.png "Powered by vBulletin")
Bike is a 77 GS750. I checked the compression and it was great. The vent tube is the one that runs from the head, right above the airbox and is connected to the frame. Bike seems to run fine? What could be the cause.
-
-
Oil over-filled??1983 GS 1100 Guided Laser
1983 GS 1100 G
2000 Suzuki Intruder 1500, "Piggy Sue"
2000 GSF 1200 Bandit (totaled in deer strike)
1986 Suzuki Cavalcade GV 1400 LX (SOLD)
I find working on my motorcycle mildly therapeutic when I'm not cursing. -
I ran out and checked it. Not overfilled.Comment
-
Sounds like blowby. What causes this?sigpic
82 GS850
78 GS1000
04 HD Fatboy
...............................____
.................________-|___\____
..;.;;.:;:;.,;.|__(O)___|____/_(O)|Comment
-
That isn't exhaust, at least it shouldn't be. That vent tube is the crankcase vent, and it's venting blowby from the crankcase (which is normal). If there's a large amount of blowby your bike is burning oil due to rings or valve guide seals. A small amount of blowby is normal. If you have an airbox on your bike it's channeled into the airbox. If you don't then it's venting to the atmosphere.Comment
-
That vent tube should run into the airbox. There will be some venting, how much are you getting?-Mal
"The only reason for time is so that everything doesn't happen at once." - B. Banzai
___________
78 GS750EComment
-
If I plug the hole with my finger I can hold it for 5 seconds or so before the pressure builds.Comment
-
Run it to the airbox like it's supposed to be and forget about it.sigpic
82 GS850
78 GS1000
04 HD Fatboy
...............................____
.................________-|___\____
..;.;;.:;:;.,;.|__(O)___|____/_(O)|Comment
-
If the bike hasn't been used much lately, there is a reasonable possibility that the blowby may diminish with renewed use. Rings sometimes gum up after sitting.
Some venting from the crank case is to be expected. That is why every motor has a vent. The flow from the vent isn't supposed to be oily. It isn't supposed to be smokey.
Hook it to the airbox and ride the bike. If it is excessive, oily, or smokey, Hook it to the airbox and ride the bike. A repair to fix excessive blowby is too much trouble unless it is super horrible. There is suposed to be some mesh in the valve cover to collect oil mist in the blowby. In my experience, it is sometimes missing.sigpic Too old, too many bikes, too many cars, too many things
Comment
-
You can pull all the plugs and put an ounce or so of a 50/50 acetone and ATF mixture in each cylinder and let it sit overnight. This will eat any carbon making the rings stick. Be mindfull that its gonna smoke like a locomotive till the juice burns out of the cylinders...so start it up OUTSIDE. If you dont have the stock box, like was said it just vents to the atmosphere and many put a K&N looking little filter on the end of the tube.MY BIKES..1977 GS 750 B, 1978 GS 1000 C (X2)
1978 GS 1000 E, 1979 GS 1000 S, 1973 Yamaha TX 750, 1977 Kawasaki KZ 650B1, 1975 Honda GL1000 Goldwing, 1983 CB 650SC Nighthawk, 1972 Honda CB 350K4, 74 Honda CB550
NEVER SNEAK UP ON A SLEEPING DOG..NOT EVEN YOUR OWN.
I would rather trust my bike to a "QUACK" that KNOWS how to fix it rather than a book worm that THINKS HE KNOWS how to fix it.Comment
-
Originally posted by allojohn View Post
You can buy those little things at the parts store way cheaper.sigpic
82 GS850
78 GS1000
04 HD Fatboy
...............................____
.................________-|___\____
..;.;;.:;:;.,;.|__(O)___|____/_(O)|Comment
-
It's not just blow-by from the combustion chambers. That line equalizes the pressure underneath the pistons and the crankcase. As the pistons rise and fall, they decompress and compress the air underneath them in the crankcase. For most 4-cylinder engines, the two outer pistons rise, creating a partial vacuum, while the two inner pistons fall, pressurizing the crankcase, but since the inners and outers move oppositely at the same time, the air more or less moves back and forth under the pistons. Since there is stuff in the way (rods, crank, cam chain and slippers), this airflow is not even and local pressure variations occur. That breather line lets the crankcase breath so that the pressure never gets too far in either direction, with air sometimes going out, sometimes going in. Since the rubber line is cool, oil mist condenses in the line and the line will slowly "drip" oil, even in a perfect engine. It's a good idea to use a filter as allojohn suggests to keep the engine from sucking dust back into the crankcase.
Of course, piston blowby does cause the overall flow of air to be net out of the engine crankcase through this line.
Harley engines tend to be real air pumpers in and out of the engine because both pistons share a single crank and the pistons are not 180 degrees apart as is done in a BMW boxer engine.
Most modern engines run that crankcase line to the air cleaner to capture and burn any escaping crankcase fumes through the engine. The main air filter also ensures that any air sucked into the crankcase is filtered as well.Comment
-
Ajay, do you think one of those Umbrella Valves like the Hayden Crank vent + would help an inline 4 at all. They are designed for the older Harley Evos to keep them from blowing gaskets by maintaining a vacuum in the crankcase. About 99% of the time I don't burn any oil, but at random times I do loose some and was wondering if it was through the opened filtered vent. Hayden claims that the valve would keep 3 to 5 lbs. of vacuum in the crankcase on our bikes and the umbrella valve is also ported underneath so it doesn't exceed that amount of vacuum. They also say that it will stop the misting you see coming out of the breather on stock motors.Last edited by OldVet66; 03-07-2012, 03:31 PM.http://www.thegsresources.com/_forum...ine=1440711157'78 GS1000E, Dyna-S ignition, Dyna Green Coils, K&N pods, Delkevic SS 4-1 exhaust, Dynojet Stage 3 jet kit, Russell SS Brake Lines, Progressive suspension, Compu-Fire series Regulator 55402 and Advmonster cree LED headlight conversion.Comment
-
I wasn't familiar with that Hayden valve, but will look it up. Pulling a partial vacuum under the pistons would probably save some pumping losses and even boost power a tiny bit. But I don't think it would do much good for an inline four cyl engine, since the pistons do such a good job offsetting each other.Originally posted by OldVet66 View Post
The Harley single-crank pin design results in the pistons sort of rising and falling together, but out of phase by the amount of the V-angle. Worst would be a vertical twin with the pistons going up and down together. Best twin would be a flat boxer twin where one piston shoots away from the centerline at the same time the other piston moves towards the center. Like the inline four, the volume under the pistons stays pretty constant as the pistons move. This is why the Harleys and some vertical twins pump so much air in and out of the crankcase. Your Hayden valve would reduce the pressure in the crankcase, reducing friction losses of the flowing air, although the pistons then might lose power to the vacuum they pull underneath.
FWIW, most piston airplane engines are a flat boxer design, but, because they are built to run 75% power full time and for extremely long service life (2000 hrs), they tend to run with a lot of blow-by as they get old. You can install a special oil trap for that line that lets the water vapor out, but catches the oil and feeds it back to the crankcase. That makes a big difference when your engine is blowing about a quart of oil per hour of operation.
In summary, I don't think you'd see much advantage for a 4 cyl Suzuki motor. Hope that didn't bore everybody.
Comment
Comment