How To Perform a Leak Down Test on a 4-Stroke Motorcycle

[@user-mj6fe5jf9z]

Good video. I have been doing leak downs for years to decide the health of my engines. One thing that I have found is when the engine is set at DTC on compression you may get a false reading because of the auto decomp. holding an exhaust valve open. This may lead you to believe the E. valves are not seating. Rotating the engine just past DTC will deactivate that auto decomp. As mentioned it is easier if the valve cover is off. That way you can see that the valves are all closed with no cam/auto decomp. contact on the valve. The other option is to deactivate the auto decomp at DTC at the cam with a wire or something that works on your model. This will let the E. valve seat.

[@jcaashby]

Solid Tip!!

[@davidb9323]

Does leakdown require you to take the engine out of the frame ?

[@ryanlester761]

No it does not, as shown in the video.@@davidb9323

[@desertrider325]

Good video. That dude was definitely nervous as hell tho lol. He did a great job. And the thought of looking at the engine as an air pump was a new way of thinking which I like. Good stuff guys.

[@sendit1158]

New way of thinking? We have been saying an engine is a air pump for 30 yrs

[@brucebanner2039]

😂😂 definitely not a new way of thinking

[@tomw3215]

I just bought a motion pro leak down tester today, in my hands, thanks for the video , I will come back for more videos if you make them

[@GNX157]

Your best benefit for this tool is to use it on a brand new bike or engine or after every rebuild and then at regular intervals thereafter. Keep a record and you can track the health of your engine better. Also whenever you have a question on performance or power dropping off, you can immediately do a leak down to see if it’s engine health or some other component, before you start chasing the tune, plugs, jetting etc.

[@zakcourt7419]

Thank you guys at Rocky mountain atv mc, these are great videos you do they have really come in handy for me and this leak down test was very well explained and strait forward, I am looking forward to the next videos👍👍

[@tracyenlow8344]

Most leak down test rigs use two gauges. This Motion Pro and a few others just use one gauge. Is one set up better than the other?

[@beatbeat4378]

Would you be able to identify if it was just valve seals?

[@jcaashby3]

THX. The instructions were a little hard to gauge. Wish it had pictures with it lol :)

[@nalyd6386]

Hello, thinking about buying a MT-324 snap on leak down tester from eBay, planning to do a leak down test on my 2008 Crf250r. I’m not sure what size the adaptor is that come with it, are they universal or will I possibly have to buy a new adaptor hose? Thanks!

[@gs8282]

Good video . But how to know if my atv engine has compression leak?

[@MrMrsregor]

if it doesn't hold pressure, is has a leak

[@davidb9323]

What bike is that ? My Husaberg has everything possible in the way of the spark plug hole.

[@rmatvmc]

This bike is a Yamaha YZ250F.

[@davidb9323]

@@rmatvmc Thanks, I used this video to determine my compression was about 50psi after quite the struggle pulling out the plug with the frame in the way. I’m puzzled because my 350 still runs. I was afraid to screw the adapter too tight because I would then never get it out but I didn’t feel any pressure escape. Definitely will be doing a top end.

[@cachepilll286]

2 stroke video plz

[@justbraaapit2311]

Would bad oil seals cause low compression?

[@justbraaapit2311]

Because I have a 94 dr125se and I did a leak down test and im getting air from the stator side so to me its gotta be a oil seal. First I put new rings in it and it went from 125psi to 140psi. And when I had it apart the valves looked good and clean and didn't leak when I did the test. All ne gaskets and o rings to

[@MrStroker408]

No. Oil seals just prevent oil from running down the valve stems and entering the combustion chamber. The valves themselves seal off the combustion chamber and if they aren't sealing you will lose compression. Worn piston and rings are the other main culprit. If you were getting pressure in the crankcase on a 4 stroke motor the ring seal is probably bad. The leaky seal itself shouldn't cause a loss of compression on a 4 stroke.

[@daddy5225]

I believe you are supposed to so the leaksown test on a engine that is up to running temperature, not from cold.

[@daveyt4802]

Crank vent, rings. Exhaust, exhaust valves. Intake, intake valves. Coolant bubbles, head gasket. Wondering if my cheapo HF leak tester is even worth it.

[@CaptainTimA]

I see a Maddox at HF for more than a quality OTC one. Check out an OTC! Love mine, laess than $80.

[@96joe]

Awesome... great video

[@motorcyclebettereveryday2373]

very cool video💪 thank you

[@kawasakijim9695]

How do u know what is wrong if you have compression but lose it on kick start

[@mrwildman2607]

When you kick start it does it not give you any resistance. If so, you could be missing some of the gear spacers or retention clips. Its possible for some of the gears to slip out if their place and not transfer the power onwoards.

[@mrwildman2607]

Your kickstarter can also be slipping on its rod. Maybe you're missing a gear. Who knows. 🤷‍♂️

[@kawasakijim9695]

It's a come and go compression wen I put a new plug in is wen I lost compression

[@kawasakijim9695]

Wen I pulled the motor apart the rings were stuck to the piston

[@mrwildman2607]

@@kawasakijim9695 Then maybe you've found your problem. change the piston rings. They have to be tight agains the cylinder to get compression. The sparkpluggs also have washers that need to be tightened hard so they expand and keep a tight seal. And og course you need a good head gasket.

[@Drain09]

We need a motion pro 2 stroke leak down test video next. @rockymountainatvmc

[@HybridEdits]

Do one on a 2 stroke next.

[@kawilifezx10r23]

No do it on my bike next for free

[@stoplogicmotorsports]

Pretty much same thing except you need to have a way to plug your exhaust at the engine.

[@seanottaway1615]

I’ve got air coming out of my weep hole. Is that supposed to happen? I’m almost certain that my piston is under the hole at TDC. My leak down test rates a 5% loss.

[@CaptainTimA]

What is your "weep hole"? Notice I held off on a sarcastic comment here..

[@TheZakkmylde]

Stupid question. Leak down test vs compression test. 🤦🏻‍♂️ Is leak down just multiple tests vs compression being one value?

[@gohobby9934]

It's my understanding that you can't do a compression test accurately on a 4 stroke with auto decompression. Leak down is the way to go.

[@jca110]

Compression test is air pressure created naturally in the engine when you kick it over, this is then recorded to make sure as the piston rises everything stays compressed to near factory standards. Where as a leak down test you pump outside air into the engine and see how much pressure it will hold. If it won’t build high pressure the engine may not be sealed well. Whether that be ring wear, hole in piston, scarred barrel, bent valves or incorrect valve clearances. Worse case scenario apart of the engine is cracked but sometimes it may be very simple. Leak down tests tell you an idea of where the problem is whereas compression tests just give you an idea of if it’s holding pressure. Also you must decompress the system on a lot of 4 strokes