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Old 12-20-2012, 10:12 AM   #1
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Damper Replacement

I just came across this in my files from 13 years ago and thought it may be of use to someone. I believe I posted it with MTOA.
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Having just done this, I wanted to share the information with the List. While the work done here was with a Perkins 6-354 and a Borg Warner Velvet Drive transmission, it may be similar to other engine/transmission combinations.

For those who don’t know, the damper is a disk device with about a half a dozen springs used to dampen the shock being transmitted from the engine to the transmission. It looks similar to a clutch plate on a car without the throw-out bearing. The disk is bolted to the flywheel and the transmission shaft is connected to the disk through a spline. These two pieces are connected to each other using the springs, which are about 1” in diameter and about 2” long. As these are continually transferring the power from the engine to the transmission, they are always being worked. Over time, they will start to wear the plate and themselves, and start to break into pieces and eventually fall out. If this happens, the worst case is no power being transmitted to the transmission. You may think the transmission is broken, but it is not. Also, pieces of the springs can get lodged behind the flywheel and lock up your engine. Also check this out if you believe you have a locked up engine.

The symptom of wear and possible failure is noise coming from the transmission while running at low RPM’s. It has been described as marbles running around in an empty coffee can or stones in a hubcap.

Since I knew my damper was worn, having seen it three years ago while having a rebuild done on the engine, I knew it would need replacement eventually. Since I now had the telltale noise, I decided to do it this fall after haul out. I also used this time to replace the cutless bearing and check the drive shaft for trueness.

The first thing I needed to do was pull the shaft to have room to slide the transmission back. Since I have a single, the propeller is protected by a rudder that is mounted on a skeg. I pulled the prop and thought I could push the rudder to the side enough to pull the shaft out after unbolting the bottom rudder bearing from the skeg. No such luck. Since I am on hard gravel, I dug a small trench about 12” deep and 3” wide perpendicular to the keel. I had enough clearance to drop the rudder in the trench and remove it completely from the boat. Pulling the shaft (‘s) was interesting. There are two sections, each about 10’ long. These are supported along their length with two pillow block bearings. These were difficult to remove but with a liberal application of Kroil and a wooden mallet, I was able to pull these out. I used a Sawsall to cut out the cutless bearing. I’ll take these to a shop to have them checked for run-out.

The Perkins 6-354 is supported at the front by two engine mounts bolted to the block and at the rear by two mounts bolted to the bell housing. The transmission is then bolted to the bell housing and does not have any of its own mounts. This is interesting since the bell housing must be removed. The easiest way for me was to support the rear of the engine using a small hydraulic bottle jack. This was positioned under the engine so it would come in to contact with the rear edge of the block. This is not very wide and must be done carefully since the oil pan is aluminum. If you don’t do it correctly, I would expect the jack would go right through the pan.

I disconnected the two wires from the transmission switch on the right side which is used to be sure the transmission is neutral prior to starting. I removed the transmission shift cable and the two hydraulic hoses that run from the transmission to the cooler. I disconnected them at the cooler since all the oil had already drained back into the transmission. I covered all the fittings with plastic wrap to keep them clean. You also need to pull the starter off. I marked the position of the two mounts and unbolted them, then removed the bolts holding the bell housing on to the engine. When you do this you will find that two bolts are run from the engine side into the bell housing at the bottom of the engine. There are about a dozen bolts in all. When this is done, check to be sure the jack is just high enough to support the engine but not lift the transmission off its mounts. Now, just simply pull the transmission back about 6”, it will slide easily. The transmission and bell housing are balanced enough that it will not tip over on you. You may want to put a block of wood under it to support it for safety. My damper was 13” in diameter with the 6 bolt holes, 6” apart and 6” from the center. The disk was well worn, 3 springs had their last coil broken off and they were laying in the bell housing. American Diesel sold me a universal unit that has various bolt patterns to match different flywheels. I used a thread locking compound and bolted the new damper in place.

Now came, for me, the difficult part, sliding the transmission shaft into the damper spline. You need to be exactly lined up to get this to fit properly. After a few tries, I got the surfaces within a ˝” with an easy slide. I was in! Now it was just a matter of bolting everything up and re-attaching all the hoses and wires. I was careful in lining up the mounts to make sure they were exactly where they were originally.

Total time - Removal: 3 hours, which included a lot of time understanding the layout and position of all the parts. Installation: 2 hours, which included the false starts in aligning the transmission to the engine.

Terry Hoy
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Old 12-20-2012, 10:25 AM   #2
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Greetings,
Mr. meridian. Thanks for the info. I dread the day I'll have to do that but you make it sound not as daunting as I expected. MY only concern is, from my perspective, can I do it while the boat is still in the water?
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Old 12-20-2012, 12:12 PM   #3
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Sounds familiar, I've been dead in the water only twice in my life and both times due to drive plates failing w/o warning. By w/o warning, I mean I could not hear the telltale rattle through the engine room sound insulation. Both times involved being towed in and changing the plate on my mooring (also Perkins T6.354)
The last time, I looked for a drive plate with "get home" ability and found the R&D plate made in the UK and distributed in the USA by PYI.
I would encourage anyone needing a drive plate to look at this product.
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Old 12-20-2012, 02:32 PM   #4
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Greetings,
Mr. meridian. Thanks for the info. I dread the day I'll have to do that but you make it sound not as daunting as I expected. MY only concern is, from my perspective, can I do it while the boat is still in the water?
Yes this is a job that can be done in the water or out. No real difference. I did mine a few years ago (Lehman 120/Velvet Drive). The boat was on the hard but I did it all from inside the boat. I did mine as a PM since I had removed the tranny and was rebuilding it. It made sense to replace it then since the labor was done.
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Old 12-20-2012, 02:59 PM   #5
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Greetings,
Mr. Brooksie. Wow! I count about 10 pieces. Play this twice...

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Old 12-20-2012, 03:28 PM   #6
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When the plate goes, you aren't any more. We replaced ours in 2008 figuring it was easier to do it on our schedule. We had no idea of the age or condition of the plate. The old one looked good and is now part of the spare inventory. On the FL SP135, the transmission and bell housing are aft of the rear motor mounts. We had a enough room to slide the shaft and transmission back (we did separate the transmission from the shaft at the coupler). Then the bell housing was removed and we changed the plates, all done in the water.
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Old 12-20-2012, 05:12 PM   #7
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Greetings,
Mr. meridian. Thanks for the info. I dread the day I'll have to do that but you make it sound not as daunting as I expected. MY only concern is, from my perspective, can I do it while the boat is still in the water?
Something that may have made slipping the trans back in a little easier. Put the transmission into gear then proceed to put the assembly back together. With the trans in gear the front shaft stays still (does not rotate). Now you can rotate the complete trans back and forth while exerting forward pressure on it. It should slide all the way home all at once. I would be very careful with using the bell housing bolts to move it the last 1/2". When you tighten the bolts the next thing you might hear is the crack of the AL case if it isn't aligned exactly correct. If you are out a 1/2" take the trans out of gear and giggle it around while pushing it home. You will know when it is in all the way.

I learned this lesson the hard way on t truck transmission along time ago. Broke the ear off of the cast iron transmission case. One was enough never again.
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Old 12-20-2012, 10:32 PM   #8
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Fishermen in Alaska running trollers can tell you that slow speed running like trolling all day is terrible on dampers. At higher speeds I think the springs are always loaded in one direction like the springs on the suspension system of a car. But on a boat at slow speeds the springs load back and forth (bouncing back and forth you could say) and is worse w a deep reduction gear and big heavy prop. Also much worse w a diesel than a gasser. And the fewer cylinders the worse the punishment on the damper plate.

There are high tech damper plates that use plastic wedges (ect) that do damping over a much wider range of crankshaft rotation than the standard old springs. I have used such a damper plate assembly on a 3 cyl diesel over a period of several years and worked very well without any problems at all.

Meridian ... excellent post.
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Old 12-21-2012, 12:09 AM   #9
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Vinny,
I left that part out of my post. Yes, I snapped off an ear with 1" left trying to use the bolts to pull the units together.
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Old 12-21-2012, 07:42 AM   #10
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The eng -tranny damper sometimes can be replaced by a unit better rated (tho more costly) than the stock item,ask the folks that mate commercial trannys. twin Disc ,ZF .

Remember most engines also have a crank damper , which as part of PM should be changed at times too.
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Old 12-21-2012, 07:43 AM   #11
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There are high tech damper plates that use plastic wedges (ect) that do damping over a much wider range of crankshaft rotation than the standard old springs. I have used such a damper plate assembly on a 3 cyl diesel over a period of several years and worked very well without any problems at all.
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manyboats, One is the R&D plate sold by PYI that I mentioned. It also has "gethome" ability inthat, unlike the spring type, if the polyurathane parts should give way, the driving and driven posts come together and allow you to continue albeit without any damping action. Well worth the slight extra cost
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Old 12-21-2012, 10:14 AM   #12
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I'm quite sure that's the DP I had but I don't recommend dealing w PYI. Talk to Mike at Harbor Marine in Everett Wa if your in the area. Or ANYBODY else.
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Old 12-21-2012, 04:23 PM   #13
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I'm quite sure that's the DP I had but I don't recommend dealing w PYI. Talk to Mike at Harbor Marine in Everett Wa if your in the area. Or ANYBODY else.
Surprised to hear that. I've had good dealings with them (name ?) on both engine mounts and drive plate. I think they are the only source for R&D products in the USA and R&D is the only "non-spring" drive plate I know of for the Perkins 6.
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Old 12-21-2012, 08:19 PM   #14
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It's the owner I had issues with and as long as you avoid him your'e good but as far as I know the company may have been sold 5 years ago. My problem was 10 yrs ago.

Also there may be an R&D store not too far from PYI.
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Old 04-24-2020, 06:35 AM   #15
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I am about to do this job on my Golden Star 38. I will need to shift/slide the starboard engine forward with crow bars as there is not enough room to move the shaft back 6" before hitting my packing gland. My main concern is a bottle jack on the bottom of the hull lifting/supporting the 6 cylinder Perkins I am worried I may but a hole in the bottom of my boat, still in the water - any thoughts?
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Old 04-24-2020, 07:22 AM   #16
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6” may be enough room. You just need to clear the splined shaft. I used some plywood to spread the weight on the bottle jack. Mine wad a Perkins also.
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Old 04-24-2020, 07:31 AM   #17
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Thanks for the quick reply! Just to clarify, you had the bottlejack directly on the hull with the load spread with ply? Also, after I slide the engine forward do you suggest I bolt down the forward engine mounts, while I have the bottle jack under the rear of the engine?
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Old 04-24-2020, 07:39 AM   #18
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I slid my trans back.
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Old 04-24-2020, 07:44 AM   #19
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I replaced mine at around 5,000 engine hours. I don't know if it had been previously replaced, I would guess so. It was loose and showed some wear but had not failed.

I suspect that single engine trawlers are significantly harder on dampers than many other boats, particularly twins. When I "bump" from forward to reverse to kick the back end around it must put quite a bit of strain on those springs. Plus trawlers are pretty heavy and generally spin a pretty good sized wheel.

Oh well, it's a "wear" item and not that big of a deal or expensive to replace.

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Old 04-24-2020, 09:43 AM   #20
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I don't think you need the shaft to slide back six inches for tranny to pull out. I think 3-4" will do it. Once spline pull out of damper, you can tilt the back of the tranny up and get it out.

Note the VD geabox with reduction is pretty heavy, easy to blow your back out trying to lift it hunched over. Best to rig it out or if no room hire some young bucks to grunt it out.

Bottle jack under engine is ok. Hull wood or glass? Glass no issue, wood yous gots to be careful. In any case, use pieces of wood to spread the load both top and bottom of jack.

You may be able to pry up the rear of the engine using prybars or 2x4's and add shims of sliced plywood and 2x4 chunks between fw hsg and hull. Don't use bottom of oil pan, it is fragile. Bottom of fw hsg is ok to support half engine and all gear weight. Might not need jack at all.

Bestest way is to rig from above if that can be arranged.
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