Rave valve theory question

[IDoSeaDoo]

Hey guys, so I've seriously started considering making some aluminum rave pistons for my 787 to replace the ridiculous plastic design. I mean really, who makes plastic exhaust components?? It's great for those aftermarket manufacturers who just cash in when we have to spend $20 every time one of our pistons melts (which is several times/season for some of us), but quite frankly I'm F#&$ing tired of this bs. And yea, there are going to be those of you who don't know me and are going to say "replace your valve and housing". Well I did, many times now. I have a box of old and dirty components. Every time I replace them (shelling out $200) they go bad in a month. I'm not kidding. They wear out and melt pistons in a month. It's so frustrating...
SO either I cut my riding down to just 10 hours/season, OR I could rectify this design flaw. However, realizing that the aluminum rave pistons weigh more, do you guys think that I could achieve the same functionality by just decreasing the spring load at the cap? I know that if something weighs more, it has more tendency to stay still, and require more force to get it moving. Could easing spring load compensate or would the raves never open fast enough?

 

[AdamXP800]

Subscribed.

My GTX melted a few of those Pistons last season. When I upgraded to the slotted raves and rebuilt them it finally solved my issue. I was at the point of replacing the housings but thankfully did not need to. Could your cases actually be worn causing the new housings to still melt the pistons?
I'll be interested to see if this works. If so I want some!

 

[LouDoo]

Are you talking about part #9? Maybe I've just been lucky, but I've never had one melt. Are you changing the "O" ring when you service the RAVE valve.

http://partsfinder.onlinemicrofiche...c&a=300&b=5&c=0&d=-CYLINDER,-EXHAUST-MANIFOLD


Lou

 

[IDoSeaDoo]

Are you talking about part #9? Maybe I've just been lucky, but I've never had one melt. Are you changing the "O" ring when you service the RAVE valve.

http://partsfinder.onlinemicrofiche...c&a=300&b=5&c=0&d=-CYLINDER,-EXHAUST-MANIFOLD

Lou

Yes, and yes. I changed everything, including O-rings. I've even tried fatter o-rings. Nothing helps. My theory is that I do have worn out jugs, allowing the raves to play too much inside the channel. But I have about a dozen jugs that I've collected over the years, and I couldn't notice a difference in how much wiggle room the guillotine part of the valve has inside any of the jugs. Neither do I know how to accurately measure this. In either case, I have no idea how I would fix THAT aspect of the problem. Any used jugs out there for sale are a roll of the dice in terms of their condition.
Also, I believe I too had slotted raves (have two channels on the back side, right?). They wore out just like the rest.

 

[330xi]

Weird, I've never seen this before. Would buy some though..

 

[Matt Braley]

This is my GSX 787 I found a pair for it but the bellow loves to slide off the billet aluminum even though it has a nice groove. I'm gonna try to replace my O-ring next.

 

[Sportster-2001-951C-Stock]

Does yours have items 15, 16, 17 inside as the 951 does, I don't see them in the drawing referenced above?

http://partsfinder.onlinemicrofiche...asp?Type=18&make=seadoopwc&a=256&b=6&Action=O

 

[SabrToothSqrl]

My 951 doesn't swwm to have this issue... Can you post some pics?

 

[Bonmotwang]

Does yours have items 15, 16, 17 inside as the 951 does, I don't see them in the drawing referenced above?

http://partsfinder.onlinemicrofiche...asp?Type=18&make=seadoopwc&a=256&b=6&Action=O

My 787 engine doesn't have those parts. And the exhaust gases entering the bellow not only through the small air passage, but also the clearance about the shaft. The clearance only get blocked by the oring when valve is fully opened at pressure.

The red knob could be adjusted low (manual says flush with the cap), so that valve opens at higher pressure, which means higher temperature I guess. And also in this case, oring seals later.

What is the knob setting on the rave. Backing it out may solve the problem.


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[IDoSeaDoo]

No, the 787 does not have parts 15-17 depicted for the 951. What do these do?

View attachment 28037

This is my GSX 787 I found a pair for it but the bellow loves to slide off the billet aluminum even though it has a nice groove. I'm gonna try to replace my O-ring next.

I too managed to find some already made billet aluminum caps. So glad, as I know very little about building foundries and casting metal. Wednesday should be warm enough to ride teh SPX, I hope they're in by then I couldn't believe I found some. I've searched for these many times before and noone had them in stock. I couldn't believe they were back until I saw them in the Checkout screen :cheers:

Matt, did you have to dial in a different spring load on the red cap to compensate for the weight of the new caps? What RPM do your raves open at?

 

[spx800]

Where did you get them?

 

[IDoSeaDoo]

http://topsidepowersports.com/cart/cart.php?target=product&product_id=56&substring=rave

BTW Matt, you can shorten the rave bellows retainer spring by unscrewing it where it mates to itself and clipping off a few coils. I've successfully done that to mine. Might help with it coming off. Otherwise, maybe try gluing it with some sort of polymer, silicone maybe?

 

[Sportster-2001-951C-Stock]

No, the 787 does not have parts 15-17 depicted for the 951. What do these do?

These three parts work together from the inside, to provide a dynamic seal around the RAVE shaft to keep exhaust gasses from traveling up the shaft bore into the bellows area.

I doubt your RAVE base is machined to accept these parts but I think this may be the upgrade that helps eliminate the problem of gasses entering the bellows area.

I think the aluminum piece you're looking at will not require a different spring tension due to additional weight.

I strongly suspect this issue you're experiencing is related to an aftermarket bellows that doesn't produce the proper actuation.

 

[Bonmotwang]

Do you have a picture of melt plastic? I believe it happens at the thread?


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[IDoSeaDoo]

Man, hope these metal rave pistons fix the problem, otherwise I think I"m going to look into how to upgrade to 951 raves.

I've had the pistons melt in two ways. Half the time it would just strip the plastic threads out. Other times, the part where the rave screws in would just break off and go up into the spring, leaving a dime size hole in the rave piston, and causing a lean condition.

 

[Bonmotwang]

Pretty sure that metal piston will solve the melting problem.
But it would be nice to find out why the rave shaft is over heating on your engine.

 

[IDoSeaDoo]

I don't think the shaft itself is overheating. The theory is that the jug where the wide part of the valve travels up and down is worn, allowing the whole valve to wobble, resulting in increased wear of the shaft/housing. Once the shaft is worn out, too many hot exhaust gases travel up into the bellows area and cause all sorts of damage, not to mention an ugly oily mess. And we all know how well synthetic oil likes to stick to stuff.... It's the most annoying/persistent problem I've ever faced with any engine.

 

[Bonmotwang]

I don't think the shaft itself is overheating. The theory is that the jug where the wide part of the valve travels up and down is worn, allowing the whole valve to wobble, resulting in increased wear of the shaft/housing. Once the shaft is worn out, too many hot exhaust gases travel up into the bellows area and cause all sorts of damage, not to mention an ugly oily mess. And we all know how well synthetic oil likes to stick to stuff.... It's the most annoying/persistent problem I've ever faced with any engine.

Then 951 design is the only way. The bellow on my boat stays very clean.
The shaft of 787 wobbles even it is brand new. Correct me if I am wrong, I just looked at my parts and shop manual.


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[IDoSeaDoo]

Nope, you're 100% correct. Even new, they wobble. It's such a primitive design. Now that I won't be replacing valves twice a season, I'll have to worry about one breaking apart and falling into the motor :ack:

 

[Sportster-2001-951C-Stock]

Just trying to keep an open mind and consider all the possibilities. Perhaps exhaust leaking around the RAVE shaft isn't the issue, it's more of a vibration issue causing damage to the piston?

 

[Sportster-2001-951C-Stock]

Then 951 design is the only way. The bellow on my boat stays very clean.
The shaft of 787 wobbles even it is brand new. Correct me if I am wrong, I just looked at my parts and shop manual.


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Do you think the 951 RAVE parts might work in the 787? I don't have a 787, so I can't check this very easily.

 

[Bonmotwang]

Just trying to keep an open mind and consider all the possibilities. Perhaps exhaust leaking around the RAVE shaft isn't the issue, it's more of a vibration issue causing damage to the piston?

I tend to agree with you sportster, because the exhaust air isn't "flowing" through continuously . It gets into the bellow, then "sits" there if there is no leak.
And static air is a good isolator for heat.
The metal blade is the heat conductor, which based on my theory, indicates exhaust gas is too hot.


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[IDoSeaDoo]

Actually, it does have somewhere to go... back into wherever it receives the pulse from, which I'm guessing is somewhere in the intake chamber. As for it breaking apart due to vibration, maybe, but seeing the melted pistons suggests otherwise. The exhaust gasses just past the raves are about 1100F. That's according to my old pyrometer I had installed on my Challenger (back when I had a 787 in it). I'm not sure if that's too hot or not, but the plugs suggested it wasn't.

 

[Sportster-2001-951C-Stock]

Actually, it does have somewhere to go... back into wherever it receives the pulse from, which I'm guessing is somewhere in the intake chamber. As for it breaking apart due to vibration, maybe, but seeing the melted pistons suggests otherwise. The exhaust gasses just past the raves are about 1100F. That's according to my old pyrometer I had installed on my Challenger (back when I had a 787 in it). I'm not sure if that's too hot or not, but the plugs suggested it wasn't.

Good points, you're the guinea pig I guess. I'm kinda thinking though the mechanical damage occurs first then once a leak develops a cascade of heat enters and melts everything in sight. So the root cause of failure looks like heat but it's really mechanical failure.

I have a plan to eventually install bushing in my 951 RAVE bases as opposed to buying new ones, drill them out with a drill press and drive bushings into the bore. Not there yet, though.

 

[IDoSeaDoo]

I've actually already tried that. The bushing was even taller than the base, but I believe the end result was the same: broken rave piston. It's been a long time, but I remember that in the end, it wasn't noticeably better than it was. Also, finding an exact match for a bushing is very hard. I found some on grainger.com but they turned out to not be true "tubes", but rather a flat peice of metal folded. There was a seam where it came together. Perhaps this allowed the extra gasses by.