SeX Viper
Member
So I did a leak down test on my viper with 8000 miles last night and it was holding 98 of 100 psi on all 3 cylinders. I kind of expected it to fail based on the reading I have done on this site since I have never re ringed it. I do use Yamalube and am really good about warming it up though. I built my own tester which I researched quit a bit online and am fairly confident that I did everything correctly. However you can hear air coming out of the exhaust and also feel the pressure build up if you put your hand over it so now I am second guessing everything. Is this normal or do I need to re ring and re think my home made tester? Sorry for starting two threads in a row but I have found from past experience that if you ask two different questons at the same time only one tends to get answered.
super1c
Super Moderator
http://www.totallyamaha.com/snowmob... down test/How to Cylinder Leak down test.htm Here is a post from daman. SHould help to see if your doing anything wrong.
if you can hear air or feel air coming out the exh then it has leak down indicating rings need changed. When you do a leak down you apply the pressure to the cylinder with it locked at tdc or at least with the exh. port closed 100%, apply the air then watch the guage, ((you shut off the air supply)), so your monitoring the intial 100lbs applied to the cylinder.
09nytro
New member
100psi is pretty high isn't it....
bluewho
Active member
09nytro said:
Not at all if you look at running compression on a srx at 115 to 120 ?
.
mile9c1
New member
If you can hear air coming out then it probably isn't holding 98psi. You turned off the supply side air, right? What's your compression on each cylinder, using a compression tester?
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SeX Viper
Member
Logic told me to turn the air supply off but in all of the reading I did, including daman's write up in the tech section, it never tells you to. So no I did not turn the air supply off. I do have over 100 psi compression but as it has been stated many times before that only tells part of the story. I will plan ordering up new rings and gaskets so it is ready for next winter. I would do the test again but my clutch is also off for a rebuild so I have no way to hold the crank. Based on how much air I could feel coming out of the exhaust I am sure it would fail.
mile9c1
New member
I'm guessing the fancy testers have a knob which closes off the supply side air, after the cylinder is filled. I just ordered one after reading this thread so I'll know soon. Anyway with 8,000 miles, why aren't you replacing the pistons too? I'd at least measure them while they're out.
SeX Viper
Member
Not that I am on a budget but I guess I didn't know where to draw the line on what to replace. I think I will take your advice and measure the pistons when I take it apart before I decide to replace them or not. Keep me posted on the tester when you get it, I am curious as to what you find out. Out of the 3 different home made ones I found online non of them included a valve to shut off the air supply but I could easily add one to mine.
staggs65
Moderator
the leak down testers you buy do not come with a shut-off. The first gauge will be regulated pressure and the second will read in percentages of the first gauge so you dont have to do the math. I havent read the link to Damans thread from above but if it's a home-made tester you most certainly have to do the math to determine the percentage loss between the gauges. The key as Mrviper said is you need to lock each cyl at TDC.
mile9c1
New member
SeX Viper said:
Staggs is correct, the gages don't have a shutoff. Mine came in and that knob is actually a pressure regualtor. So, 98% seems to indicate your rings are in excellent condition
Maybe sleds are different but I've seen a few dirtbike pistons crack with fewer hours on them. This is why IMO I'd replace the pistons too since it's almost no extra work on top of a ring change.
hmmm some of them DO indeed have a shut off like mine does, depends on what model you get, how good of one you buy. You need to monitor how much of the inital 100lbs you lose from the cylinder, not how much air is going in. I see on evil bay the cheaper ones just have a regulator in front.
Any of them(leak down testers) can give you an idea if you need rings. The cheap ones will still do a much better job then any compression tester does because its how good the pressure is "captive" not so much how fast it can build it as to the condition of the rings. Rings lose tension over time with the heat cycling.
Yamaha srx and vipers use a powder forged piston, they tend to last quite some time with regular ring changes. The sx,sxr motors used a cast piston that wears a little more quickly. I would measure out your skirts and compare to spec and then see if you need to replace them.
Any of them(leak down testers) can give you an idea if you need rings. The cheap ones will still do a much better job then any compression tester does because its how good the pressure is "captive" not so much how fast it can build it as to the condition of the rings. Rings lose tension over time with the heat cycling.
Yamaha srx and vipers use a powder forged piston, they tend to last quite some time with regular ring changes. The sx,sxr motors used a cast piston that wears a little more quickly. I would measure out your skirts and compare to spec and then see if you need to replace them.
