S&S V107t crank case breathing issues
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Joined: Mar 2021
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From: Atlantic Canada
S&S V107t crank case breathing issues
Hello, Ive got an old s&s 107 evo crate motor and im having issues crank case breathing under power. The bike ran fine at idle and low loads but when i put it under a heavy load i was blowing out the oil cap and spraying oil on my bike. I mentioned it to my mechanic and he asked if it was a bottom or top breather, i had no idea and he was too booked up to take a look at it but said dont worry about it unless it gets worse and he'll have to take a look at it when he has time. Unfortunately hes a seasonal bike mechanic so that was last year. At the end of the riding season something happened where i was full throttle going up hill and the bike sort of coughed and i lost power. the bike still ran and drove me home but it was rough and its been parked since. Ive been looking online and found that it might be a breather valve? I just want to know if anyone else has had that issue with an older S&S evo, and how you were able to solve it. Id just like to have the bike up and going for riding season soon. Any help is appreciated and if you need any more info id be glad to provide it.
Thanks
Thanks
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From: poway
Don't know how old you 107 motor is but it probably has both crankcase and engine case vents available. The choice is left up to the builder on which way to go. Chances are that it's not the breather valve unless something went through it.
Anyway you need to identify where the motor vents and make sure it's clear. You can remove the bolts going into the head and look to see if they have holes going through them. If not then there will need to be a hose running off the lower rear part of the crankcase that should be clear.
Look for them, if they are clear, you might have something wrong with the scavenge system. Loosing power is a sign of sumping so it's possible the scavenge pump ate something it didn't like. Motor could be toast and need a rebuild if it was running fine before the issue occurred.
Anyway you need to identify where the motor vents and make sure it's clear. You can remove the bolts going into the head and look to see if they have holes going through them. If not then there will need to be a hose running off the lower rear part of the crankcase that should be clear.
Look for them, if they are clear, you might have something wrong with the scavenge system. Loosing power is a sign of sumping so it's possible the scavenge pump ate something it didn't like. Motor could be toast and need a rebuild if it was running fine before the issue occurred.
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Joined: Mar 2021
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From: Atlantic Canada
Thanks for the help, I know there are hollow bolts holding the air filter on that were plugged with silicon when i bought the bike, so im assuming they used the hardware for a top breather and just plugged it and went for the bottom breather when building the motor. Im hoping that the bike popping the oil cap off under power means that the venting was clogged in one of the hoses. Ill take a look and see what i can find and hope to hell that hose is blocked by something. I dont even want to know what a s&s rebuild will cost, maybe if its fine and doesnt need a rebuild ill just pull it out, sell it and pony up the money for a warrantied 124 for the piece of mind. Double time season is just around the corner after all. Again thanks for the help
Last edited by B M; Mar 28, 2021 at 09:55 AM.
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do you have a tachometer on the machine?? if so, what are the RPM's at the onset of the issue??
before i would do anything, i would do engine diagnostic, aka, static compression and leak down to determine condition. a borescope inspection wouldn't hurt either.
hippysmack on the xlforum has a nice write up on crankcase pressures using a manometer, i used my machine as a test mule for some of that to 6k rpm. it is on the SPORTSTERPEDIA. this carries over into the BT's as well. my readings are not loaded so under load, things will change as cylinder pressures are higher due to fuel burn.
you will find it interesting, the crankcase transitions to a positive pressure @ the 5k range.
before i would do anything, i would do engine diagnostic, aka, static compression and leak down to determine condition. a borescope inspection wouldn't hurt either.
hippysmack on the xlforum has a nice write up on crankcase pressures using a manometer, i used my machine as a test mule for some of that to 6k rpm. it is on the SPORTSTERPEDIA. this carries over into the BT's as well. my readings are not loaded so under load, things will change as cylinder pressures are higher due to fuel burn.
you will find it interesting, the crankcase transitions to a positive pressure @ the 5k range.
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Joined: Sep 2017
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From: Dubuque, IA
do you have a tachometer on the machine?? if so, what are the RPM's at the onset of the issue?? i would do anything, i would do engine diagnostic, aka, static compression and leak down to determine condition. a borescope inspection wouldn't hurt either.
hippysmack on the xlforum has a nice write up on crankcase pressures using a manometer, i used my machine as a test mule for some of that to 6k rpm. it is on the SPORTSTERPEDIA. this carries over into the BT's as well. my readings are not loaded so under load, things will change as cylinder pressures are higher due to fuel burn.
you will find it interesting, the crankcase transitions to a positive pressure @ the 5k range.
hippysmack on the xlforum has a nice write up on crankcase pressures using a manometer, i used my machine as a test mule for some of that to 6k rpm. it is on the SPORTSTERPEDIA. this carries over into the BT's as well. my readings are not loaded so under load, things will change as cylinder pressures are higher due to fuel burn.
you will find it interesting, the crankcase transitions to a positive pressure @ the 5k range.
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