Hello all. Im new to all most all this.(computers and atvs) so i just bought a cheep 99 warrior that dropped the vales.The piston now has a hole in the center. The head was destroyed as well. I took the cylinder to a shop and they said it had been punched .40 over and it has some small nicks it. It can be taken to .60 over with out a problem. So my question is should i go to .60 over?whats the pros and cons? Or should I get a new cylinder and piston back to the stock size of 83? Thanks for any input
piston size
- Thread starter bulldog
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Warriorfreak99
Well-Known Member
it put a hole in the piston because it jumped timing, get a new cam chain and sprocket along with a new head, the good about the 0.060 over is, depending on your intake/exhaust/carb setup, you will have more power, but it could run a little hot but you could get an oil cooler setup like the one in the link and there's a possibility you'll have to rejet the carburetor because you need more fuel but it's all really simple stuff, and by the way welcome to the forum! http://www.yfm350.com/forums/showthread.php?t=23592
1998yamahawarrior
Well-Known Member
The over bore would really be your call. You can actually go as big as .080 over which would be a 366. Any over bore will run slightly hotter than stock, but as freak siad oil cooler would counter act that. In my eyes even bone stock warriors can benefit from a cooler.
sparkymichigan
Well-Known Member
As far as the bore goes, 60/40/stock doesn't matter. Negligible power increase. Heat is always a problem on these bikes.
We need a little more info on the head damage. Did a valve break and wedge itself between the piston and head?
99 is correct to change the timing chain.
We need a little more info on the head damage. Did a valve break and wedge itself between the piston and head?
99 is correct to change the timing chain.
Warriorfreak99
Well-Known Member
ive got a parts bike that i bought off my buddy and it has a hole in the top of the piston, because it jumped timing, unless a valve came completely off there shouldnt be any other ways for it to happen..
thanks for the replies. I do not know how to put pictures on here but it did snap the valves off.The head is done and looks like hamburger.I think the previous owner tried to pull start it over and over again to make that much damage.So I need to (a)bore the cylinder bigger to .60 over (b) resleeve it back to stock (c)get a new cylinder all together. When I can convince my lady friend to help me I will up load some pictures
so this is all I know about the atv. It has a hot rod crank rod. Nerf bars. A DG push bar. Hole shot tires. What appears to be all stock carb and the previous owner said he thought it had a blue trax axle. but he did not seem to know to much about the four wheeler
Warriorfreak99
Well-Known Member
all 3 would work its all up to you, buying a new cylinder altogether and a stock piston would run you about $175 give or take the 60 over near the same and a resleeve is out of the question if you ask me its not needed. Get a nice used head on ebay or buy it from someone on here i have one but i havent ever used it.
duneracerweston
Well-Known Member
if you buy a *NEW* cylinder and jug thats around 300$
bore and hone and piston is the cheapest. i would do that if i was you.
i resleaved mine last rebuild to comply with race class regulations that cost me about 240$
no matter what you do you will need a set of valves and while your there you might as well go with a stronger set of springs which will open up your cam options later down the road if you wish to change cams.
i would change the cam chain and the guides while tou have it apart. they are cheap enough to make it worth it. after all nothing is worse then blowing a new motor the same way twice... i should know...
remember head torque specs are 36.8ft/lbs on the 4 mains and 23.4 on the 2 smaller bolts. (yes that was by memory. ive bult 10 stinking 350 motors and 9 of which were mine..)
bore and hone and piston is the cheapest. i would do that if i was you.
i resleaved mine last rebuild to comply with race class regulations that cost me about 240$
no matter what you do you will need a set of valves and while your there you might as well go with a stronger set of springs which will open up your cam options later down the road if you wish to change cams.
i would change the cam chain and the guides while tou have it apart. they are cheap enough to make it worth it. after all nothing is worse then blowing a new motor the same way twice... i should know...
remember head torque specs are 36.8ft/lbs on the 4 mains and 23.4 on the 2 smaller bolts. (yes that was by memory. ive bult 10 stinking 350 motors and 9 of which were mine..)
thanks dune. I just ordered a new timing chain and a new jug. I was looking in to a complete gasket kit and i am wondering if there is a difference in the kits. I seen some say yfm350 and some say yfm350x etc. How can i tell what motor i have?
1998yamahawarrior
Well-Known Member
The gasket kits your looking at are the same. As long as it says YFM350 thats the warrior/raptor motor. Now if it siad yfz350 that would be the Banshee!!!
