Im no mechanic, but that looks bad, real bad, whats it from, cam chain in the middle must be an older bike? cat? im sure it can be saved, but the time and money needed is it not esier to buy a new top end from ebay??? or a scrap yard? looks like water go in, but im not qualified to say1
I would say that was excessive heat causing the valves to burn up like that. Either poor mixture (lean), poor cooling system (partial blockage), or possibly over-advanced ignition - or a combination of!
Could also be poor quality fuel and a lack of regular maintenance. _________________ Andy.
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hahah NSR is in the works..but getting a nice MC21 and shipping it to canada is not an easy task.
in anycase, this is from a fzr250. mostly due to a non-existant maintenance for 20 years.
as you can see, when i pulled it all apart, there was sand, gravel inside..dont ask me how it got in there!
so in regards to cleaning that sh*t out, what are some 'ghetto' money saving techniques? light sanding? can i take out these pistons to clean them? _________________ dennislo.com | PHOTOGRAPHY
A big bucket of coke-cola! _________________ MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball
It's no myth about Coca Cola and carb parts though! Works a treat!
Try oven cleaner to clean that lot. I never realised it was sand in the barrels though! I wouldn't hold out much hope! _________________ Andy.
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Looks like thats been running with an object of some sort hammering the piston and head.
In the second pic down, the piston appears to have a small hole appearing in it, this will need replacing. If the others clean up and they are still 'piston' shaped, you might get away with it.
While the heads are off, I'd also get the valves out, clean them up and re-seat them, you might even need new seats / followers (depending if there is any play).
not to be disrespectfully but it doesnt sound like u know much about engins (not saying i know evertything about them) but if u dont know what those things (air/fuel and exhaust valves) are and how to pull the pistons out should u be putting a 4t apart u probably have to drop the crank out to get the piston to come out and i would say that head needs replasing (doesnt look useable) changng motor is going to be the cheapest option in my opinion. _________________ 94 mc28 SE
thanks! we all learn somewhere sometime....playing = learning, and honestly this is more of a toy project for me. sure i could easily buy a new motor, and have a shop throw it in, but what will i learn?
either way, do you have any suggestions for cleaning these pistons and exhaust valves? _________________ dennislo.com | PHOTOGRAPHY
You can be pretty rough with the valves. You need a propper valve spring compressor to remove them though. The spring compressor is like a big G-clamp. Once the springs are compressed, pick out the retaining collets and lift off the valve cap. Once the valves are out you can simply scrape the carbon off and clean them up with fine emery paper. Both the valves and their seats are bound to need recutting though; this is a job for the machine shop. You can "lap" the valves in for final seating.
Wind some old spark plugs into the holes to protect the threads. Carefully clean the combustion chambers with something like oven cleaner. Don't get heavy with a scraper or wire wool on the alloy head!!
The pistons will undoubtedly be shagged and need replacing!
To get the pistons out you need to remove the sump. You can often unbolt the big-ends and lift the pistons/rods out the top of the block without removing the crank, but you will want the crank out anyway to look at the main bearings. Not sure on the FZR250, but the engine block may be in 2 parts, with the cylinders lifting off as a unit.
If it's purely an exercise in pulling it apart to see how it works then great, but if you are going to recon' it, don't bugger about, get a Yamaha Workshop Manual. I would imagine it's very very similar to an FZR400, so get a manual for that too, as it will be in English and the information will be very relevant.
Finally, don't ask how I know anything about 4-strokes... it's my Forum, and I can ban anyone for asking the wrong questions!!!!! _________________ Andy.
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Pretty much anything can be brought back from near death, but that looks rather nasty.
It also looks like it'll expensive to get back to tip top condition.
If the valves are hammered get new ones. Buy the whole assy including collets, springs, seals etc 'cos they're probably all shot to bits. The seats will definitely need cutting. This is always a good idea even on a new bike. If the cutting is done correctly then you don't even need to lap the valves in, but you will need to check that they seal.
If the pistons are toast (highly likely) then there's a chance that the bores are smoked too. So that's gonna be a bunch more dosh.
While it's open you may as well fit new shells to the rods and crank.
Anyone keeping score here?
In a nutshell I'd hoss the lot in the biffa and invest what I would've spent on another stroker.
But that doesn't teach you anything, so keep soldiering on old boy, it'll come good in the end.
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I wouldn't hold out much hope! 
u probably have to drop the crank out to get the piston to come out and i would say that head needs replasing (doesnt look useable) changng motor is going to be the cheapest option in my opinion. 