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Measuring O-Rings

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Oddjob:
I was looking for something else yesterday and found 2 old oil pumps for the 500/550 lying in the bottom of a huge box, I decided on a whim to restore them, both were complete except one has one of the small collars missing that have the bottom O-Rings around, will probably find one of those somewhere. So I took them apart and cleaned them both up, must say they cleaned up very nicely. However the O-Rings will need replacing so I decided I'd see if I can find them without having to buy genuine Honda. After recently seeing a tappet cover O-Ring provided by an Ebay seller which claimed to be a perfect replacement for a genuine Honda O-Ring and finding it so bad I couldn't trust using it, I decided this time to source my own. The problem though is that Honda are kinda sparse with the info for the oil pump, the pressure relief valve (both of which were stuck BTW, that's both oil pumps and 3 filter bolts now where the relief valves are stuck, that could be from standing so long, they've been in that box since before 1980 I reckon) is the only one listed with it's full info, 19.4 x 2.8mm. Honda state the big O-Ring is 47mm but no section is listed. Same for the 2 collar O-Rings, just 14mm is listed, no section. The O-Ring under the cap isn't even listed as being available and it isn't included even in a full genuine Honda gasket kit so that will require some thought.

I looked online on advise on how to measure an O-Ring, looked easy enough but nope that didn't work. The 47mm O-Ring now measures 52mm, the 19.4mm is the closest to being correct at 20mm, the 14mm is now 15mm. The other problem is, if the diameter has changed so has the section, being squashed distorts them over time. I measured them all and wrote down what I thought they were, then I remembered having a genuine bottom end set in the loft, so that came out and I measured a brand new non distorted O-Ring and they were quite different. None of the measurements I'd carefully taken were correct, which means the one not even listed will have to be carefully thought about. It's now a loose fit on the top of the pump, it fits inside the cap just fine but there doesn't seem to be any compression taking place when the cap is fitted with the old O-Ring, I reckon it must have been a tightish fit around the flange on the top of the oil pump when new, it must be slightly taller than the flange as well or it wouldn't seal too well.

So now I have some on order, I've done a few choices for the cap O-Ring, I'll see which one I feel is best.

One word of caution on buying none genuine Honda O-Rings, first off they are all nitrile rings (AFAIK) and unless the ring comes into contact with petrol that should be just fine to keep using. Viton is usually harder to compress, not a huge difference TBH, a normal ring is 70 and Viton tends to be 75 or 80. A number of the genuine Honda rings are also really odd sizes, that can normally mean they aren't available to buy from a UK manufacturer, the tappet cover is one, which is also the same ring as the inlet manifold rubbers, on a tappet cover is not absolutely vital to get a perfect seal but on an inlet manifold that's another matter. The one I was given to fit was so bad I ended up robbing an old one from a tappet cover and fitting the new one there instead. You cannot buy these rings off the shelf, you have to have them made specially and the minimum order is normally 500. It's the same for the pressure relief valve cap on the oil pump, it's such an odd size they don't make it anymore. Incidentally it's also the same ring that fitted to the 3 oil gallery bungs in the crankcase, that's why there are 4 of them in the gasket kit. You'd need to order 500 specially to get a perfect fit, that can be expensive.

I'm in contact with a large UK manufacturer of O-Rings about getting some rings specially made for me,  tappet covers and inlet manifolds will be one, the relief valve and oil gallery plugs will be another if I feel my replacement doesn't fit the bill well enough.

Orcade-Ian:
Ken,
Not sure if this might be useful but many years ago I wanted to re-furbish my Lake and Elliot Trojan trolley jack which was failing due to deterioration of seals (I bought it new in the early 80's). My seals were special and most places needed an order of 1000 units.  I contacted Barnwell services in Birmingham and they made some for me.  Might be worth a call or email
(web site http://www.barnwell.co.uk/) They were very helpful and not expensive either.

Ian

This is the story of the jack

http://www.stallard-engineering.co.uk/stories/other/Trolley%20Jack.htm

Oddjob:
Just checked the site Ian and nothing close to what I need, Honda didn't seem to use normal sizes, they seem to like restricting you to buying theirs at inflated prices.

Nice try though Ian, thanks. I may contact them to see if they can price up some specially made ones though, depending on the price I get from my other source, who BTW are very big in manufacturing them. Their range is very big and even they don't stock the ones I need in most cases.

Bryanj:
Ken, long time ago now i had an oil pump cover leak and spent some time at Dowty seals working out what to use and came up with 46x2 as a size which stopped the leak.
Thicker holds the cover too far off and pressure drops, smaller leaks.
There is  honda O ring that size used in a Goldwing.

I have a very early parts book that gives O ring sizes, even the carb seperate ones with sizes and part numbers.

Oddjob:
I've measured the flange that's on the oil pump Bryan, as far as I can work out it's somewhere between 43 and 44mm, 43 being maybe just a midges too small and 44mm a midges too big. The flange height is hard to judge but 1.6 to 1.7mm is my best guess. I'm trying 3 different variations of those sizes to see what I feel would work the best, 46mm I'd say would be the internal size of the cover which sits on top of the flange and 2mm I would say would be just a fraction too big in section, 1.8 or 1.9mm would be my guess of the ideal section.

I'd love to see that parts book Bryan, never even heard of that being around, saying that I bet the partsman knew about it. If you have a copy of it anywhere please send it to me.

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