Piston options

Advertise with us
shop deals on amazon
Shop deals on ebay
Yamaha Raptor 350 & Warrior Forum

Help Support Yamaha Raptor 350 & Warrior Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
S

steveau

New Member
Joined
Dec 22, 2011
Messages
2
Reaction score
0
Been thinking about upgrading the piston and cam for my raptor 350 and wanted to know what piston options are available for a stock stroke. Was hoping to get the highest comp piston that can run on pump gas (98 RON in Australia, about 93 AKI). The options are:

10.25:1 or 10.5:1 from Vertex, Wiseco and CP
12:1 from JE

Is 12:1 too high for pump gas? Are there any 11 or 11.5:1 options available or can I fiddle with gasket options to get the 10.5 pistons up a bit more

As for the cam, the HC2 is by far the cheapest option even though its not the best. The shipping to/from Australia for a regrind cam like the web is just too much $$$, especially when you add the cost of springs. So looks like I am stuck with the crappy HC2

Steve
 
use RVT instead of the base gasket that will bring the compression up a little
 
Go to wiseco and je's websites. They have more piston choices there. I personally like to use the base gasket. It's there for a reason. But, using good BLACK rtv will work. Also, get the cometic EST gaskets. They have a couple different choices. The one I used has a .007" thinner head gasket. Having your head decked will help to raise compression as well. Mine is decked .015". With the stage 1 hotcam I have there is no valve interferance. Several of us on here have them and like them a lot. If you ride more trails than anything you make want to look into the stage 1. If I were you I'd go with a 10.5:1 piston, cometic est gaskets, and a vito's +4 key. The key will advance your ignition timing the 4 degrees. Will make the bottom end hit harder, and will work well with the hotcam and piston. If you're going to get the head rebuilt have it ported. It'll get the most out of the cam, and will flow better in general.
 
I say go with the JE 366 10.5:1, and work on performance from there..

Pat has some good advice on here..
But don't just use RVT to seal up the jug, use a base gasket. It'll save torquing issues, and I would be worried about the sealant blowing out.. (But that's just me)
 
I just mentioned it cause I heard it mentioned on a few other builds on here. Not recommending it just heard it was a way to get more compression.
 
That's why I don't like the RTV idea^^^. The gasket is there for a reason. The better way to do it is decking the head. Which gives you a MUCH better quench area and is truely flat after the decking. I wouldn't go more than the .015". Decking the head kinda helps the hotcams, too. It slightly advances their timing, so the power comes on a hair sooner, which is good because their ramps are "fatter" so they don't open as fast as a Web Cam. Figure my bike has a total of .022" smaller chamber, so the head sits .022" lower... you do the math. lol!
 
The RTV option doesnt mean just any RTV it specifically is recommended Black or grey, I will guarentee that they will hold up atleast as long as the cheap paper gasket that most kits use for the base gasket. I deal with paper gaskets and RTV made gaskets(youd be surprised how many newer cars use just a bead of RTV to seal things from the factory). I will almost bet that any RTV setup using the proper RTV will last longer than the paper. The oil pan gasket on my 7.3 powerstroke Diesel is just grey RTV from the factory and it can hold back the pressure of that and the 4 gallons of oil for over 200,000 miles. I think Ive made my point!!! LOL

On the same front though, if RTV is going to be used you will want to check your clearances closely. If your just a little to close the first time you rev high your valves will look like the ones that came out of the head I got from akaguppy, and we are not even sure how his happened. But they were just ever so slightly bent, just enough to loose enough compression for it not to run. Quick glance before removing them I couldnt even tell they were bent. Rolled the stem on a flat surface and watched both the heads dance!!


Piston wise though Id recommend either wiesco or JE. I ran a wiesco in my old 98 and Im gonna be running a 85mm JE in my 99.
 
Well I've done a lot of work on 2 strokes, and have used RVT to seal up the base.
(It helps lower the squish, hence more compression. It also helps to stop heat quench in the head)

Although on most 2 strokes the ports follow the jug down into the case, putting more stress on the sealant (gasket). I've learned that just RVT alone doesn't cut it, and just the gasket alone doesn't cut it.. I've blown shitloads of base gaskets..
Now I use both.. lol
A bit of RVT on the gasket helps to stop blow outs, and save a pricey rebuild..
I also make my own gaskets these days to, knowing the compressed thickness of most gasket materials.

But yah, I just thought I would add that..
 
Oh dude I know exactly what you are talking about with newer cars mosly using RTV from factory. I work on that crap all the time, too. I just prefer gaskets for most things. But yeah, RTV can withstand some ****. Like intakes and such. Biggest prob is people use the wrong **** and it leaks. That and the idiots at the auto parts store have NO FREAKIN CLUE WHAT THEY ARE TALKING ABOUT! It says black rtv they give red. It says red, they give blue. IDIOTS! That grey **** is tough as nails though. Some oil pans are a pure bitch to take off. Atleast about the only time you have to take one off is when you do engine swaps and you have the engine on the stand and can get around the whole thing, lol. We personally use the Versa-Chem Black. Have never had any issues with it.
 
Gen1Pat said:
There is some **** you have to use both on, when doing repairs.
Click to expand...

lol.. True enuf.
Most of these old air cooled 2 stroke aren't all that square anymore. I like to think it just keeps the gasket from wanting to slip?

And the Permatex grey RVT is the shiznit.
 
Mathius said:
lol.. True enuf.
Most of these old air cooled 2 stroke aren't all that square anymore. I like to think it just keeps the gasket from wanting to slip?

And the Permatex grey RVT is the shiznit.
Click to expand...

Ah there it is I forgot exactly what brand and such, but the minute you siad that I remembered. Thats exactly the RTV I use unless Im in a very high heat area(cant remember the color but I know there is one for such areas). That Grey is the **** that my 7.3 has for a oil pan seal and that **** holds back the pressures in that engine.

And Ive done the paper gasket/RTV deal before, like on my cars thermostat housing. 24 year old stamped steel housing flush mounted on a cast iron head. Ya a chinsy paper gaskets really gonna seal that!!!!LOL
 
Thanks for the replies. Should've added that I mainly ride trails and dunes.

So far this looks like what I'll be doing:
10.5 JE piston (85 mm)
Cometic EST gaskets
stage 1 hot cam
have the head decked by 0.015"
vitos +4 key
run with 98 octane (RON) fuel

now just gotta find the right machine shop (in Sydney) to do the head and cylinder
 
You won't be dissapointed. I've found the valves like to be adjusted to .004". The only thing different than my set up is mine in 84mm not 85mm. Just rotate the engine before you start it, to make sure you have no interference. You shouldn't because (A) I don't have issues, (B) people run without the base gasket w/bigger cams and are fine, (C) These bikes have a decent size chamber to begin with. But it never hurts to be sure. Lol. You'll be impressed with this set up.
 
You must log in or register to reply here.

Latest posts

Back
Top