Mercruiser D1.7 RW pump

[martynwhiteley]

Mmmm..

Having sold the two BMW petrols from my Birchwood 27, I'm now looking forward to collecting a new Mercruiser 1.7 diesel/alpha drive unit on Saturday. (Shame I can't afford a pair!).

However, I've just discovered that the Raw Water pump is mounted inside the alpha leg on the Mercruiser. Guess this must be ok for trailable boats, but I don't want to have to pay £100 everytime I want to check the impellor - and where do I put my Vetus strainer?

My use is primarily river/canal. I'm beginning to wonder if the Merc is designed mainly for sea/lake use in small boats.

Research suggests it's possible to fit an auxiliary jabsco type pump on the larger Merc diesels, but not the 1.7, and run this from a separate sea-cock.

Any advice? Is it feasible to run an electric pump from a sea-cock, teed into the raw water engine inlet for emergency use?

Is it possible to change an impellor in the leg with the boat in the water.

Any general comments on the 1.7D or twin to single conversions would be appreciated.

<hr width=100% size=1><font color=blue>Oh well, maybe next weekend....</font color=blue>

 

[tr7v8]

In answer to your last question, no you cannot change the impeller with the boat in the water as the lower housing has to be dropped. From memory, Mecury recommend i's renewed every 2 years and do a kit of bits 'cos it's not just a rubber bit, generally you change the housing liner and a few other bits.
I believe that the diesels use a seperate pump inboard an don't use the leg on at all. I see no reason why you couldn't use a seperate pump and water pick up although the Mercruiser warranty may have an issue. Not sure about river use have a chat to who you're buying from or Ray Stapeley Marine in Chatham as he must have some on the non-tidal medway.

As I've said before I really lust after the 1.7 and a pair would be brill in the Draco although the cost would be horrific. A single wouldn't be worth the effort as the performance would be too poor. Spannerman hereabouts on these pages raves about a Draco 2500 he converted with a pair of 1.7Ds.

Being nosey did you get a good price on the 1.7?, list is £8,800ish. Whisper in a PM if you don't want to go public.

<hr width=100% size=1>Jim

Draco 2500

 

[Chris_B4]

I understand that it is nice to check the impellor but if its replaced at the same time as the drive is serviced, say every two years, then its not likely to cause a problem anyway

I have 4.2 litre Merc diesels and they do indeed have Jabsco pumps driven off the camshaft. I have just overhauled the pumps and replaced the impellors and have no plans to look at them again until they have served another two years (unless I see some other symptoms suggesting they are failing)

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[spannerman]

Jim is correct in his reply about the impellor in the Alpha drive, I can confirm that they will easily go 3 yrs between replacment unless you are in really dirty water i.e. sand. You will need to have the bellows replaced around then anyway so its best to plan 3 yearly major servicing intervals, obviously changing the drive oil yearly and checking the zincs of which there are now 6! Is it possible to hang anymore on a drive I ask myself.
I assume your boat is semi displacement or you only intend to cruise at low speed as a 27ft boat is never going to plane with only one 1.7 as long as you are aware of that you will be very pleased with the engine as I have had glowing praise from the nine owners I have done conversions for so far. One thing to be aware of is sometimes you may hear a growl from the drive in nuetral when irs warm, this is nothing to worry about as owners of Bravo drives with diesels will know. Its because a diesel runs erratically at idle compared to a petrol and its gear chatter which disappears as soon as you increase the revs, so if you hear it dont think there is something wrong, enjoy your new engine, Steve

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[martynwhiteley]

Thanks Steve,

Following your's and Jim's repiles I'm feeling much more confident with the set up now. (Too late to change my mind anyway!).

All I need to find out now is the dimensions for the transom cut out, can't find it anywhere on the net, perhaps I'll have to wait till I collect the unit. If you know the approx size and relation to the crank c/l I'd be glad of the prior knowledge.

Like you say, I suspect the Birchwood 27 will stick at about 11-12 knts and not get on the plane. Obviously a twin installation would be great, but the best part of £20K would be way out of reach and I doubt the boat would be worth much more than £25K even with a new pair of 1.7's.

My use is mainly the tidal Trent, Ouse, Humber and connecting canals, so It should be well adequate. I was getting a bit fed up of running down the canals on one engine, then debating whether to fire up the other one for locks/bridges, or hope for the best. The Birchwood has a prominent keel, and although regarded as a planing hull, seems to lend itself to semi-displacement river work quite well.

Any advice on connecting my domestic hot water pipes to the 1.7? Do you recommend any supplimentary instruments?

Thanks again,

Martyn

<hr width=100% size=1><font color=blue>Oh well, maybe next weekend....</font color=blue>

 

[spannerman]

Hi Martyn, regarding the transom cutout, the shape of your hull will determine this. First you have to find the centre of the transom, best done with 3 people, one each side holding long straight edges against the bottom edge of hull for-aft and one to measure, mark centre point and measure again up under the rubbing strake or some other convenient moulding line, join the dots and you have the centreline.In the transom assembly box is a pattern, first you find out the transom angle to the keel usually between 10 - 12 degrees, then from the chart relating to your drive you get a measurment vertically up from the bottom of the transom. This is your 'X' point or crank centreline, overlay pattern and tape on, cut out centre and drill holes remembering to angle drill so that they are at 90 deg to transom. Fit transom assy and install engine temporarily by fastening rear mounts complete with washers springs etc. Then supporting just front of engine adjust height to find where the motor mounts need to be built up, you will need the alignment tool for this job to check correct alignment of motor to transom. then remove engine finish interior work and reinstall, recheck alignment and fit drive.
Regarding hotwater, on the port side above the servo oil res there is a metal pipe with a square plug, that is the outlet, the return is on the port side of the heat exchanger near the front, again a square plug but you will need a 90 deg bend as another pipe runs near to it. You will also need an electric circulation pump as there isn't enough pressure to make the water go around your extra pipework.
Hope this helps, regards Steve

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[martynwhiteley]

Mercruiser 1.7 Installation

Many thanks for your time and interest Steve.

I have read up a bit on the 'X' dimension and conclude it needs to be close on 360mm. Perhaps a bit less rather than more, because the boat is now likely to be semi-displacement, so 350mm might be about right.

However there are large structural rib sections running all the way from the transom forward. These seem to provide the support for the larger than average skeg keel. The twin engines sat comfortably each side of these, but the single will sit on top. Cutting them down would seem a bit drastic. (and expensive!).

If I don't touch them, and leave a min of 13mm clearance between the lowest point on the engine, and the top of these ribs, I've calculated an 'X' dimension of 380mm. At least 20mm above recommended, however the prop will still be much lower than the position of the old twin props, and top of prop blade well below bottom of transom. If it was lower, I'd begin to wonder about constant grounding on river beds.

Do you think an 'X' 20mm more than recommended will be a problem? Will a prop type change help?

By the way, I presume that if I fit an electric pump to circulate for hot water, if it's not running, the normal cooling circuit will remain fully operational. Yes?

Many thanks, Martyn

<hr width=100% size=1><font color=blue>Oh well, maybe next weekend....</font color=blue>

 

[spannerman]

Re: Mercruiser 1.7 Installation

I don't think it will be a problem with your installation to have the X point 20mm higher as this boat is never going to be up on the plane which raises the drive correspondingly in the water. In which case you run the risk of prop ventilation and sucking air into the water inlets, but as you say you are going to be running at displacement speeds so I think it will be just fine. I would stick with the prop supplied I guess it will be a 17" or 19".
And yes the extra pump is electric, and if its switched off the coolant just goes round the existing system so no problem there.

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