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Old 02-04-2016, 01:19   #1
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Perkins Diesel breaking engine mounts

I have a Perkins P 3 144 engine in my 38 foot yacht. I keep on breaking poly flex mounts and engine mounts and I am at my wits end.
I have had engineers check the alignment, I have slipped and pulled the shaft which had no deflection or error, there is a flexible coupling between the gearbox flange and shaft. The cutles bearing is good.
After a 200 mile trip with new mounts the front port mount and aft starboard mounts had shattered the steel plate between the poly / rubber insert and the lock nut.
I have new and heavy engine brackets for the mounts, the engine when running appears to have little vibration but must be something there to be doing this damage.
My hope is someone may have experienced this issue and can point me in a direction to fix this issue once and for all.
I am starting to think the issue may be with the engine and the harmonic balance, or in the gearbox as I have mechanical box.
Any clues would be appreciated!
Cheers.... It's driving me to drink not my next island
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Old 02-04-2016, 02:09   #2
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Re: Perkins Diesel breaking engine mounts

With catty-corner mounts breaking, that would indicate the motor is twisting. But w/o seeing he whole setup it's really hard to really say. It still sounds like a coupler misalignment. Do you really trust your engineer. Was it aligned while afloat?

You say a flexible coupler? What kind/brand name?
What prop do you have? Length and size of shaft? Can you see it when it's running?
How long have you had the boat and when did the problem start?

It's a process of elimination!
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Old 02-04-2016, 02:57   #3
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Re: Perkins Diesel breaking engine mounts

How high above the mounts base plate are the engine feet sitting? Any chance of a Photo? Are they proper marine mounts or Industrial?
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Old 02-04-2016, 03:09   #4
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Re: Perkins Diesel breaking engine mounts

Greetings and welcome aboard the CF, Gazza.
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Old 02-04-2016, 03:46   #5
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Re: Perkins Diesel breaking engine mounts

Can you quantify keep on breaking?

Couldn't place the P3 so looked on YouTube - there are a few videos of them running in tractors.
If yours runs as smoothly as the ones I saw and the bearers are definitely level I'd wonder about the mountings possibly being from a faulty batch, especially if you bought them all in the same place.

Obviously check bearers again, especially if it's the same 2 mountings failing every time. If the engine's balancing on the other two...

Might be a way around it - do you remember the engine top mounting strut & bushes on the original Mini's? Maybe do something similar if nothing else works.
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Old 02-04-2016, 04:26   #6
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Re: Perkins Diesel breaking engine mounts

Very interesting! Some random thoughts...

I take it the mounts are mounted flat, and the studs are the right size for the slots on the engine brakets. And located down low on the stud as has been mentioned.

A sneaky alignent nudge can cause problems when you tweak just one mount a bit, without letting them all equalise back up, and therefore put more tension on just one mount. Also you might unevenly adjust the mounts up and down, and end up with something like a wobbly for legged table. If you crank down hard on the hold down nuts the wobble will stop, but one mount will be taking more load.

One mount is going to take more upwards load anyway, due to the torque of the engine and the fact that the mounts are often above the line of thrust from the shaft. Say on with a righthand prop the fwd starboard mount will take more upwards load in ahead, and the aft port in astern. The downwards load will be reversed.

Going from hard ahead to hard astern is pretty hard on mounts, but its a good way to spot any mounting issues. Sometimes the static alignment is ok, but when the engines under load the mounts can move and compress enough to cause problems, or even the engine bed can distort or be loose, and mounting bolts can be sloppy. Best checked by watching how the whole engine moves when load is applied.

I take it all the nuts on the top are properly tensioned down. And the engine brackets for the mounts are bolted on tightly?

Even given all these potential issues those polyflex mounts are pretty tough, and shouldnt have failed so quickly.

Good luck, and since I have the same mounts I am keen to hear what the issue is.
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Old 02-04-2016, 09:21   #7
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Re: Perkins Diesel breaking engine mounts

I have a Perkins P 3 144 engine in my 38 foot yacht. I keep on breaking poly flex mounts and engine mounts.

If you are breaking flex mounts and engine mounts you have an engine that is not sitting equally on all four. The mounts that are not breaking are supporting the load and the mounts that break are loading the non breaking ones and are extending the two others. You are breaking opposites. If you were breaking two on the same side... this would be attributed to a hit or jam with a line over the side... a wrap around the prop shaft. Other reasoning is that the bolts through the motor mount is not straight with the bracket, you might have to use a wedge shim to correct this. I had this problem of breaking mounts and to prove to myself this, I had some one at the controls engage the transmission while you wrap the motor mount with your hand. The one that flexes most is the one that is extended. Do the same at the rear of the engine and the opposite ones should flex more. The ones that do not flex are loaded and the weight pivots on those two. Hope I am explaining this so that you understand. I would do this under load and the I would disconnect the prop shaft and try to move the engine only by hand and try to move from side to side with a pry bar and recheck. All mounts should flex easily and equally. When you mention that you break engine mounts... did you ever break the steel mount or always the rubber part? Another question... when you operate or under way do you have any vibrations at different revolutions? Also I would check the stringers to see if there is rot in them... Roger.
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Old 02-04-2016, 14:19   #8
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Re: Perkins Diesel breaking engine mounts

All good suggestions from previous posters. I am curious what type of "yacht" this engine is mounted in? Is this a sail or power boat?

My first impression is the possibility of your engine stringers / beds may be compromised. I ask what type of yacht you have because a faster motor yacht may be subject to greater pounding than a sailboat.
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Old 02-04-2016, 15:02   #9
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Re: Perkins Diesel breaking engine mounts

Thanks for all your replies
Delmarrey - I have had some dubious engineers repair and inspect, charge a lot and no sooner have I left and the engine brackets had broken and mounts were flogged out. I had a new rear bracket made from k47 steel with minimal welds, the fours
forward bracket had its feet strengthened. The flexible coupling is a polyflex red.
This time no issues with the brackets just mounts.

Shakes Doug - the mounts have little clearance and the top plate has a lock nut and a adjusting nut. They are marine polyflex mounts made in Brisbane.

Snow Petrel - sea breeze -the last engineers I had inspect it and checked alignment,the alignment I did myself first off and it was within 5 thousand. Prior to leaving my last port I checked all was tight, ran her up and could feel little vibration on the mounts, and nothing through the hull. As she goes up in revs there is band of vibration between 800 and 1200, once through that I have cruising revs at 1250 with flat out at 1500.

I am thinking there may be a mechanical issue and I am unsure where to look but first is the harmonic balancer behind the pulley on the crank shaft,

I went from Brisbane to Townsville , 12 mounts, 4 different engineers and welders.

I was feeling confident that the issue was fixed only to find it had not.

We ran with motor and sail over the day and night in light to moderate conditions, all seemed good. Come morning she picked up to 25 to 30 on the nose and rising seas, she was pitching, I wonder as well if that may have contributed to the issue
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Old 02-04-2016, 15:08   #10
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Re: Perkins Diesel breaking engine mounts

Also the boat is a 38 ft fibreglass cutter rig sloop, I built her 30 years ago, engine is regular serviced. This issue started when I broke a forward mount foot coming over a bar, since repairing the bracket and mount it has been constant
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Old 02-04-2016, 15:12   #11
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Re: Perkins Diesel breaking engine mounts

been running a P3144 for about 35 years now, firstly in a Bristol PD48 dozer then I marinised it in 82 and dropped it into a 22' cat boat, rebuilt/ freshened it up twice in that time and though several people tried they could not get the balance factors/ numbers to do the dynamic balance thing....yep they do bounce and clatter at certain RPM,, I run a shaft mounted thrust bearing and universals in the drive shaft so no probs with mounts shattering, have you done a thorough search inspection on what the mounts actually bolt to? (hull bearers etc).... apart from the usual pommie oil check method (if it aint leaking it aint got none) I have found this to be a reliable almost bulletproof motor, they can be a bit cold blooded to start cold with the inline injector pump but start 1st revolution everytime when warm
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Old 02-04-2016, 17:40   #12
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Re: Perkins Diesel breaking engine mounts

Can you get a dial indicator on your coupling?
If not can you get it as close as possible on the shaft?
Get someone to run the motor under load while you watch the dial, you will see the affect and indicate your problem .5thou would be OK
If your harmonic balance has moved on the crank shaft you will see the rubber sticking out between the crank shaft and the balance ring. Or get a marker (white) and mark your crankshaft and the balance ring run the motor under load then check your marks ,if they have moved and dont align,that is your issue.

Where is your thrust race? I assume it is in the transmission, that could be the problem , buy yourself a mechanics stethoscope and listen to the box,you will have to do it underway,as it needs load to create the noise . The noise you hear normally is just a "whurring" sound if the thrust race is at fault you will hear a deep rumble.
Obviously check all mounts with a depth gauge make sure they are all equal.
IE they are carrying the load equally.
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Old 02-04-2016, 18:06   #13
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Re: Perkins Diesel breaking engine mounts

I had the same problem with poly flex and after the third set I replaced them with hard wood solid mounts. This was 5 years ago and everything is perfect now. My boat is a steel H36 with steel engine beds. I still use the flexible prop shaft coupling.
All the best, Ray.
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Old 02-04-2016, 19:13   #14
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Re: Perkins Diesel breaking engine mounts

Thanks barney, already done the dial indicator, with the alignment and coupling checks all good.
I will have a listen to the thrust bearing in the gear box, and check for rubber protruding from the crank pulley.

There is a difference in the stud heights on each mount on rear it is 6 mm and forward is 3 mm
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Old 02-04-2016, 20:12   #15
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Re: Perkins Diesel breaking engine mounts

OK Front to rear difference sounds OK they both need to Equal across the bearers.
Have you tried all engine mounts to bearer connections,I can imagine you have.
Dont go solid mounts route as this will just transfer the problem,and will do more damage ,just later on.
If you have or can Borrow?? a tension wrench make sure all mounting nuts are to mount manufacturers spec. (I wont lend my Tension wrench to anyone who doesnt know how to look after it)
When the engine is run under load can you put your hand on the rocker cover and feel if there is a period vibration, if harmonic balancer is good .
Do you have a shear key on the shaft? as opposed to a cone fitting.
I am thinking there is an issue from when it ran aground.
Can you put a socket on the crankshaft front and move it back and forth (25mm)with someone or you watching the corresponding movement on the propshaft, measure the front a movement on the front to the corresponding movement on the propshaft. You will have some backlash loss in the gearbox. (10mm?) . Take very careful note if you hear any noise. The oil in the gearbox will hide most of the gearbox noise/ backlash. Let me know how this goes.
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