Dropped Rave Valve

[69DartGT]

We were riding our 2 96 GTX's Saturday and my son noticed he lost power in his. We pulled over and I checked the raves and noticed oil coming out of the Mag Cylinder one. I pulled the cap and the rave was pulled out of the piston. So we decided to head back and we were just about back idling in the channel and the rave dropped into the cylinder, not a good sound to hear. So I don't know if the rave was loose to begin with and rattling around pulled it out of the piston then finally breaking when it was free floating on the way back. Any thoughts on this? Thanks Scott.

 

[mikidymac]

I would say age. Here is no mechanical stress that would cause them to break.

 

[69DartGT]

Are the newer style that are slotted supposed to be less prone to breaking?

 

[mikidymac]

No, they just prevent them from sticking. Some engines would get stuck at 4,500 rpm and the slotted ones would help that, other engines of the exact same year had no issues.

 

[etemplet]

I suspect the valve clearance was pretty tight to begin with and the rattling around cause it to wear and drop a little further contacting the piston. I'd presume the top part of the valve broke after it contacted the piston. Gotta remember idle is 2800rpm so it's bouncing around quite a bit and a 5 minute ride is close to 15,000 times. Check to see of the piston isn't .25mm over standard. You can get away with not cutting the raves when boring to that size but you lose clearance. Get those chunks out of the engine. You can do the cylinders with the engine in the ski. Good Luck !!

 

[69DartGT]

That is my theory too, that the rave was worn and when it came out of the piston and rattled around it aloud it to drop just a little farther and
made contact with the piston. It has never been bored, this was an untouched motor that just turned 200 hrs on Saturday.
It really sucks because this is one really nice clean original GTX. But I am going to go .50 over on the cylinders and move on.
Thanks again for your time.

 

[69DartGT]

Well, I tore the motor apart this weekend and a couple of the crank bearings were a little noisy. So I am now going
to do a complete rebuild with new crank, CB, pistons and bored .50 over. I sold my 96 XP project a couple of weeks
ago, so this is my new winter project now.

 

[JJinSC]

The rave housing where the valve stem slides through starts to wear and the clearance is increased. This allows the valve to start oscillating/vibrating. The stress from that will eventually cause the stem to break. Annual maintenance for Raves should include checking wear in the housing and the clearance.

 

[69DartGT]

The rave housing where the valve stem slides through starts to wear and the clearance is increased. This allows the valve to start oscillating/vibrating. The stress from that will eventually cause the stem to break. Annual maintenance for Raves should include checking wear in the housing and the clearance.

I measured the housings and the rave stems. The housings are within specs, it is the valve stems that were worn. I Think when the rave came out off the piston it started to vibrate even more causing it to break. I am putting new OEM raves in it now after the rebuild.

 

[etemplet]

I put some new rave housings on a jet ski in and in ONE HOUR of riding they had opened up to a size LARGER than the ones I replaced. I saved a couple and considered installing brass bushings in the housing but did not. I believe, not certain, that in some cylinders... perhaps the slide section is worn.... but the valve rattles in the cylinder fit and this causes all the problems. I can't prove it but I've taken some serious measurements using and measuring adjustable parallels. The rave valve slide FIT on the RFI cylinders is much tighter than the stock 787. I dunno... it is strange what these things do. You're valve should have never broken.

All I can figure, conjecture is that your rave was lacking clearance over the piston and dropped just a bit contacting the piston. For that that is worth. LOL

 

[69DartGT]

I put some new rave housings on a jet ski in and in ONE HOUR of riding they had opened up to a size LARGER than the ones I replaced. I saved a couple and considered installing brass bushings in the housing but did not. I believe, not certain, that in some cylinders... perhaps the slide section is worn.... but the valve rattles in the cylinder fit and this causes all the problems. I can't prove it but I've taken some serious measurements using and measuring adjustable parallels. The rave valve slide FIT on the RFI cylinders is much tighter than the stock 787. I dunno... it is strange what these things do. You're valve should have never broken.

All I can figure, conjecture is that your rave was lacking clearance over the piston and dropped just a bit contacting the piston. For that that is worth. LOL

Well, I will see what happens after I get the motor rebuilt. My crank, CB and Cylinders are done. If the rave does the same thing in the same cylinder than your theory might be correct. If you are right and the rave breaks again I will be done with these 2 strokes.

 

[etemplet]

Well, I will see what happens after I get the motor rebuilt. My crank, CB and Cylinders are done. If the rave does the same thing in the same cylinder than your theory might be correct. If you are right and the rave breaks again I will be done with these 2 strokes.

I'm not saying the rave will break again. I'm just musing about my experience. I think your rave clearance may have been too tight. I don't like the damage to both end of the rave and none in the middle. That is something I scrutinize when I'm filing for clearance. I make sure the ends have ample clearance. If you build it right you shouldn't have any problems. I'll never be done with 2-strokes.

 

[69DartGT]

I'm not saying the rave will break again. I'm just musing about my experience. I think your rave clearance may have been too tight. I don't like the damage to both end of the rave and none in the middle. That is something I scrutinize when I'm filing for clearance. I make sure the ends have ample clearance. If you build it right you shouldn't have any problems. I'll never be done with 2-strokes.

I was wondering about that. With the wear in the cylinder allowing the ring to expand a little bit bringing it closer to the rave and the wear on the rave allowing it to drop a little bit farther that is why they made contact and the rave broke and fell into the cylinder. I have another 96 GTX in the same condition and hours as this one, I am going to put new raves in it and trim them just a bit. Hoping to avoid the is issue in that one.

 

[etemplet]

How are you going to trim the raves and how are you going to measure the clearance? I use a coarse Half-Round file and I look at the web thickness as a guide. It doesn't take much to shave off (.010") I try to keep it even. I use BENT (.020") shim. I stick it in the exhaust port with the head off the engine, engine laying on its side. Good lighting and a pair of 45 degree needle nose pliers. I push down on the rave valve and make sure the shim has clearance. No rubbing. I rock the rave and check both sides to make sure they cannot touch the piston. I'm not worried about spot on (.015") clearance I don't want contact. I keep it close as I can but excess clearance is preferable.

I am not sure the engine shops take those painstaking measurements. Speaking to 1 engine builder he said if I machine the valve for a 1mm overbore piston it will have plenty of clearance. That's not my way. I believe excessive clearance may degrade the performance of the valve. That is only my opinion of course but it makes sense to me. Give it the proper clearance and I don't see why you would have any problems.

 

[azsxr]

I’ve had a valve breaking off problem 2 new top ends done in Less than 5 hrs.
The slot in the cylinder had been worn out over time it had almost 200 hrs on the original top end. It must have been flopping around and snapped off. All valves and bases were OEM . I never had another problem after changing out cylinders.

 

[69DartGT]

I’ve had a valve breaking off problem 2 new top ends done in Less than 5 hrs.
The slot in the cylinder had been worn out over time it had almost 200 hrs on the original top end. It must have been flopping around and snapped off. All valves and bases were OEM . I never had another problem after changing out cylinders.

I hope that is not the case for me, I just had the cylinders bored .50 over.

 

[etemplet]

I’ve had a valve breaking off problem 2 new top ends done in Less than 5 hrs.
The slot in the cylinder had been worn out over time it had almost 200 hrs on the original top end. It must have been flopping around and snapped off. All valves and bases were OEM . I never had another problem after changing out cylinders.

This is what I was wondering about. My Mag cylinder was the only one having problems. Mine was pulling the threads out of the rave valve piston. This happened with a one hour run time... twice in succession. I ordered an aluminum piston. Tom at SES told me that rave is getting hot and the threads are getting soft and pulling out. That seems strange but it fits the scenario better than vibration. I prefer the larger orings at the bottom of the rave housing. I'm gonna keep an eye on this thing for certain. I believe the slot is worn on this cylinder.

As I mentioned I tried measuring one a while back but the measurements varied so much it was pointless. I even though about aluminum welding the rave and machining it to a tighter tolerance. Thanks for posting. Good info for me.