tappet cover o ring size

[exvalvesetdabbler]

Starting to work through a laundry list of minor maintenance tasks,one of them being oil weeping from one or more tappet covers. O rings are probably original as I have not changed them in the 45 odd years I've had the bike.

Does anyone know the correct size, parts book only mentions 30.8 .

Nearest I can find is 31 ID x 3 cross section.

Looking at some of the ridiculous prices some folk are charging for genuine ones, it might be cheaper all round to order new covers from China that come with o ring.


Regards
Dave

[Oddjob]

30.8 x 3.2 is the correct size. However they ain’t available off the shelf, special order of 500 minimum is the general rule. Most sellers tell you they are the correct size but they’ll be 31x 3.0 normally. Sometimes they work and sometimes they don’t. Tappet covers are generally ok but the same ring is used in the 500/550 inlet ports and it’s very important they seal well.

There are 12 of them in a genuine top end gasket set so I use those just for the inlet ports and use close enough for the tappet covers.

I’m betting the chinese covers are using close enough as well.

[exvalvesetdabbler]

Thanks Ken,

At least my measurements and % gland fill calculations agree with what you're using.

Regards
Dave

[exvalvesetdabbler]

Found some in FKM,

OD 37mm CS 3.1mm  £5.67 for ten.  I'll report back once received and fitted.

Regards
Dave

[Oddjob]

I did float the idea of having some specially made in Viton but I was warned that the hardness of them could mean they wouldn’t crush properly. Personally I didn’t believe that but I thought I’d repeat it just in case.

I may have some made the correct size if my claim pays out enough. Won’t be any time soon though.

[Nurse Julie]

I sell them in Nitrile and a % of all my sales go to run this forum. I've sold thousands of them and we also fit them to all our own CB SOHC 4'S. Viton shears too easily for this application

[exvalvesetdabbler]

Ease of compression depends on the hardness.  Shore 70 is the norm for most stuff.  When I worked  we would use SH 70 Viton on underwater housings rated to a few thousand meters water depth. A bit of fluff or debris during assembly was the biggest risk.

Regards
Dave