787 RAVE Valve Missing Nut

[martin18152]

Broke the threaded stem on one of my RAVE valves, when I removed the top end, the other end went into the bottom of the boat cavity. I ordered the new valve and a couple of parts that melted, but did not order the plunger. The plunger looked good, did not think about the nut being part of the system. Called the parts house, they say the nut comes with the plunger? I am thinking of using a regular nut of sorts, a washer, and some high temp silicon sealant. I want to put the boat in the water this weekend, but the new plunger and nut won’t be delivered in time.

Any opinions on this temporary fix, or a better idea, or will it work at all?

 

[Guest_User]

Stop! don`t trailer park repair the boat that way!!! sheesh...

the exhaust valve piston is threaded, it has a HEX on it so you can spin it on with a wrench...

wait till you get the new parts to assemble and run... or your on your own...

good luck...

silicone won`t stick to any of that... your asking for more trouble if you podunk repair the boat that way...

what about the condition of the Bellows? retention spring? cap with adjuster? and exhaust valve spring?

 

[martin18152]

your right, did not look at the assembly correctly, there is a plastic cap that was melted into the case that comes with part #9, the bellows is attached to it, pretty much have to wait for the part. boating season is slippiing away. I did order all the parts you mentioned, the rubber bellows is in good shape , its just the plastic cap that melted, but you have to order both as part # 9

 

[LouDoo]

Check your local dealer, maybe he has the part, we don't have too many weekends left.

Lou

 

[Guest_User]

your right, did not look at the assembly correctly, there is a plastic cap that was melted into the case that comes with part #9, the bellows is attached to it, pretty much have to wait for the part. boating season is slippiing away. I did order all the parts you mentioned, the rubber bellows is in good shape , its just the plastic cap that melted, but you have to order both as part # 9

you can buy the piston and bellows separately from SBT.

usually the housing gets out of round, lets the hot exhaust gas escape thru the valve stem, them wooops, bye bye plastic piston...

This is a serviceable item anyways, so just another thing to keep an eye one with these RAVE engines.

 

[martin18152]

Check your local dealer, maybe he has the part, we don't have too many weekends left.

Lou

I found the piston local, thanks for the advice. If the other parts come in this friday, per UPS schedual, I will be ready to go. They have few of the other parts, but no valve. I'm going to pull all the valves and clean them. I will mic. the new OEM valve to the broken one, and if the broken one is the same sized, then I may have the reason the valve broke in the first place.

 

[Biffitis]

Make sure your valve and housing don't look like this or you'll be putting a new piston and bellows in again shortly. As mentioned above, there's usually a reason the piston fails...

 

[martin18152]

Make sure your valve and housing don't look like this or you'll be putting a new piston and bellows in again shortly. As mentioned above, there's usually a reason the piston fails...

I see your point, I will be cleaning up all my rave valves tonight, and hopefully be on the water tomorrow. As it stands now, I am pretty sure that the leak was strait up the stem, due to the fact that it broke off, no stem, no seal. Everything melted strait up, including the piston, the bellows was completely intact and in good shape. Still wondering how that stem broke, considering that it was probably new, and the engine was just rebuilt – not by me. This same engine, had a failing seal at the worm gear, classic oil leak into the crank, it also had a RAVE valve break and fall into the crank, the engine seized up completely.
Just a note: I pulled the valve covers on the other engine, and pulled up and down on the valve and bellows, they are so lose vertically, that it almost feels like that are not there. When I pull them out it will tell the story.

 

[martin18152]

I know sometimes tec. Manuals are not the best; however, this seadoo manual seems pretty good, and I read a lot manuals for my work. This is what is exactly stated for an overbore engine.

“BORING PRECAUTION
In its stock configuration the RAVE valve guillotine has a minimum of 0.5 mm (.020 in) clearance to the cylinder bore measured at the center line of the cylinder. This is the minimum production clearance. There is only a first oversize piston available for the 787 engine. That piston is 0.25 mm (.010 in) larger in diameter than the stock piston. When the oversize is installed, the guillotine will have a minimum clearance of 0.375 mm (.015 in) with the cylinder bore. This is the minimum operating clearance the guillotine should be used with. Clearance less than 0.375 mm (.015 in) will require reworking of the guillotine to achieve the proper clearance and radius."

This makes perfict sense to me, the original clearance is .020, the diameter is increased .010, therefore, the radius is increased .005, so the decrease in clearance is .020 - .005 = .015 per the specifed min clearance. This tells me that if you go to the next piston size you do not have to shave the guillotine.

With all that said, there may be an andendum that I do not have. So what is the deal on shaving the valve?

 

[Guest_User]

the valves are shaved by machine, machine shop equipment.

did you call SBT to see if they have a valve already in stock to accommodate your needs?

 

[martin18152]

what I am saying here is that acording to the shop manual, I may not need to shave the factory valve.

 

[Guest_User]

what I am saying here is that acording to the shop manual, I may not need to shave the factory valve.

do you know exactly what the overbore size is, what is stamped on the piston dome? there are more than one overbore size avail now... and was it proven the valve nailed the piston head, ringland/skirt?

 

[martin18152]

No, I do not know if it hit the piston, or the cause of the stem breaking. I have a text into the rebuilder to find out the overbore.

 

[Guest_User]

No, I do not know if it hit the piston, or the cause of the stem breaking. I have a text into the rebuilder to find out the overbore.

early RAVE valves snapped at the stem, this was a common issue, I think the numbers stamped on the guillotines were 350, 351, then revised to 352, 353 to combat the issue and these seemed to do well... If the engine was over bored by the rebuilder then he alone should have known what to do and how much to trim for clearances. There would be evidence of the blade scrapping the side of the piston and doing damage. The corners do not need to hit anything to break off if these were of the earlier design. These exhaust valves oscillate tremendously especially when the groove and or housing gets very sloppy allowing the valve to move even more...

This is one of those part assy`s that need attention and maintenance.

NOTE* in my build thread here, there is quite a bit of talk about the RAVE valves...

 

[martin18152]

It appears that there are two types RAVE exhaust valves, ones with two grooves across the face, and one without. Just wondering if they are interchangeable for the 787 – their dimensions are identical?

I’m guessing that the engineers found out that when the valve gets slightly gummed, they do not let enough dynamic exhaust pressure go by the valve for quick bellows movement, and therefore, the reason for the groves. Metal base assembles are Identical, with the same bleed hole for bellows pressure. I also noticed that there are two types of bellows caps, every one of the caps on my boat failed, they were the white wimpy types, the caps broke, or the stems pulled out. The other type of bellows cap is black, and it has a cup on the top around the 10 mm fitting. My assumption is that I did not clean the valves, they stuck, and eventually the caps broke loose. Three of my valves had broken corners, and the valve that did not have the grooves, had a broken stem. All the valve housings were in very good shape, the guide holes were not out of round or worn.

I would like to blame all the failures on myself, and that they were caused by not cleaning the valves – that would be the easy button, just clean the valves; however, the right engine was just rebuilt, and only had 4 hours of operation on it, and the valves moved freely. I’m guessing like you said these were early design valves defect issue, I hope the new ones do better. The builder kept one of the original valves, and replace one with an ungrooved valve.

I should have all my parts this week, and get the boat in the water this weekend. I will just have to check and clean the valves at the end of each season, or twice a season. Once all the valves are working correctly, I should get a better top end. I could go 55 mph with the valves broken and not working; probably get up to 60 with them working properly.

 

[martin18152]

early RAVE valves snapped at the stem, this was a common issue, I think the numbers stamped on the guillotines were 350, 351, then revised to 352, 353 to combat the issue and these seemed to do well... If the engine was over bored by the rebuilder then he alone should have known what to do and how much to trim for clearances. There would be evidence of the blade scrapping the side of the piston and doing damage. The corners do not need to hit anything to break off if these were of the earlier design. These exhaust valves oscillate tremendously especially when the groove and or housing gets very sloppy allowing the valve to move even more...

This is one of those part assy`s that need attention and maintenance.

NOTE* in my build thread here, there is quite a bit of talk about the RAVE valves...

Three of the valves were 358s, there was one with out grooves, no decernable model number, the ones I bought are 358s