Rotary Valve Gear Damage

[etemplet]

I sure would like to understand what causes the damage to the rotary valve gear. I have extensive experience with root cause failure analysis and I just don't get the failure of these gears. I've done a lot of Seadoo engines the past few years and some had lots of hours on them and the gears looked fine and the bearings were in good condition. I don't get the spring and I don't get the destruction of the gear. Living in an oil bathed environment they should be happy for a long time.

I just removed this gear and the bearings are free, shaft turns easily. When a brass gear gets destroyed we often think of a lubrication failure. The valve isn't damaged and I can't imagine a lot of drag on the valve which could be a possibility but not likely with this engine.

 

[etemplet]

Oh well, I went to my buddy to look at replacing the gear on the crank and he said he wouldn't do it so... I'm gonna replace the assembly and bearings and go with it. I don't understand the root cause of the gear failures but I can say with conviction the engine has to come out and the crank removed. There isn't an easy quick fix for this.

Basically the torque/pressure on the gear can cause the oil film to be lost. I wonder if hitting something with the impeller or shock loading the engine can begin the failure process. Huge amount of wear. I'll do some serious work to figure out how this happens. I'll definitely find a suitable high pressure gear lubricant to put in the reservoirs from now on. I worked in a lube oil additives plant for 28 years so I got the skinny on that kinda stuff. Touchdowns all !!

 

[TheGTIjetguy]

Wow, interesting. I too share your bewilderment on the abnormal gear wear. Have you looked at the rv valve clearance? They expand when heated and could potentially bind if the clearance is too close. Just a thought

 

[etemplet]

Wow, interesting. I too share your bewilderment on the abnormal gear wear. Have you looked at the rv valve clearance? They expand when heated and could potentially bind if the clearance is too close. Just a thought

Good thought but I didn't replace the valve and I just reassembled the same engine. The crank is a WSM replacement crank and it was new. I wish I could get some data on the failures and what they had in common. I'm definitely gonna look at gear mesh. If I can figure something out I'm gonna split this crank and replace the gear. I talked to a engine builder and he said the gears are the same so.. this will be another Seadoo adventure.

 

[etemplet]

OK here is a BIG heads up. Both oil lines to the Rotary Valve chamber had massive amounts of brass in them. It took a bit of time to get that all cleaned up... a lot of time but I didn't want issues. I even pulled the oil tank and cleaned it out. I cleaned the oil pump feed line and replaced the filter.

If the gear fails brass is everywhere in the system and it needs to be flushed and cleaned. I'm installing a different engine that I just rebuilt in this ski so I'll have time to decide what I want to do about the failed gear.

 

[JC-SUPERJET]

Some things to consider:

"In gear applications, bronze parts act as sacrificial components. Generally you are dealing with a bronze-to-steel mating application, where the bronze component is sacrificed to protect the more valuable steel component. In these cases, the steel surfaces must always be harder than the bronze surfaces."

"Brass is a soft metal that may be used in cases when a low chance of sparking is necessary."

The Brass Gear is a sacrificial wear item by design. Cheaper to replace the Rotary Valve Shaft then Crank Shaft.

"Scuffing, also termed "scoring" (incorrect according to gear standards), is a severe type of adhesive wear which instantly damages tooth surfaces that are in relative motion. In fact, a single overload can lead to catastrophic failure.

Scuffing welds together unprotected surfaces in metal-to-metal contact. Metal particles detach and transfer from one or both meshing teeth. During successive rotations, these particles can scratch teeth flanks in the sliding direction. This type of damage generally happens in areas of high contact pressure and sliding velocity, far from the pitch surface. Conditions there are less favorable to form a protective lubricant layer that would prevent direct metal-to-metal contact. This protective layer could be a thick oil film (relative to surface roughness) or an adsorbed or chemically deposited layer established by lubricant additives.

In any case, lubricant and lubricating conditions, not material strength, are responsible for scuffing damage. Scuffing often happens to new gears when tooth surfaces are not yet well run-in. Experiments show that a newly manufactured surface is able to carry only 20% of the load of a well run-in surface. The risk of scuffing goes up as lubricant degrades over time or becomes contaminated with metal particles or water. It is sometimes difficult to distinguish between surface scratches from instantaneous scuffing or those from wear.

Wear is a continuous, abrasive process of material removal from mating gear teeth that happens with or without abrasive particles in the oil. For example, hard asperities on gear flanks can remove material from mating flanks. Removal of the hardened layer from surface-hardened gears accelerates wear. Extremely worn spur gears have pointed teeth and a reduced profile contact ratio. Continual wear of tooth roots weakens the gear until it breaks.

Wear typically happens under boundary or mixed lubricating conditions lacking a thick supporting oil film that would otherwise separate tooth surfaces. Mild anti-wear additives that help protect surfaces with adsorbed or reacted layers under critical lubricating conditions lessen wear."

Engine Flooding Events bring Grit into the moving parts of the Engine. This would accelerate the abrasion of the Brass Gear.

Worn Gear Teeth on the Crank Gear can also damage the Brass Gear. Out of Tolerance Gear Teeth Size and Backlash will also cause damage.

There is a Backlash Tolerance spec in the Seadoo Manual.

 

[etemplet]

Yep, I've rebuilt a lot of gearboxes and I worked on mechanical equipment all my life, really big stuff and everything in between. We always establish a root cause so it doesn't happen again. Too expensive not to. Seadoo has a chicken shite design all the way around. The gear, the crappy lubrication, very little if any lubricant flow, no way to drain the sump, etc... Once the gear starts to wear it's done.

This sure looks like a straight up lubrication failure. There is a chance that someone may have put gas in the oil tank. That happens. The viscosity of the oil in the tank didn't seem right to me but no way for me to verify. The more I think about it... the more plausible this seems. There is simply no reason for that gear to fail that quickly. No damage to anything else. I see some oolilshing on both sides of the rotary valve but not much wear and no scouring on the engine surfaces. So I can't see where the gear could have been over-torqued. It takes HEAT to do that kinda damage.

On a side note, if the gear is bad you gotta split the cases to get the metal out of there. It's impossible any other way. I also had to use gas to flush the brass out and I bet I did that 6 or 8 times. No amount of wiping will get it all. Make sure you flush the hell out of those oil lines or replace them. I ran a white paper towels through all of the lines SEVERAL times and fushed with gas SEVERAL times. You can see a picture of top as to what I found. Diligence pays off in the end.

 

[etemplet]

My new plan for all my skis is gonna be a "sump flush" and the addition of a light weight gear oil into the reservior. Those gears need a high pressure lubricant, worm drives always do. I'll take a look at what is available. a 50/50 mixture 75W90 might do the trick. I could also install a Tee in the oil line and make it real simple. Clamp both oil lines, vacuum out the oil, put in a couple ounces of gear oil and VOILA.... done.

Some may say it isn't needed, I'll say it sure won't hurt. LOL

 

[etemplet]

Another tidbit.... I didn't see any evidence that the reservior oil makes it all the way up the return line and back into the oil tank during normal operation. I would have seen metal particles at the top of the return line and I didn't. There was a lot of metal in that line...." a lot" but it didn't make it up that high. As I mentioned, I removed and flushed the tank I didn't find any brass or shiney metal in the tank which was good news for me.

If we are going to keep these old skis running for a long time we need to address Seadoo's design shortcomings. I'm not knocking Seadoo but this is a failure path that we can do something about. Touchdowns everyone !!

 

[JC-SUPERJET]

If not a Lubrication issue...

Possible Hint from Full Bore that might explain why the Rotary Valve Gear gets damaged:

"When rebuilding the top end of a Sea-D00 580,650,720 or 800 the cylinders need to be aligned properly. After sliding the cylinders into place install the cylinder bolts finger tight. Bolt on the exhaust manifold this will properly align the cylinders then torque the cylinders. Note be sure to put Loctite to the threads of the inner (cylinder) bolts on the rotary valve side of the engine."

Since the Rotary Gear Shaft seats in the Upper Crankcase, which mates to the Cylinders, is it possible that when the Inner Cylinder Bolts are not properly torqued or vibrate loose a smidge, the Rotary Gear Shaft "Housing" distorts or deflects enough for the Gears to bind or clash?

Just like a torqued Exhaust Manifold can slightly "deform" a Cylinder in or out of round, do the Inner Cylinder Bolts contribute to keeping the Upper Crankcase within tolerance/spec around the Rotary Gear Shaft?

Before the Cylinders are torqued down, is it critical to align them first by bolting on the Exhaust Manifold prior to clamping them down?

 

[Gritzlor]

I saw mentionong of a brand new WSM crank in there. I just rebuilt a couple of 787 RFI’s with brand new WSM cranks. Before we were done breaking them in, one started acting up…misfired like shit over 3000rpm and didnt have any power. Chased this around thinking it was an electrical or fuel problem. Nope. The brass gear was eaten up almost through a full tooth, hadn’t skipped over yet when I found the problem but timing was well over 10degrees behind. This ski had an OEM brass gear in fine condition when I put it together, didn’t see any reason to replace it.
Now to the other engine. Was already losing some power on last hour we were breaking it in, so I pulled the oil return tube off of the oil tank and lowered it to bleed down in a tray down in the hull. My precious 2stroke oil had turned green in there and was saturated with bronze just like the other one.
That one needs to have the gear out too, which was a new aftermarket assembly, new shaft and all. However I think I’ll not put that brand in again.
Anyways, I now have 2 WSM cranks along with 2 different bronze gears failing within a few hours of run time. Called WSM and they didn’t know of issues, but didn’t completely rule it out either.
Ordered WSM bronze gears to put in them since their stuff is usually good quality and MIGHT be cut in a way to match better than WSM to OEM or other brands.
What a headache this is, and yes I’ve rebuilt engines before without these problems, including these very bottom ends with SBT rebuilt cranks about 200 hours ago. One was shot because of bearing/gear failure and other I replaced for good measure.
I have no intent to badmouth WSM, but it would be practical to collect info about potential incompatibilities with this, it’s too damn much work to have this fail out of nowhere.