67mm kit

[Phil67]

Ok, had my cases bored, got all new parts and reassembled the engine. Had the head ported and chamber polished etc, port matched the manifold all good to go. Got a new shift drum and forks cause the ones that came out had a fair bit of wear. Engine went together really easy, they really are simple. Whilst I had the cases apart I cleaned up all the oil returns in the cases which had heaps of burs, one was even fully closed with casting, one of the ones next to the crank bearing. I de burred all the oil areas on the head as well, was gonna paint the internals aka the old boat race engines but thought that was wayyyy overboard. So engine is back in let's fire it up. First kick, this has some serious compression, can barely move the kick starter. Second kick it backfired and almost broke my leg. Third kick it fires, nice. It needs a decomp for sure, you just can't kick it, too much comp. so with the kickback I will have to do the flywheel mod to retard it a litte, should give more bottom end grunt as well, I doubt losing a bit of top end will matter with 201cc. Now the best thing, went to put it in gear and it got jammed, awesome, cases are split again now to Suss out what shimming it needs.

So if your thinking of going 67mm, do it, but MUST have decomp, either cam, button or lever. I will get the lever I reckon. Oh also leave out the base gasket, the piston is wayyyyy down the bore, doing this gives you heaps more bang too.

 

[zwebx]

Good to hear mate im considering whether to bother with my pitty or selling it and going to big bikes..

 

[Blender]

Good to hear mate im considering whether to bother with my pitty or selling it and going to big bikes..

Why not both

 

[zwebx]

Why not both

Apprentice wages...

 

[Phil67]

2 races down and maybe one practice day the case decided to let go. I thought it was just the clutch cover but when I pulled that off the hole centre case has a split from top to bottom, not a small one either. Found some teeth in the case so thought it was the gearbox, nope, it was the TB Parts billet clutch basket left some teeth behind, nice, back to a stock basket I suppose. Gearbox is still like brand new, so I should get out of it with just a new rhs case, case bore and kick start idler gear, bonus.
Rode the bike like that for 2 motos at the races with oil pissing out, the ol girl still held together!
Going to do the flywheel mod to help kickback at starting while im at it. Oh if you have the manual decomp lever like I have, put Teflon tape on the adjuster the o ring it comes with just doesn't cut it.

3 weeks till the races!

 

[zwebx]

**** 3 weeks.. id better start working on mine..
I hope yours gets together okay

 

[Phil67]

It'll go back together no worries. I like these yx motors, I'm determined to stick with them. The long start straight at Tooradin will make me decide if it needs more power or not, if I get a hole shot that is.

 

[Phil67]

Back together like a dream, just gotta tighten the clutch, crank and flywheel nuts with the old rattle gun at work and I'm done. Went to the track yesterday, it's got some tight turns and some long flat out sections, should be good.

 

[Phil67]

Engine is back in the bike. Set up the decomp, turned over the engine half a dozen times, put the plug boot on and bang, fired first kick. The flywheel mod has helped starting this mongrel unbelievably, it's like a stock 50 to start now, very pleased, should save the kick start gears and case!

If I knew a good welder I would go 70mm next time.

 

[zwebx]

Engine is back in the bike. Set up the decomp, turned over the engine half a dozen times, put the plug boot on and bang, fired first kick. The flywheel mod has helped starting this mongrel unbelievably, it's like a stock 50 to start now, very pleased, should save the kick start gears and case!

If I knew a good welder I would go 70mm next time.

Wicked man Good luck to your new cases the flywheel mod should let them last a bit longer hey...
i will ask around i know a welder not sure how he does alloy but

 

[my67xr]

Phil with your 201, how's it holding up ?

what is left of the 3.5mm-4mm's of alloy between the skirt and timing chain void once it's been bored ?
it is worth having the skirt turned down a mm ?
and i remember you mentioned having a good conrod in your engine, are there any markings i can check against mine ?
and how is the TB Piston holding out ?

i'm still working things out for my Z155Ho, i have a fair list of parts so far i need to find for it.

 

[Phil67]

Going well Craig.

When case boring there is very minimal left, almost looks like it bows it out at the side, but it's ok. I know some do turn the skirt down, but it's not worth it I reckon. Hmm can't remember marking son the rod, it's just a yx 160 rod, nothing special. I've case bored mine twice as i had the kick start gear circlip come off and hurt the case. When i had it apart it all looked good as still. It was only one race old though.

Not TB, it's a china special, probably form the same factory! Same kit as that pommy mob sell, I forget their name. It has a much larger dome on it, same as the 63 kit I used to run. Ceramic cylinder.

All in all it cost me the same as a stock or 63mm kit so I didnt mind doing it. Case bored it at work so no cost there also. I added the manual decomp, absolute must, you won't start it without one. Kosta runs the same set up. If you want to run a TB head then you probably should use their 67 kit as the piston is a fair bit lower.

Good trick is to trim the base of the barrel or leave out the base gasket, they run a lot better, give more hp obviosuly as the piston is farther up the bore. Terry writes a fair bit about it somewhere.
I still feel I need more though, haha

 

[my67xr]

ok, thanks mate,
i'll be running my Z Ho head for the moment, which i have been cleaning up myself.
i got my new Rotary tool last week, and got a set of 10 assorted size carbide burrs for Singapore, and i am just waiting on a heap of various grit sanding drums to arrive
i still have a bit more work to do around the guides, and taper off the guide bosses etc
i need to find some better valves for it, i think a +1mm stainless or even Ti inlet and maybe? an oversize Stainless or Ti exhaust
will see if i can research the dimensions on the Ti retainers too, then find some springs (easy enough)
this is where my head is at atm,-











i think i know the UK site you were talking about, Motosyko ?
the pistons they have look pretty good, i just need to get my set up happening when i sell something so i can start dummy-ing it up and checking clearances etc
a local machinist has a boring plate that will work for my cases, and another guy i use for my 2 stoke stuff has boring benches too.
so that's all covered.
the second guy said if i need it, he can make up, and fit a sleeve to whatever size bore i want for around $280 from scratch.
he is a magician with some of the work he does!
so i'll need to do a lot more research into pistons yet.
i might even get onto FPM Terry and see what he can do too.


but i don't like hearing you are thinking about more cc's though !!

cheers for your help!

 

[Phil67]

Yep I pretty much did the same to my head it actually helped a lot for a stock head. It's ooracing that has the kit I used, I checked before for ya, huge domed piston but it's the same as the 63 kit I had previously so I knew it would work. Outlasted my tb set up too. Rings are easy to come buy as well, I'm thinking the vertical china engines use the same ring sizes. If your guy can do whatever you want you may as well go 70 mm then, just need to weld the cases before boring, not sure what size the case bore is, maybe 73? I'm toying with the idea of putting a Daytona head on mine somehow, dunno, I just want to do things differently. Clearances shouldn't be an issue as the piston is still down the bore a fair way, I was going to go silly and machine here and there to get it up higher but ran out of time before the race meet. So IMO bigger is best, go as large as you can. Only drawback is kick start gears are weak as piss. I've replaced the one behind the clutch twice now, easy enough to do I suppose. I also ran the last 3 motos with a massive crack in my case when it let go, still ran and got 1 st outright for the day, although my right boot has never been the same since, oil stained hahah. If you go 70 mm I am too, keep me updated

 

[Phil67]

Btw, terry does a 70 mm kit now, crf piston I think. Talk to him, I haven't spoken to him in ages but he is a great help

 

[my67xr]

the 250cc Honda clones use the 67mm rings.

reckon with a 70mm bore, the case bore would need to be taken out to at least 76mm ?
the skirt would need to be 3mm minimum, and a slight champher near the bottom


and yeah the Daytona head would be nice, but it'd end up being too dear for me by the time i got the piston to suit .
i'm guessing they make 4v pistons in 70mm ?

the first machinist i mentioned above, his son can harden gears
i might take a set of gearbox and kick start gears down to him and get his son to give me a price ?
i wonder if it's worth having the shafts done too ?

i had my Planetary gears in my XR 9" diff done 20+ years ago and they are still sweet

 

[Phil67]

I almost case hardened mine, I was close to doing it but it was Friday, hahaha. The gears hold up ok it's the kick start gears that are the problem, have to be super diligent in starting technique, you know how you can get excited in a race and kick like crazy, that's when stuff happens. Actually the shafts would be worth doing as the circlip area is their weak point. I'm pretty tough on my gearbox though, I flat change all the time, doesn't really matter as a gearbox is like 50 bucks.

Yes 250 clone is 67 that's what I mean for getting new rings. I have seen the kit on alibaba, I suppose it's the factory oo racing and everyone else get theirs from, kits are under 50 bucks from memory. The factory still emails me non stop with specials, hahaha.

So I reckon for cost go the china 67 kit, use your head and at least a 26 mm oko and your set, oh don't forget manual decomp. You could almost use a chainsaw decomp button, exact same part number Harley uses and I've seen them on eBay for about 15 bucks.

I'll only use a Daytona head if I see one out the back of braaap sitting there doing nothing, and if I get pauly excited to do it for giggles.

 

[my67xr]

i was thinking that after i posted^.
my kick start shaft is the 13mm one, hope that holds out for a while?
might even need the ring gear off the flywheel done too?
the biggest problem is when you get rid of one week point, what is next to fail , lol.
i found that out with my Car many times...

i have the OKO 26 already, the Decomp lever kits are cheap on Ali.
i have the Daytona/Lifan 150 Outer Rotor, so retarding it a bit won't be a problem.
it really helped my Lifan 150 engine, but i was running a stock 125 stator on it.
i could probably make an electronic retard circuit too and add that into the wiring, then just switch it over to start it.

but everything will need to wait till i can see what bikes/parts i can sell :11doh:

 

[Phil67]

Yeah I'm wrecking my DL LTD to fund some new stuff on the bike and the new BA I just got.

I forgot about the flywheel mod and retarding the timing, that was the biggest help in starting it. It starts first or second kick when cold now, same as when it was a 60mm stocker.

Kick start shaft will be ok, it's the gear behind the clutch that chews teeth off. I have also killed a TB billet clutch basket, but I think that happened when the case split. Now that I have the knack in kicking it over it's a breeze.