MD series Ruggerini. Suitable powerplant or not?

[Ih8Suvs]

I asked in another thread titled "Centaurus" where the frames are cracking on these bikes. That stimulated some discussion about engines, vibration, and why the frames might be breaking. What I would like to do here is have a thread that discusses those things and leave the other one to hopefully find someone who has had or seen a Centaurus break and gain some insight into where the frame is weak.

That said, Thank you Avery for the link to the service manual, and to Sam and all others for their suggestions.

Sam you asked the very good question is there any reason I need to use an Enfield. Well no, I don't have to, but I want to. I already have the Enfield, I like having the transmission, I like the style, lightness and handling of the Enfield. Enfield spares are also readily available and cheap. Its also possible to find nice new cosmetically perfect donor bikes with engine troubles for sale. Also in my opinion a diesel engine in an Enfield makes an aesthetically pleasing package. There are very few Japanese motorcycles in any form that I find particularly attractive, however they do perform very well.

oldbmw suggested a post '62 big twin Enfield frame. I think this is a great idea and am on the lookout for one. They tend to bring quite a bit of money around here though and if I do find a complete bike and it is not a complete basket case I would feel compelled to restore it to original and not modify it with a diesel engine. Thats one of the main reasons I don't go after a Norton or BSA or other historic machines. I like to see these kind of bikes restored and preserved. There are examples of these that due to the overall poor condition make good sense to re-engine and modify however.

As for what diesel engines to use, I am interested in more input about the MD series Ruggerini. I have one, a MD151, which is the 654cc 16.3 horsepower version. I believe the MD series is the same engine as the Lombardini 25LD series. Physically this MD151 looks perfect. It is an easily usable size and shape. It is robustly built without being heavy, well lubricated, easily rebuildable, and should run for a long time. I have not run mine yet though so I have no idea of the vibration levels. I have, however, run my Hatz 2G40, another inline twin with a staggered crank, and that is very smooth. That engine is either going into a Ural/Dnepr when I find the right donor bike, or is going to power a Corbin Merlin but at this point all I have is the body and a rough idea for a frame rattling around in my thick skull for that.

I know the staggered crank gives an uneven firing, but the reciprocating mass balances, one piston is going up while the other is coming down. Years and years ago, back in the dark ages when I was young, I had a Honda CB350. This had a staggered crank twin. It was reasonably smooth. A friend had the newer CB360 which had both pistons moving together for an even firing order. Much more vibration. I liked my 350 much better funky exhaust sound aside.

Sam, how do you find the vibration levels on your RD's? Your Yamaha looks like a nice ride.

It seems like a lot of people are interested in the Punsun at the moment. It does look like an interesting engine. Wouldn't it fit nice in a Moto Guzzi? Is there a source for them in the States? How is the overall quality? I do have a Yanclone in an Enfield that I have put about 4000 miles on and it seems to run fine and be built ok so I would assume the Punsun is about the same for build quality. It would be nice to hear more from those with first hand experience with the Punsun/Rotek/whatever else name they are going to be sold as.

It would be also nice to hear from those with first hand experience running MD/25LD series engines. Are they inherently rough running? Has anyone tried a good balance job on one of them? Do they cool ok on a motorcycle without the blower?

Tim

[sbrumby]

The vibration on the yam is ok this has a RD180 750cc about 15hp but the bike is about 300kg. So it does about 60mph but because of the weight it doesnt get there fast, once at 60 it is quite happy. The VF Honda with the RD211 950cc 24hp only weighs 250kg, with 6 gears is quite fast at getting to 70mph. At 50mph I get a vibration but at 55mph its gone. I think the vibration is more to do with simple harmonic vibration and if I was to add a load more weight it would not show itself. That said I had to add mirror dampers to the arms of both bikes as the mirrors were useless without them. But I can just remember my british bike days 500speedtwin you could not see out of the mirrors when fitted on it.
Vibration is like the Tekoma bridge ( prob spelt wrong) everything has a natural vibration like a tunning fork, if the engine at a certain revs matches that of the bike the vibration is increased. The centurus probably had it and the frame suffered.