I took my engine apart!

[pandos]

So I finally dragged my MD21B into the Saloon and took the sump off, (head taken off before last lockdown).. everything inside looks remarkably clean and nice and new, only the tiniest bit of movement at the ends of the conrods/drive shaft. A little bit of gunk in the sump and nowhere else with some jelly on the oil pickup.

All of the external parts are in top condition no corrosion or wear except for small areas of corrosion wherer the paint is just lifting from the Aluminum parts.

The sump was obviously off in the past. I suspect this engine had a very good rebuild at some stage and the reason it allowed a bit of oil into the coolant may be because the bolts were not re-torqued??

Cylinders look a little shiney but no scoring (I did not do a compression test before disassembly (I forgot...I even have a tester)

I am undecided whether to continue stripping and then have the fear of making a boo boo (sheared bolt, one coming loose in time).

or get the head skimmed and put the whole thing back together, new oil seals where I can, give it a good coat of paint and get the boat ready for coming season.

I may fill the four cylinders with Diesel and see how they hold compared to each other and at different stages between TDC and BDC...

I am also curious about the oil pump and how it is driven...any one know?

Also the engine seems to have a white coat of primer covered in a thin coat of volvo green, is hammerite/smooth adequate to go on over this once cleaned up.. or do I need to go back to bare aluminium/special primer ? I think hammerite will be grand on the steel.

If anyone is curious how to get an MD21B into the saloon on a HR352.. take out the bolts that hold the mounts down, put a 2m plank underneath the sump, Stand on the plank, put some packers in so the whole lot is level, Take off the engine mounts, drag the engine out along the plank... (surprisingly easy, I was thinking about all sorts of pulleys and tackle)

 

[LadyInBed]

If anyone is curious how to get an MD21B into the saloon on a HR352.. take out the bolts that hold the mounts down, put a 2m plank underneath the sump, Stand on the plank, put some packers in so the whole lot is level, Take off the engine mounts, drag the engine out along the plank... (surprisingly easy, I was thinking about all sorts of pulleys and tackle)

Where's the video? ?

 

[pandos]

Where's the video? ?

The plank, who would have been the star, insisted on being pixelated to protect his identity pursuant to GDPR , and the 2m pixalates were stuck is a traffic jam in Calais

 

[pvb]

I am also curious about the oil pump and how it is driven...any one know?

Gear-driven by the crankshaft, I think.

 

[RichardS]

So I finally dragged my MD21B into the Saloon and took the sump off, (head taken off before last lockdown).. everything inside looks remarkably clean and nice and new, only the tiniest bit of movement at the ends of the conrods/drive shaft. A little bit of gunk in the sump and nowhere else with some jelly on the oil pickup.

All of the external parts are in top condition no corrosion or wear except for small areas of corrosion wherer the paint is just lifting from the Aluminum parts.

The sump was obviously off in the past. I suspect this engine had a very good rebuild at some stage and the reason it allowed a bit of oil into the coolant may be because the bolts were not re-torqued??

I'm not sure where the bit of movement is but if it's in the big or little ends or crankshaft bearings then it's too much. There should not be any detectable up and down movement at all. A little end-play is normal.

Loose sump bolts would obviously not allow any coolant into the oil but head bolts would. If the head was torqued up properly in the rebuild I would not expect the absence of a re-torqueing to cause a problem.

If the bearings are all sound and the bores look good and there is no lateral piston movement and thin engine oil does not run straight past the pistons, I would have the head checked/skimmed, lap the valves and rebuild with new gaskets etc. There's probably little point in stripping down further unless you believe that there was a compression issue before the strip down.

Richard

 

[Bilgediver]

I'm not sure where the bit of movement is but if it's in the big or little ends or crankshaft bearings then it's too much. There should not be any detectable up and down movement at all. A little end-play is normal.

Loose sump bolts would obviously not allow any coolant into the oil but head bolts would. If the head was torqued up properly in the rebuild I would not expect the absence of a re-torqueing to cause a problem.

If the bearings are all sound and the bores look good and there is no lateral piston movement and thin engine oil does not run straight past the pistons, I would have the head checked/skimmed, lap the valves and rebuild with new gaskets etc. There's probably little point in stripping down further unless you believe that there was a compression issue before the strip down.

Richard

Don' t forget to deglaze the bores. I use a drill mounted hone. It makes a big difference .

 

[Moodysailor]

Depending on the tools & information you have (good torque wrench and engine manual), and your confidence/ability, I would drop a couple of bearing caps (mains & big ends) and inspect the mains, bigs and thrust bearings for wear.

Whilst you have the engine down this far I would also replace the front and rear crankshaft oil seal simply as good engineering practice. If possible, rotate the flywheel one set of bolts round so that the starter motor contacts the ring gear in a different place (an old trick but still works).

I wouldn't advise filling the cylinders with diesel - all it will do is make a mess. Cylinders/liners are bored as a taper, ever so slightly larger diameter at the bottom than the top - this is so that the liner becomes dimensionally identical once the engine is up to operating temperature (greater heat at the top of the cylinder will cause greater expansion in that area). Plus as it is a cold engine the ring gaps will be so large the diesel will just work past.

As mentioned in an earlier post, a small amount of end play (inline with crank) movement is desired (and required), but there should not be any movement vertically around the bearing journals.

If you have had oil in the coolant this is most likely from the head gasket, but a possibility could be an oil cooler if you have one fitted (it's been too many years and I can't remember on the MD21). Definitely send the head away for cleaning, measuring and pressure testing - the shops that do this are specialists and will be able to tell you if it is cracked or needs to be skimmed. Make sure they do hot pressure testing as some cracks only leak when up to temperature.

If the head requires skimming then I would get a proper straight-edge and also check the block face for bow & twist - a straight head on a warped block will still leak!

Regarding painting - it's expensive but the genuine VP green paint is very good. Some good primer and this and the engine will look like new - if you can get over the price tag per can! ;-)

 

[Moodysailor]

Don' t forget to deglaze the bores. I use a drill mounted hone. It makes a big difference .

This is a good suggestion, but I would add to this suggestion to only do this if there is obvious glazing or a compression issue. New piston rings should be fitted when a cylinder is re-honed and unless the bore is measured or evidently needs it, I would personally advise against machining any more than absolutely necessary on the bores.

If the cross-hatching is clearly visible and there are no compression issues, it is highly unlikely that the cylinders will need any work. If the bores are glazed or there is a suspected compression issue then the cylinders should be measured to determine if they can be machined within tolerances for the pistons. Even a glaze-buster hone is still quite an aggressive tool in the context of the small dimensional tolerances of a bore.

A great suggestion if the situation warrants it ?

 

[rogerthebodger]

If the sump is off I would replace all the bearing shells and seals as said.

This also allows you to check for any bearing scoring.

I paint my engines white as its then easy to see a water or oil leak.

 

[RichardS]

If possible, rotate the flywheel one set of bolts round so that the starter motor contacts the ring gear in a different place (an old trick but still works).

I've never heard of that before. Flywheels often have a locating stud or two so I'm not sure it would be feasible but why would the starter motor does contact the ring gear in the same place anyway.

Richard

 

[Moodysailor]

I've never heard of that before. Flywheels often have a locating stud or two so I'm not sure it would be feasible but why would the starter motor does contact the ring gear in the same place anyway.

Richard

You are correct in that if the flywheel is keyed or located by a dowel then this won't be possible. I'm not sure if this is the case on an MD21. it's also only worth doing if the flywheel has a different number of bolts to the number of cylinders as this will allow the flywheel to be rotated at a different angle. Typically flywheels of this size will have 6 bolts so can be rotated 60 deg.

On a diesel engine, the engine will always come to rest in the same locations depending on the number of cylinders, the reason is due to compression at TDC. On the MD21, the starter will always engage with the same 2 locations on the ring gear as it's a 4 cyl, 4 stroke engine. Only two cylinders are ever at TDC so the points on the flywheel will be opposite.

The resting position will depend on the number of cylinders an engine has, and its cycle (2 or 4 stroke) For 4 stroke engines its one position for a single cyl, two for a 2/4 cyl and three for a 3/6 cyl engine. On engines with an even number of cylinders it's half the number of cylinders due to the fact that two cylinders are at TDC at the same time and the camshaft rotates at half crank speed.

On high hour engines (typically commercial) it was common for us to rotate the flywheel as part of a rebuild, and on some which had very high start/stop frequency (ferry, inshore fishing etc) I have changed a number of ring gears.

I doubt that significant wear will have occurred on this engine, but it is one of the things that I would do on my engine if I had the flywheel off.

 

[Daydream believer]

, is hammerite/smooth adequate to go on over this once cleaned up.. or do I need to go back to bare aluminium/special primer ? I think hammerite will be grand on the steel.

Might be worth checking the temperature rating of Hammerite. I seem to recall that it is not high enough for engines. The info is on their web site

 

[PaulRainbow]

If the sump is off I would replace all the bearing shells and seals as said.

This also allows you to check for any bearing scoring.

So would i, be silly not to IMO.

I'd also pop the pistons out, give the bores a very light hone and put new rings in.

 

[scottie]

Before moving the flywheel check for timing marks !!

 

[Bilgediver]

Depending on the tools & information you have (good torque wrench and engine manual), and your confidence/ability, I would drop a couple of bearing caps (mains & big ends) and inspect the mains, bigs and thrust bearings for wear.

Whilst you have the engine down this far I would also replace the front and rear crankshaft oil seal simply as good engineering practice. If possible, rotate the flywheel one set of bolts round so that the starter motor contacts the ring gear in a different place (an old trick but still works).

I wouldn't advise filling the cylinders with diesel - all it will do is make a mess. Cylinders/liners are bored as a taper, ever so slightly larger diameter at the bottom than the top - this is so that the liner becomes dimensionally identical once the engine is up to operating temperature (greater heat at the top of the cylinder will cause greater expansion in that area). Plus as it is a cold engine the ring gaps will be so large the diesel will just work past.

As mentioned in an earlier post, a small amount of end play (inline with crank) movement is desired (and required), but there should not be any movement vertically around the bearing journals.

If you have had oil in the coolant this is most likely from the head gasket, but a possibility could be an oil cooler if you have one fitted (it's been too many years and I can't remember on the MD21). Definitely send the head away for cleaning, measuring and pressure testing - the shops that do this are specialists and will be able to tell you if it is cracked or needs to be skimmed. Make sure they do hot pressure testing as some cracks only leak when up to temperature.

If the head requires skimming then I would get a proper straight-edge and also check the block face for bow & twist - a straight head on a warped block will still leak!

Regarding painting - it's expensive but the genuine VP green paint is very good. Some good primer and this and the engine will look like new - if you can get over the price tag per can! ;-)

I agree that honing should be avoided if the original cross hatching is visible however in an earlier post the op described the bores as a little shiny.

I find that putting the old rings back in a liner they bed in to their new position much quicker if the liners ars honed and I would not describe this procedure as machining.

 

[RichardS]

On a diesel engine, the engine will always come to rest in the same locations depending on the number of cylinders, the reason is due to compression at TDC.

That would explain it. I've only ever stripped down petrol engines and the wear around the ring gear has always been more or less the same all the way round.

Richard

 

[Stemar]

Might be worth checking the temperature rating of Hammerite. I seem to recall that it is not high enough for engines. The info is on their web site

I did mine with Smoothrite and it's been fine, but it might have been long enough ago that Smoothrite was still Smoothrite and not the castrated version it now seems to be

 

[pandos]

Thank you all for the excellent replies.. I was hoping to be told not to touch any bolts and put it back together but common sense does winout, sometimes... I'll dig deeper...

The explanation in the flywheel is very sensible when thought about . But it's something I never ever considered...If possible I will rotate.

I had forgotten to get the oil cooler pressure tested... It may indeed be the cause of the oil in coolant...

There was no compression issues afaik and the engine was powerful, quick to start and ran on almost no fuel with with no overheating and no oil consumed,

But I was always wary of the amount of rust and peeling paint in parts and feared a catestrophic faulire in an oil line or sump or an internal blockage due to gunk or the like....

As it happens the only bad piece discovered so far is the water connection to the transmission... Definitely the weak point in the installation...

 

[Hydrozoan]

I did mine with Smoothrite and it's been fine, but it might have been long enough ago that Smoothrite was still Smoothrite and not the castrated version it now seems to be

If this Technical data sheet (of May 2018) still applies, the temperature specification of Hammerite (smooth and hammered) is as follows:

'Limits: Minus 20ºC (-4ºF) to 150ºC (300ºF) maximum intermittent when fully cured. Continuous 80ºC (180ºF) when fully cured. Note: Colours may fade after prolonged exposure at temperatures exceeding 50ºC (120ºF).'' 7_hammerite_2.3_prep_directtorust metal paint 2018 rev3.pdf (an-platform.com)

I don't know if that's high enough - but I use a Vauxhall Carmine Red automotive touch up on my Beta, without problems.

I had occasion recently to use Rustoleum Combicolour (albeit in a room temperature application) as I wanted a Steel Blue and could no longer get it (at least in small enough quantity) in Hammerite smooth. I thought it was very nice to apply, and its temperature specification is as follows:

'Heat Resistance: 90°C (dry heat), at elevated temperatures discoloration may occur.' https://www.rust-oleum.eu/static/datasheet_cc_org_en.pdf

 

[Plum]

If this Technical data sheet (of May 2018) still applies, the temperature specification of Hammerite (smooth and hammered) is as follows:

'Limits: Minus 20ºC (-4ºF) to 150ºC (300ºF) maximum intermittent when fully cured. Continuous 80ºC (180ºF) when fully cured. Note: Colours may fade after prolonged exposure at temperatures exceeding 50ºC (120ºF).'' 7_hammerite_2.3_prep_directtorust metal paint 2018 rev3.pdf (an-platform.com)

I don't know if that's high enough - but I use a Vauxhall Carmine Red automotive touch up on my Beta, without problems.

I had occasion recently to use Rustoleum Combicolour (albeit in a room temperature application) as I wanted a Steel Blue and could no longer get it (at least in small enough quantity) in Hammerite smooth. I thought it was very nice to apply, and its temperature specification is as follows:

'Heat Resistance: 90°C (dry heat), at elevated temperatures discoloration may occur.' https://www.rust-oleum.eu/static/datasheet_cc_org_en.pdf

I painted my Vetus diesel with Hammerite smooth on top of the hammerite primer 18 years ago and it is still good. See Spots of rust on VP - How to treat?

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