Cylinder damage questions

The coating peeled off and lost compression. Still runs but serious loss of power.

Less than 100miles

Running very safe rich

50:1 good 2-stroke oil

Temps never crossed 380°

What would cause the coating to peel off like this?

PXL_20201011_201349776.jpg
PXL_20201011_201320755.jpg

Re: Cylinder damage questions

Must have got hot and piston expanded and tore shit up. Air leak mabye?

Re: Cylinder damage questions

I have a temp sensor on the head, you can see it in the pic hanging. I never got over 380° but expansion would explain it... But the rings were gapped to .18mm...

It's also a DMP kit and poor coating would also explain it.

But I'm also very insecure about my tuning and still blame my tuning.

I was constantly watching the temp due to insecurities in my tuning.

Re: Cylinder damage questions

Didn't even think of air leak .... Going to dig into that...

Re: Cylinder damage questions

Did you gap your rings?

Sometimes nikasil coatings from certain manufacturers are lower quality as well, what cylinder are you running?

EDIT: just saw you answered all that while I was typing my question, either you were running lean or you just got bad luck with a faulty cylinder imo. (edited)

Re: Cylinder damage questions

I didn't have to change the gap on the rings. They came perfectly gapped. It was odd in my opinion but the feeler gauge don't lie.

I can run lean but not hot and still damage cylinder?

Re: Cylinder damage questions

Dirty30 Dillon /

I'd you ran no oil it might do that to a new bore.

But that looks most like a bad out of box cylinder. Where did you get it from?

Re: Cylinder damage questions

Wow looks like it just all flakes apart......may have gotten a bad cylinder for sure.

Re: Cylinder damage questions

That's pretty wild, never seen one come unglued like that. You can see where the ring stops at the top of the bore, it was definitely caused by the ring, but even if the ring gap was off I don't think the plating would peel like that.

Re: Cylinder damage questions

I think I'm going to gap the next rings a little bigger than the recommended .18mm to .2mm. I used to the turbo car huge ring gap standards..heh...

The kit was from Dos Cycles I did send them an email to see what their opinion is too.

The coating just wore down soooo fast. I did 1 trip around town..about 1/2 gallon of gas and the cross hatches were wore off the nickisil coating. I just think this coating was super soft.

I will be taking this cylinder to a local machine shop and having a sleeve pressed in and cut the ports. The usual turbo car bits. Lul.

Re: Cylinder damage questions

I was wondering why you would put a sleeve in such a cheap cylinder, so i looked up what you guys have to pay for it. Lets just say it's cheaper to buy one at JMPB and ship it overseas.

Re: Cylinder damage questions

I'd sleeve it just for kicks. It would be nearly free for me to do it.

But jmpb is super cheap. I will prob grab the athena AJH off this website if the current supplier won't warrant the dmp.

The athena just looks like higher quality.

My case is already matched to the dmp and the AJH looks to be similar.

Re: Cylinder damage questions

It's tough to ask for a warranty on a blown up kit, dos might hook you up just because they are that awesome but it's definitely one of those things... If you are used to aftermarket car stuff you know the deal.

At the very least they'll probably hook you up on a killer deal, at cost, for a new one.

I dunno how sleeving it is going to work, it's a lot of work porting the sleeve and the cylinder gets really thin when you bore it out for the sleeve. It's one thing if you are saving a vintage or rare cylinder or doing something fancy custom, but saving a cheap taiwan cylinder that's not very good to begin with seems like a waste of time.

Re: Cylinder damage questions

> Graham Motzing Wrote:

> -------------------------------------------------------

> saving a cheap ... that's

> not very good to begin with seems like a waste of time.

Hmm , seems like that could apply to a lot of mopeds , but , we do it anyway . ;)

Re: Cylinder damage questions

Dirty30 Dillon /

> Graham Motzing Wrote:

> -------------------------------------------------------

> It's one thing if you are saving a vintage or rare cylinder or

> doing something fancy custom, but saving a cheap taiwan cylinder that's

> not very good to begin with seems like a waste of time.

Yeah man, it's just a DMP kit. A sleeve will cost more than the cylinder.

Re: Cylinder damage questions

Look at the piston , probably seized. Sometimes its the tune , assembly by mechanic , and with cheaper cylinders sometimes its quality . Go back to stock or get a new kit , i got a cheapy k star 70 For 50 shipped .

Re: Cylinder damage questions

The piston burn pattern or piston wash is WAY RICH.

Re: Cylinder damage questions

♣Slew Foot♣ /

Iron rings or chromed?

Re: Cylinder damage questions

Prob some flavor of iron. Chromed sounds expensive and that's not DMP. Sooo. Heh.

Re: Cylinder damage questions

> Grant Marshall Wrote:

> -------------------------------------------------------

> Prob some flavor of iron. Chromed sounds expensive and that's not DMP.

> Sooo. Heh.

They are about the same price . Chrome is only applied the outer 'side' of the rings that actually contact the cylinder wall . And , it's not the same chrome you see all bright and shiny on a '57 Chevy . ;)

Re: Cylinder damage questions

* inspection intensifies *

Re: Cylinder damage questions

Grant

Do you have a inside mic? I was just wondering how much chrome was taken off the walls.

Re: Cylinder damage questions

All the chrome/nickisil was taken off. Was worn completely thru. The coating was beyond thin.

The rings got worn some too. But I guess that's part of the break-in process.

The piston is chowdered from the coating flaking off.

The cylinder went back to Dos for further opinions so no more pics.

From what I can think of the only 2 things it can be are

-running too rich to the point the oil is no separating from the gas and it's thinning the oil to the point it is not lubricating correctly.

-running lean at 98%-100% throttle and heating up the rings to the point they touch and expand and wear the coating straight off.

Re: Cylinder damage questions

1st set images

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PXL_20201014_234814643.jpg

Re: Cylinder damage questions

2nd set

PXL_20201014_234807380.jpg
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Re: Cylinder damage questions

so the big x-factor with this stuff is always the piston, the supply chain on this stuff is so screwy its not uncommon for the lower end brands to have a random piston swapped in that isn't quite right...

the tune on that looks really good, i'm not seeing any of the signs of overheating. one thing i was thinking it could be, would be a bad break-in which can cause exhaust gasses to blow down past the rings, heating them up way too much and expanding them in the bore- not the case here, your break in looks perfect.

i think its pretty obvious the ring is the problem, it either butted from not having enough end gap. I always grind to 6, 7 or 8 thousanths depending on how hot i plan on running the kit, 6 for 'stock', 7 for most performance stuff and 8 for soemthing i'm really gonna pound on.

or- the ring is the wrong material, i know cast iron on chrome bore is bueno, i think chrome on nikasil is bueno but i think chrome on chrome is no bueno? some googling of people who do more high end 2t stuff should get you an answer.

and yes, the coating is always thin as shit, it should be like 3-7 thou. its just a plating. Its not impossible for it to be messed up from the factory, but its pretty unlikely, its a very tightly controlled process and people making hundreds or thousands of cylinders a day don't usually have just one or two mess up.

my money is on the ring not being gapped correctly or somehow switched with the wrong piston/ wrong ring material. Good news is your tune is spot on, maybe a little rich and a little too much timing or the wrong head.

Re: Cylinder damage questions

Thanks for the advice. I think we got it figured out. The piston was pretty tight in the cylinder to start with and expanded to.. well.. too big.

I do have the rings gapped to your 'imma beat on it' setting .18mm top and even looser on bottom ring. I always lean on the side of safety on everything.

I will say with this new kit the loud tick and oddly noisy operation sound is no longer. The piston has a slightly looser fit in the bore too.

Will be scooting around this weekend and hopefully complete the break-in.

I'll post an update with what will hopefully be a after break in success story.

Thanks for the help!!

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