How-To: Perform A Leak Down Test On A Motorcycle 

Simply excelent! Thanks from Argentina!

Excellent video! Perfect amount of explanation and video. Loved the fast forward on the engine build!

Matt - Your video ranks as one of the top I've seen so far on MC engine maintenance. Extremely well done. Very informative. The fast-forward engine rebuild at the end... brilliant. Thanks for taking the time to put this together and sharing your knowledge. Much appreciated. Looking forward to going through your video library.

Thanks Dan - excellent job!!!!

Excellent job and explanation. Very useful information.

Great video! Seeing it all work and comparing before and after is very helpful 👍

Great video. Great explanations. You got another subscriber man. Thanks

Very well explained. Thank you

Happy I found this video helped me big time. Big subscribe. Wish I found this video sooner

Awesome video!

Nicely explained , just subscribed

Thank u for information

Great!

If you don't get any misfires when it is finally started, then you know that the compressions are good. On my dodge ram, the minium PSI is supposed to be 100, yet I am getting a misfire at 150psi on num 7 cyl. It's a v8.I am still learning !!!! and things don't always make sense. Good video!!!

Great vid.

This is great Matt. I did a compression test on my ‘81 Honda CX500 and had exactly 135psi on both sides, engine was in the bike but cold, I don’t think I opened the throttle either so I’m going to go back and redo the test, the bike runs fine anyway after I did a CDI replacement for an ignitech. One thing though, I assume that if it was rings issue there would be smoke which I don’t have at all, so could be just valves or doing the test properly that’s needed. I haven’t had the engine out as yet, so trying to avoid it. Thanks, Rich

Hi Matthew, enjoy your videos. Question: My .040 drill bit is inexplicably missing from my set. Can I use a .041 bit or will that cause a problem? I also notice that the specs say “0.250 in (6.4 mm) long, 60-degree approach angle” Is that .250” depth critical to get exactly right? And what do they mean by 60-degree approach angle”? Is the hole to be drilled at an angle? Ok, I figured out the approach angle LOL Now the question is, is the .250” length INCLUDING the approach angle on both ends or EXCLUDING the approach angle?

awesome video.

Have you replaced piston rings for new ones?

Excellent video! I have one question, If I want to build the engine for racing, what is the best leakage number?

be carefull cranking on the large nut points side,it only engages two little drive ears and snaps easily,bump the air test pressure up and youll have more leak percentage,lock the motor from turning under that pressure,testing low gives optimistic results.

The cylinder compression increases once the rings have fully seated, I had a Stihl hedge trimmer that was like that when I fitted a new cylinder kit onto it. The compression was 105 PSI when brand new but once the rings seated in it went up to 120 PSI !

Hey Matt I'm trying to carb sync my V4 Honda right now and having trouble getting cyl #4 to sync. I've tried adjusting it a million times now and still can't get it to sync. It still climbs slowly on the manometer, then if I rev the bike very little, it drops back down, and then slowly continues back up. I have a video of it on my channel. Someone said that a bad valve seat or ring seal could cause a manometer to "dance" like that and basically you'll never be able to get it to sync properly. Have you ever had that happen to you? I haven't done a leak down test yet which is why I'm on this video.

#1 cyl TDC or each one as your doing leak down? Also, valve lash or is it a torque spec? What is spec for either one? Great job on video… I’m a heavy duty diesel tech, this is a little out of my realm but my 15 yr old son got a nice ‘79 CB 650 and we’re gonna rebuild it together. Where can I get a worthy mechanic manual for these engines? Appreciate your time and effort!!!

I think you say there is more information of that restrictive hole (between regulator and T) Can you tell me where? Thanks Matthew!

Great video, thanks. However, are you sure that you get a more accurate result using a compression tester with the valve at the end of the tube. Surely, when the gauge is reading the pressure, the valve is open and so the volume of the tube will still reduce the pressure read at the gauge. Or am I missing something? Thanks again

I know this is an old video but I have a question. I need to do a leak down test on my Honda CR250 and have watched a few videos now. Some people use the restricter and others don't. In this case I have a two stroke engine but I'm not sure if it matters. Would it be okay to build one with a pressure regulator with a one way valve that allows you to pump 7-10psi into the engine and then disconnect the air hose, take off the expansion pipe and plug it with a freeze plug, take off the carb, hook up the contraption in the intake where the carburetor would be (leaving the spark plug in place), pump 7-10 psi into the engine, and watch the gauge over 5 min or so to see how much pressure is lost. If a leak is located you could then spray everything with soapy water and have the radiator cap off to check for bubbles. With your tester I understand that you're able to quantify the leaking with a percentage but is that entirely necessary? Thanks for your videos, I've learned a ton from your channel!

Hi. Sorry about the stupid question but you did it with the oil in the engine or the only oil in was the one you had on the test? Thanks

How do you connect an engine like in the clip to an ignition source if the engine is not on a motorbike? Thanks

Great video Matthew! Just one question: the bit where you mentioned the added volume due to the schrader valve position close to the gauge, does it really affect the pressure measurement? It would definitely affect the compression ratio cause thats a ratio of volumes but I think the pressure value (compression pressure value) will stay the same independent of the location of the schrader valve (of course there will be some losses depending upon the flexibility of the pipe etc.). What do you think?

Hello ! From Costa Rica ? Where can I get a compression tester like that one ??

Just watched your linked video where you speed rebuilt the upper engine. Awesome. Now I'm tempted to do a compression test on my cb750k3. I've avoided it up to now... It passed 8 years ago, when I did a semi restore on the bike, and now I just did another one (actually what I'd think of as an almost complete restore except for the engine and some other odds and ends)... but one of the exhaust pipes (#3) has a much throatier / deeper sound than the other 3. It makes me suspect a burnt exhaust valve, because there is also more pressure on that pipe...as if it might be blasting through a leaking valve? On the other hand, this engine only has about 9200 miles on it. In theory it shouldn't be at that stage, yet, right? And believe it or not, the bike still purrs... Positively purrs, because of the carb cleaning, new spark plugs, replaced fuel lines/filters, shimming and carb sync and re-tensioned cam chain... enough other things are right that the bike is still sounding prime. Even used a strobe to do the timing, and got the F to match perfectly with the mark, under that strobe (this bike still has points though, so i also had to gap the points and replace the condensers). Anyhow I'd better check the compression on #3, and at least see. Thanks for the video.

why its not possible to seal completely??.thanks for the info...great job

my 2000 gsxr 600 alstare has 50,000km on it and was less than 2% leakdown

Hi , very clever Guy and nice video . But with my english it s litlle hard to understand. Could you put here the calculation please ? Thanks a lot

How did you connect the starter to a battery?

How do you set up the motor to bench test like that?

Would different air pressures not change the outcome ratio? Just wondering

I thought the valves were supposed to be loose on top dead center