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MD5C120S versus MD5B110S differences

danielbeek

New member
"Hi,
I know the obvious stuff


"Hi,
I know the obvious stuff, like different saildrive leg, higher RPM limit, and output power.
What I'd like to know is:
- could the 110s gearbox be coupled to the newer MD5C which doesn't appear to use the rubber coupling/three tooth drive?? What's the most cost effective method?
-Could the MD5C "coupling housing" (between engine and gearbox) be swapped with that of the MD5B so that the bolts line up (engine-to-couplinghousing-to-gearbox) to the 110S?
- What gives the MD5C more power??? Looks like the same engine essentially. Can't I just replace some parts or modify them to make a MD5B perform the same as a MD5C? ie modify the governor to raise the RPM? They appear to have same bore/stroke, and everything! What could be limiting the power output? Commercial engines are de-rated, did Volvo do the same to the MD5A and MD5B?
Look forward to some qualified suggestions!"
 
"I might give an answer, but p

"I might give an answer, but perhaps not excactly what You want.
The MD5 no matter A,B,C is NOT an engine I would recomend putting any money or too much time into. The eventually 'power encrease' You get is only on paper and perhaps a fine tuned test bench, but not in real life. The rpm encrease was made mainly to reduce the black smoke which all small Volvo diesels are famous for!
The 'C' model was a 'bastard' made to fit the 120S drive and to fill the gap until the 2000 series was launched.
To 'modify' the 'B' to 'C' is fully possible but only to recomend if You have two units, one with broken engine and one with broken drive, and a spare engine bed! Not to forget plenty of time to waste!
The rating difference leisure and commersial was never a question in that hp range, You must be joking."
 
"Hi Morten,
Thanks for that.


"Hi Morten,
Thanks for that.
The reason I am pursueing this seemingly fruitless excercise is because I only have a 26 footer (2 tonne, racer/cruiser), to which the extra 2hp would make a substantial difference when battling a headwind (ie 7.5hp only just gets the boat to hull speed with ideal conditions - folding prop also..).
As for being worthwhile - it is to me. The engine runs beautifully, quieter than anything else I've heard of this size and 100% reliable.
Replacing would require me to buy an engine worth half the price of the boat - not quite ready for that reality yet! Yeah, I realise the "commercial" applications don't exist! But all the same is it possible that it's somehow de-rated?
So, any ideas what could be the difference between the two?
Also, would you know what new engine would drop straight into the same engine bed if the day comes? Heard something about the Lombardini doing it, can you confirm this?
Thanks in advance!"
 
"Governor springs and injectio

"Governor springs and injection pump is the major difference, but letting the engine up another 500 rpm takes away the 'quieter' and 'beutifylly' You mentioned.
As for replacement on the bed, anything of similar size, You will have to make new engine mounts to make it fit. The more difficult part is to hook it up to the drive.
The engine was never de-rated, Volvo re-rated it to make it more competitable and be able to encrease the price! You will probably never notice any difference, and to gain the 500rpm You most probably will have to change Your prop.
As a curiosity, the engine was built in Norway by Mandal Motorfabrikk!"
 
"Hi Daniel

I had a similar


"Hi Daniel

I had a similar decision to make about a year ago. I have a 28 footer with an MD5B/110S. The engine needed work and I had to decide to rebuild or to re-power. My rebuild was done by a diesel shop and came to about 5K$ (CAN). This included piston, sleeve and bearings etc. A re-power with a 2000 series engine, new saildrive and engine bed (2000s don’t fit onto a 110S) would have cost me over 10K$.

I had the MD5 overhauled and I’m happy with the results. It runs really sweet and it moves my boat at hull speed in most situations. I think there are some rating games played in the specs because the 7.5 hp moves my boat a lot better than similar boats with 9.9 outboards. My boat has the big two blade fixed prop so the difference is probably due to torque rather than hp.

The MD5 is old in design with raw water cooling but if it lasts another 25 years it will outlast my ownership (or me!).

When the re-builder worked on my engine he had some problems with the governor. It is very fragile and easily damaged. If you do work on the governor, be careful that the governor does not rotate into the throttle linkage during removal. The linkage flops around when disconnected from the injector pump rack and it can strike a rotating governor bending the weight assembly pins. A new governor is about a thousand bucks!

I found out later that Kabota makes replacement engines that fit the 110S and MD5 bed. These are sold under the Beta name (betamarine.com). The 110S engines are special orders from the factory."
 
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