Gear-box chatter - fixing it

[carioca1232001]

I have a pair of (2:1 Ratio) Borg Warner 5000 Velvet Drives connected to the twin prop shafts in my boat.

I had noticed a "chatter-type" noise from the port Velvet Drive in idle or at low revs, which disappears as engine rpm goes above 1000 RPM.

Recently I pulled out the engines and Velvet Drives, having noticed that the port (noisy) Velvet Drive input shaft has some rotational play, while the starboard (silent) Drive has none.

Would it be an expensive repair ?

Or is it simple to correct as when there is play on the prop shaft of a rear-wheel drive vehicle and shims are used to adjust the degree of meshing between the pinion and ring gear-teeth in the differential ?

To make things worse, I do not have a BW 5000 Velvet Drive maintenance manual - and the local reps have long gone out of business.

[Big Red]

It might just be the bearings. So probably not expensive if you do it yourself. Probably pay to have them fully serviced if they are showing signs of deterioration.

[carioca1232001]

Big Red wrote:

It might just be the bearings ......

I am not an expert but worn bearings would show up with "in-out" and/or "up-down-sideways" play.

The play I have encountered is purely ROTATIONAL

[Gary E]

"I had noticed a "chatter-type" noise from the port Velvet Drive in idle or at low revs, which disappears as engine rpm goes above 1000 RPM."

I would start with the selector valve position, make sure when shift lever is in neutral it really is neutral and the output shaft is not turning.

From there make sure pump pressure is correct, low pressure will sort of engage the clutches. Since you say it goes away above 1000 RPM, low pump pressure is a prime suspect. Make sure the oil is clean and cool, it should have a heat exchanger to cool the oil. Make sure the clutch disc's are not distorted or warped, which can cause drag and overheating which will make it worse.

All gears will have lash, how much depends on a lot of things, and the typical pitch line clearance or backlash for this is (and I am guessing here) in the area of 0.004 to 0.010 inch.

If it does have more lash than that, I would not worry to much about it, because when in gear the load from the prop shaft will keep the lash all to one side.

If you are not comfortable taking this apart, find a young fellow at a automatic transmission shop that would be willing to take it apart and inspect it, it's not a big job, and he will know what he is looking at.

[carioca1232001]

Many thanks Gary.

The oil is clean and the oil-cooler is working OK.

I believe the root cause is excess lash, as a "clunk" is heard at the limits of the input shaft´s rotational excursion when turned by hand.

A reputable mechanic confirmed that the present degree of lash is perfectably acceptable, as he´s seen worse cases do fine.

This lash may have been caused by the port prop struts that were out of alignment. A certain amount of torque was required to spin the port prop by hand, after which it turned freely. In comparison, starboard prop could be turned with a finger.

BTW, how accurate is the axial alignment of those low-cost, pen-like, laser-light pointers used during demos and presentations ?

I was thinking of machining parts that would fit over the axial part of the props struts, one with an embedded low-cost laser-light pointer and the other with a transparent disc and cross-hairs, to ensure perfectly aligned struts - get it ?

[rdapron]

For what it is worth – I’m not a transmission mechanic, but the chatter in Velvet drives is a common complaint. Often, broken clutch springs (also common on Velvet drives) can lead to this excessive lash resulting in chatter at low RPM’s or low-load conditions. Mine made the same noise that you described. The solution was to tune the engine. A smooth running engine at low load will usually eliminate the chatter caused by excessive lash by delivering power to the clutch at an even and smooth rate. A friend of mine whom is a mechanic also informed me that it was nothing to worry about.

[carioca1232001]

rdapron wrote (quote):


For what it is worth – I’m not a transmission mechanic, but the chatter in Velvet drives is a common complaint. Often, broken clutch springs (also common on Velvet drives) can lead to this excessive lash resulting in chatter at low RPM’s or low-load conditions. Mine made the same noise that you described. The solution was to tune the engine. A smooth running engine at low load will usually eliminate the chatter caused by excessive lash by delivering power to the clutch at an even and smooth rate. A friend of mine whom is a mechanic also informed me that it was nothing to worry about I read an account once of a fellow who "tuned the injection pump" on his Volvo Diesel to mitigate chatter.

Diesels are supposedly more chatter prone, due to the impulse-type force exerted on the piston as per the nature of the combustion process.

In this context my port diesel-transmission combo (noisy) is not as gutsy or as smooth as the starboard assembly (noise-free). Both engines are supposedly "identical", but there could be subtle differences....

The only settings I am aware of on the injection pump are "advance-retard" timing, aside from the fuel metering. Do you know some other ?

As all the mechanicals have been removed from the hull for the present overhaul, would be expedient to fine-comb the port diesel.

Yes, and re-align port prop-struts.

[Gary E]

"BTW, how accurate is the axial alignment of those low-cost, pen-like, laser-light pointers used during demos and presentations ?

I was thinking of machining parts that would fit over the axial part of the props struts, one with an embedded low-cost laser-light pointer and the other with a transparent disc and cross-hairs, to ensure perfectly aligned struts - get it ? "

Yeah, I get your idea, and I would not try it. That does not mean it wont work, just that I have allways used feeler gages and dial indicators to line things up and I know that works.

[rdapron]

Diesels are supposedly more chatter prone, due to the impulse-type force exerted on the piston as per the nature of the combustion process.Sorry, you did not mention what engines you where running and I assumed that you had gas engines. Not sure as to what to suggest for smoothing the pulses of your oil burners at low speeds. Perhaps posting your question on this board will generate a response.

http://www.marinegears.com/techboard/index.html

[carioca1232001]

Gary E wrote:


Yeah, I get your idea, and I would not try it. That does not mean it wont work, just that I have allways used feeler gages and dial indicators to line things up and I know that works. Is there a USCG (or AYBC) recommendation and/or procedure for aligning prop struts, using feeler gauges and dial indicators ?

I recall reading a report by a reputable Yacht Surveyor discussing the issue of prop strut alignment within the broader context of maintenance of underwater moving parts , whence it surfaced that the best alignment attainable in real life situations was of the order of 1/8"

[carioca1232001]

rdapron wtote:


Sorry, you did not mention what engines you where running and I assumed that you had gas engines. Not sure as to what to suggest for smoothing the pulses of your oil burners at low speeds. Perhaps posting your question on this board will generate a response The only drawings I have of my BW 5000 gear-box are due to this rather helpful site !

I asked for their advice about the play - they said that if I heard a "clonk" at either end of the input shaft´s rotational excursion, I ought to fix it.

In my humble estimation, the wear may have arisen from misaligned prop struts on the port side, and not to the feebler performance of the port power plant as compared to starboard.

[Gary E]

"Is there a USCG (or AYBC) recommendation and/or procedure for aligning prop struts, using feeler gauges and dial indicators ?"

I was not in the CG, so I have no idea. No idea what aybc means.

"I recall reading a report by a reputable Yacht Surveyor discussing the issue of prop strut alignment within the broader context of maintenance of underwater moving parts , whence it surfaced that the best alignment attainable in real life situations was of the order of 1/8" "

Reputable?? what a joke. Fire that guy and ignore everything that so called "reputable" idiot says. 1/8" can be done blindfolded.

Any decent mechanic familiar with alignment can align a shaft, it's strut bearings and mid shaft bearings, stuffing box and the transmission flanges well within a few thousanths of an inch.

[carioca1232001]

Gary E wrote:


No idea what aybc means. Your very own American Yacht and Boat Council.

As for some of the follies and misconceptions related to shaft alignment and overall engine/transmission/shaft alignment, look at:

http://www.yachtsurvey.com

A great deal of what David Pascoe writes down makes practical sense.

BTW, current motor-car steering system verification and adjustments are carried out using laser-light sources embedded in traditional hardware

[ohiomike]

hi here are some common chatter problems, check these before you get crazy with line pressure, alignment, bent or bad shaft logs and strut bushings

first check the engine for low idle miss a bad spark plug or wire can end up costing you alot of money. check for water in fuel again will cause low idle miss, fuel mixture after making sure engine is tuned correctly

now it starts to get bad..

the drive plate is a the other part i would check before anything else, cause its what supports the input shaft of your trans all the foward and reverse shifting, the drive plate takes most of the shock.

as you did mention some end play on the noisy trans drive plates will cause that..

best of luck let us know what u find

ohiomike

[carioca1232001]

ohiomike,

Mine are oil burners. Drive plate assemblies have been checked and are OK.

Would be happier if instead I had installed rubber (elastomer) couplers.

The port prop struts were out of alignment and the respective prop shaft needed considerable effort to turn by hand, but was OK once it got going.

Starboard in comparison could be turned with a little finger.

So this could have forced the port trasnsmission´s input shaft and generated backlash over time. It is not only perceptible but a great deal more than the starboard transmission´s backlash.

Anyhow, thanks for your input.