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  1. #1
    Join Date
    Jul 2019
    Posts
    3

    Default Smoking' MD2B / piston removal & refitting procedure

    HELLO all!

    New to sailing, new to engine overhaul!!! and new to the forum - Please help...

    We took our westerly centaur out for a spin at the weekend equipped with the MD2B and after about 10mins at 3-5kts quite a lot of smoke began steadily coming out of the filler cap - there's a short vent pipe there.... I'd previously run the engine up to temp on several occasions (but not under any load) for 40ish mins each time and didn't notice any smoke.

    Long story short, I suspect blow-by of exhaust gasses past the pistons or a head gasket issues or valves in the cylinder head need re-grinding/seating

    so I proceeded to take both cylinder heads off figuring I would install new head gaskets at the very least. I will re-grind the valves and valve seats actually. The waterjacket paths happen to be 75% filled with corrosion/minerals so will do my best to clean these throughout.

    This is the part I need the most help with:

    I'm thinking I may as well replace the piston rings with the engine half apart. Right?
    • I see in the workshop manual that I simply lift the cylinder blocks upwards
    • Then I have to guess (not mentioned in manual) the next step is to unbolt the con rods?
    • Then I'm guessing I next re-fit the piston on the bench (using ring compression tool)
    • Then bolt the con rod back on via the inspection window????

    Otherwise i don't understand how i'd get the piston rings compressed if refitting was simply the reverse of removal step (lifting the crankcase straight up)

    Thanks so much for any help!

  2. #2
    Join Date
    Nov 2013
    Location
    Perth WA
    Posts
    2,064

    Default Re: Smoking' MD2B / piston removal & refitting procedure

    There's quite a few instructional videos on YouTube.

    If you don't know what you are doing it can become very expensive (just ask me: I've been there and done that!)

    Engine Rebuild 101 - Part 7 - Piston Ring & Crank Removal
    https://www.youtube.com/watch?v=UNCiVXxxPQ4

    How To Assemble an Engine Block
    HumbleMechani
    c

    578K views1 year ago
    Putting together an engine block means installing pistons, a crank shaft, and bearings. Today we will also be installing piston

  3. #3
    Join Date
    Apr 2005
    Location
    Shropshire
    Posts
    8,828

    Default Re: Smoking' MD2B / piston removal & refitting procedure

    I did this on a single cylinder MD1 engine. You don't need to unbolt the con rod unless you intend to replace the big end bearings. Just tap out the gudgeon pins and the pistons will come free. I cant remember if the gudgeon pins have retaining clips like in the YouTube clip or if they are just floating so check that before you try tapping them out.
    Getting parts can be tricky but Google is a big help - I seem to remember that head gaskets are fairly rare.
    Ideally you need a piston ring compressor to re-insert the pistons but on a single cylinder engine (yours is two single cylinders) you can usually compress the rings with your fingers and shimmy them home.
    Good luck
    I'm no mechanic but managed OK
    Last edited by ghostlymoron; 23-07-19 at 07:07.

  4. #4
    Join Date
    Jul 2002
    Location
    Home: Kent. Boat: Chichester
    Posts
    43,433

    Default Re: Smoking' MD2B / piston removal & refitting procedure

    Quote Originally Posted by phammy View Post
    HELLO all!

    New to sailing, new to engine overhaul!!! and new to the forum - Please help...

    We took our westerly centaur out for a spin at the weekend equipped with the MD2B and after about 10mins at 3-5kts quite a lot of smoke began steadily coming out of the filler cap - there's a short vent pipe there.... I'd previously run the engine up to temp on several occasions (but not under any load) for 40ish mins each time and didn't notice any smoke.

    Long story short, I suspect blow-by of exhaust gasses past the pistons or a head gasket issues or valves in the cylinder head need re-grinding/seating

    so I proceeded to take both cylinder heads off figuring I would install new head gaskets at the very least. I will re-grind the valves and valve seats actually. The waterjacket paths happen to be 75% filled with corrosion/minerals so will do my best to clean these throughout.

    This is the part I need the most help with:

    I'm thinking I may as well replace the piston rings with the engine half apart. Right?
    • I see in the workshop manual that I simply lift the cylinder blocks upwards
    • Then I have to guess (not mentioned in manual) the next step is to unbolt the con rods?
    • Then I'm guessing I next re-fit the piston on the bench (using ring compression tool)
    • Then bolt the con rod back on via the inspection window????

    Otherwise i don't understand how i'd get the piston rings compressed if refitting was simply the reverse of removal step (lifting the crankcase straight up)

    Thanks so much for any help!
    Yes basically remove the rocker assemblies then the heads , lift off the blocks, withdraw the wrist pins and the pistons are free. ( no access to the crankcase needed unless you want to also get at the big ends)

    There is a special type of piston ring clamp that fits round the pistons , and allows the blocks to be lowered over the rings before then removing the clamp and fully lowering the blocks. I feel sure it will be illustrated in the tools section of the workshop manual.

    Make sure all parts go back in their original locations

    Take care of the oil feed pipes which must be disconnected from the rockers and straightened slightly.

    You may do all this, spending stupid amounts of money in the process and be bitterly disappointed if the bores have become slightly oval ( they almost certainly will be)

    An MD2B is so old,, spares are so expensive or now becoming unavailable that it might be more sensible to put your money towards a nice new Beta

    You do realise that the breather pipe from the oil filler cap should vent into one of the air cleaners ?
    Last edited by VicS; 23-07-19 at 09:08.

  5. #5
    Join Date
    Jul 2019
    Posts
    3

    Default Re: Smoking' MD2B / piston removal & refitting procedure

    Quote Originally Posted by VicS View Post

    You do realise that the breather pipe from the oil filler cap should vent into one of the air cleaners ?
    No I did not know this actually - there is about a 15cm length of pipe sticking out of the filler cap??? and that is where the a large amount of smoke is emanating from.

    Thanks for the clarification on the piston and tool, it gives me the confidence to push on

    i'm at the £200 mark on parts but if it needs any major items then I'm going DIY electric!

  6. #6
    Join Date
    Jun 2001
    Location
    Scotland
    Posts
    6,280

    Default Re: Smoking' MD2B / piston removal & refitting procedure

    Most of what to do and how to do has sent covered by others however a few other hints. On each head on the manifold side there is a small water passage drilled down from the gasket surface. This can completely block and not be apparent but will need to be carefully drilled/prodded clear. Much of the mud and crud collects in an annular space opposite the drain cock port. Injecting water through the drain cock helps loosen and removing this. I also open the block drain cocks from time to time with the engine running to remove mud and sand. Do this when cold . The drain cock insert does screw right out to make this easier using a hose.

    Yes the blocks should lift upwards leaving the pistons exposed. The pistons are easily removed leaving the con rods in place. A dodge to make reassembly go smoothly is to put two lengths of wood under the piston before lowering the block these can be jammed between the piston and crankcase holding the piston in an upright position. Adjust the piston rings to the required position and then carefully lower the block over the piston rings. There is a chamfer on the liner bore so the rings should enter without a compressor. They usually do..

    You talk about grinding valves . Note the instructions in the manual regarding valve seat overhaul. The seat in the head should be reground to a different angle to the seat on the valve to give a narrow seat . This can be done by machine shops specialising in head overhaul. Stay clear of marine workshops that may charge premium prices. It is unwise to just hand grind badly worn valves.

    I have managed to get the desired result using a BMC seat cutter and then turning the valves to the correct differential angle on a lathe to match the cutter.
    Eastern Scotland and beyond.

  7. #7
    Join Date
    Jul 2002
    Location
    Home: Kent. Boat: Chichester
    Posts
    43,433

    Default Re: Smoking' MD2B / piston removal & refitting procedure

    Quote Originally Posted by phammy View Post
    No I did not know this actually - there is about a 15cm length of pipe sticking out of the filler cap??? and that is where the a large amount of smoke is emanating from.

    Thanks for the clarification on the piston and tool, it gives me the confidence to push on

    i'm at the £200 mark on parts but if it needs any major items then I'm going DIY electric!
    It should just poke into a hole in the back of the rear air filter "frying pan".

    If the engine starts easily, runs well with no nasty noises put the hose back where it should be and save your money.

  8. #8
    Join Date
    Feb 2003
    Posts
    15,550

    Default Re: Smoking' MD2B / piston removal & refitting procedure

    Quote Originally Posted by VicS View Post
    Yes basically remove the rocker assemblies then the heads , lift off the blocks, withdraw the wrist pins and the pistons are free. ( no access to the crankcase needed unless you want to also get at the big ends)

    There is a special type of piston ring clamp that fits round the pistons , and allows the blocks to be lowered over the rings before then removing the clamp and fully lowering the blocks. I feel sure it will be illustrated in the tools section of the workshop manual.

    Make sure all parts go back in their original locations

    Take care of the oil feed pipes which must be disconnected from the rockers and straightened slightly.

    You may do all this, spending stupid amounts of money in the process and be bitterly disappointed if the bores have become slightly oval ( they almost certainly will be)

    An MD2B is so old,, spares are so expensive or now becoming unavailable that it might be more sensible to put your money towards a nice new Beta

    You do realise that the breather pipe from the oil filler cap should vent into one of the air cleaners ?
    Wrist pins! Piston ring clamp? What website in America did you cut and paste from? Really Vic! A quintessentially English gentleman using American terms!

  9. #9
    Join Date
    Nov 2001
    Location
    scotland
    Posts
    3,385

    Default Re: Smoking' MD2B / piston removal & refitting procedure

    If you do remove the blocks watch out as the “ gaskets” between block and crankcase are in fact shims and must be restored with the same total thickness as this determines the bump clearance!

  10. #10
    Join Date
    Jul 2019
    Posts
    3

    Default Re: Smoking' MD2B / piston removal & refitting procedure

    Quote Originally Posted by VicS View Post
    It should just poke into a hole in the back of the rear air filter "frying pan".

    If the engine starts easily, runs well with no nasty noises put the hose back where it should be and save your money.
    yes it starts easy, runs well but it really was quite a lot of smoke - should that really be recirculated into the air filters? It was enough smoke to warrant evacuating the children out of the cabin and opening the deck engine hatch to vent the smoke.

    I have taken the heads off already now and clad i did as the water jackets were +75% blocked (4 out of 6 rectangular water passages were 100% blocked)

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