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Cylinder leak down testing

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OK, what am I missing here. Purchased the Harbor Freight cylinder leak down test system. Hooked it up to the first cylinder and followed the test instructions to where it says to open the regulator to adjust the cylinder gage to Zero. OK, I got that. Then it says to read percentage loss on this gage. HUH??? It is of course setting on the zero. What am I missing, seems like you would isolate the air or something then read the gage. I must be a little worse off than I thought or am I supposed to know what the next step is before I read the gage? Zero leak down would be nice but this can't mean anything with the air still supplied. Anybody out there to help the disabled? Thanks, Ray
 
Cylinder leak down tests are a measurement of your cylinder's ability to seal. First of all, you have to have the cylinder being tested while it's positioned at top dead center so that both valves are closed. You should also take the precaution of locking the flywheel so that the engine doesn't turn over when pressure is applied. I suggest using a large wrench on the nut on the end of the crankshaft. With a small gasoline powered engine such as a lawn mower, this can be a real hazard. With a bike engine, it would probably not be dangerous but you're not going to get a usable reading. You then crack open the air to build pressure in the cylinder. Gently use the wrench on the end of the crankshaft to rock it back and forth around the TDC point. The idea is to help the pressure seat the rings for a better seal as would be happening if the bike were running. Then you simply read the second gauge as a percentage of leakage. BTW, you have to start with a warm engine to get the most accurate reading. If you only have a one gauge unit, you have to zero the gauge to the incoming air pressure so that it reads zero. Then when you apply air under the above circumstances, it will read the leakage directly. Let me know if this isn't clear.
P.S. Leak down tests are used in conjunction with cylinder pressure readings to pinpoint the cause of a weak cylinder. If all of your cylinder pressure readings are within 5% of each other, you should also expect your leak down readings to be the same spread. Also, only remove the spark plug from the cylinder being read. By leaving the others in place, you're helping insure that the air pressure won't turn the engine over. You can convert your reading to a percentage directly by using 100# input. If you're using some other input pressure, then you have to do a little math.
Don.

Ghostgs1 said:
OK, what am I missing here. Purchased the Harbor Freight cylinder leak down test system. Hooked it up to the first cylinder and followed the test instructions to where it says to open the regulator to adjust the cylinder gage to Zero. OK, I got that. Then it says to read percentage loss on this gage. HUH??? It is of course setting on the zero. What am I missing, seems like you would isolate the air or something then read the gage. I must be a little worse off than I thought or am I supposed to know what the next step is before I read the gage? Zero leak down would be nice but this can't mean anything with the air still supplied. Anybody out there to help the disabled? Thanks, Ray
Click to expand...
 
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lol,
that bike engine will spit the wrench right into someones skull when a cyl. is pressurized...
DANGER DANGER WILL ROBINSON!
 
Sure it will with three cylinders with plugs in them helping hold the crank in place plus the leverage afforded by the vertical position of the connecting rod on the cylinder being tested. :rolleyes: If you're concerned at all, use a breaker bar and socket and brace it against the floor. Or maybe you think that it will use the leverage of the breaker bar to launch the bike into orbit. :-\\\ I've done leak down tests on everything from V-8's to 1 cylinder lawn mower engines and my skull is still intact. Well, maybe my ex would say that it was fractured to begin with but this is a normal test that is performed all the time by knowledgeable mechanics. Besides, when the cylinder being tested got to the bottom of it's stroke, the exhaust valve would open and make it really, really difficult to continue pressurizing that cylinder.
 
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My question is more of a procedural question, as the instructions are a bit sketchy. I decided to try setting the zero on the tester before connecting to the cylinder and then connecting and checking the gauge readings. On the GS1000 all cylinders were at about 10% and this was on a cold engine, so I am happy with that. On my son's VFR, not so good and the reason for getting the tester, looks like a tear down. Number 1 is very leaky, air blowing out the intake valve, but the others are pretty descent at around 20 percent leakage. I'm thinking I'll just pull the rear head and check it out. Thanks for your help guys. Ray
 
Texas Don said:
Sure it will with three cylinders with plugs in them helping hold the crank in place plus the leverage afforded by the vertical position of the connecting rod on the cylinder being tested. :rolleyes: If you're concerned at all, use a breaker bar and socket and brace it against the floor. Or maybe you think that it will use the leverage of the breaker bar to launch the bike into orbit. :-\\\ I've done leak down tests on everything from V-8's to 1 cylinder lawn mower engines and my skull is still intact. Well, maybe my ex would say that it was fractured to begin with but this is a normal test that is performed all the time by knowledgeable mechanics. Besides, when the cylinder being tested got to the bottom of it's stroke, the exhaust valve would open and make it really, really difficult to continue pressurizing that cylinder.
Click to expand...

most the people on this board are not professionals of the internal combustion engine such as yourself.
when putting 80 PSI in a cyl. at TDC..the engine will spin and if a wrench is on the crankshaft...it will remove itself.
my previous post was a warning to those who attempt a leak down test for the 1st time.;)
 
blowerbike,
Read, learn.
www.motorcycleproject.com/motorcycle/text/leakdown.html
This is not just for pros. If you read my public profile, you would see that I'm in sales, not a professional mechanic. This is basic knowledge for anyone wanting to learn more about how to repair their bike engines. It is not rocket science I assure you. Just basic physics.
 
Texas Don said:
blowerbike,
Read, learn.
www.motorcycleproject.com/motorcycle/text/leakdown.html
This is not just for pros. If you read my public profile, you would see that I'm in sales, not a professional mechanic. This is basic knowledge for anyone wanting to learn more about how to repair their bike engines. It is not rocket science I assure you. Just basic physics.
Click to expand...

i know how to use a leak down tester..
thanks anyways.
 
so who the hell says pressurize it to 80psi??
leak down is leakdown, i though 5-9psi was good enough, all your checking is to see how long it takes to leak down
and that doesnt say whats wrong (rings, piston -cyl clearance too great ,or the valves could be leaking),,its kinda shooting in the dark


i dont get synqing carbs because of these problems as well, your compensating ware ,by opening/closing the butrflies, if parts are wore out theres no fixing them by doing this, i.e. (not enough compression)
it just changes air flow,and wide open is still wide open, flow rates of each carb should be equil,cylinders should be equil, (cc,ing heads)tuned pipes ect... anyone understand what i am thinking?, or is it a magical fix it way to tune bikes:-k
as i havent done this yet, i would need to read more into the process
 
cyclefvr2 said:
so who the hell says pressurize it to 80psi??
leak down is leakdown, i though 5-9psi was good enough, all your checking is to see how long it takes to leak down
and that doesnt say whats wrong (rings, piston -cyl clearance too great ,or the valves could be leaking),,its kinda shooting in the dark


i dont get synqing carbs because of these problems as well, your compensating ware ,by opening/closing the butrflies, if parts are wore out theres no fixing them by doing this, i.e. (not enough compression)
it just changes air flow,and wide open is still wide open, flow rates of each carb should be equil,cylinders should be equil, (cc,ing heads)tuned pipes ect... anyone understand what i am thinking?, or is it a magical fix it way to tune bikes:-k
as i havent done this yet, i would need to read more into the process[/QU

WOW,
ARE YOU SERIOUS:confused:

FYI
the pressure is for creating leaks if you have any and then listening to the crank vent/exhaust/carbs to see where your leaks are.
there is more to this so go read texas dons link and learn.

WTF IS 5 PSI GOING TO DO?

does your engine run on 5psi???
takes around 75psi in a cyl. to make the explosion.
geeeesh!
Click to expand...
 
cyclefvr2 said:
so who the hell says pressurize it to 80psi??
leak down is leakdown, i though 5-9psi was good enough, all your checking is to see how long it takes to leak down
and that doesnt say whats wrong (rings, piston -cyl clearance too great ,or the valves could be leaking),,its kinda shooting in the dark

Holy crap. Did you actually read any of the link that I posted? The pressure differential is instantaneous and 5-9 pounds of pressure is hilarious. It is a test that will tell you exactly what is wrong, if anything. You do actually need to know how to read a pressure gauge, but that isn't too challenging for most folks.
Click to expand...
 
Oh this is getting entertaining....:lol:

200938003.png
 
blowerbike said:
cyclefvr2 said:
so who the hell says pressurize it to 80psi??
leak down is leakdown, i though 5-9psi was good enough, all your checking is to see how long it takes to leak down
and that doesnt say whats wrong (rings, piston -cyl clearance too great ,or the valves could be leaking),,its kinda shooting in the dark


i dont get synqing carbs because of these problems as well, your compensating ware ,by opening/closing the butrflies, if parts are wore out theres no fixing them by doing this, i.e. (not enough compression)
it just changes air flow,and wide open is still wide open, flow rates of each carb should be equil,cylinders should be equil, (cc,ing heads)tuned pipes ect... anyone understand what i am thinking?, or is it a magical fix it way to tune bikes:-k
as i havent done this yet, i would need to read more into the process[/QU

WOW,
ARE YOU SERIOUS:confused:

FYI
the pressure is for creating leaks if you have any and then listening to the crank vent/exhaust/carbs to see where your leaks are.
there is more to this so go read texas dons link and learn.

WTF IS 5 PSI GOING TO DO?

does your engine run on 5psi???
takes around 75psi in a cyl. to make the explosion.
geeeesh!
Click to expand...



no mine is runing on 98 psi, suppose to have 184.5psi, i figure if its leaking -rebuild it,unless its a air boot or o ring,or something simple
Click to expand...
 
Rebuild what? You can't be leaking compression through an air boot unless you have bad intake valve sealing. You will leak compression through the muffler if you have bad exhaust valve sealing. You will leak compression through the oil fill hole if you have bad rings. You will leak compression through an adjacent spark plug hole or out of the engine block/head junction if you have a blown head gasket. A cylinder leak down test will tell you where you are losing compression exactly. You could just have a valve too tight so that it isn't sealing properly, thereby causing your low reading in one cylinder. Wouldn't you prefer a valve adjustment instead of a complete rebuild? Pinpoint the problem before you start throwing parts and money at it.
The link that I provided shows you how to build your own leak down tester for a few bucks. No hobbyist who works on his own bike should be without one in his tool kit. You can actually use a leak down tester to tell you if your valves need adjusting before you remove the valve cover.
Don
 
So if I read some of this info right, the fact that I have 95 psi in one of my cylinders, and 130 is the highest of the four, I have serious issues to contend with?
 
crapwacker said:
So if I read some of this info right, the fact that I have 95 psi in one of my cylinders, and 130 is the highest of the four, I have serious issues to contend with?
Click to expand...

yea theres a small percentage ratio that your allowed to be off in each thats all, or they wont run right,or perform right together,and cause drag ect.. on the other cylinders
 
Well at any rate, I did score 850 jugs and pistons for a swap that will be a winter project. I suspect an exhaust leak in #3, as sync readings there where low, and that is the 95psi cylinder. I'll find out this winter
 
i thought it was just a bad dream..
i had to come back here and read this one more time just to prove it to myself.
OMG,
it was not a dream...
i think ill grab a can of air freshener and go do a link down test..
that should be enough pressure to check my rings and valves and such for leakage.
plussss,
my exhaust aroma will be soooo delightful :lol:
 
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