New Member from Virginia, USA - '78 900SD

[mb848]

Hello! My name's Matt and I live in Northern Virginia in the US, a little ways west of DC. For a living I'm mostly on a computer, but in my spare time I enjoy working with physical objects and making things fit together and work just right (hence Ducatis, very satisfying to set them working just right!). When I was looking for my first bike I got interested in desmo Ducatis, and after owning and working on a couple of more modern Ducatis for a few years I started wanting a classic desmo Ducati to learn about and maintain, especially one of Ducati's first desmo V-twins. I didn't want to feel guilty if I ended up putting a fair number of miles on it, so the 900SD seemed ideal and I finally managed to pick up a 1978 Ducati 900SD Darmah at auction back in July.

I've only been riding on the street since 2018, but also have a 2006 S2R800 (my first street bike, still my favorite daily) and a 2013 Streetfighter 848. I've done the usual things like valves, belts, fork rebuilds, and electrical work on both of those, but the bevel driven cams and even just 4 stroke carburetors are a new experience for me. I'm embarrassed to say I only knew some basics around the early desmo Ducatis and looked at the few recent 900SD auctions I could find to see what it seemed like they were going for, so I really didn't have much criteria beyond "900SD, good condition, reasonable price". The previous owner had it for 43 years and had some paperwork and parts to go with it... it has some modifications, but seems to have come with most (all?) of the original bits. It also came with an unmarked black 2-into-1 exhaust system that the previous owner said he had installed, then immediately decided it was too loud and had the Silentiums put back on. I've had trouble finding anything on that exhaust system. I happened across a video on YouTube where a guy was starting a 900SSD that had an identical-looking exhaust... I asked him about it and he said his was also unmarked and was made by Nepoti Caracchi Racing, so maybe that's what it is!? Less than a month after picking up the bike I found some lightly scratched/dinged early ~1980 Contis on eBay and the seller said they came off a Darmah he used to own. They basically just needed a little touch up sanding of isolated scratches and then general clean up and polishing to make them hold up to anything but a very close inspection, so they seemed a steal at $500.

The brake calipers were recently rebuilt, calipers themselves look nearly new as do the steel braided lines. The engine looked very clean, but the first time I took it out and then parked it in the garage it was dripping just a little oil from somewhere at the back of the rear cylinder, so I'm sure it was just cleaned up for the sale. I knew it had an aftermarket Derale oil cooler, but I hadn't even realized the other modifications made along with that, i.e. the oil filter cap has an oil line coming out that goes through the cooler, and then after the cooler the line branches off to the center of each of the cam supports. I didn't notice until just this week that the cam support is usually just a flat surface on the outside and that either the stock ones were modified or these are aftermarket ones with oil fittings. It runs reasonably well overall, but the idle is a little rough and it's become noticeably harder to kick start, especially when it's hot.

I was emailing Steve a bit when he approved my account on here, and I believe my next steps are going to be rebuilding the carbs, replacing valve seals (it seems like the front cylinder is getting a bit of oil in it), replacing intake and exhaust seals, and bringing the valves back in spec (closers are loose at around 0.03mm, openers are around 0.13-0.15mm). Nice thing is I'm pretty sure the shim set I have for the S2R800 will also work for the 900SD since my S2R is an early one with the 8mm valve stems! Actually amazing how nearly identical the cams and rockers are between the S2R800 and 900SD given the 28 year difference.

Well that was long winded... I look forward to getting to know this bike and looking back through other people's experiences on here!

[Craig in France]

Hi Matt,

Welcome to the Forum.

Interesting story, interesting bike. I don't recognise the exhaust-silencer combo, so can't help you with that. But looking at it, I can see why no-one would want it on a street bike. Contis are already loud enuf ...

You should definitely do the valve clearances, preferably before anything else. If you're already familiar with the desmo system, and you have the right tools (tdc finder, dummy rocker pin etc), this is just a question of time, care and having the right shims!

The carbs will most likely benefit from an overhaul. It's not something particularity difficult to do, but it does help to have a bit of experience. So unless you're very keen to attempt it yourself, I would recommend out-sourcing it.

The leak from the rear cylinder will almost definitely be because the O ring between the head and the barrel is feeling a bit tired. There's no gasket here, just the O ring. Unfortunately, it's a PITA to replace because you need to drop the engine to do it. So you may decide to live with .

Be aware that the ignition has an annoying weakness in that the insulation around the pick-up wires falls off with age. What happens next is that the ferrous particles in the oil, which are attracted by the magnetism of the pick-ups, accumulates on the now bare wires ... and eventually they short out, and the bike starts missing and popping etc.

Cures:
Immediate action: Clean the ferrous sludge of the wires. Obviously this is not a permanent fix.
Longer term: Replace the insulation on the wires. Not as simple as it seems because you want to do this without removing the pick ups. This is because re-positioning the pick-ups requires the use of a special tool, and (often) quite a dose of patience. Steve A. will advise you here.
Permanent: Junk the original ignition system for a modern one. Various options are available.

Anyways, that's enuf for now. Enjoy the bike!

Craig

[mb848]

Thanks Craig!

I really appreciate the insights, exactly the kind of tidbits I was hoping to pick up here

Yeah, I was thinking I would do a lot of things at once and end up removing the heads when I do the valves and valve seals, but since it only seems to be the front cylinder getting oil in the cylinder I may try to do the rear valve shims in place and only remove the front head to get at the valve seals so that I don't have to drop the engine... so the rear cylinder may have to just ooze some oil until I end up needing to do more and have to drop the engine later it doesn't seem like it'll cost me any more inconvenience to do that separately from the front one.

And very good to know about the pickup wires! It sounds like I should probably a look at that when I change the oil since that cover has to come off I guess I should have a gasket on hand for when it goes back together... may as well be ready to redo the wires at that point I suppose as well just in case

Thanks again!

[BevHevSteve]

I have a kit available with everything you need to replace the pickup wires ... Includes pedantic instructions with photos to do the job right. I can't remember if we already discussed this?

https://store.bevelheaven.com/Electrica ... h-MHR-etc/

[wdietz186]

Steve's wire kit is good but as Craig warned it can be a bit daunting to install. The other ignition options are a better choice but will require coils and a bit of fabrication. If/when you go through the carbs, replace the choke pistons as the rubber seal in them gets hard and leaks causing rich running. When you are checking the valves wiggle the stems with the valve partly open and see if the guides are worn, might explain the oiling in the horiz. cyl.

[mb848]

Steve, I don't think it came up, but I'll probably get one of those here soon as a winter project. Thanks!

wdietz186, Good to know... I think as long as I can avoid moving the pickups it actually doesn't look too bad. And got new choke pistons as part of the rebuild kit!

On the valves, is there some spec for how tight the valve guides should be? Each valve *does* shift when I wiggle it, just enough to feel/notice.

[baddean]

The exhaust could be a Verlicci.
Pics are hard to come by.
A friend of mine had a Verlicci on his 750F1B. The sound was incredible.
Closest I got was a Phil Ansley photo.