Help with 787 Rotary Valve Gear

[lilngineer]

Just wondering if anyone with experience in 787 rebuilds can tell me if the rotary valve worm gear from my engine looks worn.

It doesn't seem right to me. The teeth of the gear are sharp almost knife-like. With the crank in the case, there seems to be a lot of back and forth rotational play on the RV shaft.

Also, are there any creative ways to pull and insert the shaft in the case without ordering the special tools called out in the manual?

Since I have the engine apart for the rebuild, I want to get it all.

Any opinions/help is much appreciated.

 

[timmyboy76]

dont think that gears good. Look'n at another picture of gear, and it doesnt have the "sharp" lip, that your picture shows...

 

[captain scale]

Running dry?

Looks like the rotary gear didn't have a proper bath of oil!

 

[lilngineer]

Looks like the rotary gear didn't have a proper bath of oil!

The case dumped a bunch of oil when I disconnected the lines. Is it possible the RV shaft is bent?

The engine failure was the connecting rod bearing at the crank on one piston. Maybe this contributed to the wear?

 

[captain scale]

You have gear oil in the area where the balancer shaft is and 2 stroke oil where the rotary gear is that comes fom the oil tank. Maybe there was an interruption to the supply of oil, maybe an air pocket in the oil line. Or as you said, maybe the shaft was beant or the bearings were worn out making it have an inconsistent mesh. What does the gear look like on the crank? Should look about the same wear.

 

[lilngineer]

You have gear oil in the area where the balancer shaft is and 2 stroke oil where the rotary gear is that comes fom the oil tank. Maybe there was an interruption to the supply of oil, maybe an air pocket in the oil line. Or as you said, maybe the shaft was beant or the bearings were worn out making it have an inconsistent mesh. What does the gear look like on the crank? Should look about the same wear.

Strangely enough, the crank gear looks normal; no visible wear at all. The crank is being replaced as part of the rebuild due to the bearing failure.

I just don't want to change out the gear only to have it happen again.

 

[lilngineer]

Well I went and picked up a new RV gear today. The dealer looked at the old one/case and thought maybe the previous owner used the wrong oil. The oil in the tank was blue, so maybe it was TCW-3?

After the rebuild, I guess I will be draining the tank and running the BRP full synthetic.

 

[timmyboy76]

Well I went and picked up a new RV gear today. The dealer looked at the old one/case and thought maybe the previous owner used the wrong oil. The oil in the tank was blue, so maybe it was TCW-3?

After the rebuild, I guess I will be draining the tank and running the BRP full synthetic.

it doesnt take much, for that gear to "explode" again. With it being shot, i'd replace thee entire assy. From what i gathered, it only takes the shaft to be out,.002, and it will kill the gear again...:cheers:

 

[lilngineer]

I measured the RV shaft deflection and it is .0015. The service manual specs the wear limit to be .003

I am wondering if I need to replace it. I really would prefer not to dump the extra $100 for a shaft assy, but I don't want to be stupid and have to tear the engine apart again just to change the brass gear again.

What do you guys think?

 

[timmyboy76]

Wouldn't even give it a thought stud, I'd change it.

 

[IDoSeaDoo]

Gear is worn

You don't have to replace the whole assy, if you believe your bearings are okay. You can replace just the gear itself for around $50 (if I remember correctly). It's the same gear for the 587 (and probably 650 and 720) as the 787. You'll have to remove a few snap-rings, but it's not hard. But I'm pretty sure you shouldn't have sharp gear teeth like the ones in your pic. I've also had a connecting rod bearing fail in my jet ski, but that destroyed the whole motor, including my rv gear and valve itself. The bearing pins rained death into the inner workings of the engine. Will be replacing those on the new (used) engine I bought. Check out one of my other posts on how to re-set the RV Valve when you're ready to put it back together (unless you have it properly marked).

Good luck!