Twin Disk Slipping?

[John F.]

Crows Nest has DD 8.2s with what I believe are Twin Disk 502s. The starboard side tranny is "slipping." After about 1800 rpm, she feels like you pushed the clutch in and the motor revs. Time for a gear rebuild? Any idea on cost? Are 502s good gears worth rebuilding?

I plan on eventually (maybe sooner rather than later) repowering with Cummins. Anybody using these behind 6btas? I'll probably go with 210s or 250s.

[Bruce]

Oil level good?
Going all the way in gear?
Screen clogged?
Check pressure before yanking to confirm.

Rare, but I saw twice in 29 years was sheared shaft key and spinning prop.

[scot]

First.. what Bruce said.

In my opinion, yes Twin Disc 502 is worth rebuilding. Personally I feel like TD has always been the best gears on the market, very robust, commercial grade gears. Their sizes range options are not so good for smaller engines like ours, they appear to have pulled back from the small gear market, with few current offerings and when compared to ZF at the same rating, are typically twice as heavy and made of cast steel vs ZF's aluminum. ZF has really focused on the little gear business and has higher Hp ratings than TD on their small gears 63 & 220 etc, that's why you see so many of them! Cheaper, lighter and higher Hp ratings.

TD gears have always been under rated (relative to what they can actually handle) from a horse power capacity table standpoint. There is a built in, considerable safety factor in their capacity tables... very conservative.

Check the HP ratings on the 502, I think you will find they would be fine behind a 6BTA at 210-250 Hp.

Good luck.

[John F.]

Thanks Bruce and Scott. I need to check that screen, and my mechanic/friend is going to come by and check it out. The gears are behind DD 8.2s at 300hp, so if they're worth rebuilding cost-wise, I'm guessing that they'll be OK with Cummins 210s or 250s. Thanks again.

[John F.]

I went for a ride with my mechanic/friend and she ran fine. He had pushed the shift lever on the gear up another 1/2" or so, and thought that the gear just wasn't quite going all the way in and was coming out. I changed the gear shift cable from the middle of the arm on the Morse control to the outside, and played with the adjustment thing on the cable, and picked up that 1/2" so the selector lever is as far as it can go. I've run her for about 2 hours now with no problems, so I think I'm good. Bruce and Scott--it was #2, not going all the way in gear. Only weird thing is its been that way I'm sure since Doug got her in 2001, and probably before that. I moved that shift cable (didn't disconnect anything) when I was putting new belts/hoses on the motors, and may have caused it to move enough to effect something. Whatever, it works. Thanks a lot. A real lot.

John

[Carl]

I went for a ride with my mechanic/friend and she ran fine. He had pushed the shift lever on the gear up another 1/2" or so, and thought that the gear just wasn't quite going all the way in and was coming out. I changed the gear shift cable from the middle of the arm on the Morse control to the outside, and played with the adjustment thing on the cable, and picked up that 1/2" so the selector lever is as far as it can go. I've run her for about 2 hours now with no problems, so I think I'm good. Bruce and Scott--it was #2, not going all the way in gear. Only weird thing is its been that way I'm sure since Doug got her in 2001, and probably before that. I moved that shift cable (didn't disconnect anything) when I was putting new belts/hoses on the motors, and may have caused it to move enough to effect something. Whatever, it works. Thanks a lot. A real lot.

John

Could have been on the very edge before you moved cable...cables stretch a little, don't slide as well as they used to...could be any or none of those or a combination. Good to hear she's working as she should.