For the future try and do leak down tests rather than compression tests especially on 4 strokes that have auto decompression systems on the cams, it is more accurate and a great way to help diagnose engine issues.

Just in case you're not sure, a leakdown is done with a similar tool as a compression gauge but instead of using the starting system to build compression you force a set amount (mine is 60psi I think??) of compressed air into the cylinder with the engine locked at TDC on the compression stroke. From there you listen for leaks. If you hear air coming from your intake system you can assume there is an issue with your intake valves, air from the exhaust is an issue with the exhaust valves and air from your oil fill plug is a piston issue. It does not tell you exactly what the problem is but gives you a pretty good idea of where to start before you tear it down.

 

As far as I know my duke doesn't have auto decompression (I though that was kickers mostly!?) but I see your point, I had the compression tester handy. I should invest in a leakdown tester at some point.

I'll take all the measurements tonight and see whats what, the rings and values are looking to be the primary culprits but as you said I need to check and make sure.

I cant see any impact marks, the ring gaps are all within spec but it still looks like carbon build up below the rings. I'll post a picture later to illustrate what I mean.

 

As for your repair issues, get a manual and have the proper tools. If you don't then use a local machine shop.

Your piston / cylinder questions can be answered by measuring the tolerances listed in the manual. If its out of spec, replace it. Remove the rings and check the ring gap as well. Is there valve contact on the piston surface? Valves usually don't bend without contact so that is a very good indicator as well.

Your valve issue could be a couple of things. If your piston has impact marks then you can assume valves need to be checked. Check the cam journals for wear it is possible that the cam(s) is sticking. Also check the valve levers / rocker arms for smooth operation, they also could be sticking. Once they have both been checked, removed and eliminated as possible culprits then check the valvetrain itself. If you do have any bent valves I would definitely be checking the relevant valve guide for wear and the seat as well.

 

Holy Carbon Batman! How many km on that motor? Any fuel mods done to bike? You can see all sorts of ****e even in the oil ring. Is that the stock piston? The black edges make it look like Wiseco or those ****ty Nakamura's or whatever they're called. Looks like a heap crap build up of fuel / oil

Based on no background info and pics only, personally I would throw that piston in the garbage and not even bother with it. I can see a ton of crap built up in the ring grooves that you will probably never get out. Also the pic of the piston on it's side looks like there is a nice line forming on the skirt. I would also DEFINITELY put a hone through that cylinder and make sure it is within spec, probably a $20 job from a local machine shop. Drop them the new piston too and have them set the ring gap so all you have to do is slap it in.

If you have that much built on piston you can pretty much guarantee the inner edges of the exhaust valves are coated with crap as well. I have seen valves bend from impact in higher compression engines just from the amount of crap on piston / valves. Also that buildup won't let exhaust valves close which can build heat.

Is it just me or do you have a chip of material missing from the head in the pick showing the valves. Look to the right of the valves, big chunk gone? It's right at the edge of the combustion chamber, if it is that then plan on welding or scrapping that head.

 

I am talking about this...

 

Just some tech to help you out. You can use the open end of a 14 to 17mm wrench (depending on size) to push down on the retainers. While they are pressed use a magnet to get the locks out. Its not ideal but it works and will let you see the eextent of things without a spring compressor.