$17 Leak Tester (2-Stroke)

[Faded]

This is a re-post to replace the original that was recently deleted. I apologize if most of you have seen it, but I feel that it is important enough to warrant another posting. . .

I've realized the importance of a leak tester on a 2-stroke for quite some time now, but have always steered away from purchasing one due to the cost (Motion Pro unit = $200). Air leaks will destroy a 2-stroke motor in just a short period of time. It is very important that you make sure that your 2-stroke engine does not suffer from an air leak in order to avoid disastrous and costly engine damage. I would recommend using this tool on suspect motors, after top ends, etc. to preserve the health and well being of your power plant.

After doing some research on the net and getting different ideas on how to make one I finally broke down and bought the required hardware to build my own leak tester. As the title says, my leak tester’s total cost was less than $17.00 (before tax).

The sizes I make reference too are the ones my bike required. You might take the time to measure your intake and exhaust manifold prior to purchasing parts to insure that you are picking up the correct pieces. Also, with this tester there are no provisions for leaks that might occur around the various power valve assemblies out there. My kit was designed primarily for a Honda CR250 so if you have a different bike be prepared to address possible problems that may arise.

Disclaimer: I am not trying to take credit for the design or the idea, I'm just basically passing along the information, giving people an idea for parts, and showing how easy/cheap one can be made. With that said, here you go.


The parts I used are as follows including the price I paid for each:

• 3/4" Pipe Pressure Gauge (used to test natural gas pipes), Home Depot - $12.98
• 3/4" to 3/4" Pipe Coupler, 1-1/2" Long, Home Depot - $0.74
• 1-1/4" Schedule 40 PVC Pipe Cap with 3/4" internal threads, Home Depot - $0.75
• 1-5/8" Expansion Plug, Local Auto Parts store - $2.49

Here is a picture:




When assembling the Pressure Gauge/Coupler/PVC Cap I would recommend the use of some pipe sealant/dope. I had some laying around so I didn't include this in the cost. My carb is a 38mm Mikuni TMX and the PVC fits very snug. I would imagine this would work for most bikes equipped with a 38mm carb. For the exhaust I realize some of the smaller (125cc) bikes might be different. Don't worry, you can get the expansion plugs in 1/8" increments and they expand to 1/8" over there 'listed' size (my 1-5/8" will go up to 1-3/4") and the cost is relatively the same.

Here is another picture with it put together, I've shown the intake and exhaust manifolds so you get the idea of how it's suppose to fit:





After you’ve built your leak tester you’ll need to install in onto your motor. The idea is to pressurize the engine and monitor the loss of pressure over time. It has been recommend that you start with 6psi over a six-minute time period. Ideally your pressure loss should be minimal at most, but if you loose more than 1 psi over a one-minute period, you have a serious problem. While you’re loosing pressure you can trace the leak by squiring WD-40, Windex, etc. over all gasket surfaces and/or other suspect areas. If you see bubbles you’ll know that you’ve found your leak. Good luck.

[Faded]

[EDIT]: The pressure gauge shown goes up to 30psi, I've found that you can get a lower pressure gauge that maxes out at 10 or 15psi and would be better suited for this application. Be sure to look for one of the low(er) pressure ones when doing your shopping.

[IwishIcouldride]

Awesome info faded. I will be making one of these for sure.

[Faded]

Originally posted by IwishIcouldride
Awesome info faded. I will be making one of these for sure.

Glad you like it. I think you'll find that once you have one you'll wonder how you lived with out one.

[CR250oldtimer]

Faded, the pictures will not show up for me.... I'll PM ya for more info!

Thanks

[squizzleboy]

dude ur a genius

[mylesc]

I've built this tester and have used it many times. Thanks again Faded for sharing! On my 97 CR250, I found that I needed to use a 1-7/8" expansion plug instead of the smaller one that Faded is running. 92-01 CR250's will probably all be this size.

Some other differences were that I used a 90 degree elbow 3/4" to 3/4" coupler. This allows me to see the guage easier. I also scrounged an air bulb/pump off an old office chair at work. It allows me to pump it up by hand and not have to use a bicycle pump.

[Faded]

mylesc,

Thanks for the picture! It gives a better visualization and shows the low(er) pressure gauge.

[Roostman]

Great post Faded, as Im (still) working on my top end. I will definately put one of these together and test my motor when finished.

[CR250oldtimer]

Thanks again Faded.

[Faded]

Thank you!

Have fun with it Roostman!

[Woody_393]

Lets make sure this bad boy makes it to the KB this time. Let me know when you want it moved.

[OlSchoolFool393]

Another way to check for a trans leak into crank is drain oil and put in atf it will smoke white if sucking into crank!
and for other leaks spray either around cases and magnito
and moto will rev. if sucking air !
But I'll be building one of these gauges Myself Thanks
Don W.

[Woody_393]

Moved to KB to preserve for future ATM'ers

[RoostRM125]

Originally Posted by mylesc

I've built this tester and have used it many times. Thanks again Faded for sharing! On my 97 CR250, I found that I needed to use a 1-7/8" expansion plug instead of the smaller one that Faded is running. 92-01 CR250's will probably all be this size.

Some other differences were that I used a 90 degree elbow 3/4" to 3/4" coupler. This allows me to see the guage easier. I also scrounged an air bulb/pump off an old office chair at work. It allows me to pump it up by hand and not have to use a bicycle pump.

Does anyone have a picture or tell me where the leak tester mounts to the carb?

[mylesc]

You take the carb off and put the leakdown tester in its place

Here's a full article on how to do it: [Only registered and activated users can see links. ]

[acw592]

Faded, sorry for the stupid question, but I'm wondering how to pressurize the motor. I'm not sure where to pick up one of the bulbs shown in the lower pic and the pics you had with yours did not show up. Are you putting a shrader valve in the tester somewhere and the pressurizing with a bike pump? Thanks

[TUK101]

Thanks for the info. The picture is not showing up for me though.

[YeloBlammo]

No pics for me either?

[frosti108]

NICE. this is very similar to what we use for boost leaks on our turbo cars. just a pvc cap with an air nozzle jb welded onto it haha