YPVS power valve failure

[Sloth]

Unfortunately at Berm Buster in Taupo last weekend my bike died while idling, luckily at the end of the second day.

After pulling it apart, I found that the power valve failed, and the dowel pin decided to embed itself in the side of the piston.



PowerValve and piston are ruined, but I'm not sure about the cylinder, so a few (possibly stupid) questions:

Can the cylinder be repaired, possibly with a rebore or a sleeve fitted?

Is it possible to run these engines without the powervalve?

Any recommendations on who to take the cylinder to in the Waikato to get it looked at?

[F5 Dave]

Oh dear that's a big fucked, and unlucky as they are the most reliable design. If the bushes got too sloppy and carbon build up too much, anything can fail.

Try trawl eBay and see if 2nd hand parts are available. Clearly not a common bike in NZ.
PV is likely the same as an RZ and there are aftermarket ones about but I'd ask first.

Chances are you can get a sleeve but if it is plated it can be welded and replated which is always best. All this is going to cost so ask yourself what is the bike worth compared to buying a GasGas or KTM 200 which will be a decade more modern.

I rebuilt a cheap DT200 so I won't get too preachy but always worth askn oneself.

[Sloth]

Thanks for the good reply.

I suspect this cylinder has been sleeved before as there looks like a different material for about the first 3mm of the cylinder wall. Also, a magnet sticks to the inside of the wall as per photo, which I don't think it would do if it was plated?



I'm guessing what the previous owner might have done is sleeved it, bored it out and gone to an oversize piston, but not bothered to shave the powervalve, which let the power valve make minute contact with the rings. Eventually this caused the powervalve to fail.

If it is a sleeve, then it looks like the damage is only to the sleeve itself.

I'm going to take the cylinder to a few places see if it can get repaired. Worst case, I can buy a new cylinder for $US330, Wiseco piston kit for $US130 and new power valve for $US120.

This bike cost me next to nothing, already has rebuilt suspension, new tyres, new brakes, good gearbox, so I figure if I do rebuild, it is still a relatively cheap bike with brand new internals that does everything I want it to do.

Buying another second hand bike, I could just be buying someone else's problems. Plus the potential divorce if I put another bike in the shed..

[Ocean1]

If it's been sleeved it may well have been these guys that did it: http://www.o2engineering.co.nz/services.html

Either way they'll be worth a call.

[F5 Dave]

Sounds like you are well ahead of the game. You won't get it sleeved for that price I'd doubt so your path is clear if freight is reasonable. Check their postage vs youshop.

[Sloth]

Well I took the cylinder in to Hamilton Cylinder Services and they confirmed it has been sleeved before, and that it is only the sleeve that is damaged, so I have a new Wiseco sleeve, Wiseco piston kit, Cometic gasket kit and OEM PowerValve on the way from USA (along with a bunch of other bits for some general maintenance).

[Sloth]

UPDATE so I bought a new powervalve, rebuild / gasket kit and sleeve in from USA, and got O2 Engineering to do the bore and sleeve, as well as providing a new Wossner piston kit.

Reassembled the bike last weekend, started on 3rd kick, and after run in and some tweaking of the powervalve, she seems to be running better than ever.

Now I just need to find somewhere to take it for a ride this weekend, so I can gain a bit of trust in the rebuild before heading to Western Blast in 2 weeks time.

[F5 Dave]

Good stuff, have a beer. I'll have one on your behalf & send you the bill.