Replacing engine mounts?

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August 7, 2011 at 21:11 #5401
Moderator
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Keymaster

Has anyone replaced the engine mounts on the Perkins 4-108, and have words of advice?

Now that we have a vibration free shaft bearing (with our new white metal bearing), we’re looking to get rid of engine vibration too.

August 7, 2011 at 22:03 #9931
Arild Jaeger
Arild Jaeger
Participant

I replaced the engine mounts when I replaced the white metal bearing. I put in Yanmar mounts, but they are a bit too high, so you will probably need different ones to fit correctly (depending on your exact measures). The original mounts were very stiff after 40 years…

August 7, 2011 at 22:08 #9941
Ronar M
Ronar M
Participant

Hi

I intend to replace the mounts on Ronar M’s 4107 this coming winter and have done some research. First of all it is possible to do the job with the engine in the boat though I suspect it may be necessary to detach the exhaust pipe before lifting the engine enough to remove the old mounts and slip in the new ones. I have tried in vain to find out the specification of the original mounts (Perkins ie Sabre Marine don’t seem to know) so I will base my choice on the weight of the engine (info which is available). This may mean the bolt holes in the engine bearers may not match up with the new mounts but I am told by an engineer who has tackled the job before that it is possible to drill new holes with the engine in place with a long drill bit. Of course it will be necessary to realign the engine/gearbox unit to the prop shaft, a ‘black art’ I believe, but my engineer contact says he has done it many times so even if I replace the mounts myself I will get him to do the realigning. He will also make the choice of mounts as the right ones can reduce noise and vibration. Hope this helps. Will keep you posted about how my job goes.
Trevor
ps only the front mounts need replacing but I will do all 4 as I have been advised it is unwise to do half the job even if the other 2 look ok because their rubber will have a different hardness to that of the new ones.

August 8, 2011 at 05:46 #9961
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Moderator
Keymaster

I wonder whether the engine alignment is so critical, if your Nic 38 has the same incredibly flexible shaft couplers that ours does. When we replaced the white metal bearing, the coupler closest to the gearbox is so flexible that we could swing the intermediate shaft downwards and pull the tail piece inboard after unbolting only the aft coupler.

The mechanic involved with our white metal bearing job marvelled at Rainshadow’s shaft couplers, and then said that they must be a way to avoid precise engine alignments. So maybe this is not such a concern.

Arild – I wonder what you found about engine alignments?

Marilyn

August 9, 2011 at 20:54 #9981
Arild Jaeger
Arild Jaeger
Participant

Marilyn,

I decided that the intermediate shaft with flexible couplings at each end would absorb a little misalignment. Anyway it was difficult to measure alignment when everything is flexible…

It seems to work fine, but I guess the end result of any misalignment could be increased wear of the bearings in the gearbox and in the stern tube. If the misalignment is really bad, I suppose other things could happen as well.

Arild

May 2, 2012 at 04:31 #11521
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Keymaster

Trevor – did you replace your engine mounts over this last winter?

I’m just looking into this again now, and I found that the US supplier Bushings Inc claim their DF2207-2 is the right choice for the Perkins 4-108. They think the hole spacing is 4″ – I’ve not been to the boat to check that out yet. Here’s a link to their brochure for the DF-2200 series.

I also found Thermoboat Yachtsman series, looks like the YC-4-110-300-5/8 should work. Their brochure is here.

And finally, out of Australia the PolyFlex P # 4.5 CTF 60-15-16 is supposed to work.

I’m wondering if anyone who has already tackled this job can offer more advice before I start ordering parts?

Marilyn

May 2, 2012 at 16:43 #11531
Ronar M
Ronar M
Participant

Hi Marilyn

Yes, I have got new engine mounts. In the end I got a marine engineer to do the work because his price was so reasonable and I had a lot on myself at the time – I stripped down the holly and mahogany floors in the saloon and forecabin and revarnished them with International Paints one pot polyurethane with very pleasing results. I also rubbed down the floor in the after cabin, which I had stripped the winter before, and put an enlivening coat on that so the whole boat is looking great at the moment.

My engine is a 4107 and I now have aluminium alloy mounts which will not go rusty as the old ones did. My engineer also sprayed them with wax oil to protect them further. I was told the engine mounts were unusually low – most of the ones I was looking at would not screw down low enough for the 4107 so make sure you measure the old ones before you order and check that they will do the job. Over here we often measure things in metric (though we still use imperial when it suits us – pints (of beer) and miles (on the road) and, of course nautical miles at sea) and I know that the engineer told me the bolt spacing was 400mm which equates to 4 inches.

Good luck, Cheers Trevor

May 5, 2012 at 08:08 #11571
Ronar M
Ronar M
Participant

Hi Marilyn

I forgot to say my engineer was worried about engine alignment – there are usually two flanges, one on the back of the gearbox, the other on the forward end of the prop shaft and Ronar did not have these; apparently they are brought together and a feeler gauge used to check the alignment. Anyway he was happy once he got started on the job as she has two flexible couplings between the gearbox and the stern gland which reduced the near for accurate alignment – just as Arid suggests. Cheers, Trevor

May 8, 2012 at 08:37 #11601
Happy Dolphin
Happy Dolphin
Participant

Do try hard to get mounts with same bolt centres on engine beds as changing these on the bed is usually very difficult.
As you have flexible couplings (which are necessary on fixed shaft/flexible engine mounts) height will not be an issue
to check alighnment (not nessasary)you will need a longer dummy shaft with coupling in positionmounts can be got from Lancing Marine UK (google it)
my boat has had a perk 4108 in at one time but now fitted with yanmar 4 cyl

May 26, 2012 at 18:26 #11721
Moderator
Moderator
Keymaster

OK – we’re still on the quest for new engine mounts. Our bolt centers are 4″, and there are plenty 4″ mounts to choose from, so that’s not a worry. It’s the clearance that’s the issue.

Our mechanic recommends R&D Marine “supermount” style 800-010, because they are designed to survive rollovers. But he is concerned about their their minimum clearance at 3.05″ (77.5 mm). We measure our old mount’s clearance to be about 2.25″ (57mm). Our current ancient mounts appear to be “bottomed out” – we are thinking the engine may have settled as their rubber compressed. We’re also thinking the flexible couplers are rather flexible….

I can buy a Polyflex P#4.5F-60-11-16, which has minimum clearance of 2.42″ (61.4mm) – but the installation manual for these repeatedly stresses that the engine bed must be parallel to mount base (within .005″ or 0.127mm), or the life of the mount is compromised. They also have only a 1 year warranty, and mention nothing about rollover tests. So the R&D Marine mount sounds like the better quality product.

Does anyone with a Perkins 4-108 who has replaced their mounts have any advice about the clearances?

Finally, the mechanic is planning on supporting the engine during the job by wedging some wood under the engine so it is temporarily supported by the fiberglass pan under the engine, rather than by the stringers. Is the fiberglass pan strong enough to take the weight of the engine?

Cheers –
marilyn and van

May 27, 2012 at 09:46 #11731
Happy Dolphin
Happy Dolphin
Participant

i would think pan is well strong enough i stand in mine and it doesent give
the 3/4 inch extra height RnD will make no difference with your flexi shaft couplings
i hope they are the type to take forward and reverse prop thrust tho

May 27, 2012 at 20:33 #11751
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Moderator
Keymaster

That’s encouraging Roy, thanks for the reply.
The R&D Marine couplings claim to have variable flexibility, with greatest rigidity in the prop thrust dimension. Here’s the quote from their brochure:
“Soft vertically and at right angles to the crankshaft to isolate vibration, stiff fore and aft to take the propeller thrust.”

More details on the 800-010 is available on their website (providing link to UK site):
http://www.randdmarine.com/enginemres.asp

June 25, 2012 at 06:42 #11821
Moderator
Moderator
Keymaster

Van finally got our engine mounts replaced, which has resulted in a lot less vibration. We used the Bushings Inc DF 2207-2 mounts, which I recommend because they have the correct minimum clearance. All other mounts I mention above have too high a clearance for ideal engine/shaft alignment.

I’ve made a posting on our own blog about this saga, if you want to know more.

The posting also describes the laser alignment jig that Van made to detect misalignment. It seems on our boat, the sweet spot for best alignment is a clearance between engine bed and engine bracket of about 2.375″ (about 60 mm). Most engine mounts do not have that low of clearance.

Marilyn and Van on Rainshadow

April 6, 2021 at 23:06 #26900
Czarina Blue
Czarina Blue
Participant

I have an original Perkins 4108 with front end Bowmans heat exchanger on Czarina Blue.

I have just replaced my mounts since one had sheared, the one below the raw water exhaust elbow, possibly due to corrosion of the engine foot there from drips from that elbow periodically. The lower lock nut was now above the foot plate due to a rusted hole in the plate! Two of the other feet had to be repaired, re-welded and straightened, I guess the engine had started to dance around a bit. Also the mechanic noticed that the starboard engine fibreglass bed was flexing slightly so he bolted in a rigid steel plate on that side.

All this possibly aggravated by a very worn prop shaft bearing.

Thanks to Rainshadow for their blog on all this. Often useful.

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