I'm reinstalling my RK TEK head. Slapped it on the day before race day and didn't get a chance to test it properly (suggested 0.040"). Didn't work the way I think it should. My squish was too high at 0.065" according to a solder test I performed. There wasn't enough time to go get a thinner base gasket and reinstall so I ran it anyway. Got my arse wooped. This week I've took it all down, got the cylinders off, cleaned up any rough castings in my reed cage & intake ports with water paper and elbow grease. Got a thin 0.4mm gasket and some 480 main jets. Gonna give that a try.

I contacted the manufacturer and explained my situation but I'm a little confused. I was asked to do a piston height measure rather than a solder test. According to the new measurements I wasn't too far off spec. Shouldn't I have noticed a power increase or is it only noticeable with smaller main jets?

I'm a little afraid that if my new base gasket is too much thinner that I'll be too close on the squish. It's all so hard to measure. The thing is do I go strickly on the addition of piston height + o-ring + head indent or do I reassemble with the thinner gasket and do another solder test. Does the compressed o-ring yield a measurement or is it merely sandwiched between both metals? The indents on the head measured 0.035 so I have to make up an extra 0.005 in piston height?!

Kelsey from RKTec does not believe in the solder method. If your sure the piston is at TDC, and you've measured correctly(only on the two sides of piston where the wrist pin is), then use this measurement. How much height did you lose by changing base gaskets?
What's the compression ratio for the head?
What elevation are you at?
What octane fuel are you using?
I had my stock head recut by Kelsey, and my exaust temps went from 1250 deg.@WOT, to under 1125 deg. So, I would think you'd have to rejet, especially if your rich to begin with.
Oh, and the o-ring has no effect on height, just deck measurement plus recess in head(all measured at the outer edge) = squish.

Blokhead is correct, Kelsey does not like the solder method. If I check mine with it I come up with 62.5 thou. His head likes to be jetted down. I am running 480's with the 942 needle in the second from the top position. I am still a little fat on the bottom but the rest is good. My sled runs better today than it ever has. I had to add a bunch of pin weight with the head which in turn sez it making power.
Brian

I have done the squish both ways to compare-solder method usually reads .020" thicker than the other way. Solder .060" = .040" measured directly. Sounds like you need a base gasket .1mm thinner than you had. Definitely jet to 480's.

I have a RKT head on my '01 800. with the solder method I get about .060. Actual deck height + step in head comes out to .040. I would believe this number before the solder number... What I don't get is where the .020 descrepency come into play??

I have 170lbs. of cylinder pressure when cold... jetted to 420's and the sled absoulutley rippss!!! seen 115 or better many times on the lake...

Thanks Kelsey!!!!

Pete,
I wounder if its because solder is pretty stiff, and doesn't really want to compress? I'd like to try something like Plastigage(for measuring bearing clearance), and see if it gives a different measurement. Although I don't know if it comes in that big a size.

I just checked, Plastigage (http://www.dana.com/perfectcircle/Plastigage.htm) maximum is .020.

Yes Blokhead I would have to say they don't make plasti-gage that big..(good thought though). Might want to try the clay method as used on hypo engines for checking piston to valve clearance..

Either the solder isn't fully compessing( like you said) or the piston is rocking in the bore.. JMHO..

Got instructions from Kelsey... Man, this guy is excellent! I bought the head second hand and he still offered tech support! I installed a little thinner gasket and rejetted 6 sizes on the main from 500's to 440's. The machine much more lively! Took 1st place in the 660' drags yesterday (600 Modified). Worst thing now is $ for more mods!

Blok Head, are you happy with this RKT head? I am thinking of getting one for my 02 700 VES. Kelsey was very informative on the phone. Customer service definately can make a sale happen.

Every material has a certain amount of elasticity, even solder. The difference you are seeing is it "springing back" after it is squashed. You can help the accuracy by choosing solder or lead that is real close to the size your measuring, less squash less springback effect. Also it seems that the more times it is struck the more it takes a set. Try holding the solder and having another person pull the cord, insted of simply rolling the motor over once. Even then, the most accurate way is the deck height + or - head inset or step measurements.

2blu7,
The head made more of a difference than the reeds, and boost bottle. Although it does require rejetting. Make sure you buy his head, and don't have your stock one recut. Polaris's casting process leaves a lot to be desired, its very porous, and all the machined surfaces had tiny pits. Kelsey did warn me this might happen, but I got the work done for free, because I traded him something he was looking for.
Oh, and it now seems better on gas.

Here is part of the story on measuring squish with solder, the first part
was mentioned earlier, solder that is close to the squish clearance and
rocking the piston back and forth over top dead center at least half a
dozen times.

Now here is a even more important part of it. I used to measure squish
the lazy way (through the spark plug hole with one piece of solder) when
I had cut the head and squish on a 617 rotax I had put in a Phazer Mtn sled.
The squish was right at about 40 thou and and it ran well but a few months
later I had the head off and I could see the piston had been kissing the head
just a little. So I have never done it that way again. I take the head off and
put a dab of grease on both sides of the piston over the " wrist pin" and put
a short piece of solder on both sides of the piston in the grease. Then bolt
the head back on and rock the piston over top dead center half a dozen times.
This will give a much more accurate measurement. Now it will still get a little
tighter at max rpm but with a reasonable clearance, no problem. The other
thing you clearly see with the solder method is the taper of the squish clearance.
When it opens up moving toward the plug it is more forgiving of low octane
and detonation. If its the same from one end to the other theres not as
much fudge factor on octane or jetting.

The other problem with solder now days is I believe they may have taken the
lead out of it. The thicker rosin core solder seems to be a bunch harder than
years ago.

Good Luck

Originally posted by LRD@May 25 2004, 04:19 PM
Here is part of the story on measuring squish with solder, the first part
was mentioned earlier, solder that is close to the squish clearance and
rocking the piston back and forth over top dead center at least half a
dozen times.

Now here is a even more important part of it. I used to measure squish
the lazy way (through the spark plug hole with one piece of solder) when
I had cut the head and squish on a 617 rotax I had put in a Phazer Mtn sled.
The squish was right at about 40 thou and and it ran well but a few months
later I had the head off and I could see the piston had been kissing the head
just a little. So I have never done it that way again. I take the head off and
put a dab of grease on both sides of the piston over the " wrist pin" and put
a short piece of solder on both sides of the piston in the grease. Then bolt
the head back on and rock the piston over top dead center half a dozen times.
This will give a much more accurate measurement. Now it will still get a little
tighter at max rpm but with a reasonable clearance, no problem. The other
thing you clearly see with the solder method is the taper of the squish clearance.
When it opens up moving toward the plug it is more forgiving of low octane
and detonation. If its the same from one end to the other theres not as
much fudge factor on octane or jetting.

The other problem with solder now days is I believe they may have taken the
lead out of it. The thicker rosin core solder seems to be a bunch harder than
years ago.

Good Luck
you can get differant versions of solder,as stated earlier you want to use stuff close to the thickness your measuring (.040=use approx .060 or so solder)also the hard solder is the stuff mandated by government for use in potable water.as you may have guessed it doesnt contain any lead as stated earlier because of the lead poisining issue in drinking water. the good newsd is leaded solder which is much softer aka very easy to compress is still available just ask your local hardware or plumbing store to help you.one more thing make sure you use rosin core and not solid or BY ANY MEANS DO NOT USE ACID CORE IT WILL EAT YOUR PISTONS AND CORRODE YOUR CYL!!!!!