Hello out the there.

On taking my cylinder head off to clean any carbon that may be stuck to the ( dome shape)? Iam quite shocked to find its heavily scorred and pitted. Looks nasty, pock like.

Could anyone tell me what may of caused this and what I need to do.

Thanks for any help.

Squid

usually the best method for diagnosis is to look at the piston [1]; most of the scoring i've seen in two-stroke heads are as a result of exuberant cleaning in the past. Apart from carbon build up something i dont usually see

[1] There is a really good downloadable guide for two-strokes http://ericgorr.com/2%20stroke%20top%20end...performance.pdf

Hi, it sounds like the remains of a broken piston ring at some point in the past has been bouncing around the head ?

Thanks to both Malcra and Andy T.

That link to the articles interesting.I'll have to get me head around that lot.

Andy it does seem like somethings been banging around in there at some point. The marks are deep and random and you'd have to of been wacking it with a chisel.

I guess I need to replace it?

Cheers.

Squid.

Thanks to both Malcra and Andy T.

That link to the articles interesting.I'll have to get me head around that lot.

Andy it does seem like somethings been banging around in there at some point. The marks are deep and random and you'd have to of been wacking it with a chisel.

I guess I need to replace it?

Cheers.

Squid.

Yes that's what a broken ring would do. If the bike runs ok with that head then just ignore it, pick one up cheap off ebay when you can if it bothers you.

i have a few cylinder heads like that from race engines, almost certainly piston ring debris, sometimes the ring can clip the exhaust port lip or the locating pin comes out of the piston and the ring turns and the end of the ring clips the port

i can also be main bearing cage debris or if there's a shim on the big end that can disintegrate too, even the big end - if theres nothing on the piston crown itself then it's a previous failure, the piston has been replaced and the head is unlikely to cause major problems other than a bit of carbon build up

check theres no damage to the top edge of the barrel ports, check that there is a good chamfer on your exhaust port and transfer ports, especially if it's been rebored at any stage, the ring can snag the roof of the port, some 450 grit wet-n-dry wrapped around a small wooden dowel will give a good chamfer

you could take off any high spots on the head with emery cloth then wet-n-dry but clean all grit out before re-fitting

good luck

tony

Thanks again Andy T for the last snippet and a big thanks also to Tonybroad. Its great to get such clear info. Brilliant.

Cheers again.

Squid.

Does the top of your piston look anything like this ??

.....if so its pre-ignition, so check out your timing.

Martin

Hello MartinM.

The top of my pistons very black but its smooth,well, hopefully under the carbon.

Thanks for the pic n tip.

Cheers

Squid.