Going to do a leak down test

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wayne-o
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Going to do a leak down test

#1

Post by wayne-o » Mon Jun 28, 2010 12:43 am

My fornt cylinder is blowing out white smoke out hte pipe so I am going to try a leak down test. Can anyone tell me what kind of air pressure to do this with, and anything else I might need to know? i'm a rookie with motor work. And if i can't find anything there I will try the manifold test, Can I find a tool for the air hook up, to purchace? or can I make one with steel?



steve_wood
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Re: Going to do a leak down test

#2

Post by steve_wood » Mon Jun 28, 2010 12:59 am

Here's an interesting article.

http://www.motorcycleproject.com/motorc ... kdown.html" onclick="window.open(this.href);return false;

But it might be a whole lot easy to head down to the autoparts store and just buy one.

socalrider
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Re: Going to do a leak down test

#3

Post by socalrider » Mon Jun 28, 2010 2:37 am

check your head bolts . make sure they are torqued down
buena suerte,
arnulfo

Dave_R
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Re: Going to do a leak down test

#4

Post by Dave_R » Mon Jun 28, 2010 2:55 am

Whenever mine blew out white smoke it usually indicated a blown head gasket (by the oil passage to the top end).

They are not hard to change.

Use the blue teflon gaskets, not the black paper ones, and definately stay away from the "fire-ring" ones. If you have the "fire ring" gaskets already, then you must use them again, since they probably left thier impression in the heads already.

wayne-o
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Re: Going to do a leak down test

#5

Post by wayne-o » Tue Jun 29, 2010 6:01 am

All the head gaskets Ive seen blown you could hear them right away. I will check it though. I still need to know what air pressure to do the leak down test with. Is it the same as what compression should be?

steve_wood
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Re: Going to do a leak down test

#6

Post by steve_wood » Tue Jun 29, 2010 11:12 am

You can use fairly low pressure. 15 lbs should do it.

pan620
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Re: Going to do a leak down test

#7

Post by pan620 » Wed Jun 30, 2010 1:40 pm

When I do a leak down instead of a compression test I use 100 lbs so the math is easier, you do have a leak down tester dont you??

steve_wood
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Re: Going to do a leak down test

#8

Post by steve_wood » Wed Jun 30, 2010 2:10 pm

Wayne-O:

Just to be clear, when I mentioned 15 lbs, that is for a simple leak down test where you just listen for leaks at the carb, exhaust, rocker cover and timing hole.

If you are using a leak-down tester tool, with dual guages, then go with 100lbs as stated by pan620. It definitely makes the math easier.

By the way, if you're using 100lbs pressure, make sure the piston is at top dead center with both valves closed. Put it into 4th gear and make sure the rear cannot spin. That much pressure will easily send the piston to bottom dead center and you don't want that to happen.

NightShift
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Re: Going to do a leak down test

#9

Post by NightShift » Wed Jun 30, 2010 4:00 pm

Dear Wayne-o,
I have opened up many a motor to find burnt headgaskets that never made a peep.
Headgaskets dont blow themselves by the way, its all about heat caused by something else that makes the head warp.
Of course the heads gotta be flat in the first place!

A squirt of soapy water around the gaskets under the exhaust ports might show some bubbles when you kick her.

R'spectfully,

wayne-o
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Re: Going to do a leak down test

#10

Post by wayne-o » Wed Jun 30, 2010 6:18 pm

Thanks for everones info. I will attempt this leak down test tomarrow and I will ether build a tool or use a compression tool nobody in my town has a leak down tester. A I'm not sure what math I need to know for the 100psi test can someone explain? Also last night I checked my valve ajustment on the pushrods and the front exaust was a little loose could this be part of the issue?

NightShift
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Re: Going to do a leak down test

#11

Post by NightShift » Wed Jun 30, 2010 7:31 pm

wayne-o wrote:Thanks for everones info. I will attempt this leak down test tomarrow and I will ether build a tool or use a compression tool nobody in my town has a leak down tester. A I'm not sure what math I need to know for the 100psi test can someone explain? Also last night I checked my valve ajustment on the pushrods and the front exaust was a little loose could this be part of the issue?
Dear Wayne-0,
A true leak-down test is a calculation that splits hairs. Hey if its broke its broke!
So if just putting some air pressure to it tells you something like where the air escapes, then thats a pretty good answer huh.

Aint it better to shut the barn door before the cows get out? Id start at the manifold and then bump the pressure as I turn the motor to check each combustion chamber with soapy water on the outside.

Wash it off good afterwards.

Seriously,

Bosheff
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Re: Going to do a leak down test

#12

Post by Bosheff » Thu Jul 01, 2010 3:01 pm

While I can certainly appreciate wantin to know what's goin on inside the mill, it sounds to me like yer pickin fly shit outta pepper here. It ain't rocket science. Find TDC. Pump some air into the cylinder. Listen fer leaks. The toughest part of the whole operation is keepin the cylinder at TDC. Put the tranny in 4th and stick a broom handle through the rear spokes if ya have to. The rear brake thing never really worked very well for me. What ever ya do, don't stuff anything in the primary chain to lock the engine. Relatively speaking, the larger the bore size, the more leaking you will have even in a primo engine. No internal combustion engine is 100 percent leak free when it comes to rings and valves. A leakdown tester is not an absolute necessity. All it does is tell ya what percentage of the incoming air that is escaping. If ya pump air in and can't hear the leak, then ya can resort to a more extravagant method of detection. 99 times outta 100, it is obvious where the leak is. Clean the wax outta yer ears and listen up. You should hear the leaking air....bosheff

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