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Post by sprints on Sept 27, 2008 17:26:12 GMT -5
As I was buttoning up my lower end on my SR today I noticed that the chamber where the vent is located on the rear of the cases goes to nowhere. My SR uses a large hose that connects through a snorkle to the aircleaner, the XT uses a small can filter instead. The chamber is completely isolated with no access to vent the crankcase at all - anyone got any ideas? You sure don't need a filter or hose on it, you could just block it off - Rod
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Post by solo2racr on Sept 27, 2008 20:09:14 GMT -5
DO NOT block it off. As much air as that engine moves, it needs as much area to let it escape and suck back in as possible. Here are photos of each side and you can trace the path back and forth on down into the crankcase. You have to look at both sides to be able to see it.   |
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Post by wotavidone on Sept 28, 2008 20:40:38 GMT -5
I've never had one apart, and even with the photos it took a long time to pick the path for the venting, but I assure you that if you block this thing off, you'll have dramas. I can imagine it being just about impossible to kick over. It would come up against compression on every down stroke of the piston.
If you run an SR with the airbox open, you will find the small hole that lets the crankcase breath in and out of the air box. It most certainly shifts a lot of air. About 499cc out, and 499cc back in, every revolution of the crank.
Mick
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Post by solo2racr on Sept 28, 2008 21:49:26 GMT -5
It most certainly shifts a lot of air. About 499cc out, and 499cc back in, every revolution of the crank. Mick This is exactly why I don't believe in one-way valves inserted into the vent line. I have seen a number of big single cyl. bikes with one-way valves that only let air out but not back in with claims of HP gains. Hogwash. The volume inside the crankcase will vary up and down the same amount as the engine displacement. Ideally, there would be 0% restriction in air flow, in or out, beneath the piston. |
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Post by wotavidone on Sept 28, 2008 22:29:54 GMT -5
One way valves??? Can't quite follow how that would increase horsepower, eh? I'd believe it they said it increases oil consumption, cause every down stroke would be pressurising the crancase to at least some extent, surely, thus causing a little more oil to be forced past the rings.
Mick
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Post by solo2racr on Sept 28, 2008 22:45:08 GMT -5
The idea is to create negative pressure inside the crankcase. I think it's suppose to make it easier for the piston to travel downwards on the power stroke. Sounds great till you figure in the power taken to overcome the neg pressure on the up stroke.
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Post by wotavidone on Sept 29, 2008 2:02:41 GMT -5
Yeah, mate. Every action has an equal and opposite reaction, or some such equation.
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Post by colinjay on Sept 29, 2008 2:30:47 GMT -5
There is a mob here in Aust. that have developed one of these one way crankcase ventilation systems for single and twin cylinder engines. Although they make claims about power increases, I think their main market is with the British bike and early Harley fraternity, where having a slight negitive pressure in the crankcase stops/reduces the amount of oil leaks when the engine is running.
CJ
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Post by flyereddie on Sept 29, 2008 4:14:42 GMT -5
The one way valves were used in older engines to create a slight negative pressure to help with oil sealing Briggs and Stratton stationary engines have them so too do lots of older car engines which also vent the gasses into the inlet manifold. The amount of air going through the vent is only 500 cc at kickover speed, at running rpm the volume going back and forth decreases dramaticly as their is a large volume of air underneath the piston and in the crankcase/ gearbox which just compresses /expands a little with each stroke.
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Post by davedunsboro on Sept 29, 2008 6:44:33 GMT -5
It's called a breather too!(how long can you hold your breath for ?)The SR lasts about that long too(before it starts to run like a hairy goat).Don't ever block it off! Cheers Dave.
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Post by davewfc603 on Oct 15, 2008 14:29:03 GMT -5
Hi, been playing with my latest $250.00 sr500, I seemed to everything working... he... & then all of a sudden it started smoking.. like an old 2stroke with a rich mix. The valve adjustments, carb & I even put in another just to rule that out. Compression is 180 on 5 kicks ( there's already some oil in the piston) I had planned to lap the valves at least over the winter. The breather on the top of the engine is not blocked. I'd love some opinions.... has anyone have a valve oil seal go & oil runs back into the engine. Additionally when the bike has sat for a couple of days/ 4 hours it starts right up, about 30 seconds later smoking & stalls. You guys proud of me or what for this one, Thanks Dave
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Post by caferacercarl on Oct 19, 2008 1:41:47 GMT -5
Drain the oil and see if it just happens to have double the right amount in it,, it has been done many times before, owner checks dipstick without running engine first/ tops up untill it reads , they will still go and usually blow the front sprocket oil seal out the first time you give it a big rev.....
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Post by davewfc603 on Oct 19, 2008 8:37:31 GMT -5
Hi Carl, a little of my history on the bike. It was a non-runner. I cleaned all contacts, rebuilt the stator, drained all the oil, rebuilt the carb, brakes,cables before I ever started it. I was so impressed that on the 1st. or second kick it started. It still had some carb issues but I got them pretty well taken care of. I have run the engine about 10 - 20 times for short periods because it still needed to be accurately timed (heat concern). It's a nice quiet engine, smokes some a little on startup for about a min. Oil levels stayed accurate. I pulled off the exhaust, the valve & port have an ugly oily tar build up, the exhaust valve seat looks wet & dirty, intake looks perfect.. My guesses or processes of thought are (maybe) valve oil seal, guide seal. The bike will run for about 30sec. before it smokes & dies, a lot of oil getting there. I plan to take the engine out this week & start the hunt. Additionally, I can tell the engine has been apart before and has about 18000 miles on it. Once again I wood love opinions, thanks Dave Oh yea, damm cold here in NH this am.
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Post by solo2racr on Oct 19, 2008 9:59:03 GMT -5
Generally speaking, a leaking valve seal will smoke at first and then stop or become much less severe . What happens is they will let oil drain past them when the engine is off. If it is taking a little bit before it starts to smoke, it could be a stuck oil ring on the piston. You said when you got the bike it was a "non runner"? I am assuming that it was sitting for awhile then.
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Post by davewfc603 on Oct 19, 2008 11:17:35 GMT -5
I would say it sat for years. I had probably run the bike about 2-3 hours worth of time trying to "reseat & clean" things and it was running very nice, Dave Compression is up to 180 at about 6 or 7 kicks, Dave
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