Head / barrel oilway o-ring

[Geordie]

Just coming up to 100km since motor rebuild and a lube oil leak has appeared at the top of the barrel.
The o-ring came in a kit from a reputable supplier (although the left side cover gasket was a poor fit so I made my own).
I can order another but the ratio of postage to item is ridiculous (30:1) and I don't want another failure. I recognise that it could be an assembly fault on my part and will assess at strip-down.

There is a good hydraulic parts shop nearby. But what to order: the Mototrans narrowcase part dimensions are 7.66 x 1.78 mm and online parts supply either don't list sizes or list as 8mm.

7.66 x 1.78 or 8 x ? and nitrile or viton?

Recommendations?

[Jordan]

I'm using a size BS 011 O-ring made of Viton on my 350 widecase lately, after finding nitrile doesn't last long enough.

Size is nominally ID 5/16", OD 7/16".

[ducwiz]

The 1974 parts catalog says GACO OR107HR. Taken from an old GACO list, this is
Dimensions 7.68 x 1.78
HR = Viton/FPM

Hans

[Geordie]

Thank you both. I will go with the Duc dimensions and use Viton with its higher temperature tolerance.

[Ventodue]

The 1974 parts catalog says GACO OR107HR. Taken from an old GACO list, this is
Dimensions 7.68 x 1.78
HR = Viton/FPM

FWIW:

1. GACO is/was the trading name of George Armstrong (edit: ANGUS) and Company. Being a pioneer manufacturer of seals (see below), 'GACO' became something of a generic name for all oil seals.

(Company started out as a leather business in Newcastle in 1788. Ended up making gears, rubber industrial products including oil seals, fire hose, belting, protective clothing etc. At one time, the factory in Walsall was, I have seen it claimed, the largest manufacturer of oil seals in Europe).

2. 1.78mm is a standard O-ring cross-section, even today. (Smaller is 1.6, larger 2.0.)
Ref: http://www.jameswalker.biz/es/pdf_docs/ ... de-issue-7

3. "OR 107" is a code that was originally set down by UNI, L'Ente nazionale italiano di unificazione. However, I think this code is now obsolete. Don't quote me on this; but read on ...

4. This O-ring, under part no. 0400.17.030, has a long history with Ducati, cropping up for example as the small head-to-barrel O-ring in the twins. Here, however, it gets a different UNI/GACO code: OR 2031.

And OR 2031 has dimensions of 1.78 x 7.65. And THAT O-ring, folks, is widely available from pretty much every bearing and seal supplier ...

[ducwiz]

You are perfectly right with 7.65. 7.68 was a typo.

Hans

[Geordie]

The parts book entry - out of interest

O ring.png

Thanks for the GACO clue!

FWIW

GACO was originally George Angus & Co, Wallsend which, unsurprisingly, was the town where I was born.

[ducwiz]

175 Mototrans ?

..

[Ventodue]

GACO was originally George Angus & Co, Wallsend which, unsurprisingly, was the town where I was born.

Ta! Lawd knows why I wrote 'Armstrong' not 'Angus' .

Hey ho ...

[Ventodue]

The parts book entry - out of interest

Same dimensions given in the parts book that I have for the 250-350 Road (albeit written in a different - but correct - sequence ...)
7'66 x 11'22 x 1'78.

O ring.jpg