broken rave valve

[05sportsterle]

I am new to seadoo boats and here is my latest. Bought the boat a few months ago. its an 05 with from what I can tell has an 03 or older engine(951). Starts great runs great. Was able to get the boat to 65 km/hr, 15 km/hr short of what it should do. Last time out I was only able to get to 55 km/hr and it was stalling after giving throttle. So I looked at the rave valves and found I had a broken upper spring that holds the bellow. decided to take them completely apart and clean. Tthat is when I found the broken valve. Would this along with the missing spring on the rave bellows cause the losss of power?? I did notice that the top end gasket was replaced so I am thinking this happened a while ago......but no new rave valve. ANY input would be great. THanks

 

[Coastiejoe]

Last two digits of the HIN are the year and unless the engine has been changed, it should be a year behind the boat.


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[05sportsterle]

its definitely not an 05.............pretty sure engine has been changed at some point.

 

[Sportster-2001-951C-Stock]

With the tip missing off that RAVE, I'm thinking this would cause a rougher idle and rough low speed operation but it shouldn't affect performance at the top end. That is, assuming the valve was open, and not in the closed position. These are power vales that are supposed to open to allow the engine to breath at the top end and they close for smooth low speed.

If you have a compression gauge, it's time to confirm compression is good. A perfect 951DI motor should blow around 145psi, I believe. If it blows 125 or better and even between the two cylinders that's okay and rebuild those RAVEs with good parts and go from there.

Anyway, the RAVE opens somewhere around 5,000 RPM for my carbed 951, I think it's the same for the 951DI....

If the boat doesn't reach speed, that might not be a fault of the engine, there could be something going on with the jet pump. We really need to know if your engine RPM are closing in on 7,000 RPM

I was able to reach 80 KPH on the speedometer with my carbed Sportster LE a couple times, the water was ideal and not much wind. The engine was running about 6850 RPM Otherwise, 72 speedo KPH is about tops.

Most Sportster 951DI owners commonly report ~80 KPH or slightly more, I think.

 

[05sportsterle]

the boat does idle a lil rough but I just give it a little throttle and it smooths right out. Tach does not work.....I will have to read up on how to do a compression test and what I need. I also believe I have a carbed 951 but again not 100% sure. learning a lot from here though. Thanks again

 

[Sportster-2001-951C-Stock]

Yeah, that chip off the edge of the RAVE might not destroy idle completely, they'll still idle even if one cylinder isn't firing. A new RAVE blade might smooth out the idle a little bit though.

DI is the fuel injected engine, the last couple years of the 951's were direct fuel injected and there was an overlap period where both were available.

You can download a BRP Seadoo factory service manual for jet skis (no boats, sorry!) that used the 951 engine, there's a lot of important detailed info you need and most of it applies to the boats as well.

A new rave blade might need to be trimmed to make it shorter if the engine cyliner was bored oversize, so don't just stick any RAVE blade in there b/c it might scrape on the piston rings. Try to measure or find a way to confirm your engine bore (usually piston crown has the bore size if oversize). Just be careful your RAVE blade isn't too long....

 

[05sportsterle]

Cant I just measure the new one against the old one?
I think the di blades have a slot vs the carbed that are smooth??

 

[XP 787]

Have you located the broken tip of the rave? Do a compression test to make sure it didn't do to much damage to the cylinder/piston.

 

[05sportsterle]

ok just did my first ever compression test and .......130 psi in the cylinder with the broken valve and 125psi in the cylinder with the bellow that has no upper spring. Good or bad? Maybe the piece got spit out the exhaust?

 

[05sportsterle]

What is considered a good compression reading and what is BAD. Just for future reference, seems to be tough to find.

 

[crundell73]

I have a 787 with the same looking valve I just found , that is a 97 with a 130 psi in both cylinders , I have not seen the piece of valve either , looks to be done before I had the boat !

 

[Sportster-2001-951C-Stock]

Yes, one method of replacing the RAVE with new is by measuring the old one and cutting the new one to same length. This does assume the old valve was the correct length, and is probably how I'd do it UNLESS of course the engine was already apart or I wanted to remove the head to make sure (new head gasket required, for 951).

I kinda doubt this can be easily measured without experience but some top race engine guys can probably slip a feeler gauge down past the RAVE and touch the piston, measure then cut based on the measurement.

But, a missing tip isn't consistent with loss of speed unless some damage occurred when/if the tip broke off. Inspect the piston skirt and rings carefully through the RAVE port for signs of damage, such as bent or broken rings, also measure compression.

 

[Sportster-2001-951C-Stock]

What is considered a good compression reading and what is BAD. Just for future reference, seems to be tough to find.

135psi is a good fresh 951 carbed motor, 120psi is getting near the limit depending on how hard it's being run. Less than 100psi if it does make it there, the cylinder probably won't fire at low speeds.

What happens is as the combustion blow-by increases, the piston skirt eventually gets torched by hot exhaust gasses and the oil film fails resulting in a piston melt down. The 2nd possibility is the piston skirt cracks and falls off down into the crankcase due to piston rocking from excess clearance.

One thing about 2-strokes that some people don't realize is rebuilding them before they grenade is expected part of regular maintenance. Engine cases aren't free, out of production and might be getting hard to come by, so a spare rebuildable core isn't a bad idea if you like the ski more than perhaps you should, lol.

A couple more years and you too can buy a worn out 4-tec, now there's a nightmare to consider!

 

[Danosll]

be sure to check your housings and bellows(all soft parts) as well. replace if questionable. for what they cost jobber ,it is safe insurance.next time you brake a valve the outcome could be much worse. where in canada are you located?

 

[05sportsterle]

southern Ontario........order one new bellow the other looks goood

 

[Danosll]

make sure to check your housings . I changed mine and it made a world of differance. I have a good parts guy in vaudrauil which is close to ontario border..