L23 SL Volvo Penta MD 2002 Rebuild -2 

Leisure 23SL Part 2 

Refurbish/Rebuild of a 9hp Volvo Penta MD2001 Engine

I had arranged with the owner of the yard to use one of his workshop so the engine was quickly wheeled, on a trolley, into the shop and hoisted up onto a work bench. There, with plenty of light and power available, I could comfortably work on the beast.  Photo 2

Before reaching for my socket-set in anger I took some time turning the engine this way and that to have a good look all around. 

Apart from the leaky head gasket, all seemed pretty good until I noticed that the starboard engine mount was noticeably lower than the port hand mount and had in fact given up the ghost. (Job number two!) In retrospect, I was aware of the odd ‘clonk’ when starting or ticking over at low revs. Pounds to pennies I had just discovered the cause!  See Photo 5

Next I removed alternator, starter motor and the starter relay complete with bracket and wiring loom socket just to give me clear access around the engine. All nuts, bolts and washers etc were put in yoghurt, ice cream or margarine tubs which I had saved for the purpose. The fixings, in their pots were placed adjacent their respective components (alternator etc).

At this point I removed the thermostat cover and prised out the old thermostat - which was badly scaled-up and I wasn’t convinced it was working at all. In part 1 believe I said that I had already removed the diesel feed and bleed off pipes, from the injector pump to the injector. This was not the case; my notes say that I did it at this point. (Apologies).

I had already purchased top and bottom sets of gaskets from Parts4 Engines, so now was time to start work in earnest. Off came the rocker cover to expose the valve springs, tappets and of course the head bolts. 

Next I began loosening the headbolts in the correct sequence. You can download the MD2001 workshop manual from online - this gives the correct sequence to undo and tighten the bolts to avoid distorting the head casting). The bolts were put in their own tub along with the rocker cover bolt and spacer and placed beside the rocker cover.

A few careful taps with a hammer against a block of wood and a bit of judicious prising with a blunt chisel seperated the cylinder head from the main block and It could now be lifted clear.

Be careful! It is surprisingly heavy. Make sure that the inlet and exhaust push rods (valve lifters) stay in the main casting and don’t come away with the head. When you do remove them be very careful to identify which is which and do not mix them up. (I pushed them through a piece of cardboard which I had labelled ‘inlet and exhaust’ and placed them in a pot with the other cylinder head bits).

Now, with the head lifted clear I could see both the cylinder head, valves, valve springs, rockers etc and also in the main body of the engine the piston, cylinder bore, oil and water coolant channels.  (See photos 3 and 4|)

The first shock was what I thought was a huge hole in the top of the piston! My heart sank - until I noticed that the edges of this ‘hole’ were neatly machined and with huge sign of reIief, I realised that this was the initial combustion chamber into which the injector ‘spits’ its diesel.

With the adrenaline from that shock still coursing through my veins, my brain was working overtime and I quickly logged the following: The cylinder bore looked very good but the main coolant water channels looked restricted by limescale. The cylinder head gasket was indeed ruptured towards the rear of the engine. There were no other major problems evident!

I decided to work on the cylinder head first. The valves and the head needed a decoke (unsurprising after forty four years) but were not too bad at all. 

The first job was to clean off any bits of the old head gasket and make sure that the head casting was unmarked. Then, I unbolted the rocker arms and, using a valve spring compressor, I removed the collets, springs and finally the valves themselves. Take care to keep inlet components and exhaust components separate and clearly marked. 

The combustion chamber of the cylinder head was carefully cleaned of soot and build up using a scraper. Next I cleaned the valves and examined the valve seats. 

They were fine, not pitted or burnt so I just gave them a light grinding-in (using fine grinding paste and one of those sticks with suckers on each end) to reseat them. 

After a thorough clean of all components (remember one grain of grinding paste can cause a lot of trouble) and a light coat of clean engine oil it was time to reassemble the cylinder head.

I prised off the old valve stem guides and pressed on new ones (supplied as part of the head gasket kit) then carefully put everything back together.

The only exception was the push rods (valve lifters) which would not be needed until the head assembly was about to be reattached to the main engine block.

I was now about to turn my attention to the main engine casting; specifically the bore, oil and coolant channels in the upper engine before inspecting the main bearings, crank shaft, big end and little end bearings and the piston and piston rings .

 I had already decided not to touch the diesel timing, injector pump or the injector as this is all specialist stuff and way beyond my experience. Even so, before delving any deeper into the ‘innards’ of Sirius’s beating heart I decided to ‘phone a friend’.

Tony is probably the best engineer I have met in my life. A retired blacksmith, he rebuilds and restores Spitfire engines and breathes new life into vintage tractors for fun. He built a his own beautiful Mitchell 32 from bare mouldings and generally can fix anything that is fixable! He knew what I was up to and kindly offered to cast an experienced eye over things.

Tony arrived at the boatyard and I ushered him into into the workshop. Fifteen minutes I hovered breathlessly about like an expectant father. Tony poked, sniffed, rotated, probed with a feeler gauge and listened intently. 

To be clear, it was the engine that was rotated not Tony! Eventually, like a Harley Street consultant, he delivered his pronouncements. The bore was unmarked, the piston and rings were fine and for an engine of forty four summers it was in excellent condition. 

When I mentioned taking the sump off to inspect the main shaft bearings, the ends and the oil seals, he just looked at me and said, “Why”?

Crestfallen, I blustered on about ‘while I’ve got the engine out’ and ‘I might as well’ etc,etc. He just shrugged and asked what the oil pressure was like before I started? (49 PSI). 

Did the engine burn oil (No). How much diesel did she get through (half litre per hour). How well does she start? (On the button). 

Then he summed up: “You could take it all apart and check or change it all, but it will not go back together and run as smoothly as it does now. My advice is: Finish the decoke, descale the water channels, change that engine mount then reassemble with all new gaskets and seals. Then go sailing. She’ll run for another forty four years!”

I was always told that only fools ignore good advice. So full of confidence I set to work reassembling the engine.

I applied a thin smear of Stag Wellseal to both faces of the new head gasket and laid it in position, I carefully slotted the inlet and exhaust pushrods back into there respective cam followers and gently lowered the reassembled cylinder head assembly back onto the main casting. 

After locating the pushrod ends into their rocker sockets it was time to replace the head bolts and tighten in the correct order.

Tightening the head bolts is done in two parts. First tighten all bolts to the ‘first’ tension. Then after a few minutes tighten again (following the same sequence) ‘to the second’ tension.

 USE A TORQUE WRENCH - DON’T GUESS. The actual tensions are given at the back of the workshop manual (available on line).

The last job in this sequence was to reset the tappet clearances before replacing the (new) rocker cover gasket and tightening down the rocker cover. 

I carefully replaced the diesel feed and drain-off pipes between the filter, injection pump and injector using new copper washers at the banjo joints and making sure all pipe connections were scrupulously clean.

I needed a 2 gallon bucket, a length of suitably sized, clear plastic hose, a descalant solution and a small electric bilge pump. The bore of the hose is dictated by the bilge pump outlet spigot and the diameter of the coolant water pipe where it enters the engine block.

I re-fixed the exhaust elbow (and gasket), reconnected the copper coolant pipes and the thermostat cover.

With a jubilee clip I fixed the clear plastic hose to copper pipe that takes water from the water pump into the thermostat housing. Note, the thermostat was not installed - I wanted the descaling solution to flow all around the engine coolant channels. 

Lastly I put the bucket at the rear of the engine with the exhaust hose from the exhaust elbow directed into it. The bilge pump was placed in the bucket and I added about a gallon of water to the bucket. (Photo 6)

I wanted to check that there were no leaks before I added an acidic descaler to the water - so ran it initially with just water. I connected the bilge pump supply cables to my leisure battery and watched carefully as the water was drawn up by the pump, forced through the clear hose and into the engine coolant channels, entering at the thermostat housing and exiting into the exhaust elbow injection point. From here it was directed via the rubber exhaust pipe back into the bucket.

Once the odd minor leaks , mostly at the copper pipe to engine casting unions, were tightened it was time to add the descalant.

A minor, but important point: always add concentrated acid or strong alkali solutions TO water. 

NEVER ADD DILUTING WATER TO A CONCENTRATED ACID OR ALKALI.

There are many branded ‘Marine’ descalants in chandlers and on line. They are all expensive. There are many catering machine and coffee machine descalers available online which are not so expensive. 

The choice is yours. The important thing is that the final choice of descaler a) does the job and b) is harmless to your engine.

 After a lot of searching I decided on a commercial catering descaler called Orca A4 Appliance descaler which can be purchased from Screwfix (about £10 per litre bottle).

I added one litre to the gallon (4.5 litres) of water already in the bucket - creating a 20-25% solution - then switched on the pump and left it to circulate for 3 hours. 

As I checked it from time to time the solution in the clear plastic hose went from clear to ‘latte’ colour and finished a strong ‘flat white’! 

I switched off the pump, disposed of the mucky brown descalant solution and replaced it, after several rinces of the bucket, with clean water. This was then circulated through the engine using the bilge pump for 20 minutes to flush out any descalant residue.

I can say from experience that Orca A4 at this concentration did a brilliant job. When I later removed the thermostat housing (previously scaled up) to fit a new thermostat unit the inside of the housing was spotlessly bright metal.

I was on the home straight! The starter motor and alternator were bolted back on and a new fan belt for the alternater fitted.  Then I attached and connected the wiring harness and starter relay. 

The copious amounts of water being ejected from the exhaust showed that the descalnig had worked well and the ease and speed with which the engine picked up when the throttle was opened was remarkable. 

The alternator was charging well and the oil pressure showed 45 psi on tickover (800 rpm) and 49 psi (1500 rpm and above). Forward, neutral and reverse gears all operated well. There were no coolant or oil leaks apparent. (Photo 8)

At the time of writing (May 2026) I have now used the engine for a total of 16 engine hours and it has not missed a beat. The engine starts on the button, vibrates less and picks up quickly and smoothly. 

Fuel consumption is still about 500ml of diesel per hour but I seem to get improved cruising speed at lower engine revs. 

All in all I feel it was a job worth doing. I have gained increased confidence in the engine as a result of spending a week or two over the winter doing what really amounted to long overdue maintenance and now have a better insight and understanding of workings and condition of my engine.

I am not a diesel engineer nor a mechanic. I’m just an ordinary, hands-on sort of sailor with a bit of common sense. So I reckon anyone who is fairly handy could attempt and succeed doing the same.

Terry Able Leisure 23SL Sirius