F****d Top End. Piston and rings have become one

[Galloway96]

So I was running at 50 PSI and decided to take the top end off my Raptor 125 today. It wasn't pretty...

The piston and the piston rings have decided to become one (see image). This is from the PV clearance being miles off. I went into my local workshop and they said that the cylinder is also worn due to this. They said that my options are to bore out the cylinder and get a new piston and PV fitted and the clearance properly set, or buy a whole new top end.

I don't want to send it off to get bored out as it can get expensive and then finding pistons and rings may be tricky if i need to replace them again. So I'm planning on getting a new top end.
But... top ends aren't sold with power valves, and I've heard that they are quite tricky to set? So I'm wondering if anyone can shed some light on the best way to go about it?

1) Buy a new cylinder with piston and rings and then a separate PV and fit it myself? or...
2) Try and buy a second hand whole top end with PV already fitted?
Or maybe a third option that I haven't thought of?

Also, I'm not sure if the current PV is actually usable? It had a burr (if that how you spell it) on the shaft that goes through the bearing that I've filed off so now it slides pretty freely. But I'm not sure how to check the clearance or how to check if there is damage to the moving part - I can take some photos if that would help.

Any help, advice or discussions would be great.

Cheers,

Tom

[Pete.]

[Nobby the Bastard]

Compression and powervalve?
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trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Triumph Sprint ST 1050

[Galloway96]

[Galloway96]

Just took a photo of the piston and rings

[Pete.]

Well the piston is trashed, how about a photo of the barrel.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[Galloway96]

[Teflon-Mike]

[Galloway96]

Cylinder wear can be seen in these photos. Not sure how bad it actually is though?

[Galloway96]

Teflon Mike:

Yes I have corrected myself regarding the comments on clarity. As I said, I am not claiming to understand what is going on fully. Which is why I'm here, to try and learn.

The images are posted in the thread, I had to go and take some.

Yes the power valve is a rotary one on the bike, you are correct.

I can only say what the mechanic told me. He said that the rings and piston have been in contact with the power valve because the clearance has been set wrong. This has then caused it to rub on the barrel.

Yes it is clear I don't have the knowledge to tackle this job. But I do have the manual and I do have a mechanical mind. And the whole reason I have this bike is because I am interested in learning how to fix it.

Like I have said... I AM NOT CLAIMING TO BE AN EXPERT. All I want to do is try and get a little bit more knowledge so I can have a go. And I thought that I might get some good advice from the people on this forum. I didn't think that I would get every word scrutinised because I don't know as much as some.

If you have some advice, can explain where I've gone wrong with my explanations or can elaborate on what I have been told, then please throw it my way.

I have the workshop manual and I will be using it when I decide what the best way forwards is. I just need some help making that decision

Cheers,

Tom

[Teflon-Mike]

Right; pistons fcukd, bores fcuk'd.
Rebore is usually cheaper than a new barel; you take it to a specialist to get it done, decission between teh two is down to you and the cost.
Power valve? Needs some care and attension. no pics. cant say if it's fcukd.
I wouldn't but 2nd hand barel or piston for a two stroke, as said they are 'service spares' like an air filter. 2nd hand PV blade would be just as risky, so be hoping to meaure up the one you got as 'true' and polishing out any damage, or replaceing with OEM replacement, and eating the lickely cost of it.
Then down to following the instructions in the book to put it all back together, very very carefuly.

You dont need to become an expert over night to tackle this; just get brave, and a bit more clued up, and a little more decicive!
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[Galloway96]

[Triton Thrasher]

[Galloway96]

[Kickstart]

Hi

The Cagiva engine doesn't use a rotary power valve like the YPVS system (or like the Gilera system). It is a Rotax style blade that is lifted up and down via a rotary bar.

There is an adjustable stop on the power valve, to control how far it can move towards the piston. Get this wrong and the piston can touch the valve causing major damage.

On the Cagiva engine there is a plated bore which cannot be rebored. Your options are to have it replated, bored out and a cast iron liner fitted or replaced.

Mitaka make cheap replacement barrels, which is probably your cheapest option.

All the best

Katy
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[Galloway96]

[Kickstart]

Hi

Depends on the damage and the risk you want to take. If the shaft has weakened then it could later snap and drop down onto the piston. A tiny bit of damage you could maybe clean up if it hasn't clouted the piston hard.

You need to adjust the stop carefully. Even unbolting the power valve housing and bolting it back with the same gasket is likely to change the clearance.

All the best

Katy
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[stevo as b4]

I'd buy a new exhaust valve blade, and get the OEM cylinder rebored either a liner fitted or bored out to past the damage and re-plated, if there are oversize pistons available? You'll need to rebuild it carefully and check gasket thicknesses and powervalve and squish clearances when you do, so nothing is touching.

As others have said check the oil pump is working correctly and there are no leaks or damage to the feed lines, as if it's not getting enough lubrication, you'll knacker the rebuilt engine straight away.

For a fun non budget project, personally I'd be having the crank rebuilt and then fitting a Polini 165 kit, and having a one off pipe made to suit the cylinder. But that's silly money for people with no sense and who know how to re-build engines properly too.

[ZebraDriver]

"It had a full tank of oil that I drained"


Nobody has commented on this but surely if it has a full tank of oil then that means its not using any............


I think I would be checking the oil pump before I put any other work into this

[Galloway96]

[Kickstart]

Hi

This is a good point from ZebraDriver.

However pumps are generally very reliable. I would check the oil carefully. Some oils are not designed for use with pumps and may be far too viscous to get through the system. Some oils react badly with other oils (castor based oils for example).

But the main thing to check for is air in the lines. It is not uncommon for people to forget to put oil in, run it out and then fill the tank up to hide their mistake. But with the engine not running the line from the pump to the intake is probably not filled.

All the best

Katy
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[Galloway96]

Hi

Ill try and check the lines for a blockage and I'll get some decent oil for when its running.

If it does have air in the pipes how do I go about fixing this problem?
It will have to be done when I have at least got the engine running I'm guessing? No point doing it now as the pipes are just hanging off?

Can I just get it back together and put some oil in the spark plug hole to lubricate the piston then run it for a while to get the oil pumping through the pipes?
Will this clear the air out? Or is there a certain way to do it?

The other option i found by looking on the internet is to disconnect the pump and just run premix. This might turn out to be a easier (and cheaper) option if something is wrong.

Cheers,

Tom

[Kickstart]

Hi

I wouldn't run premix unless really necessary. You will land up with the mixture never being right (as the amount of oil needed is not directly related to the amount of fuel being used - for example throttle closed down a hill), and the hassle of rejetting.

If it has been run with the pump disconnected for a while then it will likely have damaged the pump (ie, it needs that 2 stroke oil to lube the pump).

Normal way to bleed it through is unbolt the pipe from the tank to the pump (at the pump) and allow the oil to flow down and fill the pipe up. Then put some premix into the tank (quite a rich mix will be fine) and run the bike with the lever on the pump held wide open until the pipe from the pump to the carb has filled (and a bit longer maybe).

All the best

Katy
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[stirlinggaz]

Hi,
apologies if this has already been said, but I cba'd reading all the replies (blame TEF)
Havnt looked at any pics either, as I'm on a crap mobile with a comedy screen.

Anyway, DON'T get it rebored as its nicasil lined, unless you want an iron liner pressed in (bad idea on a cagivas & most other modern sports 2t's IMHO)
So just do what other mito owners do & send the cylinder to langcourts.
IF it can be rescued, these are the guys.

& if it can't be repaired, your gonna have to find a replacement cylinder anyway but it doesn't need to be new.
Plenty ppl sell old cylinders (that CAN be replated) cheap on eBay.
If you want the exact same "model" of cylinder (not necessary BTW as some models are better than others) you need the 5 digit (iirc mine are 73037) number on side of cylinder.

Then you just need to fit a standard piston kit etc.
Next, what condition is your CTS blade?
If its f*cked, replacements can still be bought.
So pull it out & post a pic (if you havnt already done so)
& when it comes to CTS adjustment, just follow the wsm or repost when you have a "new" top end & I'll talk you through it, its not difficult but extremely important to set it up correctly (as you have found out)

Cheers,
GAZ

[Galloway96]