logo
Thread Tools
Old 08-27-2019, 05:26 PM
highonthai is offline
Find More Posts by highonthai
Registered User
highonthai's Avatar
United States, CA, Los Angeles
Joined Feb 2014
203 Posts
Mini-HowTo
Gas engine "LEAK DOWN" testing

LEAKDOWN TEST

Wondering why you canít get your engine to idle correctly? Engine running lean? Youíre sure you have checked everything and still canít figure it out?

Well you probably have an air leak somewhere.

How do I find out if I have an air leak thatís effecting my engines performance?

Well, the best way to figure out if your two-stroke RC airplane engine has an air leak. Test it!

These leaks include anything coming from the crank seals,cylinder head gasket, base gasket, the spark plug threads, intake manifold, or exhaust manifold. No matter where these air leaks originate, they affect the performance of your engine, making the engine difficult to tune, and are not normal for a healthy engine and will eventually end up costing you your engine if not the whole plane.

Performing a leak down test is the best method for determining if and where air leaks are coming from. A leak down test is fairly simple to perform test (if you have the right equipment) and can provide tremendous amounts of information about the health of an engine.
I typically like to perform a leak down test on an engine if Iím having trouble tuning the engine consistently, if Iíve bought a used engine with a suspect past history,or when Iím finishing up assembling a new engine.
The biggest mistake I see allot of people make is when they rebuild an engine with new parts and skip the leak down test. I cannot count the number of times where I have rebuilt an engine with new parts and then performed a leak down test to find a gasket that was not sealing properly or another part that was causing a problem.
The leak down test is imperative and ultimately becomes a form of cheap insurance against the time and money that has gone into the build...


Highpoint 2 Stroke Engine Leak Down Test.
Pressure testing is a test performed on a two-stroke engine to ensure that the engine has no air leaks. An air leak in a two-stroke engine can cause a lean condition in engine fuel-air mixture. This in turn can result in engine overheating, piston seizure, detonation, hard starting, erratic idle, etc.

WARNING!
Donít not use an air compressor.
Wear eye protection to prevent eye injury from escaping gas and/or flying particles. We recommend that a qualified mechanic in a properly equipped shop perform this procedure.

1. To perform a leak down test on the engine: cylinder, head, reed cage, intake manifold and spark plug must all be installed and torque correctly. Exhaust pipe and carburetor must be removed.

2. Seal the exhaust ports with the correct size block off plate and rubber gasket.
3. Seal the correct size carburetor adapter block off plate.
4. Attach the hose (from the pump/ gauge assembly) into the Schrader valve.

5. With all test equipment in place and the piston at bottom dead center, use the hand pump to pump 6 PSI of air pressure into engine. Never exceed 8 PSI of air pressure or damage to the seals and/or engine may occur. If loss of air pressure occurs, spray soapy water over mating surfaces to see where soap bubbles appear. Repair any leaks that may appear and redo test. A leakage rate of 1 PSI per minute is acceptable; however the lower the leakage rate the better your engine will perform.
Leak down kits are available at highpoint/pro tune stick https://protunestick.ecwid.com

Scott
High point / pro tune stick
highonthai is offline Find More Posts by highonthai
Last edited by highonthai; 08-27-2019 at 06:05 PM.
Reply With Quote Quick reply to this message
Sign up now
to remove ads between posts
Old 08-27-2019, 06:17 PM
Truckracer is offline
Find More Posts by Truckracer
Registered User
Des Moines, Iowa USA
Joined Nov 2007
4,787 Posts
One of those tools that might be rarely used but nothing will replace it when it is needed. Have you thought about adding a couple of accessories so you could also use it as a carb pop off tester?
Truckracer is offline Find More Posts by Truckracer
Reply With Quote Quick reply to this message
Old 08-27-2019, 06:35 PM
highonthai is offline
Find More Posts by highonthai
Registered User
highonthai's Avatar
United States, CA, Los Angeles
Joined Feb 2014
203 Posts
Quote:
Originally Posted by Truckracer View Post
One of those tools that might be rarely used but nothing will replace it when it is needed. Have you thought about adding a couple of accessories so you could also use it as a carb pop off tester?
Truckracer,
This is one of those tools that until you use it, you didn't know you needed it. (if that makes sense?)
But without it, how would you know if you have a leak?
You wouldn't. That is why all my engines are tested frequently during maintenance.
I prefer to be proactive and when you have many engines it sure gets allot of use.
This is nothing new, leak down testing has been around the motorcycle scene forever.

The carburetor pop off test can be done with any low pressure air gauge and a piece of fuel line. Not much to make in accessories for that.

Thanks for the input,
Scott
highonthai is offline Find More Posts by highonthai
Last edited by highonthai; 08-27-2019 at 07:37 PM.
Reply With Quote Quick reply to this message
Old 08-27-2019, 08:48 PM
Truckracer is offline
Find More Posts by Truckracer
Registered User
Des Moines, Iowa USA
Joined Nov 2007
4,787 Posts
I completely understand the value of this tool because I’ve had to fabricate cover plates before when I wanted to do some pressure testing on a used engine. Your tool would have been a blessing then. By the way, the Brison engine being tested had major internal main bearing seal leaks.
Truckracer is offline Find More Posts by Truckracer
Reply With Quote Quick reply to this message
Old 10-13-2019, 07:58 PM
SMOKINMAC is offline
Find More Posts by SMOKINMAC
3W + Smoke !
SMOKINMAC's Avatar
United States, KY, Albany
Joined Mar 2011
104 Posts
Leak Down Testing - 3W 220

LEAK DOWN TESTING - Very Valuable.

I recently purchased a 3W 220 that was sent to the ďGĒ man for service by the original owner who in communications to me stated he had had nothing but problems with the engine, i.e. Hard to start, inconsistent tuning, hard to tune. So he sent it in for service. He expressed an interest in selling the engine, and based on some minor Carb diaphragm replacements and test runs the ďGĒ man assured me the engine was 100% So based on his seal of approval I negotiated a deal with the Owner and purchased the engine.

When I received the engine I mounted it to my Machined Engine test Mount and I experienced the same issues the Original Owner had experienced. So having Machine tools, I machined Exhaust Plates, and custom Air Manifolds to bolt on in place of the CARBS. Note I used a Lab Quality Low Pressure Regulator that only goes up to 3PSI, Set At Just over 1PSI when applying Air to the Shrader valve on the Air Manifold.

Findings:


1. Significant leak around the Front bearing Race.
2. Front 2 Bearings were the Wrong Bearings, they were Metal Shielded, not SEALED bearings.
3. Leak Between Front Bearing Housing and Crankcase.
4. Leak in two locations of rear Cylinder Gasket.
All leaks detected at only 1.3 PSI. Never could perform Leak down test due to severity of these leaks.
Pictures attached. I have videos of the Leaks, but you canít upload videos here. I didnít take pics of each leak, so I only could upload the Front housing leak for now.


NOTE: ENGINE is still under warranty and I am working with the ďGĒ man to work with 3W to resolve these issues. I have sent him picís and videos so he could compile and send to 3W. I should hear back this week.

Note: The rear cylinder gasket leak would not be possible to see without the Testing.

I am confident all these issues can be corrected and Iím sure when they are the engine will perform as it should
SMOKINMAC is offline Find More Posts by SMOKINMAC
Last edited by SMOKINMAC; 10-13-2019 at 08:09 PM.
Reply With Quote Quick reply to this message
Old 10-14-2019, 08:54 AM
highonthai is offline
Find More Posts by highonthai
Registered User
highonthai's Avatar
United States, CA, Los Angeles
Joined Feb 2014
203 Posts
Smokinmac,
Nice write up. It will be interesting to hear about the outcome. I'm always surprised that not enough people take the time to thoroughly check their engines
Keep us posted.
highonthai is offline Find More Posts by highonthai
Reply With Quote Quick reply to this message
Old 10-14-2019, 10:29 AM
closetguy is offline
Find More Posts by closetguy
Registered User
United States, OH, Berlin Heights
Joined Jul 2006
4,864 Posts
So for a leak down test how much pressure do you use.
closetguy is offline Find More Posts by closetguy
Reply With Quote Quick reply to this message
Old 10-14-2019, 02:27 PM
SMOKINMAC is offline
Find More Posts by SMOKINMAC
3W + Smoke !
SMOKINMAC's Avatar
United States, KY, Albany
Joined Mar 2011
104 Posts
The Author of this Thread sells a Leak Down Test Kit and recommends 6PSI and then measure the rate of leak down which should not exceed 1PSI/minute.
SMOKINMAC is offline Find More Posts by SMOKINMAC
Reply With Quote Quick reply to this message
Old 10-14-2019, 02:29 PM
SMOKINMAC is offline
Find More Posts by SMOKINMAC
3W + Smoke !
SMOKINMAC's Avatar
United States, KY, Albany
Joined Mar 2011
104 Posts
Highonthai, Will do, I hope to hear from the ďGĒ man this week.

AS OF 10-23-19, STILL NO RESPONSE FROM GERHARD.

10-31-19:
Just got off the phone with Gerhard with Aircraft International. The reason this has taken a while is I had asked that the crankcase be replaced due to some significant casting voids in 4 locations and another area that had a fair amount of porosity. Gerhard told me the crankcase is being replaced under a ďClaimĒ not under warranty and it took awhile for him to get 3W to agree to this.

It will be a few weeks before the new crankcase arrives, but after I receive it and assemble the engine with the new case and proper bearings and sealants I will repeat the Leak Down Test and if successful will do a test run of the engine and will post the final results.
I would anticipate this will occur towards the end of Nov
SMOKINMAC is offline Find More Posts by SMOKINMAC
Last edited by SMOKINMAC; 11-08-2019 at 11:28 AM. Reason: UPDATE
Reply With Quote Quick reply to this message
Old 10-14-2019, 04:46 PM
closetguy is offline
Find More Posts by closetguy
Registered User
United States, OH, Berlin Heights
Joined Jul 2006
4,864 Posts
Quote:
Originally Posted by SMOKINMAC View Post
The Author of this Thread sells a Leak Down Test Kit and recommends 6PSI and then measure the rate of leak down which should not exceed 1PSI/minute.
Thanks for the info.
closetguy is offline Find More Posts by closetguy
Reply With Quote Quick reply to this message
Old 10-31-2019, 12:46 PM
SMOKINMAC is offline
Find More Posts by SMOKINMAC
3W + Smoke !
SMOKINMAC's Avatar
United States, KY, Albany
Joined Mar 2011
104 Posts
See post above for update.
SMOKINMAC is offline Find More Posts by SMOKINMAC
Last edited by SMOKINMAC; 11-08-2019 at 11:25 AM. Reason: grammar
Reply With Quote Quick reply to this message
Old 11-01-2019, 10:34 AM
rooman is offline
Find More Posts by rooman
They're get'n lower mate.....
rooman's Avatar
United States, TX, Houston
Joined Nov 2006
3,106 Posts
If the engine is still under warranty as you say - send it back for replacement rather than go thru all the case exchange and new bearing crap .....
rooman is offline Find More Posts by rooman
Reply With Quote Quick reply to this message
Old 11-01-2019, 04:49 PM
SMOKINMAC is offline
Find More Posts by SMOKINMAC
3W + Smoke !
SMOKINMAC's Avatar
United States, KY, Albany
Joined Mar 2011
104 Posts
Quote:
Originally Posted by rooman View Post
If the engine is still under warranty as you say - send it back for replacement rather than go thru all the case exchange and new bearing crap .....
Thanks Rooman but round trip shipping would be about $136 dollars. Plus today I disassembled the engine and it was not difficult, plus it allowed me to closely examine the pistons, cylinders, etc. which as I expected are like new, showing no signs of wear. And finally, I want to be sure its assembled using the correct cylindrical bearing race retaining compound (Loctite 680) and crankcase sealants (Reinzosil 200 & 300) and then let everything cure for 24 hours before performing the Leak Down Test. With my machine shop and tools this is really not a difficult task and when Iím done I know it will be 100% !!!

And if you mean have them replace the engine, I had discussed that with Gerhard and he said 3W would not agree to that because the engine is basically still new and the only issue was the quality of the crankcase casting and the wrong front 2 bearings that were installed by a different service center when a new crankshaft was installed under warranty. Once the crankcase is replaced and the correct 2 front bearings installed this will basically be a new engine because the original owner due to the various issues never was able to run it.
SMOKINMAC is offline Find More Posts by SMOKINMAC
Reply With Quote Quick reply to this message
Old 11-02-2019, 06:24 AM
rooman is offline
Find More Posts by rooman
They're get'n lower mate.....
rooman's Avatar
United States, TX, Houston
Joined Nov 2006
3,106 Posts
That be the case , the G man should have taken care / charge of the whole situation to guaranty 3W quality (JMO)
It may pay to check flatness of the new case faces by lapping the mating surfaces , if not flat possible area to leak thus causing the lean affect

Keep us informed of the rebuild and final leak down data

May the 3W god's be with you
rooman is offline Find More Posts by rooman
Reply With Quote Quick reply to this message
Old 11-02-2019, 08:02 AM
SMOKINMAC is offline
Find More Posts by SMOKINMAC
3W + Smoke !
SMOKINMAC's Avatar
United States, KY, Albany
Joined Mar 2011
104 Posts
Quote:
Originally Posted by rooman View Post
That be the case , the G man should have taken care / charge of the whole situation to guaranty 3W quality (JMO)
It may pay to check flatness of the new case faces by lapping the mating surfaces , if not flat possible area to leak thus causing the lean affect

Keep us informed of the rebuild and final leak down data

May the 3W god's be with you
Rooman, Regarding mating surfaces Flatness, I had been thinking the same thing.
Check out the attached photo of the old case and the referenced areas. There was a leak at those locations at the cylinder gasket. There is a slight depression in those areas. Perhaps the mold plug that creates the cast form is damaged. But to your point Iím a little surprised that the mating surfaces of these castings are not machined as a secondary operation. The Cylinder mating surfaces look like they are. Anyway yours is a good suggestion.
AJ aircraft has a Youtube video showing how he creates flatness of muffler surfaces when installing mufflers:
RCTEK Episode #9 Muffler installation (14 min 52 sec)


Based on what I am seeing though, I will definitely closely inspect the new casting.

Will be updating hopefully in 3-4 weeks.
SMOKINMAC is offline Find More Posts by SMOKINMAC
Reply With Quote Quick reply to this message


Quick Reply
Message:


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools