here is a picture of my piston through the exhaust port. I took the exhaust off because i thought i had the common rattle in the power valve, plus the engine seemed kind of weak in the mid then it seemed to come on the pipe hard for a short time only to feel like it has no over rev. I was in the sand dunes 45 days ago and the bike would not pull third gear up a hill. i was pretty dissapointed. it would run fin through first and second and a shift to third and it would not come on the pipe. My dealer adjusted the float level and it seemed it maybe was starving for fuel. since then i double checked the float level and found it to be pretty low. could this have caused the scuffing? FWIW i run maxima 927 at 32 to 1. maybe 75 hours tops on the bike.
scuffed piston??
- Thread starter BryanMcc
- Start date
Jakobi
Super Moderator
Stick your finger in there and have a feel. Are they actual scratches or is just the coating wearing off?? When the bike was running weak was it a cold day? Sea level when you usually ride at elevation? What was the jetting? Any signs it was running short of fuel? Hanging idle or the likes?
Heres what my stock piston looked like at 75hrs, at which point I changed it out. The rings were still in spec but I did have a bit of piston slap happening.
Heres what my stock piston looked like at 75hrs, at which point I changed it out. The rings were still in spec but I did have a bit of piston slap happening.
Thanks for the info. I did feel the piston and you can see in the photos that there are a couple spots where it actually feels rough, but for the most part it felt prett smooth. As far as the power output, i started with a JD kit and worked my way leaner (to thier rec 170 main, red needle number 3, and 40 pilot.) this is for 5k plus feet. Not only does it come onto the pipe in an odd way there is a really tinny rattle under low rpm (like when i let off the gas and the rpms are returning to idle)...After i had the RH side powervalve cover off there seems to be some movement in the arm before i feel any spring tension, which i gather from reading means i need to pull the transmission cover off and adjust that linkage. Also...there is some lateral play where the rod connects to the triangle looking piece..Is this normal or should i tighten it, seems like it could be a souce of a rattle.
noobi
New member
Sounds like you've already found the material on adjusting the PV. Its seems to be pretty well documented on here and has certainly explained some odd rattles and poorer power problems.
Be careful with the nut that holds the actuator arm onto the triangular plate. It it locktited from factory and is not uncommon to break the weld on the stud before the nut starts to loosen. Would pay to get some heat on the nut before giving it a crack.
Also, iirc the whole PV mechanism can have lateral play, because its all mounted on a axle between bearings, however if you preload it up so theres no lateral play it may cause the system to seize up from exhaust gunge, and thats never good.
Jakobi
Super Moderator
Ahuh.. I'd personally take a squish measurement, and then pull the entire top end. Its due at 75hrs anyway. Have a gander at the reed valves and the state of the cylinder for damage/scoring. While you're in there set the port timing via base gasket stack (this is a personal preference), and then have the head machined to spec. RB has great feedback but there are others who can do it.
When you put it all back together check the tension again, and adjust if required. You will be shocked by how much better the bike runs and how much more grunt you will have bottom to top.
As noobi said, there needs to be a certain amount of tolerance in the pv assembly to allow for carbon build up.
When you put it all back together check the tension again, and adjust if required. You will be shocked by how much better the bike runs and how much more grunt you will have bottom to top.
As noobi said, there needs to be a certain amount of tolerance in the pv assembly to allow for carbon build up.
Here is mine 15h old piston (vertex) and scratchy cylinder. Works fine and was powerful too but makes little noise(piston slap) http://www.nettivaraosa.com/moottoripyoran-varaosat-ja-tarvikkeet/1354745
Last piston was wiseco and it takes 30h and lose 1mm from carburator side skirt :/ And make quite bad noise of course.
Now i have new cylinder and piston...meybe old cylinder was too scratchy and eat pistons.
standard jetting and 2% oil mix..
Last piston was wiseco and it takes 30h and lose 1mm from carburator side skirt :/ And make quite bad noise of course.
Now i have new cylinder and piston...meybe old cylinder was too scratchy and eat pistons.
standard jetting and 2% oil mix..
im going to do the topend here pretty quick... any ideas on the best piston to use? wiseco and vertex doesnt list a piston for a 2010 300, they both stop at 07. Any changes since then or can i use on of those pistons. When you talk about setting the port timing what am i looking for? right now i have three green gaskets ( i think, kinda tough to tell what its still together). Also is there any other parts i need for doing a topend? most kits come with the pistons and ring and clips but is there any gaskets i need or anything? Also two other questions... should i hold off on messing with the power valve adjustment until i set the port timeing since it changes doesnt it? also same with squish adjustment right? wait untill i have the port timing set before taking a squish adjustment?
noobi
New member
Pistons havent changed in ~10 years, so yes and 07 will work fine.
Im partial to Wossner pistons, a well known German forged piston brand. Seem to be very well priced. Vertex is also a good brand, I'm not so much of a fan of Wiseco.
You should probably get a few base gaskets, they come in different thickness's, and the 2 head o-rings.
Jakobi is referring to setting the port timing via base gasket stack height, ideally with the exhaust port fully exposed at bdc, then machining the head to give a suitable squish and volume.
It would be worth measuring the squish band before you pull the current set up apart, just to gauge where you're at.
Jakobi
Super Moderator
Noobi hit the nail on the head. I'm the same re Wossner. My choice. The stock ones are Vertex and are cast pistons. Both are good.
The port timing is set by the base gaskets and as Noobi said you probably want to look at setting the top of the piston flush with the bottom of the exhaust port at bottom dead center.
I'd also take the squish before hand, and then again after.
The port timing is set by the base gaskets and as Noobi said you probably want to look at setting the top of the piston flush with the bottom of the exhaust port at bottom dead center.
I'd also take the squish before hand, and then again after.
thanks for the info on the pistons, i will indeed buy the wossner pistons. Does anything else change going to a forged piston? i read somewhere they need a slightly looser setup due to the forged expanding more than the cast. So if i set the port timing like you said does it do anything to where the power band is? sorry for all the questions but i do appreciate the info! thanks again for helping! Also any other things needed to do a rebuild other than what comes in the piston kit?
Jakobi
Super Moderator
Have a read here. I had a big thread running on my last top end. 300 to 250 convo with squish and port timing. There are some graphs that show the effects of port timing on the engine also. Disregard the maths and techo talk if you wish.
http://www.gasgasrider.org/forum/showthread.php?t=11970
Must have parts.
Base Gaksets 2 x 0.5mm and 1 x 0.3mm (usually enough to do things)
Head Orings (inner and outer)
Piston Kit (rings, clips, pin and piston)
Small end bearing (cheap insurance)
Exhaust spigot Orings (and gasket if removing)
Other gaskets good to have spares incase of damage (RHS PV, LHS PV, Waterpump, RHS Engine, Clutch, and Head water stem)
Scotch bright (cleaning cylinder walls)
Fresh fluids (oil and coolant)
Looking at the state of your PV assembly I'd possibly consider replacing the bearings in there too. They are common at any bearing shop. Work that one out when its down.
http://www.gasgasrider.org/forum/showthread.php?t=11970
Must have parts.
Base Gaksets 2 x 0.5mm and 1 x 0.3mm (usually enough to do things)
Head Orings (inner and outer)
Piston Kit (rings, clips, pin and piston)
Small end bearing (cheap insurance)
Exhaust spigot Orings (and gasket if removing)
Other gaskets good to have spares incase of damage (RHS PV, LHS PV, Waterpump, RHS Engine, Clutch, and Head water stem)
Scotch bright (cleaning cylinder walls)
Fresh fluids (oil and coolant)
Looking at the state of your PV assembly I'd possibly consider replacing the bearings in there too. They are common at any bearing shop. Work that one out when its down.
