Drive Plate

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Oct 6, 2007
I think it was this forum where I spoke earlier about always having a plan B available and never depending on the reverse gear to stop you. This weekend it happened to me again. Second time in 28 years.

We went out for a couple day trip from Pt. Orchard where the boat lives, to Kingston WA. Pulling in to Kingston everything was fine until we were 10 feet from the dock and I put the gearshift into reverse to pull the stern in and stop the boat. There was no feeling of slowing or of prop pull into the dock. A little throttle confirmed there was no reverse thrust available.

As we were drifting slowly anyway, the wife stepped off onto the dock and snubbed the line on the cleat and brought us to a nice safe stop. I left the engine idle, planning to do some investigation after securing the boat. About halfway into that chore the engine chugged and stopped!

Pushing the starter button produced nothing. With the floorboards up I could hear the starter drive push forward but no rotation. With a wrench on the damper pulley nut, and standing on the wrench I discovered I could not turn the engine over either.

There were no odd noises, no clunks, rattles or other oddities in the 2 1/2 hour trip.

Long story short, I decided it had to be the drive plate. 2 hours later I had many pieces of springs, wire, and drive plate in my hand. A friend had been sent to Seattle to pick up a new plate when the problem was predicted. He also helped R&R the flywheel which is a real bear with the limited amount of space I had. I just slid the tranny back 6 inches and left it hanging from the floor cross member. Remember of course that the flywheel on a 120 Lehman is 87 pounds and a machined fit so it has to be reverse pressed off and lined up prefectly to be pulled back on with the bolts. Pieces of spring had wedged into the small space between the flywheel and the block which is what eventually killed the engine upon total failure.

I had thought about adding a drive plate to my stock of spares, but just hadn't done it yet. I probably won't need another for a few years but there will be one on the boat when I do.

A little know how, a few tools and a good friend to bring pieces to you on a Friday night make boating adventures a little easier to deal with.

Ken Buck
Are you talking about the damper plate? I carry a spare, but (knock on wood) haven't had to replace it yet. Here's a picture of mine.

-- Edited by Keith at 06:20, 2008-03-24


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Yep, that's the one. Also called a drive damper, intermediate plate, drive disc, etc depending on who you talk to and which replacement brand you buy. The place I got mine on Friday afternoon lists it as the drive plate, but Lehman calls it the drive damper.

It looks like you had your transmission out for service when you took the picture. You've even got the alignment studs in place for putting it back. Those make things so much easier. It can be done without, but it takes a little more effort to line things up.

Ken Buck
Believing firmly that one should admit ignorance before displaying it, how often should the drive plate/damper be replaced?* How often should it be inspected?

Stitch in time, etc.

And therein lies the problem. Inspecting the plate is as labor intensive as replacing it. One must take it apart to be able to see it. Some say that they can hear noises when it starts to go bad, but I never did. And, as I stated, it was on my mind. I suppose I should have used a stethescope to listen to it and then maybe I would have heard the springs bouncing around as they most certainly were doing.

The number I've heard most often used is 3000 hours of use makes it suspect and up for replacement. Has anyone else heard a different number?

Ken Buck
Stitch in time, etc.

Best is to talk to the tranny shop where you will get the replacement , and find out if a far heavier duty plate is purchasible

The plate installed by the origonal engine marinizer was usually the cheapest avialable , and an up grade is simple , at little extra cost.

If I assume mine is the original plate (I have no idea if it's ever been replaced) it has about 4800 hours on it. It has marginal wear, but "looked" fine when we had the tranny out. However, I could kick myself for not replacing it at that point, since we were right there anyway.

I carry a spare now, and will certainly replace the plate if I ever have to pull the tranny again.
The captain who took my wife and I out for our first training emphasized repeatedly that we should always check our reverse gear *before* approaching the dock to make sure it was working.* I'll admit that I've gotten away from doing it over the years.* Your post is a good reminder!

2bucks wrote:

I think it was this forum where I spoke earlier about always having a plan B available and never depending on the reverse gear to stop you.
2 Bucks,
I think that has been a good reminder to all of us. I am now in the process of chasing up a spare damper plate. I have about 2000 hrs on mine at present.
It will go with all the other essential spares that one should carry.
What do you guys carry as spares , just as a matter of interest.
With the astern caper I had a nasty a couple of years ago. When leasving the straddle lift after a haulout I had to manouver the boat out of a tight hole and spin her 180 deg. This was all going well with about 15 ahead and astern movements.
On the last blast astern and full stbd rudder the boat surged ahead and hit a prawn trawler, a timber boat similar to my own.
Did a bit of damage to him but none to me as my plough anchor protected me.
Morse cable connection under the throttle lever gave way. Allways worth checking these connections and retighting them with a little locktite.
My intent is to put together a package of "parts" for this job. In it will be new plate bolts, bolts to press the flywheel off, bolts w/o heads for aligning the flywheel, and bolts for aligning the bell housing back onto the engine. As well as a spare plate of course.

Having those pieces aboard would have saved me at least an hour of time and frustration. Probably $10.00 worth of stuff that would make the job easier in the future. Another benefit is it would make the job a one person affair. This time I'm not sure how I could have put the flywheel back on without the help I had.

Ken Buck
2bucks wrote: "My intent is to put together a package of "parts" for this job. .....Having those pieces aboard would have saved me at least an hour of time and frustration."

OR.... you could install a second engine, transmisison,*prop shaft, and propeller so you could come home on it and deal with replacing the failed*plate on the other side*at your leisure.
* That's what we do.

Seriously, I'm impressed not only with your ability to change out the bad plate on the spot but with your ability to mentally gear yourself*up to tackle the job.* I probably would have been calling for a tow or a mechanic to "come fix it for me."* Well done.
I knew somebody would point out the obvious!!!

What do you guys carry as spares , just as a matter of interest.

Propeller , set of injectors , and timing tool, complete bilge pump and float set , complete fresh water pump, and lots of bulbs for the various lights.

Also enough oil for 2 complete changes (even tho dry stack exhaust ) and a few fuel filters (even tho the US Navy fuel tank is ez to maintain , monel with no on deck fill, and low point drain.

As I pointed out above, our boat came with a spare engine, transmission, prop shaft, prop, and rudder. All conveniently stowed out of the way in the engine compartment or in special brackets under the aft portion of the hull. They have come in quite handy on a few occasions.

We also carry two spare fuel pumps, a spare coolant pump, a spare raw water pump, spare heat exchangers, as well as the usual filters, impellers, hoses, belts, and so on. Those are just the engine spares. We also have toilet rebuild kits and all sorts of other stuff for the non-power train systems on the boat.
It would be interesting to see what other boats carry as spares.
I have listed the following
For engine spares I carry, a spare starter motor, spare impellers for cooling water pumps, spare fuel injectors (2off), 2 sets each of fuel and oil filters and 4 spare filters for the Racor, 2 flexible spare fuel injection lines, lub oil for engines, gear box and steering, no spare engine, bow thruster or stern thruster.
I carry pretty much the same for the gen set except for starter motor.
The spare pressure plate is an addition that is on its way.
Also plenty of spare hose of various size plus hose clamps etc.
The other major is a HF radio so that while you are drifting the ocean you can talk to someone , if they care.

This equipment list is under review as I spend a lot of my time well offshore of the Australian coast and we don't have anyone like the US`Coast Guard or Sea Tow.
If you go out you pretty well have to get yourself home.
Yeah and I forgot a **** load of spare V belts, double for each size and application.

Hmmmm........ In 29 years of owning my own boat I'm almost dead even on single and twin screw boat years. I've come home one time on a single engine when the boat had twins. (starter failure) I've never been towed (knock on wood). I've always been able to make the boat come home on it's own power. That extra engine/trans/shaft and prop seem like pretty expensive spares.

I do all my own maintenance, repairs and service work. Of course having done a mechanics apprenticeship at a tender age might have something to do with my ability to do those things.

I do carry a large supply of spares so that I can fix most anything that goes wrong.

Ken Buck
I actually don't have a preference for twins over singles or visa versa. We used to charter a GB36 single before buying the boat we have now. We weren't shopping for a twin, it just happened that the GB36 that met our requirements and boating budget was one.

We've needed the second engine three times so far, once on the delivery run because of a leaking coolant pump and twice for raw water intake problems that prompted a precautionary engine shutdown.

And I like having two engines because I like operating engines, so two are more fun than one. Three would be even more fun, but it'd be tough to get around in the engine room of our boat if we stuck another FL120 in the middle down there.

Also, while my wife had no expressed qualms about the single engine in the GB we chartered, she is much more comfortable with a spare engine under the floor. Having her feel confident in the boat is important to our overall enjoyment of the boat. And she likes running two engines, too.

With one exception, everyone I have known personally who hit debris in the water and took out a prop has had a single engine boat (power or sail). They all came home on a rope. The one exception got a massive log jammed into a shaft in a narrows up north where the water swirls around fairly violently. It bent the shaft and damaged the prop but he finished his trip and came home to Seattle on the other engine.

I agree there is more protection for the prop and rudder with a single engine, keeled boat, but maybe all the twin drivers I know keep a better lookout for logs and debris than the single engine folks I know.

There are a lot of places up here that can work on the engines and transmissions we have in our boat. So the spares we carry are for those things we can change relatively easily. Anything more major than pumps, heat exchangers, hoses, filters, and belts we'll deal with after we get home on the other engine, or if necessary to a harbor with a diesel or transmission shop.
I certainly don't want to argue the merits of 1 or 2 because it's an unending discussion. I specifically wanted a single for maintenance, economy and room. I've been crammed into the tiny space between an engine and fuel tank too many times to want to do it some more. The better half reminds me that I don't have to do that, there are younger, smaller, hungrier folks that will do that for me. However, I work on the engine for the same reason I have varnished wood trim. I enjoy it.

I have friends who do all their maintenance with their checkbook. I believe they enjoy boating every bit as much as I do. I would expect that everyone who falls in between somewhere finds their level of comfort that makes them happy.

Ken Buck
No question the space in a single's engine room is a huge benefit. Fortunately the fuel tanks in our boat are all aft of the engines, so there is actually a fair amount of room on the outside of both engines. The challenge is getting round the front to get there
From Foley Engines' web site:
Hurth Gears: Care and Maintenance
Maintaining a Hurth gear can be easy if you follow a few procedures. This Tech Tip, one of an ongoing series published by Foley Engines, discusses the care and maintenance of the Hurth marine gear.

Vital Fluids

The Hurth marine gear is quite forgiving of owners who use less than ideal lubrication fluids. Many owners use common automatic transmission fluid (ATF) while others rely on shop manuals that (incorrectly) recommend SAE 20 engine oil. In our experience neither is optional. We had a major oil company develop fluid that seems to work best. We market it as Foley Hytork Fluid and supply it in gallon and half gallon containers.

Damper Plates

Whenever the engine is removed for service it is a good idea to replace the spring loaded damper plate that mounts between the gear and the flywheel. These clutch-like discs are important to the operation of your flywheel. Our shop people have seen many a gear in for total overhaul whose damper plate was neglected and rusted on to the flywheel. For boats with high duty cycles and/or multiple users, like launch operators or those who just want absolute peace of mind, we have severe duty damper plates. These are marketed under the name of the Foley Diamond Damper for a slight premium.


Like a heavy duty damper plate, adding a cooler to a Hurth will extend its life, particularly in situations where the gear is at the upper limit of its horsepower capacity. Hurth coolers are an easy add-on and we highly recommend them, especially in launch applications.

-- Edited by Keith at 06:04, 2008-03-27
Our experience with the Hurth gears is that they are rated VERY VERY optomistically.

I would suggest anyone with a newbuild , or replacing the unit go 2 sizes up on the specs from the usual recomendation.

This is usually still cheaper than a rebuilt Twin Disc , and almost as reliable.
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