Decoding part number

[chuck hahn]

This is the part number for the oring that holds the reservoir cup in the front master cylinder on my skunk. Im thinking that its telling me its a 62 MM oring but what durometer?? Am i correct assuming that it is 62MM?

59686-33620

[Nessism]

62mm ID or OD? What material? What O-ring thickness? Why not just order the OEM part and avoid these questions?

[chuck hahn]

ED its NLA and theres only 4 on ebay from Germany and i cant see buying a 30 dollar oring if i can get information to just buy a regular nitrile oring for 2 dollars.

[Nessism]

Measure the size yourself, chuck. And research. Nitrile is not good for brake fluid. You need EPDM

[chuck hahn]

Well i can at the least measure the base of the reservoir and the depth of the groove and take SWAG at it.

[oldGSfan]

The number on Partzilla (#3) is dyslexically different, 59668-33620 vs 686. Looking that up on eBay I see it's available for $8 here (and many others for around $10):

https://ebay.us/m/NJHuGM

Maybe snag it?

[chuck hahn]

Tom. I took the number from item 9 here.....
1978 Suzuki GS1000EC Front Master Cylinder (Gs1000ec | Part Shark

[oldGSfan]

Tom. I took the number from item 9 here.....
1978 Suzuki GS1000EC Front Master Cylinder (Gs1000ec | Part Shark

Could be a PN change perhaps, or a typo. Anway the 13 of them on eBay match your # and look right. I actually used the Partzilla number in the search and they appeared, maybe a 'close enough' search logic going on.

[Nessism]

O-rings are commonly sized ID x thickness. You want a little stretch, so the O-ring ID needs to be a smig smaller than the groove it fits into. Maybe 1-2mm for a 62mm O-ring? something like that. To figure thickness, you need to measure the mating O-ring groove, which in this case, will be difficult; measure the OD of the groove in the master cylinder. There is no easy way to do that. Maybe take a piece of wire, slowly cut it down to size, until it just fits inside the groove, then remove the wire and measure with calipers? Something like that.

[chuck hahn]

I discovered that with the groove Ed. The base of the reservoir cup is 45MM and i measured it a few times to be sure it was that. I like the wire idea for finding the groove depth. I will try that but im guessing its gonna be close to 2MM.

[bwringer]

Usually the two numbers after the dash seems to indicate the nominal ID in Suzuki o-ring part numbers.

For example:
09280-21013
09280 indicates a "normal" nitrile o-ring, used for oil sealing all over Suzukis.
the -21 indicates it's 21mm ID.

Same for an o-ring with the number 09280-06005 - it's 6mm ID. The infamous intake o-rings on a GS850G are 09280-38004 (38mm ID), although they are made from a high-heat material (so I'm not sure why the first part of the number is the same, or maybe Suzuki used the same material in other o-rings.)

I've never been able to find an indication that the thickness is encoded anywhere in the part number, though.

Bear in mind that Suzuki never was 100% consistent about these things.

That-ring is an entirely different material for brake fluid, and so the part number may not follow this pattern. However, 62mm is nearly 2-1/2", which seems mighty large going from memory of old master cylinders.

In other words, 59686-33620 might be a 33mm ID o-ring, or it might indicate nothing at all.

If the base of the reservoir cup is 45mm, then a 33mm o-ring might make more sense. Can you measure the place the o-ring goes, or the mating part? It's hard to picture what you are working with here. Maybe a diagram or photo?

If you can measure ID with calipers, and the depth of the groove, then you can figure it out from there and look for a standard industrial part.

For example, here's a 33mm x 2.0 EPDM o-ring (no clue whether this is correct; it just shows that these are likely available):
https://www.theoringstore.com/store/index.php?main_page=product_info&cPath=368_2278_22 82&products_id=44525

[chuck hahn]

The oring goes in the groove in the base as seen here. Then the fluid cup presses into the base. The oring seals the cup and the base so brake fluid doesnt run out.
I measured the mating surface of the cup and it is 45MM so a 33MM oring is nowhere close.

1978 Suzuki GS1000EC Front Master Cylinder (Gs1000ec | Part Shark