seized 79mod 900sd motor

Hi all, any tips? on what to do and what not to do, motor is out of the frame and in neutral, has been sitting for 12 years cylinder heads came of easy. I am concerned with doing damage to bores etc and would prefer not to hit the pistons even with a wooden drift as this may damage big end?

Put either some diesel, parafin, WD40 etc, Pepsi Cola or a similar brand down the bores and leave it to do it’s work for a few days.
Most of those will loosen the pistons/rings in the bores and the Cola dodge isn’t a joke it really works!
A bit of heat after this will help also.
Good quality Oversize pistons are available, so I wouldn’t worry too much about the bores but…
They don’t come cheap!
You might get away with a light hone of the bores and some new rings, gudgeon pin circlips.

If the motors been stood for that long, there’s a good chance that the mains and the bigends are rusty by now, so a full strip/inspection of the bottomend’s in order really.
If you don’t do this and it has gone rusty inside and then you put a refreshed topend on it, it won’t be running for very long before you’ll have to take it apart again and the damage could/most probably will be a lot worse.
The rust when combined with the new oil,will quickly turn into something not unlike grinding paste.

All the parts that you might need are still available, but as per the pistons they ain’t cheap.

So my tip is do the lot while you’ve got it apart, oh and while you’re at it I’d get the crank balanced.

Steve R …The Southern slimmer version. :wink:

God advice from Steve, as he says you should definitely strip it now rather than risk it.
I would try to get some WD40 down the 4 cylinder head stud holes on each barrel, as these tend to corrode and make it difficult to get the barrels off, I always find that my barrels don’t come off without a fight, and mind the fins while your doing it!

Thanks Mr R and Kevin Baker, have got wd in there now so I ll let yoy know how it goes, splitting the cases is going to hurt but spose it has to be done. Have only ever done top end work and this ll be my first Duke. I just keep loking at those bevels. Back to the books first.

These motors aren’t that difficult to work on, just make sure that you work clean and take your time.
But you’ll need at least one Ducati special tool* the flywheel puller, I think the club might have one in the ‘Tool Hire’ section.
*You’ll also need a dial gauge/DTI and a meens of mounting it to set the endfloat on the bottomend shafts.
If the motors got a kickstart (It should have being an SD) you MUST turn this through at least 90 degrees, to avoid breaking the splines off of the end of the kickstart shaft when seperating the cases.
I’d also have a close look at the 5th gear on the layshaft as these are prone to chipping.
I’ve replaced this gear on almost every Bevel Twin motor that I’ve rebuilt and I couldn’t possibly remember how many I’ve rebuilt over the last 30 years.

The club should also have reprints of the genuine Workshop manuals available, the Haynes ones are a pile of crap…
That’s not just IMO but a statement of fact!

Steve R

Steve, correct me if I’m wrong on any of this, but…?
They’re actually not that difficult to strip & re-build, I did my Darmah a few years ago, one key thing is the shimming, every shaft in the engine was shimmed by hand at the factory, so be careful to keep track of exactly which shim came from where.
Has the engine been apart before, you can check the 2 x M6 bolts on the bottom of the sump, there should be a lockwire between them, if it’s virgin, is the lockwire intact? (this isn’t a guarantee though)
The bevels look complicated, but unless there is rust or debris in the bevel shaft bearings these don’t really wear out, so they can be left as they are?
The shafts just part in the middle to alow the heads to come off via a half-lap joint stuated in the chrome tube, and they are simply held together by a steel tube inside!
Have fun, Kevin.

Thanks again all very usefull info. I did notice there is 1 spline missing on the end of the kickstarter so there has been a cowboy in the house. Also I have noticed the chain and the gear inside the side cover for the electric starter are missing and the cable from the electric starter has been cut, someone was not impressed, this maybe the reason for the missing kickstarter spline, but doubt you would have to split cases for that. Do they have a habit of droping gears and or starter motor chains often.

Don’t know about the kickstart stuff mine never had one…
Again as far as I know the starter chains never break or wear out, your cowboy probably took it off as the starter motor is probably US?
If the starter is US you can get them rewound, I had mine done a few years ago.