Reply with quote

binge wrote:

The valve is the same size, but the stem is 1mm longer, giving higher lift, and a longer exhaust valve duration.



Excuse me for asking but, how would a longer valve stem give higher lift and longer duration? Surely this is dictated by the cam profile and a longer stem would mean a thinner adjusting shim (assuming OHC) or the adjustment screw would not be screwed in so far (assuming rocker arms / push rods)

Genuine question, not trying to be clever.

Cheers
Stalk
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binge
Emo Kiddy



Joined: 02 Jul 2004
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PostPosted: 23:00 - 31 May 2011    Post subject: Re: Supermot Mini-Pit (CRF50 rep) Reply with quote

Stalk wrote:

Excuse me for asking but, how would a longer valve stem give higher lift and longer duration? Surely this is dictated by the cam profile and a longer stem would mean a thinner adjusting shim (assuming OHC) or the adjustment screw would not be screwed in so far (assuming rocker arms / push rods)

Genuine question, not trying to be clever.

Cheers
Stalk



I'm really not sure.

I once did it few months ago when a mates bike bent a valve.
To keep him riding, I "bodged" a 125 inlet valve into his YX140.

Later on, speaking to one of the engine tuners for one of the FAB racing teams, he said they do it to all their race bikes.

I never really put any thought into it to be honest. Embarassed



Ben
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Pete.
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PostPosted: 23:14 - 31 May 2011    Post subject: Reply with quote

Stalk is right, lift is the difference in distance between the base circle and lobe height from camshaft centerline less the valve clearance.
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132.9mph off and walked away. Gear is good, gear is good, gear is very very good Very Happy
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Damon
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PostPosted: 07:16 - 01 Jun 2011    Post subject: Reply with quote

unless he's using the same shims with a longer valve stem. This would make tolerances very tight, giving a tad more lift?
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binge
Emo Kiddy



Joined: 02 Jul 2004
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PostPosted: 08:03 - 01 Jun 2011    Post subject: Reply with quote

I've messaged the chap who told me to do this, to find out a correct reason why it's done.
Stem length was just my initial thought, but there is more than likely another reason behind it.



Ben
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binge
Emo Kiddy



Joined: 02 Jul 2004
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PostPosted: 21:20 - 01 Jun 2011    Post subject: Reply with quote

Goodies have arrived.

Internal wheel spacer, and a set of 15 to 12mm reducers for the axles.

https://a4.sphotos.ak.fbcdn.net/hphotos-ak-snc6/249656_10150206883800606_506045605_7029391_881908_n.jpg


The bike it's self. Literally needs the tyres and plastics fitting, then it's done apart from a few odds and sods like chain, and rear master cylinder.

https://a6.sphotos.ak.fbcdn.net/hphotos-ak-ash4/248429_10150206983290606_506045605_7030069_753666_n.jpg

https://a8.sphotos.ak.fbcdn.net/hphotos-ak-snc6/253512_10150207003585606_506045605_7030257_2298140_n.jpg

https://a4.sphotos.ak.fbcdn.net/hphotos-ak-ash4/249244_10150207003815606_506045605_7030262_2657392_n.jpg


And massive stopping power!

https://a7.sphotos.ak.fbcdn.net/hphotos-ak-snc6/254001_10150207003875606_506045605_7030264_6368573_n.jpg




Ben
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binge
Emo Kiddy



Joined: 02 Jul 2004
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PostPosted: 20:54 - 02 Jun 2011    Post subject: Reply with quote

New bits arrived today.

I'm after some white CRF50 rear numberboards now. Must be in good nick.
Tempted to just buy a full set then flog the rest off.

Graphics are applied from Zander. F*cking awesome job!
Tyres are fitted, Front looks a little wide, but it'll do.
Everything is ready to go now. Just waiting on a couple more bits to arrive.

Gotta fab up a rear master-cylinder mount too.
Also gotta swap the bars over when they arrive.


Cant wait to ride it:


https://a6.sphotos.ak.fbcdn.net/hphotos-ak-snc6/248190_10150207639940606_506045605_7034626_2040341_n.jpg

https://a5.sphotos.ak.fbcdn.net/hphotos-ak-snc6/248257_10150207746285606_506045605_7035651_5675586_n.jpg

https://a8.sphotos.ak.fbcdn.net/hphotos-ak-snc6/253746_10150207746535606_506045605_7035656_5567372_n.jpg

https://a2.sphotos.ak.fbcdn.net/hphotos-ak-snc6/250934_10150207746575606_506045605_7035657_6774679_n.jpg

https://a8.sphotos.ak.fbcdn.net/hphotos-ak-ash4/251539_10150207746745606_506045605_7035661_773345_n.jpg
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SpicyBlimp
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PostPosted: 22:08 - 02 Jun 2011    Post subject: Reply with quote

Looks pretty nice already, can't wait to see it finished!

You'll have to put a detailed price list at the end for us nosy (contemplating something similar) buggers Laughing
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Shaft
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PostPosted: 22:11 - 02 Jun 2011    Post subject: Reply with quote

Probably a dumbass question, but why a slick on the back and tread on the front?
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binge
Emo Kiddy



Joined: 02 Jul 2004
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PostPosted: 08:05 - 03 Jun 2011    Post subject: Reply with quote

Shaft wrote:
Probably a dumbass question, but why a slick on the back and tread on the front?



Because I got them for 99p each on ebay. Laughing

Ideally it should have MC0 (slicks) front and rear.
The front (MC21) is actually an MC0, but with a wet pattern cut into it from factory. But they work better in the dry than they do in the wet, so nobody uses them for the wet anyway.

Also, because it's such a light bike, the front wheel wont heat up very easily either. So a wet tyre up front should help things in the grip department.


Iain 007, Price wise, Very cheap so far, for what it is.
Probably doesnt even owe me £200 yet. And there is easily £400 worth of bike there.



Ben
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binge
Emo Kiddy



Joined: 02 Jul 2004
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PostPosted: 21:45 - 03 Jun 2011    Post subject: Reply with quote

Today I drilled the axles on the mini and fitted some bobbins on it.
The new bobbins I get from my mate Eadon will be going on the KZ.

Been busy tonight. And while I was in the garage, I decided to lower the KZ160SM too.

https://a4.sphotos.ak.fbcdn.net/hphotos-ak-ash4/250997_10150208740755606_506045605_7044273_1290404_n.jpg

The chain always used to rub across the top of the swing arm.
My only concern now, is it rubbing on the underside of the swing arm.

If it rubs, I may have to go with a 17t or 18t front sprocket, and up the rear by whatever it needs to be, to keep the same ratio.


I also got the mini out, stuck it on a stand in the garden, sat on a seat and just looked at it.
Something doesn't look right. And I think it's the handle bars.
I'm fitting some Pro-taper SE bars once they arrive, but still not certain they'll be high enough.
It needs some BMX bars on it me thinks.

I also think the front end needs to be even lower.
So I may have to speak to a mate about shortening the fork stanchions. I know it's possible.

https://a7.sphotos.ak.fbcdn.net/hphotos-ak-snc6/252487_10150208750885606_506045605_7044332_4482649_n.jpg

https://a4.sphotos.ak.fbcdn.net/hphotos-ak-ash4/254400_10150208750990606_506045605_7044334_1254802_n.jpg

https://a6.sphotos.ak.fbcdn.net/hphotos-ak-snc6/248322_10150208751145606_506045605_7044335_1897024_n.jpg

https://a8.sphotos.ak.fbcdn.net/hphotos-ak-ash4/251657_10150208751260606_506045605_7044336_2072055_n.jpg

[img
https://a2.sphotos.ak.fbcdn.net/hphotos-ak-snc6/251486_10150208751355606_506045605_7044337_1076537_n.jpg[/img]

https://a1.sphotos.ak.fbcdn.net/hphotos-ak-snc6/248950_10150208751470606_506045605_7044338_4137800_n.jpg

https://a7.sphotos.ak.fbcdn.net/hphotos-ak-snc6/251442_10150208751685606_506045605_7044339_6066568_n.jpg

https://a6.sphotos.ak.fbcdn.net/hphotos-ak-ash4/249775_10150208751955606_506045605_7044340_2667221_n.jpg

https://a8.sphotos.ak.fbcdn.net/hphotos-ak-snc6/253725_10150208752380606_506045605_7044343_4475726_n.jpg
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tvchimp
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PostPosted: 02:04 - 04 Jun 2011    Post subject: Reply with quote

chain looks slack! Wink
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Pete.
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PostPosted: 04:23 - 04 Jun 2011    Post subject: Reply with quote

USD forks you usually shorten with a spacer of some kind internally. I forget the details but there's no need to cut them.
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132.9mph off and walked away. Gear is good, gear is good, gear is very very good Very Happy
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binge
Emo Kiddy



Joined: 02 Jul 2004
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PostPosted: 08:35 - 04 Jun 2011    Post subject: Reply with quote

Pete. wrote:
USD forks you usually shorten with a spacer of some kind internally. I forget the details but there's no need to cut them.



Oh really?

Will have to do some digging to find that out. Very Happy

Gonna start taking that motor out of the YZF today. PITA.
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Gazdaman
I did a trackday!!!



Joined: 12 Aug 2004
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PostPosted: 12:39 - 04 Jun 2011    Post subject: Reply with quote

Did you just drill and tap the axles for the sliders? I've got a set in the garage waiting to go on the stomp and just haven't got around to it yet.

Gaz
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binge
Emo Kiddy



Joined: 02 Jul 2004
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PostPosted: 13:53 - 05 Jun 2011    Post subject: Reply with quote

Yup,

The Stomp KZ axles, I put in a pillar drill, and drilled that way.
The Axles on the mini, I just laid it on it's side, and ran the drill straight into the end of the axle.

The job is just as neat, and took about an hour less time to do.





Ben
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B10Hazard
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PostPosted: 20:53 - 05 Jun 2011    Post subject: Reply with quote

I think it need higher bars like you say bmx bars or something and the back end lowering. Thats what id do anyway . .
Looks like a right load of fun though
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Shaft
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PostPosted: 23:54 - 05 Jun 2011    Post subject: Reply with quote

binge wrote:
Shaft wrote:
Probably a dumbass question, but why a slick on the back and tread on the front?



Because I got them for 99p each on ebay. Laughing

Ideally it should have MC0 (slicks) front and rear.
The front (MC21) is actually an MC0, but with a wet pattern cut into it from factory. But they work better in the dry than they do in the wet, so nobody uses them for the wet anyway.

Also, because it's such a light bike, the front wheel wont heat up very easily either. So a wet tyre up front should help things in the grip department.

Ben


All sounds very reasonable, but why can't I find tyres for that money?!

If any of your pitbike chums have got any 3.50/10 knobblies going begging, give me a shout.

BTW, I don't agree about the bars, I think they look OK and Mrs Binge seems comfortable with them, or at least, as comfortable as you can be with your knees under your chin Very Happy
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binge
Emo Kiddy



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PostPosted: 09:59 - 06 Jun 2011    Post subject: Reply with quote

B10Hazard wrote:
I think it need higher bars like you say bmx bars or something and the back end lowering. Thats what id do anyway . .
Looks like a right load of fun though



BMX bars will be my aim.
But the back end is too low as it is.
it's either raise the rear, or lower the front, to get the geometry correct for Supermoto riding.

Think lowering the forks will be my best bet. If I fit BMX bars, I should be able to pull the fork legs up through the yokes another 20mm.



Ben
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binge
Emo Kiddy



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PostPosted: 14:30 - 06 Jun 2011    Post subject: Reply with quote

Shaft wrote:

All sounds very reasonable, but why can't I find tyres for that money?!

If any of your pitbike chums have got any 3.50/10 knobblies going begging, give me a shout.



A lad on the other channel is selling a Kenda Carlsbad tyre (10") with tube for £12 delivered.
it's brand new.

https://www.pitbikeclub.co.uk/showthread.php?t=68225
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