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Author Topic: Need Ideas For Home Made Pressure Tester,  (Read 5461 times)

Offline GrkGuy

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Re: Need Ideas For Home Made Pressure Tester,
« Reply #25 on: December 20, 2012, 06:25:23 pm »
thanks for the pic mitch, now i am gonna go look at it again.
matt send me those o rings. lol
life's journey is not to arrive at the grave safely in a well preserved body, but rather to skid in sidays totally worn out shouting "HOLY SH*T...WHAT A RIDE!"

Offline Deebo

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Re: Need Ideas For Home Made Pressure Tester,
« Reply #26 on: December 20, 2012, 06:29:34 pm »
I'll have to get to the shop and look for them. Give me a day or so.

Offline GrkGuy

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Re: Need Ideas For Home Made Pressure Tester,
« Reply #27 on: December 21, 2012, 12:15:17 am »
Matt lmk what i owe you, and can you get a few more sets of them. i might
as well have some spares. thanks
life's journey is not to arrive at the grave safely in a well preserved body, but rather to skid in sidays totally worn out shouting "HOLY SH*T...WHAT A RIDE!"

Offline MotorGeek - Jerry Hall

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Re: Need Ideas For Home Made Pressure Tester,
« Reply #28 on: December 21, 2012, 09:01:03 am »
JH, what Do you do to prevent the exhaust valve from leaking? Recommendations on how long a motor should hold air pressure?

I use a inflatable bladder that goes into the exhaust port upstream of the power valve.  Checking engines with power valves is a real pain. 

Pressure checking helps find leaks that are due to cracks and leaking gaskets.   Pressure is not a good test for crank seals if you are experiencing a lean condition.  A vacuum test is what is necessary to test the lip on the crank seal that controls leaks that cause a lean condition.

I generally use pressure and vacuum test for diagnostics before tear down not after rebuilding an engine. With enough experience, you learn where to look and correct the problem areas before assembly.

An air leak that is bad enough to cause a lean condition at and idle or high-RPM closed throttle deceleration will usually need to be around a 3  to 5 psi or more per minute leak.  The TM 38 carburetors that are bored to more than 41.5 will usually have what is comparable to a leak that is much worse than a 3 to 5 psi air leak due to bad gasket or crank seal.

A small air leak will have little effect on the air fuel mixture at full throttle.  Air leaks, worn out slide bores and overbored carbs cause the most problems at partial and closed throttle operation.



Offline MD2smoker

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Re: Need Ideas For Home Made Pressure Tester,
« Reply #29 on: December 21, 2012, 09:20:25 am »
How deep of a vacuum and how long should it hold? I have a 7 cfm vacuum pump and a micron guage, hoses, etc for hvac work.

Offline Derrik

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Re: Need Ideas For Home Made Pressure Tester,
« Reply #30 on: December 21, 2012, 12:21:37 pm »
dang,so it looks like i need to build a vacuum setup now -_-
great info tho,im learning so much!!! :D

Offline GrkGuy

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Re: Need Ideas For Home Made Pressure Tester,
« Reply #31 on: December 21, 2012, 01:52:14 pm »
ok so looks like i will need a vac tester now.
what is a good one to get, not looking to spend a bunch of money on one.
just need to test a motor maybe every year or so. will a brake bleeder
work good euough.
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Offline MD2smoker

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Re: Need Ideas For Home Made Pressure Tester,
« Reply #32 on: December 21, 2012, 09:48:54 pm »
I imagine that my hvac vacuum pump and micron gauge setup is overkill. We use these for pulling deeeep vacuum to evaporate any water molocules inside an AC system before we put refrigerant into it. What is probably necessary is a vacuum gauge used to test automotive vacuum systems... Something that measures in inches of water column.. Not microns.
If I hooked one of my pumps to a tight engine, it would probably damage the suction lip on the crank bearing seals.
Hopefully a builder on here can clear this up.
How many inches of vac. And for how long? I would like to know for my current rebuild.

Offline Derrik

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Re: Need Ideas For Home Made Pressure Tester,
« Reply #33 on: December 22, 2012, 12:09:57 am »
also more ideas on where to get these pumps and gauges at please =]
cheapest route possible!
i have to much money going out in parts -_-

Offline WestTexasKing

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Re: Need Ideas For Home Made Pressure Tester,
« Reply #34 on: December 22, 2012, 04:21:35 am »
One option to consider when building a tester is that you don't have to install the hose barb on the intake plug.
Take an old spark plug and weld a 90 deg pipe thread elbow where the spark plug turns into steel (break all of the porcelain insulation off so it's a clear shot into the engine), then screw on a steel hose barb (or quick connect if you have a good air seal in there).
Install the stubby spark plug adapter, hook up hose, and plug the other openings.

A bonus to this method is that you can also use the same plug adapter for a compression tester.
I use a similar method for differential compression tests on my radial, except that I welded 9 plugs up by installing a quick connect on the ends of every one of them.
It's important to check compression while the engine is hot, and as you could imagine removing all 9 plugs, then installing and removing an adapter for each cylinder can cause the engine to cool off before you're done.
Had the same idea for my hybrid, but I realized that there would be clearance issues with the straight plug and hose so I welded mine up with a 90.
Works great with the limited clearance!

Offline GrkGuy

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Re: Need Ideas For Home Made Pressure Tester,
« Reply #35 on: December 27, 2012, 12:12:43 pm »
would a brake vacuum tester be fine for doing the test. i found some that are pressuer tester and a vacuum tester.
life's journey is not to arrive at the grave safely in a well preserved body, but rather to skid in sidays totally worn out shouting "HOLY SH*T...WHAT A RIDE!"

Offline Iceracer

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Re: Need Ideas For Home Made Pressure Tester,
« Reply #36 on: December 27, 2012, 01:38:36 pm »
When I Pressure test an engine I use a sheet of rubber under the exhaust spigot with three holes punched for the ex studs and snug up the bolts. I have a aluminum bung I made for the carb side. I pressurize it with a harbor freight radiator tester and an adaptor I made for the spark plug. you can use anything to pressurize the cylinder, I use to use a old squeeze bulb and gauge from a blood pressure cup. just be sure the ports are open or it will take a minute to stabilize a reading if all the air has to pass the rings.

Offline Derrik

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Re: Need Ideas For Home Made Pressure Tester,
« Reply #37 on: January 27, 2013, 02:50:34 am »
so it crossed my mind a while ago but i figured i would ask a question that may be obvious to the seasoned builder.
since it is recommended to test an engine at "operating temp" so the operating clearances are achieved,do you just ride the bike and nascar pit crew the damn thing while its hot to install the plugs and pressure/vacume fitting so its as close to operating temp as possible?? or is the whole operating temp thing only important for compression checks?

Offline WestTexasKing

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Re: Need Ideas For Home Made Pressure Tester,
« Reply #38 on: January 27, 2013, 03:16:28 am »
It's important for compression testing, the rings seal better when they're hot and a fresh coat of oil.
Leak down tests, I'd say it would give you more accurate data, since clearances, seals, and gaskets change dimensions with heat.
The problem is getting it set up for a leak down test while everything is hot, and completing the task before it gets cold.
Most everyone checks the engine cold with a pressure tester, but there is a way to test for leaks while the engine is idling.
Take some starting fluid and spray it over every possible sealing surface (gaskets, seals, etc.), individually, and being cautious about the possibility of a fire hazard.
Anyway, if there's a leak on the base gasket or reed cage, spraying starting fluid over the leak will cause the engine to run rich and sputter at a reduced RPM.
Usually only good for a quick troubleshoot, or if the problem only arises when the engine is hot.

Offline Derrik

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Re: Need Ideas For Home Made Pressure Tester,
« Reply #39 on: January 27, 2013, 04:51:12 pm »
ive been using the chit out of that carb cleaner while idle method for years with cars and trucks to find vacuum leaks!!
thanks for the info

Offline Frank

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Re: Need Ideas For Home Made Pressure Tester,
« Reply #40 on: May 25, 2013, 10:14:39 am »
I think 3 - 5 minutes. but if the motor is leaking, it will show immediately on air pressure (watch the gauge when inflating) but not more than 5 bar inflate otherwise you hit with the resulting pressure from the seals around your sleeves. then you can fully open the engine again. all the best Frank
 D?
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Offline Frank

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Re: Need Ideas For Home Made Pressure Tester,
« Reply #41 on: May 25, 2013, 10:17:55 am »
Ok +k2
under-steers is when you see the tree the goes in. overrides is when you hear the tree which you were going on.
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Offline Jzilla

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Re: Need Ideas For Home Made Pressure Tester,
« Reply #42 on: July 04, 2013, 03:35:20 pm »
This is a really nice guage, it also has a schrader valve. You can just use a bike pump, I made a tester for under $25.

http://www.ebay.com/itm/350311871137?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649


Offline MotorGeek - Jerry Hall

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Re: Need Ideas For Home Made Pressure Tester,
« Reply #43 on: July 05, 2013, 08:42:40 am »
JH, what Do you use to prevent the exhaust valve from leaking? Recommendations on how long a motor should hold air pressure?

You can get a rubber bladder at a plumbing supply store that can be inserted into the exhaust port between the piston and power valve hole in the bottom of the port.  The carbon will have to be removed from the port or the bladder may not seal when inflated.

Zero leakage is ideal but a few psi per minute will not usually cause enough of an air leak to cause the engine to run lean.  Do not put over 10 psi into the crank case.

Offline All American

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Re: Need Ideas For Home Made Pressure Tester,
« Reply #44 on: November 06, 2017, 12:54:38 pm »
What happens if you put in more than 10 p.s.i. Into the crankcase?
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Offline MotorGeek - Jerry Hall

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Re: Need Ideas For Home Made Pressure Tester,
« Reply #45 on: November 09, 2017, 12:25:13 pm »
What happens if you put in more than 10 p.s.i. Into the crankcase?

It could possibly push the crank seals out of the cases if the seal was not installed correctly or the crank seal bore is loose or damaged.  The crank case can experience around 20 PSIG in a healthy highly developed two stroke. 

A pressure check will show a leaking gasket or crack in the cases or cylinder.  A pressure check will NOT always show a leaking crank seal.  For a crank seal that has worn pressure lips, more pressure will make the seal lips grip the crank "tighter" and leak less.

There are two lips in a crank seal.  One lip is made to hold pressure and the other lip is made to hold vacuum.  If the pressure lip leaks, it just causes a slight loss in power.  If the vacuum lip leaks it causes a lean condition and or it will suck oil from the transmission. 

Pressure checking a two stroke engine will not usually tell you if the vacuum lip is holding or leaking.  It is not usually necessary to pressure check an engine that has a leaking vacuum lip.  The engine will exhibit lean symptoms by having the ring-ding-dings on deceleration, high RPM idle and or acts like it is running out of fuel. If the pilot jet is not restricted and the correct size, the engine probably has some type of air leak.

Engines that have experienced a broken piston skirt, often have damaged cases and will leak air.  Engines that have had welding done on the cases will often leak air.  Engines that have had a big end bearing failure will often have case damage and leak air.

Pressure checking an engine is a diagnostic tool that we seldom have to use.  It will not hurt the engine but can be time consuming especially on the engines that have power valve systems. 

 

 

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