Vertex Piston rings q

[FFRDave]

I bought and installed a new Vertex piston and rings on my 05 gasser.

The bike has about 4 hours of actual engine run time with the first couple real mellow break ins.

I started by warming it up for about tem min. and then shut it down for the night. I repeated this again the next night. On the next weekend, I went for a nice mellow ride and shut it down after about 20 min, and allowed the engine to cool completely. I did a little faster high RPM riding and allowed it to cool. When I put it away the timer had 1.7 hours on it.
I did go to the local MX track, but I had the flu and went home after only a half hour of riding.

Today at 3.7 hours, she stopped running altogether !! A compression test indicated that I had about 90 lbs. (should have 150 lbs.). I removed the head and found scarring by the exhaust port.

While I was doing my top end (a couple weeks ago) I noticed that the piston rings each had a small "N" stamped on the ends. I wondered breifly if they were supposed to be on the top (facing up) or on the bottom (facing down), but I went ahead with the project.

Now I am wondering if I should have paid more attention to that little "N". I called GoFasters and Mark said he would research it with his Vertex vendor and get back to me.

Does anyone here know about this ??

 

[gasgasman]

The "n" faces up to indicate the notch in the ring.

Here's generic 2 stroke piston showing the notch in the ring end.

 

[gasgasman]

I don't recall if the Vertex rings have that notch or not.

 

[iancp5]

By coincidence just been speaking to my dealer having had my cylinder returned from replating. He said they use the contractor they do because they do a good job including chamfering the ports so the piston doesn't catch when there's wear.

Might be worth checking? Although the piston is new if the cylinder is worn just perhaps it wobbled enough to catch?

It's hard to put the rings on wrong because of the locating pin it should be obvious which way is up. However ... you can put the piston in wrong. There should be an arrow on the crown pointing forward. Although I would've thought getting that wrong would result in instant failure. The piston must be oriented so the ends of the rings cannot flick out into the ports.

Apart from that maybe it was a "normal" seizure - too lean, too cold, no oil etc etc

 

[Eric K]

When I put in Vertex rings, there was no difference between the top and bottom of the ring. They look/fit the same either way.

Did you check/set the ring end gap? Typically the ring end gap is too small and the ring ends need to be filed to meet the GG engine manual spec. (Check GG manual on line)

 

[widebear]

Assume nothing and take nothing for granted. You absolutely have to measure both the piston and the cylinder.I have a freshly plated 200 jug that was done in conjunction with the B piston that was provided as a reference, the outcome 3.5 thou piston to wall clearance, now I'm looking for an E or F piston to correct the clearance surplus. I have also seen brand new off the shelf KTM 200 pistons out of spec and unusable.Do yourself a favour do it once but do it right! I once srcewed up a perfectly good kx cylinder partly due to undertaking the job after consuming copious amounts of good European beer. I was going to re ring a vertex piston using non vertex rings. I measured the end gap which was ok then I went ahead and miked the ring thickness ,ok no prob same a vertex, then I had a couple of more ice cold Becks. What I neglegted to do was to measure the new rings depth in the ring land, they looked ok to through my beer googles no prob, fifteen minutes later after breaking the top end in, in the back alley a mysterious loss of compression resulted. End result and a screwed cylinder. All I can say is good thing I did'nt go to the bar lookin for company!

 

[RBD]

Sounds like you put the piston in backwards....... the arrow on the top of the piston should point to the exhaust.

The ring end gaps should be on the intake side of the cylinder, if you hooked a ring end-gap in the exhaust, the piston was put in backwards.

Also, maybe a piton pin clip came out, they can be hard to get in and it takes some experience to know when they are seated properly.

JMO, Ron

 

[FFRDave]

The Rub...

The whole front of the piston is rubbed off, right over the rings and everything !! The rub is about 11 thousanths of an inch deep and extends down the piston from top to the skirt and about 2.75" along the front circumfrence.

The arrow was pointing the right direction (forward) and both of the rings gaps were over the nubs in the groovs as shown in a previous post. Both piston pin clips were properly seated, in place and in tact.

The wrist pin was a major Bi#*h to remove. It was in there way way tight. It installed real nice !! I used two stroke oil on all of the assembly locations (wrist pin, & bearing, and both rings). The little "N"s stamped into the ring ends are both facing up (but I am told it doesnt matter).



RBD Ron, do you do sleaves or Nickl-seal ??

 

[widebear]

You did't mess up putting your powervalve in wrong did you?

 

[FFRDave]

I know what happened now

It wasnt the PowerValve either. I never removed it.

I didnt really think of it at the time (last night), but I remembered (this afternoon) that as I was removing the forward base nuts, they seemed to come off way too easy.

I think I had an air leak in the front base gasket and that is what burned up the front of my piston. I just didnt have the nuts torqued properly.

Now Im gonna upgrade to a 300 jug from GoFasters and chalk it up to an expensive lesson learned. My origional jug is a complete loss. It has a big crack that runs horizontaly between the exhaust port and the PV barrol bore.

 

[iancp5]

What should piston clearance be on a 300 and how should it be measured?

I am just rebuilding with new plating and piston and I have way more than 3.5 thou measured, very roughly at the rear of the crown near top of cylinder. I didn't measure it accurately as only have feelers and didn't want to damage the piston jamming them in. But ... I got a 12 thou in no problem so the clearance must be more like 15 thou+ where I measured it. The ring end gap looks spot on with the manual maybe a little tight at about 15 thou. Piston feels snug pushing it up in the bore but when near the top you can wobble it slightly, without rings of course.

 

[iancp5]

You did't mess up putting your powervalve in wrong did you?

Is that possible?

 

[GMP]

Unless you have very good measuring tools, the numbers are meaningless especially when considering the piston micro sizes(A to D vary by .01 mm each size). A caliper will not do for the cylinder. You really need a calibrated three point bore micrometer. With this you can get a proper measurement at various points in the bore and see if there is uneven wear. We have a set in work, they are not cheap. Take everything to a shop with the proper tools and have it measured if you are in doubt.

The piston is tapered so its normal for the crown to rock slightly. The plating shop should have honed the bore to the correct size/clearance for the piston provided.

The main PV flap can be installed upside down. I do not recall if it will interfere with the piston however.

 

[iancp5]

Unless you have very good measuring tools, the numbers are meaningless especially when considering the piston micro sizes(A to D vary by .01 mm each size). A caliper will not do for the cylinder. You really need a calibrated three point bore micrometer. With this you can get a proper measurement at various points in the bore and see if there is uneven wear. We have a set in work, they are not cheap. Take everything to a shop with the proper tools and have it measured if you are in doubt.

The piston is tapered so its normal for the crown to rock slightly. The plating shop should have honed the bore to the correct size/clearance for the piston provided.

The main PV flap can be installed upside down. I do not recall if it will interfere with the piston however.

Think I'll just run it up and listen!
I installed the PV flap copying the parts breakout diagrams so hopefully they are correct. Looks right when I operate it - will sit flush.

I read something somewhere that PV preload can be adjusted. I can't see how. The manuals don't discuss this?

Thanks

 

[blitz11]

Cylinder-Piston Clearance

There is an easier, reliable way to measure piston-cylinder clearance.

You just need long feeler gages. see
http://buy1.snapon.com/catalog/tools.asp?tool=all&Group_ID=1130&store=snapon-store

These are $2.70 each. If you get these, you can measure cylinder/piston clearance to 0.0005". As Glenn mentioned, the pistons A-D each differ in diameter by 0.0004", so you can double check your clearance pretty easily and inexpensively.

You can look for eccentricities by placing the feeler gages at different points in the cylinder circumference. It's not as accurate as Glenn's method, but it is close enough for what we're doing here. It's also less expensive, and accessible to everyone who does a top end.

That's how we did it at the shop 30 years ago, and we never had piston-cylinder clearance issues, and we did a lot of engines.

 

[iancp5]

But it's the wrong shape!
I mean the blade is wide and flat, the cylinder curved??

 

[blitz11]

Right shape

You don't wrap the feeler gage around the piston. You put the feeler gage alongside the cylinder wall. The length of the feeler gage will be up and down in the same direction the piston moves. Once the feeler gage is there, you then push the piston into the cylinder. The feeler gage takes up the slack between the piston and the cylinder.

The feeler gage then represents the difference between the piston diameter and the cylinder diameter. That's your clearance.

 

[iancp5]

You don't wrap the feeler gage around the piston. You put the feeler gage alongside the cylinder wall. The length of the feeler gage will be up and down in the same direction the piston moves. Once the feeler gage is there, you then push the piston into the cylinder. The feeler gage takes up the slack between the piston and the cylinder.

The feeler gage then represents the difference between the piston diameter and the cylinder diameter. That's your clearance.

Yes I realise I don't wrap the feeler around the piston! But even inserted length ways its width is a significant factor when measuring a few thou. Anyway I seem to have located the source of my confusion after a bit of research. The crown is designed to be a much looser fit than the skirt to allow the rings to work. By the way special thin feelers are available for measuring piston clearance - more like a piece of wire. But the recommended way is to use a bore guage although I hear these are expensive for occassional use.

 

[blitz11]

Not an issue

You have to step back from this a bit. You're making it way too complicated.

You're NOT dealing with concentric cylinders (the hollow cylinder and the solid piston cylinder). These aren't concentric, but share a common intersecting line.

I made the following drawing to explain what the feeler gage measures. the width of the feeler gage is irrelevant. (Well, irrelevant if you use a reasonably sized feeler gage). What matters is the thickness of the feeler gage.

I've tried to attach a drawing which exhbits this. Hopefully, it works.

I've done this for 30 years, and it works. What it does is find the clearance between the cylinder and the widest part of the piston - the clearance which really matters.

craig

 

[iancp5]

Blitz,

That may be fine for the tight part at a couple of thou but at the crown I have around 15 thou and a 15 thou feeler is pretty stiff and doesn't easily deform to follow the circumference. When I measured approx 15 thou at the crown I was worried as clearances are stated as more like 3 thou or less - now having found out more I'm not panicking.

What seems to be the case is a large clearance at the crown is acceptable as long as the fit at the skirt is tighter. Plus you have to consider the pistons are actually a little oval to expand to the right shape.

Anyway I'm going to stop worrying and start it and listen!