Super Jet Squish opinion wanted.

amitchell · Feb 23, 2014

So it looks like increasing squish via dome cutting may be the best option for me, should I go for 0.050in? I read 0.045in for freestyle but I like to WOT a bit too.

Harbor · Feb 23, 2014

Ok I measured my similar ski's squish, both the stator side and coupler side are at .055--- I would suggest not going lower than this

Cranking compression 175 psi each hole on this ski

amitchell · Feb 23, 2014

Thanks, I think I should cut 0.020in to match what was decked. Then I would be at what ADA designed the head for.

amitchell · Feb 23, 2014

When you measured did you use two pieces of solder? I noticed when I didn't use two pieces my squish showed about 0.038in

Harbor · Feb 23, 2014

No I used only one piece, After the first bore I thought I would need to rig two pieces together but when I examined the solder closer the squish interference mark was obvious. My solder is aligned along the crankshafts center line

Harbor · Feb 23, 2014

You want a re measure?

amitchell · Feb 23, 2014

I just notice a difference between one and two pieces that's all. I aligned them with the pin one facing forward one rearwards. I would be curious if yours differs as much as mine did.

amitchell · Feb 23, 2014

The piston does rock slightly in the bore.

Harbor · Feb 23, 2014

amitchell said:
I just notice a difference between one and two pieces that's all. I aligned them with the pin one facing forward one rearwards. I would be curious if yours differs as much as mine did.

You mean you measured both both side of a single piston at the same time?

amitchell · Feb 23, 2014

Harbor said:
You mean you measured both both side of a single piston at the same time?

Yes two pieces single piston.

Harbor · Feb 23, 2014

Ok I'll go re measure it

amitchell · Feb 23, 2014

I appreciate the help Harbor!

Hopefully this thread will help others as well.

amitchell · Feb 23, 2014

waxhead said:
There is a certain amount of stretch in the con rod bearing piston etc the higher you rev it the more it stretches.

So whats the procedure to set the pistons to hit the head at 1000rpm higher than limiter? I am not sure I trust myself with that!

Harbor · Feb 23, 2014

Your welcome! Ok I remeasured the squish with two pieces of solder on the same cylinder @ the same time, each touching the cylinder wall and inline with piston wrist pin centerline, one facing coupler the other towards the front cylinder. The force I noticed to compress the solder was twice as much & it felt more solid, however the squish measurement came out the same .055

Btw this ski was used a lot for river boat chasing and surf and has a 13/17 prop

amitchell · Feb 23, 2014

I am going to triple check mine again tomorrow, doing single and double method.

Harbor · Feb 24, 2014

One thing I did was bend both ends of each piece of solder 90 degrees this way I could tell I was in line with wrist pin from outside the cylinder during the procedure

amitchell · Feb 24, 2014

Yeah I did that too, also had a flashlight in my mouth so I could see in. Pain in the ass with only one set of hands.

Harbor · Feb 24, 2014

Lol! Same here

Harbor · Feb 24, 2014

You got rings on your pistons?
I guess that would not account for piston rock on the pin axis to the tune of .007

amitchell · Feb 24, 2014

Yeah I just installed fresh pistons a few days ago. I had Gordon at pacific jet sports bore it for me and supply pistons. I measured 0.005in clearance on the pistons. 0.018in ring end gap. My crank is a newer SBT (few hours).

I am going to pull the head, re-measure cylinder height, get exhaust roof to cylinder deck measurement, re-torque and measure squish again.

I am really not sure why I could have a difference in squish measurement that large. Can anyone else chime in on this?