Cylinder pics....bad news?

I am planning on re-using the piston/ rings

Piston, yes.......rings, I would suggest no.

It wouldn't hurt to ask a shop to measure the cylinder/piston clearances. My guy would always ask for my piston when the cylinder is serviced.


Valves seaping not them?

Yeah, try it. Should be OK.

Did they charge for honing?


Valves seaping not them?

Yeah, I've found that (with the yamaha's at least) new valves that are just seeping with fresh cut seats will seal once the engine is started. You should be fine if the liquid isn't dripping through them.

As for the cylinder, what kind of a shop doesn't measure the cylinder? That is a huge red flag to me.

As for the cylinder, what kind of a shop doesn't measure the cylinder?

I could tell you stories....

I could tell you stories....

Well yeah, I have heard of many, but personally if I had a shop do work for me and they told me that they didn't measure the cylinder before sending it back, I would be finding a new place to deal with.

Yeah unfortunately this was my one and only time dealing with this shop. They charged me $10 for honing and $129 for the seat cutting/ cleaning. I was going to hone it myselft but hones cost $60 and I wasn't sure if my cylinder was still ok or not so i figured to $10 I would give these guys a try.

I told them I wasn't comfortable with the parts the way they are to install on my bike and he had offered me a full refund already, so I said I would take that offer.

I'm glad I found this recent discussion on the cylinder. I just took mine in today off an 04 YZ450. This thing is a beast, first new top end after countless hours! So anyways, I took it in, got a call back from the shop and they said they'd recommend a refinished cylinder or new one if they were doing the job. I do all my own work for many reasons, but one is i don't trust most of them. Anyways, here's a couple pics of my "honed" cylinder. What you all think? Of course they didn't measure it and when I picked it up the guy was gone. Thanks to all those who give solid advice on here! Hope these pics work.!!

Edited by jbodin18
change URL for pics

Yes there are. I will refrain from elaborating on that situation and let the results you showed us speak for themselves.

So anyways, I took it in, got a call back from the shop and they said they'd recommend a refinished cylinder or new one if they were doing the job.

Your vertical scoring looks worse than 426Cali's were, as well as worse glazing...From the looks of your pics, I'd take the shops recommendation to have it replated...

Can I lap the valves with the seals installed? The seals are already in and I'm not sure if spinning the valve in them will ruin them or not.

Dragging the valve stems in and out through the seals repeatedly in order to apply and clean out the abrasive paste (you were planning to do that, weren't you?) isn't beneficial to them, but spinning the valve won't harm them.

Why bother to lap them?

I was just thinking to obtain a better seal, but I think I am going to pass on the lapping. I tapped the valves with a hammer and punch just now and retested with solvent test. Intakes look good hardley any seapage and the exhaust have some seapage but I think I will just run them.

I'm still not sure what to do with my cylinder. I can try to find another local place to hone it and see if they can do it better and use this same piston that shows no signs of wear. Or I can spend a couple hundred having it replated. Or I can exchange it for a big bore kit and spend a few hundred dollars more. These are the options I'm debating.

What's the worst case scenario if I run this cylinder and piston/ rings combo for the time being? Just some oil burning down the road? How likely is it that the piston may break if is moves around too much? There were some up and down lines on the cylinder when I took it apart but no metal transfer from the piston.

WORST case? I don't know what's worst, exactly, but there are several possibilities:

  • Peeling/flaking Nikasil plating
  • Piston seizure
  • Piston failure
  • Ring breakage

How LIKELY any of that is is an open question, but it's obviously more likely than if you fixed it, isn't it?

DON'T reuse the piston pin circlips, and position the open end of the clips at the top.

Depending on how worn the cylinder is, you can end up with a broken piston or the piston turning sideways in the cylinder, which will take out the head, cylinder, piston, and in most cases the crank as well. That's pretty much the worst case scenario. Just measure the cylinder bore and see if it is in spec. It it is not then you need to address that issue before you put it back together.

It is within spec using the digital calipers I have on the top and bottom. I do not have a way to measure the rest of it, you know like where the rings actually travel. I'll try to find someone local that can measure...

It is within spec using the digital calipers I have on the top and bottom.

If you use a plastic ruler from the 99 cent store, at least no one will expect it to be accurate. Calipers are the wrong tool. Any good machine shop should be able to measure the bore.

Poor man's redneck bore guage:

Put the piston in the bore with no rings and push a piston ring down on top of it. Use the piston to push the ring to the top of the bore beyond where the rings normally run, and measure the end gap. Then push the ring tothe lower area of the bore below the ring sweep, but above the slots so it's in a 360 degree bore and measure again. These two measurements will more than likely be the same.

Now position the ring on a spot where you think there is wear, again using the piston to square the ring in the bore and measure the gap again. The thing about this that is interesting is that the ring gap will grow larger in response to an increase in diameter, but you are measuring changes in the circumference, which changes by 3.1416 x any change in diameter. So, an increase of .003" in the ring gap indicates just under .001" of wear.

But it's still not as accurate as a dial bore mic is. For one thing, the ring won't reveal out of round bores very well.

Oh yeah I did measure ring end gap in several spots the other day and there was not real big differences anywhere. There was slight differences on the low spots of the ridges but it was like .001 or .002" max different than the rest of the bore. The middle of the bore measured the same as the top and bottom.

I'm going to call a local place tomorrow and see if they can help or not

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