| Author | Message | ||
     Randy Roberson New User Username: randy_r Post Number: 3 Registered: 3-2007 |
Hi, I have been thinking about the oil leak problems I have read about in the Forum. In my experiences with large industrial engines, many of which use "O"-ring seals for liners and weap holes exactly as the Rolls-Royce V-8 engine, we often have engines, some of which are 60 or more years old, leaking gallons of oil per day. They are so large that some of these leaks would cost tens of thousands of Dollars to repair, because of the amount of labor needed to get the thing apart to change a gasket which would only cost a few Dollars (somewhat like your experiences, yes?). Some of our mechanics arranged a simple system to place a slight vacuum on the crankcase, which will almost completely stop the leaks; an unfortunate side effect seems to be altering the atmosphere inside the crankcase such that a crankcase explosion is more likely, so we had to stop this practice. Anyway, my point here is: perhaps there is a situation which develops with the crankcase ventilation system which is allowing a positive pressure to develop inside the crankcase, thereby forcing oil past the liner seal rings, not to mention the front cover and anywhere else it can find passage. Has anyone ever done any work on what the crankcase pressure is during normal driving, or encountered problems which would cause positive crankcase pressure? Regards, Randy | ||
| Patrick Lockyer. Grand Master Username: pat_lockyer Post Number: 709 Registered: 9-2004 |
Think i did a note on the good old pintle valve that is used some engines. It may be on one of the threads some time ago. Blocked flame trap will cause crankcase pressure. But others like piston blow by can be a cause. | ||
| bob uk Unregistered guest Posted From: client-81-108-179-55.brig.adsl.tesco.net |
My Shadow is 1974 SRH 17768 UK spec. no alterations to emission control system The breather goes from the top of the oil filler neck to the top of the choke housing. When the engine is running there is a slight vacuum but due to a scroll rear crank seal the vacuum can only ever be small. When blow by gets excessive the oil will start to leak past the scroll seal first because it has a gap. BUT on my car the bolt that attachs the pipe to the filler neck has stripped so for the last 17 years I have been meaning to take the filler neck off and helicoil it---- 1/4 UNF. This means for 17 MOT tests the emmision control is virtally disconnected and the brather just rests in the hole gently sucking away crankcase fumes which in my engine are virtually nil---LPG I cannot smell engine in the car and the engine does weep a bit of oil but does not drop oil so it must be OK. I drive the car every where and never give the engine or anything else a second thought apart from 200 mile checks. Crankcase pressure is not caused by the the pistons pressurising the crankcase by moving up and down in any engine where pistons are going in opposite directions. Single and 360 degree twins will which is why Truimph Bonnievilles have timmed breathers. ( they leak oil because the crankcases are vertically split and they fret as the engine runs) Blow by the rings is the main cause and can be detected by opening the oil filler and looking for fumes bad cases sounds chuffy. One misconception is that the gases are getting past the rings and the bore wall. What is actually happening is that the gases are going around the back of the rings and the piston grooves. Rings have mass and enertia. As the piston changes direction the mass of the rings bears upon the sides of the grooves in the piston and wears them. As the wears gets greater the ring flutters in the grooves and pumps oil above the ring and allows gases past. Which is why fitting new rings does not entirely fix an oil burner. The old rings have been worn thinner so new ones help but the grooves in the pistons are worn. Which is why Cord rings required the piston to be machined with wider grooves. Gearboxes and axles have breathers so that as temperature changes the pressure does not. (Message approved by david_gore) | ||
| Trevor P Hodgkinson Yet to post message Username: wm20 Post Number: 1 Registered: 11-2006 |
Just a thought here. We have a BSAMCC of NSW member who has developed an entirely new system for crankcase breathing on motorcycles. To date this has been 100% effective in eliminating oil leaks from lots of bikes many of which do not have much more of an oil seal that a felt ring. Rex believes that it can be applied to virtually any engine & he has just finished modifing it to fit Enfield Electras on behalf of Enfied India. I believe he is currently doing the same for Harley Davidson. If any one is interested that can contact me for his details. Regards Trevor | ||
| Bill Coburn Moderator Username: bill_coburn Post Number: 895 Registered: 4-2003 |
Trevor/ I would be interested. spur84@bigpond.com | ||
| bob uk Unregistered guest Posted From: client-86-29-86-238.brig.adsl.tesco.net |
Trouble is that many old brit bikes had vertical split crankcases. And the design due to dynamic forces causes fretting and oil squizy pumpy type leaks. In mild use such as classic bikes one a Sunday it will be fine. BUT---------- In my mis spent youth of fast women and even fast motor bike where clips on rear sets and 110mph for 20 miles with valves a bouncing before I nail it meant 1000 mile rebuilds and loads of oil leaks. I never ever actually changed the oil. Royal enfield or oilfield were well known for solid 350-500cc singles which were ok BUT-- push the bike much past 80 and it would blow the engine. An engine which did have a more tuning potential than the Bonnie was the BSA A10 I raced against one and right up to about 115-120 mph he was staying with me but he backed off because he was worried about a blow up and I was amazed to find that the engine was a standard BSA A10 RR Road Rocket. Then I raced a kawa 900cc Z1 and it was game over I could not stay with the Kawa and he even sat up at about 100mph wavied me good bye and was gone. I was in the dust. Modern bikes are amazing. I worked for the police as a mechanic and one officer told me that in an emergency he nailed a Honda Black Bird for nearly 50 miles and the bike was ticking over like a sowing machine when he got a stand down call. He told me because I asked why he worn out £400 worth of tyres in 200 miles. (Message approved by david_gore) |
