The engine went into the trailer when Ariadne was lifted and ended up in Inkoo. Before moving it to the garage, I washed it with a pressure washer because it had accumulated so much dirt over the decades.

The purpose was to find out the condition of the engine first and then replace the necessary parts. It started with compression measurements. I first measured the pressure with a Chinese miracle, i.e. a traditional mechanical pressure gauge with a non-return valve, but the gauge showed zero all the time. Oh yeah. I switched to the right brand multimeter and its pressure sensor and got good enough readings when I cranked the engine at the start. The start, however, took more power than the car’s Auxiliary Start Cables willingly agreed to transmit, which means the clips started to glow…. I bolted the starter cables of Ariadne and the smoke disappeared and the engine started spinning. I got indicative pressure values – the engine was cold – and by interpreting them, it seemed that the fourth cylinder was slightly worse in pressure than the others. Its pressures were 20% below the average of the others.

I started the disassembly by draining the oils and coolant and after that the garage floor started to fill with various engine parts such as the heat exchanger, intake manifold, starter, alternator, oil pipes, injection pump, its pipes and nozzles.

When all the external parts were off, it was time for the cylinder head. At first, I tried to open the cover bolts with a standard socket wrench, but when turning the first bolt, I decided to use an impact wrench – a Makita one. The job became light and the bolts opened easily, smarter not harder.

So far the engine had been on top of the cradle I had made. Dismantling required a slightly different cradle and I ended up getting a turnable engine cradle from Motonet on which it could be rotated. For that, the flywheel and its housing had to be removed because the engine was bolted to the cradle through the bolt holes in the housing.

After the cylinder head came off of the cylinder block (after a slight force), it was the turn of the cylinder pre-chambers on the cylinder head. Older diesel engines are typically pre-chamber diesels where fuel is injected into a small pre-chamber and combustion starts from there, unlike in new direct injection diesels where fuel is injected directly into the main combustion chamber. There were, of course, special tools for removing the pre-chambers and the threaded rings that held them in place. I had already put them in the shopping cart in the German Unimog online store, but when I couldn’t find Finland as the delivery address, I looked into the delivery conditions in more detail. Delivery to Germany only. Do I order and agree with the merchant that, for example, DHL or Fedex will pick up? Sounds complicated and laborious. Work trip to Germany? It’s hard to even come up with an excuse to travel. Do I drive back and forth to Germany in style for Ariadne’s restoration gigs with my 406 to Hamburg? Not exciting. Where else could you find a puller with an external thread M22x1.5mm for the threaded ring of the OM636? ebay.de? Yes. Ordering Vorkammer Gewindering ausdreh Werkzeug OM 615,616,621,636. It was a pity that the pre-chamber removal tool was nowhere to be found, of course it had a different thread for extraction. After a week, I picked up the package I ordered from Lantis and the tool worked well. The threaded rings opened and Makita’s 1000Nm impact wrench turned out to be the right tool again, otherwise nothing would have come of it. One of the rings was stuck so hard that it got little reformed and I have to order a new one.

The threaded rings were gone and now the pre-chambers had to be removed. The British OM636 guru also offered “sorry-no-such-tool” when I asked about the tool from him, but said that they should come off with a light tap. I didn’t even try it. Couldn’t find a pre-chamber removal tool and nothing else – not even bolts – with a matching M22x1.0mm thread online. No search results. Until finally. I found a scooter flywheel puller kit on Alibaba that seemed to have drive sockets with the right threads. However, ordering from China didn’t inspire me in the end, and luckily I found a similar series in Motonet’s selections when I was looking for special tools for the scooter engine there.

The next day, I drove to Motonet along the work route and picked up the set in question and after I got home, I wen to the garage to try it out. The puller socket fitted nicely into the internal thread of the prechamber. Good. However, the pull-out kit I purchased assumed that a bolt is screwed into the inner hole of the pull-out socket and when it is tightened all the way to the bottom and continued to be tightened, the sleeve rises. In my case, the sleeve should be lifted up by leaning on the outside of the hole and not on the inside, and for that I tried to see if the socket and the pre-chamber would fit inside the 30mm socket when the extraction bolt that came through the socket and rested on its top. Works. The pre-chambers were no longer attached to the cylinder head by anything other than 40-year-old rust, and they came off quite easily, and Makita’s nut driver wasn’t even needed.

In order to facilitate ignition and improve combustion, the pre-chambers have a small steel ball in the transverse bar towards which the fuel is sprayed and which collects heat during the annealing at start-up (see picture above). From the fourth cylinder, i.e. the most cabon build-up cylinder, the ball was almost gone, in the second it was in half and in the others it was still in place. Really weird. The missing part of the ball was not even found on the top of the piston and there were not too many traces on the piston top, so it had apparently ended up through the exhaust valve. One more line was added to the shopping list, two prechambers – if you can find them somewhere. I removed the valves, which were all fine, and left the cylinder head to wait for the workshop.

All that was left was the cylinder block with the oil pan, crankshaft and camshaft as well as the pistons and oil pump in place. I turned the engine upside down and pretty soon after removing the bolts the oil pan came off with a little knocking and the crankshaft was visible. Next, the connecting rods came off the crankshaft and after that the crankshaft bearings and I lifted the shaft off. I pulled the pistons and connecting rods off and only the camshaft was in place in the cylinder block. The cylinders need light drilling/honing, as the previously mentioned fourth cylinder was the most worn, it felt a small shoulder – a couple of tenths – at top dead center.

At this point, I throw the ball to the machine shop, which in the near future will go through the cylinder head and block and do its part, i.e. checking the head, grinding the valves and drilling the block. I hope you don’t have to start changing the cylinder tubes, because the availability seems pretty much 0. Strange, because the engine is only 44 years old.

Ariadne has had her engine compartment washed, and CRC’s Bräkleen brake cleaning spray worked great as a detergent. No holes have been found around the engine or the frame tank, apart from the one that I located and patched in the spring of 2018. Then I put a temporary spot on it and now I’m going to remove it and fix it better. In practice, it means removing a piece from the hull below the waterline and opening the tank from the top and renewing the top plate of one arch gap. In addition, I will put two inspection hatches in the tank in addition to the original one. The tank is three spans long and the inspection hatch is only in one span. After this repair, the tank is easier to clean if necessary.

After washing, I removed the paint with a needle chipper to renew the painting. My appetite grew as I ate and I removed paint from a much larger area, because the needle chipper was easy to work with. Although accompanied by a fair amount of noise, the noise level was 117dB according to the smartwatch’s announcements. The surface still needs to be brushed/sanded after the needle chipper and then painted.

The work continues…