Overheating !!

Ok here is pictures of middle piston and cylinder and the valve. All the groves are fairly deep i dont think i have any choice but to replace cylinder IMG_0008.jpgIMG_0012.jpgIMG_0013.jpgIMG_0004.jpg. yes im running stock plugs at stock gap.IMG_0005.jpgIMG_0007.jpgIMG_0015.jpg
 

take a pic of the other pistons at top dead center in the cylinders.
 
Yep^^ valve looks salvageable. That's looking like detonation.

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in my findings and observations of your pics, the reason it went down is either dirty carb jet, extended cruising on the needle circuit, poor gas or combo of all as the other 2 piston tops look fine. The mag is the hottest running cylinder on a viper, the center is the next hottest as they have higher compression then the pto does, that's why the pto has a lot more wash on top of the piston.Iits always a gamble as to which cylinder goes down, most times its the mag but have had a lot of center cylinder burn downs also over the years.

youll need to find another cylinder as like you said its done for(junk), the powervalve should clean up that's just piston debris on it that should come off.

pull the carb rack off and check the center bowl for water/debris before you dump them out, and also inspect the pilot jet, and main. squirt carb cleaner up thru the place where the pilot jet threads in and confirm it comes out the idle feed orfice in front of the carb.

While you have the rack off, do yourself a favor and raise the needles so this wont happen again. I will post a needle article for you to read on vipers.

http://www.totallyamaha.net/forums/...edle-settings?highlight=raising+needles+viper
 
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great write up mr viper makes sense.i also found a crack in both the exhaust manifold and secondary pipe after it. hoping i can weld them.After i get my parts i will start tear down of carbs and will be in contact with you for further help when needed thanks this will be a long rode i fear not a quick easy job i was hoping for. much appreciated on the help guys
 
Ok guys a few new questions I have regarding this rebuild. 1# because the head is damaged do to this centre piston chamber overheating is it possibly to get machined and still be ok to use. I'm concerned that this will change compression and not be good to have the other two still at stock. Also if I was to go the route to bore out cylinders and oversize pistons do carbs have to have new jets installed or just adjustment needed.? What is the cheapest route stock or oversize? I'm on Ontario Canada and have a hard time finding a top end rebuild kit for under 600$. Thanks
 
the cylinders on your viper are nicasil plated aluminum, therefore you cant just overbore them and put new pistons in without recoating the cylinders. The only oversize pistons offered for them is a 73mm which is what a 780 kit would use. it will cost around 175 each to replate plus the boring of the cylinder-$40 each.

the head can be slightly flat cut if its not straight but would then want to sure use the bender opticool gasket to gain the thickness back, the viper already has high compression in the mag and center cylinder. post a pic of the head, if its not bad you can smooth out the pitting in the chamber with sandpaper and rerun the head, it will be fine for a trail sled if minor.

I would only use Yamaha pistons and rings, they are far superior to the cheap aftermarkets, you should only need the 1 piston and 3 new ring sets to freshen it up.
 
The chamber is the the part that worries me it's pitted pretty bad. So wiseco pistons are not as good as yamaha ?
 
Wiseco pistons are only good for racing I think. I have seen lots of wiseco's cold seize from lack of warm up they take longer to warm up properly.
I run spi pistons same specs as OEM and are a great piston.
But really it comes down to what you prefer to run as everyone will have a piston that they like the most.
 
Hey boys just want to give an update plus ask few more questions. So turns out the overheating was from the water pump being worn out. The teeth on the gear are stripped and bent. Also the gear on the crank shaft that turns it is really stripped and some ball bearings are missing from the bearing next to the gear. Looks like a lot of metal debris is floating around causeing the case to be scored also. So..... Ya it's pretty bad shape. Where can I get parts or a rebuilt crank now. I'm in canada Ontario. Should I start a new thread for this rebuild now ? Thanks guys ps I'll post pics of damage when ever u want
 
You might want to just find a good used engine. There are some guys on here that have them for sale. Likely come out pretty close on cost. But of course if you want a full rebuild go for it. Cranks are going to run you a bit either used or rebuilt. You might only need the cross shaft.
 
bent toys in north bay, total recreation near simcoe, cycle salvage in Peterborough, cv tech. call around, it may be cheaper to find a compete motor if your into a crank, cyl piston and water pump shaft.
 
So is it even possible to rebuild a crank myself ? Does it disassemble? I can't even find a parts list or break down for the crank anywhere. Im looking in my area for a used one at the moment with little success.
 
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