LEAKING Oil into Cylinder

My Son has just bought a CB 500. I rode it back from Derby - its done 50 miles no problems. It is basically sound, had a big flat spot at high range revs, this is now sorted with a full carburettor overhaul. However now have a major problem with oil leaking into rhs cylinder. Leaking out of exhaust port flange. Terrible performance as oil is gushing into. Apart from obvious, namely cylinder head gasket is there any other simple explanation? Dave

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I can't think of anything else apart from rings which I'd hope are ok! Is it smoking?

Can't really think of many alternatives, however you would probably be advised to invest in a compression tester, for two reasons:

1. If the readings differ a lot between the lhs cylinder and the rhs cylinder you definatly have a bad problem - this is not good, but at least you know what you are up against.

2. If they do not then you can look for another (hopefully easier) explanation.

Also, have you done the normal thing of looking for oil in the cooling water and a for a whiteish (some say 'mayonaisse like') deposit under the oil filler cap (a sign of water in the oil)? These would be tell-tale signs of a cracked head or buggered head gasket etc.

I'd go with what has been said before, but years ago had a CB550 that had a similar issue, and it was oil travelling along the pipe between the cylinder head and the air filter box, then "recycling" back through the filter and the carb throats.

Got very messy for a while.....

After finding almost half a tank of petrol in the crankcase, its looking like a faulty vacuum fuel tap.

We dismantled the tap and found there was no spring in the vacuum mechanism, where there should have been...!!! Somewhere along the line a previous owner has had it off and not put it back. This meant fuel was free to run into the cylinder and oily liquid to come out the exhaust manifold.

Any idea's where to get spare's for a fuel tap from?? (quoted more than a ton for a new tap from local dealers)

My spring went slack during the last winter (but then it was cold enough for anything to shrivel up) and so I priced the diaphragm/spring assembly at the local dealer. Came to £38.

Being a mean sod, cut an old slide return spring down from a Honda Express, fitted that, no problems and zero cost as I had it kicking about in a box already

If the diaphragm's ok. perhaps you could try a similar fix?

Sheffield_S6 wrote: Any idea's where to get spare's for a fuel tap from?? (quoted more than a ton for a new tap from local dealers)

You can get a complete tap off ebay for about £15, saves messing around!
How did you get it apart anyhow; did you drill off the rivets?

On mine, the diaphragm assembly was screwed to the rear of the main tap body by 4 phillips headed screws. The tap cock plate I will admit is held in place by rivets.

chromedome wrote:If the diaphragm's ok. perhaps you could try a similar fix?

The diaphragm is a bit tatty. Probably best to replace it if possible.

teamster1975 wrote:You can get a complete tap off ebay for about £15, saves messing around!
How did you get it apart anyhow; did you drill off the rivets?

ebay is probably a good call, just wondered if there was anywhere else you could recommend looking?? can't always be sure what you're buying off ebay.

Didn't touch any rivets, just 4 crosshead screws to get to the diaphragm and stuff.

Sheffield_S6 wrote:Didn't touch any rivets, just 4 crosshead screws to get to the diaphragm and stuff.

Oh I'll have to investigate! I had to replace mine because the tap had become notchy to the point of barely being able to turn it at the click point. From memory I'd come to the conclusion that the rivets needed to come off to fix it. If I can do anything with it you can have it for the cost of the postage, I've got two of them kicking around in the "parts cupboard"