Crankcase Breather

[Oddjob]

Do a compression test, just to be safe. All the plugs out and the throttle wide open.

[deltarider]

CB550s which had the breather tube connected to the air intake - to comply with US law - often had the paper air filter element fouled. A remedy much practised was to have the oil level not higher than halfway the two marks on the dipstick. But as has been said earlier: I wouldn't loose any sleep over it.

[McCabe-Thiele (Ted)]

As is often the case my experience is more with cars than bikes fwiw I had an old Merc 300TE 4-matic that when I was driving it at speed would start to throw a massive cloud of black smoke out of the engine at high rpm. First time it happened I thought I had blown the engine on my way to Skegness as my speed dropped it stopped smoking & drove normally.

When I pulled into a lay-by I checked the oil level it was difficult to check due to what I would describe as oil foam on the dipstick - it appeared to be slightly overfull. The dipstick that had a rubber grommet where it entered the block had also been pushed partway out of it's seat.

It appeared to be that the combination of high engine revs using a modern synthetic oil had caused excessive oil mist to get past the rings. I ran the car for a further 4 years without any excessive oil consumption or issues unless I pushed it close to its rev limits.

Thinking about the sort of revs these Hondas reach it strikes me that oil misting might account for some of the fumes from the top vent - I would not be too concerned unless it started smoking excessively as well.

[Neill C]

Thanks all.