Very bad blow by - Help!

[Peter. C]

I had the same problem with my first Comet in the late 50s when the shaft turned in the gear, it took a nice man at Conways to solve the problem. It could throw out a pint in ten miles, fixed that then it ate its alloy idler,what a mess that makes. Sold it to Roland Smith in Neasden and went for Nat Service, must have left a good impression since I still ride Vincents.

 

[Ducdude]

As I said,for a quick test, you can just block off the timed breather and fit the 'D' breather to any tappet adjuster hole (either of the middle two would be best) and then just see if you have temporarily solved the problem.

Why not just leave the timed breather attached such as it is to get the most possable venting?

Thanks,
Eric

 

[timetraveller]

Because if the timing has slipped either by the pinion turning on the tube or the spindle turning in the crankcase, then the breather might be open on the upstroke meaning that air will be sucked in and the other breather will have more air to expel.

 

[Hugo Myatt]

I know I shouldn't meddle in things I know not of but I seem to remember BMS discovering that when he ran the timed breather and the D type breather together the D type breather sucked as well as blew and he ended up with road grit in the valve cap.

 

[davidd]

Yes, Hugo is right. The challenge is not to get the most venting, but the most efficient venting. As PEI would point out, if you have to do a lot of work on the breather, you are better off doing the work on the engine instead.

David

 

[vibrac]

I know I shouldn't meddle in things I know not of but I seem to remember BMS discovering that when he ran the timed breather and the D type breather together the D type breather sucked as well as blew and he ended up with road grit in the valve cap.

not with a little pvc valve in the line and the timed breather firmly plugged up

 

[mercurycrest]

This is starting to remind me of the old joke; "When you're up to your ass in alligators, it's hard to remember the original objective was to drain the swamp." In other words......... Do a compression/leakdown test and make sure you haven't stuck a ring or had a piston seizure before you start buying extra breathers, etc..
Cheers, John

 

[Ducdude]

Because if the timing has slipped either by the pinion turning on the tube or the spindle turning in the crankcase, then the breather might be open on the upstroke meaning that air will be sucked in and the other breather will have more air to expel.

Ahhhhh I see OK then...If I put a PCV valve on the timed breather that only allows positive pressure OUT and tries to maintain a lower presure in the crank case I can still keep the timed breather in play..

Thanks,
Eric

 

[Ducdude]

I know I shouldn't meddle in things I know not of but I seem to remember BMS discovering that when he ran the timed breather and the D type breather together the D type breather sucked as well as blew and he ended up with road grit in the valve cap.

Note to self...Keep D breather line away from the road surface..

Thanks,
Eric

 

[Ducdude]

Yes, Hugo is right. The challenge is not to get the most venting, but the most efficient venting. As PEI would point out, if you have to do a lot of work on the breather, you are better off doing the work on the engine instead.

David

PEI's logic is sound...It very well may come to that...First things first though....Let's see if I have a bum timed breather first and if the facts prove out that piston blow by is the cause of the crankcase pressure issue then rings, pistons and liners will be the order of the day...and maybe valves
Thanks,
Eric