Carbon build up.

I have taken the head off the Commando, and as you can see in the picture (if the link works fingers crossed), the carbon build up is quite different on the two pistons.
Also, this is after about 2500 miles. There seems to be quite a lot of carbon build up to me for such a low milage on one of the pistons. I am slightly perplexed as to why the other piston is so clean? Does anybody have any ideas why there is such a difference? One pot running lean? One pot rnning rich?

Once again, I cannot see the picture? Is it therefor others to see?
Last time I posted a picture, other could see it, but I couldn't on my computer???? Then after a couple of days it appeared.

I can see it fine. Do not know why you cannot. When you go to your Photobucket account does everything appear normal there?

oil is comming up past the rings and washing the carbon off the piston top, after that milage it should have bedin,unless you have been puttering around like a nanna,or it has a fault. That is a fair bit of heavy carbon for that sort of milage though.

swooshdave wrote;I can see it fine. Do not know why you cannot. When you go to your Photobucket account does everything appear normal there?I don't get along particularly well with photobucket, but seems OK to me. Ironically when I refreshed the page just now, it came up!

splatt wrote;oil is comming up past the rings and washing the carbon off the piston top, after that milage it should have bedin,unless you have been puttering around like a nanna,or it has a fault. That is a fair bit of heavy carbon for that sort of milage though.
It looks like I'll have to get the bore checked for wear for starters. I certainly don't pootle about. Most rides I at some point have it revving up at about 6500/7000rpm.

What made you pull the head off your bike to start with :?:

splatt wrote

What made you pull the head off your bike to start with

Click to expand...

It was for an un-engine related reason.

I took the pistons and barrels to the engineers yesterday, and found out that it has been rebored by the previous owner 25 thou oversize instead of 20 thou, with minimal honing, and when you look carefully, the boring marks are still evident, therefore the bore has never bedded in with the rings and the piston was a slack fit, although I don't remember hearing any piston slap, but then again I am going a bit deaf :lol:

Anyway, last year I bought off ebay some spare +40 barrels that came with new +40 AE pistons with the intention of using the barrels for a 920 conversion in the future, :idea: so what I will do is get my barrels rebored and use these pistons that came with the spare barrels in my newly rebored barrels. I just need to get some valve cutouts machined into the pistons.

So splatt, your diagnosis of oil coming past the rings was basically correct.

hi reggie,why do you need valve cut outs in the pistons,are you skimming the head or fitting bigger valves or a high lift cam

chris wrote

hi reggie,why do you need valve cut outs in the pistons,are you skimming the head or fitting bigger valves or a high lift cam

Click to expand...

I'm running a 4s cam.

hi reggie,i had piston pockets cut by steve maney

He's not that far from me, about 30 minutes.
Could I be so rude as to ask what he charges, it's just that when I talked to the engineers on the telephone about this who will be doing the rebore, they said that they could do it, but it sounded as if it was an unusual request for them to do this, and so if they have a lot of setting up time, it may be that Steve Maney will be cheaper and potentially more acurate.

hi reggie,i cant remember how much it cost exactly because i had a few other jobs done at the same time, whenever ive wanted anything i ring first to make sure hes in and drive up,hes about an hour from me,i dont think hes any more expensive than any other engineering firm but you will be sure to get the job done right,i stopped using wholesale engineering firms years ago because they dont understand what we need, i would take your barrels there for rebore also,take the pistons you are going to use , his exclusive special parts are expensive i think but you wont get better anywhere else ,

Yes, thinking about it, you're probably right. I'll give him a ring next week, and see what he says.

hi reggie, just a word of warning if you go you will be like a kid in a candy store, you,ll want two of everything lol

I'm already working out roughly how many extra days overtime I would have to work to cover the cost of a stage 1 cylinder head with manifolds and MK2 carbs.