Darmah final drive pinion LEAK

[crm114]

Hello all,

I am having a bit of a problem with my 79 Darmah SD, as described i appear to have a leak from the output shaft based on the fact that the rh side of the centre stand and s/arm are well coated after a long run and unfortunately some of this getting onto the tyre. This condition was present before and after the
pinion was replaced along with the two outermost oil seals on the shaft and the neutral light cam shaft seal. The bike has done ca. 13k miles and as far as I am aware has never been apart. Are their any known issues around or fixes for this problem or could it be that the leak is from somewhere else. Its not coming from the clutch cover.

[Ventodue]

Hi,

Yup, it's not uncommon, especially (it seems) on 1979 SDs and SSDs. The output shaft is slightly undersize and the sprocket nut comes loose and the oil starts leaking and ... eurgh.

2 fixes:
1. As told to me by no less than Steve Wynne (sorry for the name drop!). Use 2 of the special nuts* on to the shaft. But, and here's the important bit: before you fit the second one, put some silicone on to the shaft. Then fit the nut and tighten it up using the proper tools. This has been working for me for about 6 years now, btw.

* The SKF reference for this nut is a KM7, btw.

2. Buy a special version of the special nut, i.e. one that has a nylon sealing ring on the inside. Andy Nienhagen has these listed, part # 0755 16 055.1. Go Ducati Preisliste - desmo Fellbach

You still need the right tools, tho' : certainly the one to turn the nut and, ideally, also the one to hold the sprocket. You can try jamming the sprocket with a bit of timber, but it's not very clever. The nut should be done up tight - 70Nm according to the workshop manual.

HTH

Craig

[Duccout]

Yes, I must second Craig on this. My 750 used to leak until I bought the tool to tighten the nut and it hasn't leaked since. The nut needs to be really tight, and it is a real knuckle cruncher - wear leather gardening gloves while tightening!

[crm114]

Thanks guys,

I shall look into those two options, I was aware that the torqueing of the nut not only holds the sprocket in place but in doing so also plays a role in the sealing of the output shaft and therefore has to be tight. To clarify, the 30 degree canted side of the nut should face outwards ?

Are you sure about the "built in" sealing washer, obviously Andy will be able to say for sure but my translation of that part would be six sided nut with security washer, which is I guess the normal nut and crinkle washer. The previous part in the list is just nut and the .1 presumably the washer. However he does list a new part 76800 3380 but no mention of Dichtung (seal) Anyway, silicone sounds good !

PS Craig - I got my Contis on, needed to cut 5mm off the headers which still allows the silentiums to go back on if I come to the attention of the Police.

[Ventodue]

Originally Posted by crm114

To clarify, the 30 degree canted side of the nut should face outwards ?

Nope - t'other way round. Quote from page 64 of the Workshop Manual:

"... the ring nut* (should be fitted) with the chamfer next to the tab washer".

You can just see it in the photo on Fig 76 on page 65.

* as Ducati call it.

Originally Posted by crm114

Are you sure about the "built in" sealing washer .. my translation of that part would be six sided nut with security washer, which is I guess the normal nut and crinkle washer.

Ah, my bad - I read it wrong (late in the evening, yadda yadda). Sorry ... I wonder if what Andy's got is the same as Kaemner sell:
Ducati Aprilia Kmna - Tuning-Parts Catalog

No personal experience, unfortunately.

(There used to be a guy selling the Nylock type nut on eBay, but I can't find him now. I have a note that its SKF reference is GUK7, but unfortunately I can't confirm that).

Ciao

Craig

[wdietz186]

Don't forget to put some sealer on the faces of the spacer behind the sprocket too. The oil migrates out because the splines are undercut and the spacer doesn't seat fully on the face of the output gear. A second or even third seal on the inside of the output gear often stops the pesky leaks at the mainshaft/output gear area.

[Bevel-Heaven]

all good points and fixes noted above......

But don;t forget that there are 2 seals there, the small INNER seal thatposters above are talking about fixing, then there is also a large seal on the OUTSIDE of the output shaft that slips into the case.

OK now how do you tell which is the culprit? Get everything clean. REAL clean. Now spray around the areas with a foot anti fungal powder spray - yes that white powder stuff. Now fire up the bike and ride around the block and pull the sprocket cover of again and have a look. You will see where specifically it is leaking.

As a side note: if the smaller inner seal is the leaker [most likely] I suggest carefully removing the circlip thing and simply pushing in the seal etc that is there and guestimate how many additional seals will go in that area. You can get 2 or 3 additional seal in the space so why not... Get em and put in as many as you can while still being able to install that circlip or snap ring or whatever you want to call it.......

Or maybe you are just squirting too much chain lube

[crm114]

Thanks for all the advice.
It would seem that the nut is on the wrong way around. Both the small and the large seal on the output shaft are new, so I will see how it goes when it is applied the other way around, then if that does not work then i will switch to plan B then C and failing that D.
Craig, you say that this especially common on 79 Darmahs, why would that be, would not all square case engines be similarly afflicted ? As you say these KM locknuts are available as standard industrial items also with integrated seal.
Steve, ive done 2k since the seal and pinion was replaced a few weeks ago in that time I have personally only lubricated the chain once, after use I need a drip tray under the chain guard !

will keep you posted.
Andy