Rattling Velvet Transmission Topic

[rickalan35]

I know that at least Yorklyn for one, had a recent experience with a low idle, rattling velvet drive. Other members also mentioned similar experiences.

I took my (new to me) '94 trojan 370 express out for a one hour run up the lake at 3000 rpm and tabs down and cruised along at 22 knots. My GPS measures speed in knts.

After an hour's running I slowed down as I approached my buddies dock (13 miles away from my marina) and I got a loud knocking coming from the port engine and immediately got that sinking feeling that only a boater can have.

I backed it in to the dock and tied up. Then popped the hydraulic engine room hatch and had a look. The sound appeared to be originating from either the v-drive or the velvet drive. At idle in neutral, no noise. At idle in forward or reverse, lots of racket.

I phoned my own mechanic (not connected to the marina where I keep my boat) and had him come by and check the boat the next day. I was very fortunate to have been able to leave the boat at my friends dock.

My mechanic phoned me the next day to indicate that there was nothing wrong with either the transmission or the v-drive. He said that the port engine needs a tune-up so badly that it will barely idle and possibly had one cylinder misfiring and he made the following statement which is why I'm posting this: THE ENGINE IS SHAKING SO BADLY AT ANYTHING UNDER 1100 RPM'S, THAT IT IS ACTUALLY RATTLING THE GEARS IN THE VELVET DRIVES. BUT WHEN THE ENGINE RECEIVES A TUNE UP, THIS WILL DISAPPEAR.

So, he has put new wires on, new plugs, new cap etc etc but we are still awaiting delivery of the carb kit.

Just thought I'd post this now and then re-post again next week, when I get back from a business trip as to the success or failure of the tune-up eliminating the rattle. Prowler and Big D might have some helpful thoughts on this post.

Cheers

Rick

[Stripermann2]

"THE ENGINE IS SHAKING SO BADLY AT ANYTHING UNDER 1100 RPM'S, THAT IT IS ACTUALLY RATTLING THE GEARS IN THE VELVET DRIVES. BUT WHEN THE ENGINE RECEIVES A TUNE UP, THIS WILL DISAPPEAR." -Never heard that one before and it really doesn't make sense.

Velvet Drives may rattle in neutral, when not in gear after running for a bit. When I troll for fish with only one engine in gear, is usually when I hear it. It's acceptable.

[captainmaniac]

Silly question - if "the engine is shaking so badly at anything under 1100 RPMs", wouldn't you have noticed that yourself when you popped the hatch?

[rickalan35]

Good question, Cap

But I ran the thing for an hour at a higher rpm that I have up to this point. It was my 4th time out this summer. (Bought her 4 months ago and then got sick with shingles for ten lovely weeks)

But after running it up on plane, it was definitely idling rougher afterward than I believe it had been previously. Tied up to my friends dock, I slipped it into reverse and forward a couple of times and got the rattle sound plus it stalled under no load.

I'm not a mechanic, but wonder if a plug or something finally bit the dust on the 12 mile run up to my buddy's place.

Not much more to add at this point.

[todd brinkerhoff]

Hard for me to believe it's that bad if you're running 22 knots at 3000 rpm without an issue. We have similar boats and I have never been close to that. I am at about 16-17 knots at 3000 with a clean bottom. On a side note, what are your prop #'s? I know you're running 502's, but I would have never guessed they pushed it 5-6 knots faster at that speed. What's you speed at wot?

[Big D]

Ya I can see that happening. When you say "v-drive" are you talking about a Walter v-drive separate from the engine transmission (Velvet Drive)? If there is reason to believe the engine needs a tune-up, then eliminate that possibility by getting one. The alternative is much worse.

[yorklyn]

i would request that the idle rpm be set to specs while doing the tune up. im still amazed that i didn't have to tear the tranny apart to fix that noise. cant believe that raising the idle rpm reduced the rattle as much as it did.

[rickalan35]

Big D

I'm still in Vancouver on the west coast. Flying back to Ontario next Wednesday. Boat should be waiting for me all tuned up when I get home. Hopefully problem free

Yes it's a V-drive arrangement. Velvet transmission connected to a Walter V-drive. Unlike my old Tricabin, there is a 14 inch long shaft with a universal joint in between the trans and the v-drive. At first look, I thought maybe the universal pin might have popped out or something (what the heck do I know).

Thanks all for the helpful replies.

I'll report back next Wednesday.

Rick

[Big D]

....Boat should be waiting for me all tuned up when I get home. Hopefully problem free .....

Fingers crossed!

[rickalan35]

Well, I fly back east tomorrow and hope the boat will be waiting for me with the rattling an issue of the past. I spoke with the mechanic by phone and he is still soaking what he called, "The worlds dirtiest carb that still found a way to run." He's installing the carb kit tomorrow and water testing it. I won't get to the boat until Thursday but Like Big D says, "Fingers crossed."

[rickalan35]

Hard for me to believe it's that bad if you're running 22 knots at 3000 rpm without an issue. We have similar boats and I have never been close to that. I am at about 16-17 knots at 3000 with a clean bottom. On a side note, what are your prop #'s? I know you're running 502's, but I would have never guessed they pushed it 5-6 knots faster at that speed. What's you speed at wot?

Todd, I probably screwed up those speeds. I was glancing at the chartplotter while driving the boat and it was all kind of random. Once I get her out this week-end I'll do a careful check.

(I never run WOT) My wife was horified and my kids were laughing at the thought of me pinning a boat

No idea about those props but will indeed get those numbers when we pull her later this Fall.

Cheers, Rick

[rickalan35]

Just received a text from our mechanic to indicate that after sea test post tune-up and carb kit, the engine, transmission and v-drive are running smooth as silk. No rattles in the transmission or shaft between the transmission and Walter V-drive.

That's great news and also a learning experience for me.

[rickalan35]

Arrived back home last evening and arranged to meet my mechanic at the boat today, whereupon we talked about what he had done and why.

I asked him his opinion of why the velvet drive had started rattling so loudly while I was backing into my friends dock and why a tune up had fixed it.

He told me that the engine was badly in need of a tune up. Even though idling at 800 rpms, it wasn't making enough power to maintain those rpm's when shifted into gear.

He said that when shifted into gear it came under load which caused the rpm's to drop to around 500 which in turn caused the planetary gears in the velvet drive to chug.

I drove the boat from my friend's dock where the tune up had taken place, to my marina twelve miles away. The port engine started up smoothly. Ran well. Sounds much better now than the starboard engine does.

Although still idling today at 800 rpms, the rpm's didn't drop when placed under load. There was absolutely no loud rattling. I've ordered a tune up for the other engine as well.

Besides the regular tune up (plugs,cap,wires etc) a Mercury carb kit was installed after the Weber carb had been thoroughly cleaned.

Big D was correct it would seem, regarding the possibility of a tune up alleviating this issue.

Hoping this additional info is useful. Rick

[rickalan35]

I took my (new to me) '94 trojan 370 express out for a one hour run up the lake at 3000 rpm and tabs down and cruised along at 22 knots. My GPS measures speed in knts.
Hard for me to believe it's that bad if you're running 22 knots at 3000 rpm without an issue. We have similar boats and I have never been close to that. I am at about 16-17 knots at 3000 with a clean bottom. On a side note, what are your prop #'s? I know you're running 502's, but I would have never guessed they pushed it 5-6 knots faster at that speed. What's you speed at wot?

Todd, Your comment was correct regarding my probable misread of the speed. I cruised back to my marina yesterday as mentioned in the above post and sat right on 2800 rpm's for twelve miles, tabs down and she cruised at a steady 16.9 knots on the GPS.

Have a great week-end everyone.

Rick

[1967 seavoyager]

Sounds like a bad shock plate. Like a flex plate on a car.