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!!!
#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!!!
Any cylinder tested has to be at TDC. Valves have to have some lash otherwise they can be slightly open and give false readings. Try tradebit for manuals they are cheap.
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?
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
@@HTMR Ok. I think I’ve got it. With the Schrader valve at the cylinder head end (as you recommend) I was thinking that if you have 100 psi in the combustion chamber and the Schrader valve opens, then you might only have 75psi at the gauge. However, I’m now thinking that on the 2nd compression, you’d have 100psi in the combustion chamber, 75psi in the tester tube, so when the Schrader valve opens you’d end up with, say, 85psi in the tube. And after a few more turns, you’d end up with 100 psi at the gauge. Just wanted to clarify in case I confused any of your readers.
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
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!
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.
I just made a new video with the bike running. Here it is. Maybe you can tell me what you hear when it's idling. th-cam.com/video/YirlyjYYIPE/w-d-xo.html
Yes, they are all bouncing between 5 and 8 psi. Couldn't get that psi any higher without running the nut off the top of the carb slide (or at risk of it - with just a thread holding...even with locktite that is asking for trouble).
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.
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 !
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?
Maybe, but we are after a percentage drop here. A higher psi would roll the motor over and is a PITA if you are by yourself. 100psi makes easy math though.
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Great video!
Seeing it all work and comparing before and after is very helpful 👍
Happy I found this video helped me big time. Big subscribe. Wish I found this video sooner
Excellent job and explanation. Very useful information.
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!!!
Nicely explained , just subscribed
Excellent video! Perfect amount of explanation and video. Loved the fast forward on the engine build!
Have you replaced piston rings for new ones?
Simply excelent! Thanks from Argentina!
#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!!!
Any cylinder tested has to be at TDC. Valves have to have some lash otherwise they can be slightly open and give false readings. Try tradebit for manuals they are cheap.
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
Calculation is here: howtomotorcyclerepair.com/motorcycleleakdowntest/
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?
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
Here is more info: th-cam.com/video/q1H7550B48I/w-d-xo.html
@@HTMR Ok. I think I’ve got it. With the Schrader valve at the cylinder head end (as you recommend) I was thinking that if you have 100 psi in the combustion chamber and the Schrader valve opens, then you might only have 75psi at the gauge. However, I’m now thinking that on the 2nd compression, you’d have 100psi in the combustion chamber, 75psi in the tester tube, so when the Schrader valve opens you’d end up with, say, 85psi in the tube. And after a few more turns, you’d end up with 100 psi at the gauge. Just wanted to clarify in case I confused any of your readers.
Great video. Great explanations. You got another subscriber man. Thanks
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
Get the engine hot and open the throttle, you will get higher readings.
Thanks matt, your video was very clear, I basically wasn’t giving it a chance, but at least I learned both cylinders are equally balanced.
Excellent video! I have one question, If I want to build the engine for racing, what is the best leakage number?
5% or less
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!
Yes for a 2 stroke you want to pressure test it.
Hello ! From Costa Rica ? Where can I get a compression tester like that one ??
www.howtomotorcyclerepair.com/compression-tester/
Very well explained. Thank you
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.
Let me know what you find.
I just made a new video with the bike running. Here it is. Maybe you can tell me what you hear when it's idling.
th-cam.com/video/YirlyjYYIPE/w-d-xo.html
Needs more tuning. Did you vacuum synch the carbs?
Yes, they are all bouncing between 5 and 8 psi. Couldn't get that psi any higher without running the nut off the top of the carb slide (or at risk of it - with just a thread holding...even with locktite that is asking for trouble).
timing is strobed onto the f mark, perfectly, at advancer rpm, for 1-4 and 2-3
How do you connect an engine like in the clip to an ignition source if the engine is not on a motorbike? Thanks
You can supply 12V to the coils and it will produce spark. Look up which wire in the service manual.
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.
I watched the video. Are you sure there are no vacuum leaks?
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.
Thanks Dan - excellent job!!!!
I think you say there is more information of that restrictive hole (between regulator and T) Can you tell me where? Thanks Matthew!
en.wikipedia.org/wiki/Leak-down_tester
why its not possible to seal completely??.thanks for the info...great job
Sealing parts are metal to metal, never going to seal 100%. Also there is a piston ring end gap, so that is a leak point by design.
@@HTMR thanks .....subscribed...😊
@@naveedaka Cool thanks.
Awesome video!
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 !
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
Yes the motor had oil in it.
awesome video.
Thanks!
MatthewMCRepair soooooo how about a comprehensive CB750K tear down and rebuild? I’d donate!
@@jefferymontague6281 In the works: th-cam.com/video/gDDRZOioPRc/w-d-xo.html
I thought the valves were supposed to be loose on top dead center
Yes, there is supposed to be some lash.
my 2000 gsxr 600 alstare has 50,000km on it and was less than 2% leakdown
Tight!
How do you set up the motor to bench test like that?
Jumper cables from a battery to the starter.
Awesome, thanks. What if I wanted to actually run the engine out of the bike?
@@SeriesOfTunnels Probably easier to set it in frame. By the time you rig up exhaust, coils, etc..you can have it in frame already.
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?
th-cam.com/video/q1H7550B48I/w-d-xo.html
Thank u for information
How did you connect the starter to a battery?
+FormedAndFunctioned Jumper cables and had another CB500 nearby :)
FormedAndFunctioned 😳 wow!
Would different air pressures not change the outcome ratio? Just wondering
Maybe, but we are after a percentage drop here. A higher psi would roll the motor over and is a PITA if you are by yourself. 100psi makes easy math though.
Great vid.
+lmdetect Thanks!
Great!