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Old 03-11-2011, 01:49   #1
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Perkins 4108 Vibrations At Tick-Over

Hi. I have a late '80's Perkins 4108 which runs beautifully except for excessive vibrations at 480-500 RPM. All other points on the rev range are sweet but this area causes the engine to rock & resonate throughout my boat. Local engineers suggest that 480-500 RPM is correct for tick-over to preserve the transmission when engaging gear. I currently have tick-over set to about 750 RPM to cure the vibrations problem but there's a significant clunk when engaging gear at these revs. I'd be grateful for any wisdom on this matter
Many thanks
MJ
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Old 03-11-2011, 02:29   #2
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Re: Perkins 4108 Vibrations At Tick-over

I think it is normal mine and 2 others I knw of do the same thing, and if you watch the engine at low reves its like looking at a frog in a sock. I like the others just keep the reves up when idling mine sits nice @ 600 revs and I only bump it right back when going into gear. For an engine over 30 yrs old and going strong regular oil changes and clean fuel it isnt broke leave it alone.

EDIT: just had a thought I have 2 sepeate levers one for fuel and one for gear.
If you have a morse box it could be a bit harder.
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Old 03-11-2011, 02:42   #3
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Re: Perkins 4108 Vibrations At Tick-over

Simon - thanks. I do indeed have a Morse type single control, hence the concern. Good to hear though that excessive vibrations at these revs is normal. Thought it might be. Which single controls do you use?
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Old 03-11-2011, 03:14   #4
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Re: Perkins 4108 Vibrations At Tick-over

I dont know the brand but fitted each side of the pedistal.
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Old 03-11-2011, 06:22   #5
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Re: Perkins 4108 Vibrations At Tick-over

I'd suggest you check your motor mounts to see if any have worked loose. I get similar vibration from time to time on my 4.108 and it's always a sign on my boat that one or both of the rear motor mounts have loosened and the rear of the engine has lowered. Not only does the engine vibrate more on the loose mounts, it also takes the shaft out of alignment and ultimately the engine will stall out when I put the transmission in reverse.

These type vibrations are also a good reason to check all fasteners and fittings on the engine from time to time, things tend to work themselves loose. I've got a minor oil leak forward somewhere and I'm pretty sure I'm going to find an oil fitting has loosened due to the latest engine mount working loose.
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Old 03-11-2011, 06:45   #6
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Re: Perkins 4108 Vibrations At Tick-over

Perkins factory spec for the idle speed on the 4.108 is 625 to 700 RPM so 750 is not out of order. If you have a mechanical transmission (like the HBW150) it will clunk into gear and this is normal. If you have an hydraulic transmission (like the Velvet Drive), you should not hear or feel anything when you put it into gear.
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Old 03-11-2011, 06:47   #7
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Re: Perkins 4108 Vibrations At Tick-over

MJ
Perkins factory spec for the idle speed on the 4.108 is 625 to 700 RPM so 750 is not out of order. If you have a mechanical transmission (like the HBW150) it will clunk into gear and this is normal. If you have an hydraulic transmission (like the Velvet Drive), you should not hear or feel anything when you put it into gear. 500 RPM is much too low for this engine's idle speed and you can expect excessive vibration at this speed.

If the clunk that you hear is new, I suggest that you may have a problem with the damper plate.
Stanley
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Old 03-11-2011, 06:49   #8
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Re: Perkins 4108 Vibrations At Tick-over

480 - 500 rpm is very low idle speed. I would think that 600 - 800 rpm would be a much better idle. I'm not sure what the manual says but 500 rpm seems way to low.

Well, I was beat out by two other posters.
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Old 03-11-2011, 07:03   #9
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Re: Perkins 4108 Vibrations At Tick-over

Greetings and welcome aboard the CF, Masterjuicer.
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Old 03-11-2011, 08:58   #10
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Re: Perkins 4108 Vibrations At Tick-over

Raise your idle and replace the motor mounts if they are older than 10 years. The rubber isolation gets tired.
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Old 03-11-2011, 09:21   #11
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Re: Perkins 4108 Vibrations At Tick-over

I have just visited this issue as part of my repower with my Perkins 4.108.
Over the last number of years I have been trying to collect every manual that I can get my hands on relating to this engine. One thing that I find amazing is that no where in the manuals is there a central list of critical engine data, ie. oil pressure, coolant teperature, engine rpm, etc. I have found that I have go searching through the manuals to dig up the various specs when I need them, a real PITA. Feeling at initial engagement of my Hurth gear with the Morse single lever controler that the clunking of the gear upon engagement was a bit severe I went after determing and adjusting idle rpm to the factory reccomended settings. I went on the net and found two older Perkins factory manuals. The first indicated idle rpm of 520 and the second indicated 650 as the minimum.

Not releying on the elecetric tach I used a laser tach directly off the flywheel and low and behold idle was at 850rpm. Using the idle adjustment screw I set the rpm at 650 and preceeded to engage the gear
and voila success, couldn't even hear the gear engage and had to look over the transom to confirm that the prop was in fact turning.

Now to try and answer you question, I found that if I tried to set the idle to the lower setting of 520 rpm, the motor would stall and fail to start, once I got back to 650 all was good. Having a curious mind and wanting to know as much about the old Perk. as possible, I did some more reading and the idea is that you should ideally be fussing with the anti stall valve in conjunction with adjusting the the engine idle. Considering that I have solved the hard gear engagement problem, and confirmed my rpm with a very accurate instrument I am fine and will not attemt to go any lower.

If you wish I will try and find the link to the manual that will steer you straight.
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Old 03-11-2011, 16:57   #12
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Re: Perkins 4108 Vibrations At Tick-over

My old Perkins would shake at low rpm to the point where I could be standing on the bow and feel it. Once up to anything over 800 and it was just fine. Great engine just a few quirks.
kind regards,
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Old 05-11-2011, 11:55   #13
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Re: Perkins 4108 Vibrations At Tick-over

Satisfactory results with different RPMs on the same motor suggest to me that the individual tachs have not been certified. Cburger is the only one who mentions his has been checked. Would suggest verifying your tachs are accurate then proceeding. The anti stall adjustment is sort of like a mixture screw on a caburator, to lean and it stalls when put under load. To rich and it increases the RPM's. It is a fussy adjustment that usually requires mutiple adjustments to the idle setting and the stall adjustment. You first set the idle then adjust the stall untill the RPM's start to increase, turn the adjustment back slightly. I f the idle has increased readjust the idle setting and again readjust the stall. Watching your tach closely is key to your success.
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Old 05-11-2011, 12:21   #14
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Re: Perkins 4108 Vibrations At Tick-over

as I remember my idle was about 700 and smooth.
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Old 06-11-2011, 08:15   #15
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Re: Perkins 4108 Vibrations At Tick-over

Firstly, a very big thank you to everyone who offered guidance & wisdom on this matter. It's very much appreciated when you're alone, the lights fading & you've dropped the small spanners into the bilges for the umpteenth time!
OK, I've checked various areas & discovered that 3 of the 4 engine mounting bolts were loose enough for the washers beneath them to be moved by hand. These are now tightened but my boats just out for the winter here in UK so I'll check the vibrations when I change the oil & filters next weekend. Engine mounts are 24 months old & in good shape. Engine RPM was checked with a lazer digital counter & the tacho set accordingly. She never stall or labours so I'm reasonably certain that the transmission alignment is OK.
I have a HBW 125-2R gearbox & my main concern is/was the clunk when engaging gear. Local engineering warns that an excessively high tick-over will ultimately trash the damper plate. The clunk is not new. It's less noticeable at lower RPM but becomes IMHO of slightly more concern in the recommended rev range. I think I'll live with though for next season & see if the damper plate survives.
Other matters... I'm planning to replace the crankshaft front oil seal and timing case gasket to stop the only oil leak on the engine. Does anyone know the correct size spanner/socket for the large bolt holding the pulley? Digital verniers indicate 38-39 mm across the flats. Does this equate to 1 1/2" imperial? Also, does removing the timing case require re-aligning of the water pump">raw water pump drive? Finally, what's the best way to stop engine rotation when slackening/tightening this nut?
MJ
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