10 replies to this topic

[cheesebadger]

I have a 998 A series with twin HS2s and i am unsure what to do with the crankcase ventilation. I have looked at many topics and FAQs using the search function, and general opinion is to pipe it all up to the carb for Positive Crankcase Ventilation. Rocker cover breather, flywheel cover breather and timing cover breather are all mentioned, however i appear to have a breather on the tappet chest cover. Currently i have only two breathers;

One on the rocker cover that is attached to the air filter box for the carbs,
And the other from the tappet chest cover that is just open to atmosphere.

Should i connect the tappet chest breather also to the air filter box? or open both to atmosphere?
If i change the standard element filters to individual cone or pankcake filters or even trumpets, how do i a plumb into the carbs?

Thanks in advance, Rich

[Big_Adam]

Hook them all to the breather tubes on the carbs if you have HS2's.

Unless you have a top end race motor (and use it for racing) then it's better to send the vapour to the engine and keep the crank well ventilated.

As for if you get cones, the hs2s should have a fat pipe for connecting to the breather system. Unless you got some old old carbs in which case I have seen the crank brather connected to the metal back of the cone filters. So they vent inside the filters, think I saw it done with a plumbing barb.

[cheesebadger]

Think i will connect them both to the air filter box then. A few other posts suggested that this could help oil leaks, true? and why?

Unless you have a top end race motor (and use it for racing) then it's better to send the vapour to the engine and keep the crank well ventilated.

Out of interest, how do you send the vapour to the engine and how would this help ventilate the crank. Sorry if that is a silly question, i understand the basics of the a series, just not all the little details.

[cheesebadger]

Anyone have any photos of twin HS2s with this breathing attached, i can't spot the "fat pipe for the breather" as mentioned by Big_Adam? Maybe i have "old old carbs!"

[Ethel]

A PCV (positive crankcase ventilation) system helps with leaks by reducing the crankcase pressure to slightly under atmospheric. If it was the other way round the pressure would force oil through the seals - you get some gas "blow by" the pistons and heat causes expansion so a means of letting the pressure out is useful.

The standard system works by letting air in through the oil filler cap and sucking it out through the breather, this also helps the oil drain back to the sump.

Connecting only one breather to the engine's induction would draw air through the other breather which might not have enough of a flow restriction resulting in no pressure reduction and excess air going in to the induction.

Twin carbs had breathers connected to the inlet manifold via a "gulp valve" that closed if the vacuum got too high. Connecting the breathers direct to the carb could mess up their balance. Connecting them to a common filter casing would work too.

[bmcecosse]

Without crankcase ventilation - the engine leaks everywhere - and consumes oil which is pushed up past the rings. No harm leaving one pipe open to air - that ensures a nice flow of air through the block and removes any water vapour - which otherwise can form 'mayo' in the rocker cover.

[cheesebadger]

Ok, thanks for all replies. So if i connect both the breathers, from the rocker cover and tappet chest to a t-piece and then connect this to the air filter box this would help reduce the internal engine pressure and help with any oil leaks?

Alternatively, does anybody have a picture of the 'gulp valve' mentioned on the manifold so that i can see if there is one on my manifold?

Thanks again for all responses, Rich

[liirge]

i think they are reffering to the Clack valve, as seen here:
http://cgi.ebay.co.u...14#ht_500wt_956

[huw_jenks]

I have what looks like a breather pipe on top of my rocker cover (didn't have one on my last Mini) which is currently sealed up. Should I be leaving it open to the atmosphere or have a pipe going to the carb?

by the way - 1293, Cooper S head, HIF44, K&N

[Ethel]

The ebay valve isn't the one I had in mind but does look like a similar idea, a simple restriction (small hole) might work well enough.

Ideally you want the pressure at the bottom of the engine to be less than at the top to draw oil back to the sump - this is usually achieved by plumbing the top to atmosphere via a restrictor (oil cap or pipe to air filter case) and attaching the crankcase breather to the the inlet after the carb choke - but before the throttle if it's an open pipe from the breathers.

[Stevie W]

Hopefully the attached picture will show you how I have connected my breathers up on my twin 1.25" SU's.

The "gulp" valve is attached to the inlet manifold by it's lower connection. I've then plumbed in the timing chain and drop gear case breathers through a "Y" piece to the valve inlet.

I believe this was the standard set up on Cooper "S" minis

Steve.