How to modify a rave vale

[rgpbeme]

I am having to redo the top end in my 96 gsx. The machine shop checked with wesco and they have a 1.5 mm over. So they bored and honed and got the pistons and rings.
I looked in the manual to see if the rave valve should be adjusted and there it said the motor could only be bored one over and that is .25mm

It said the unless you have a min. clearance of .375mm will require reworking the guillotine to achieve proper clearance.

Anybody ever done this. Can you cut the other end instead?

The more I dig the deeper I get

 

[kustomkarl]

Do you have a seadoo manual? It is described in the manual how to cut the rave valves. I will check our Library of manuals for the info.

 

[kustomkarl]

Ok here is what I found: On the 1996 GSX Model # 5620 with a 787 engine, stock configuration RAVE valve guillotine has a minimum clearance of 0.5mm (.020 in.) to the cylinder bore, measured at the center line of the cylinder. On the 787 engine,only a first over size is aviliable that is 0.25mm(0.10in.).The guillotine will have a minimum clearance of 0.375mm(0.15in.) with the cylinder bore. This is the minimum clearance the guillotine should be used with. Less clearance will require reworking of the guillotine to acheive proper claerance and radious.
Ok, we are on the same page... as a direct quote from the manual. you can not cut the stem of the RAVE valve as the guillotine radious and length is what must be modified. The stem and bellows will stay the same.( if you cut the stem you limit the travel of the RAVE valve, that's not the goal here)
When the RAVE valve is reworked you must keep checking measurements to have the clearance. I hope this helps you with your rebuild. Let me know If you need more info, or help.
If you want more details on this subject, you could join as a premium member and download the manual and see it first hand. Click on the seadoo manual section at the top of the page for more details. Keep us posted on your progress.
Karl

 

[seadoosnipe]

Good!

Very good work Karl...
I think in this day of online company's who sell the remanufactured OEM engines, it's probably cheaper to buy than to rebuild. When you bore engines over, there is always the possibility of overheating, leading to a shorter engine life span.
When the cylinder wall thinkness gets thinner and the piston gets bigger, your cooling system has to remove more heat. I haven't heard of many people who have done rebuilds or people who have had a problem with changing engine bore. This is done quite frequently by racers, who bore and change ratio too for the increase horsepower but their engines have very short lives.
Karl's information is very well put. I'll be curious to hear of the results of grinding and polishing the new tolerance to your RAVE. If your able to find a machine shop to do this, it may be wise to jot down the tolerances Karl quoted. I think it very valuable to the machinist doing the work.
Good luck!

 

[rgpbeme]

Bore size?

I see the manual says that only a .10 over is out there. I went to the machine shop and they ordered a 1.5mm (.60) Wesco piston and ring set for that motor right out of the book. It is already bored and honed and pistons fitted
So I will have to cut 1.5mm off the rave is what it looks like to get back to the proper clearance :ack:

 

[seadoosnipe]

Yes...

Yes, that's true. The bore over on your machine is pretty great. I have no idea what the end result is going to be. If this all comes together o.k., then you'll probably add a few more horsepower.
Let us know how you come out. I wish you all the luck with this project!:cheers:

 

[kustomkarl]

1.5mm (.60in) is a large over bore! I have done large over bores in the past for Jetski race boats I used in competition. I wound up running dual water feeds with a dry water box, with stright out the rear exhaust, for maxium performance, on my 440 superstock standup. It sounded like a dirt bike and pulled close 58mph.(keep in mind it only weighed 250#)The stock water feed on your GSX should be adequate for your stock seadoo.
I would suggest that you have the shop that is doing the work look at the specs in my thread and see if they can modify the rave valves to have the clearance needed. Hopefully the shop your working with is into modified seadoos. You will have to re-jet the carb to compensate for the larger bore now as the motor will want more fuel to run efficiently. Check the spark plug readings and adjust the carbs and heat range of the plugs accordingly, and maybe advance the timing a couple degrees. It will be a power house when your finished. Keep us posted, and if you need more advise ask away. 1 question for you, why did the repair shop go with the largest over bore availiable?

Karl

 

[seadoosnipe]

Answers?

Please keep us up to date with your findings. There are many forum members inteseted in how this mod comes out. I'm very excited to see how much more power you get out of it!........:hurray:

 

[Dennis]

Modified RAVE

All of this RAVE clearance has got me to thinking. I don't know my thinking is correct. Don't know I can properly explain it but here goes. Be patient.
It was stated that because the cylinder had been bored .060 over that now the valve must be shortened .060 for proper clearance. If you look at the cylinder from above, draw an imaginary line from the top of the bore to the bottom (dividing it in half) you would have enlarged the bore .030 on one side and .030 on the other if it got bored .060. Seems to me that if that logic is correct you would only remove .030 from the valve to keep enough clearance.
Does any of this make any sense? Thanks, Dennis

 

[rgpbeme]

Why the overbore?

You are straight right on I was miss thinking the overall vs the 1/2 bore from center. The reason it was board over is I bought the ski with a new top end.

It had a or has a elect problem that was my post on reverse polarity I had only ran the ski about 30 min.because of that problem. I think I got it fixed with a new stator at least my testing out of water seem to show it fixed. I took it out for a water test and it ran about 10 min. and died. Took it back to the shop my friend is letting me use. Checked the compression 125 front 0 back. I took the heads and cylinders off. The back new piston looked melted around the outside edge. This was a new top end?
(I never had a temp light come on.)
Some one forgot to put the retaining clip on one side of the back kingpen. It had moved over and grooved the cyl. wall. We tried 1 mm over but that was not enough for the groves so went to 1.5 as that was the next piston size or go to a sleeve and pistons.
I found out the guy who did the top end never looked at the carbs. I think the whole mech. problem starts there but I have not got that far but will.
I have never worked on a sea doo but have on some outboards So I have to learn what I am doing step by step. I thought I bought a minor elect problem but have been shocked by what it has turned in to.
Your support has kept me from just sinking the thing.
I went through the push the start button 5 or 6 time and a stored code that said over temp was there.

I was thinking about the RAVE valve and why could you not just shim the mount .30 with a extra gasket or two?
Thank you all again

 

[Dennis]

Rave Shim

Shimming the mount won't work because the mount is not what stops the inward travel of the valve, the cylinder does. Dennis

 

[kustomkarl]

Oh man, I feel your pain! Buy something that was rebuilt and find out the hard way it wasn't done right. The real question...would the builder that screwed it up, make good on a bad repair job, or maybe help a little on the expense?
Well if you think about it, cutting the RAVE valve shouldn't be that big a deal if you get a machinest to do it to spec. Make a couple calls around and see what you get for prices. Keep us posted...
Karl

 

[rgpbeme]

Back to the old Rave.
After looking and measuring and not finding anyone around here that could do the Rave This is what I did.
First as I looked the front edge that goes in to the bore is blunt and only a small portion sticks in the cylinder I decided to just cut that part back the .030.

I took my calipers and set then a .030 and locked them. I then took the points and scribed a line around the leading edge.

I took a round file and cut up close to the scribe line.

I then wrapped the old piston with 380 w/d dry sandpaper. I held the Rave level and sanded up and down on the side of the piston. (I has a reference mark also)
I keep the sandpaper wet and you could see where it was cutting by the residue on the paper. Kept sanding till it was a consistent and fit the piston. I them buffed with 600 grit. Tomorrow I will put them in and run a straight edge down the bore and get a feeler gauge check.
I must say for seat of the pants work they came out real good

 

[Dennis]

Rave

Sounds like a really good method. I'll have to remember that.
Keep in mind that the piston that is being used as the sanding template has to be .060 over or the radius of the valve will be incorrect.
Thanks for the update, Dennis

 

[rgpbeme]

Dennis thank you and we are both right and wrong.

I used the old piston which was .50 mm over but I had measured the sand paper because that adds to the od of your piston if using it for a backing. I rechecked the RAVE to the new 1.5 over piston and it was almost right on. I used a back light to see the gap if any. There was a small amount in the center. I then used the new piston for a backing but with sand paper it would be to big. I just stroked the paper a few times then checked with the light It took about 10 strokes and was perfect. NO light between the new piston without sand paper. With the sandpaper a very tiny bit of light would show in the center so I just was taking the outside edges off and that is what it needed.
PS I was using 180 grit not 380 as I said:hurray:
Thanks Ron

 

[D 5UPE]

This is a good bit of reading.
Its marvelous what someone can achieve with abit of elbow grease and thinking, when the resourses arn't on the doorstep.

Hope the jobs a goodun for ya.

 

[kustomkarl]

Good Job Ron!! That info I'm sure will come in handy in the future for someone else. Please keep us posted on the project as it progresses.
Karl