Crankcase Breathers

just use the little air filters as the old pipe work gets blocked and perished and don't forget to block off the air intake when you remove the Y peace to carb i used a tight fitting bolt and clip

Later SU's had a breather connection between the needle and butterfly. This ran at slight vacuum so scavenged the crankcase fumes as well as helping reduce oil leaks (always an advantage on a Mini). Prior to that, the PCV was the best bet as it did the same thing but connected directly into the inlet manifold. Don't connect the crankcase directly to the inlet manifold. I did this once. The intermittent cloud of exhaust smoke when the engine swallowed a lump of oil was something to see! Following traffic was bought to a stop. The other advantage of running a slight vac in the crankcase is a slight power increase due to lower windage losses within the engine. I have never quite seen the advantages of crankcase filters as the gas flow is out of the engine, not into it. There are some engines that run positive crankcase breathing and still have an air inlet bleed. That's when they are useful. Early engines simply had open breather pipes. This can be used but the resultant oily fumes tend to smell and make a mess of the engine bay. The later types had oil separators. basically cans full of wire mesh that trapped the oil and let it drain back into the sump. I would treat this spec as a minimum for road cars. Catch tanks came from a motor sport requirement so that blown engines didn't dump their oil on the course. They can be used on the road but (assuming you don't lunch your engine) are of little use beyond performing the oil separation bit.

John

"jacko" wrote in message news:d63asg$2jj$ snipped-for-privacy@nwrdmz01.dmz.ncs.ea.ibs-infra.bt.com...

Sorry but I have to disagree there. While it is true that running the oil seprators to the carb does generate a small vacuum in the case and that blowby and rocker oil buildup can be somewhat contained where worn pistons are the main problem anyway, the power advantages deriving from this are minimal compared to removing oil fumes from the fresh charge. I have run both configurations with a single hif44 on a 1275 on a nackered and then rebuilt engine. On the old engine removing the vacuum produced an amaizing increase in perfomance (signicant blowby combusted gases were fed to atmosphere rather than through the inlet again), however i also ended up with oil being squirted all over the place from the rocker cover as teh increased cranck pressure prevnetd oil from returning to the crank case under the sole effect of gravity.I also had dodgy fumes entering the driver compartment. On the new engine the perfomance was again higher with the breathers disconnected as prooved on a back to back run on the dyno where approx

At the end of the day the configuartion u use is dependant on the state of your engine and bore wear and weather you might be able to put up with some oily smells under hard acceleration ;-). However i believe that venting oil fumes to the atmosphere would make your car illegal...

hope this helps

Cheers!

I have always thought that dumping oily gases into the inlet manifold wasn't a good idea.

As the engine is newly built I think I'll go for filters on the 2 breather oil traps as they must stop any oil that manages to get through the traps from getting out into the engine bay. I presume you can clean them like the K&N air filters.

Cheers

Peter

I'm not sure about the legal bit. The early cars certainly vented straight to atmosphere so were legal then. However, the law certainly changed during the 40+ years of the Min so the same may not be true for later models. I'm not sure how much crankcase vacuum affects power. I know that David Vizard did some work on that in the 80's but can't find it now. He used the suction effect of a custom designed exhaust manifold though so there wasn't the problem of mixture contamination. ISTR that he saw some significant power increases though. I take your point that a worn engine can loose power due to this but as nearly all modern engines breath their crankcases into the inlet somehow, I doubt that it's a problem with them. If you loose power on a new engine, I would suggest that your mixture needs adjusting. The oil filler cap on the rocker cover is designed to allow air into the crankcase. This weakens the mixture if the sealed breather is used so the mixture should be adjusted accordingly. I know it's a sample of one, but my engine has sealed crankcase breathing and doesn't suffer a power loss. It was set up with the system in place though so the needles were chosen to allow for it.

John