How to check the compression of your bike and more

[Isaanbiker]

 I've just done a compression test on my bike and thought that it would be wise to make a movie to show it to a friend who was asking me how to do that. It's very easy to do, a compression tester should be part of your tools when you fix your bike by yourself anyways.

 

        On Viragos, this one is a V 2 Virago with 1100 cc, the compression on both cylinders should not be less than 10 bar. I've had 11.2 on the front and 10.9 on the rear cylinder which is quite good for a 24 year old bike.

 

    What's important is to do this compression test with full open throttle, otherwise the reading will be totally wrong a snot enough air will get through the carbs.

 

    I've disconnected both coils as I was working on them anyways, but it make sense if you put a spark plug in the cap and leave it at minus that they can fire. If the high voltage currency can't unload, there's a possibility of ignition coil damage, or anything else related to the ignition, Better no risk.

 

No idea how the sound come sover, so I'd like to repeat the part when you don't have enough compression on one, or on all. 

 

Remove the extension of the compression tester, ( or the spark plug) and fill in some engine oil.Only a few ml will do the trick. Then put the compression tester back in and try it again. If your compression is higher, then you already know that your piston rings need replacement, as the oil seals for the short period of time when you're testing.

 

If the compression doesn't go up with added oil, you know that the loss comes from the head. It could be not adjusted valves, valve seats, or the valves itself. Even when 11 is a pretty good result, it can happen that an engine builds up a very high compression which could be from sediments built up on top of your pistons.

 

Here's a lot more information, I've just found for those who have more serious problems after their compression check was negative. Ride safe out there, these people don't give a da_n! 

 

https://www.ms-motorservice.com/en/technipedia/post/piston-damage-and-causes/

   

 

  

 

  

 

   

[canthai55]

Cylinder leakdown test much more comprehensive

Compression test so 1960's

[Isaanbiker]

3 hours ago, canthai55 said:

Cylinder leakdown test much more comprehensive

Compression test so 1960's

You seem to get a kick out of criticising my method of testing compression in an environment where I neither have a leakdown tester ( the Thai mechanics here haven't even seen a compression tester before), nor do I have a compressor which I'd need to do this test.

 

I've done this movie for a friend in the States and thought that it might help others here on TV if they have problems with their engine and don't knowhow to test their compression.

 

  IMHO, such a compression test is telling me enough and there's absolutely no need for leakdown test, if the compression is good.

 

A leakdown test would make sense if the compression isn't good.

 

  For those who're doing a compression test, please do it with a warm engine. The readings usually show 5 to 10 less of the actual compression, depending on the quality of the tester.

 

   It's also important that the o-rings of the tester are in good shape and no air is leaking through the tester. 

 

 

 

 

 

 

   

[Don Mega]

I agree Isaanbiker.

 

Leakdown test if there is a discrepancy noticed on a compression test.

[canthai55]

1 hour ago, Isaanbiker said:

You seem to get a kick out of criticising my method of testing compression

I pointed out that the leakdown method provides more info.

If you take this as a criticism ...

[Isaanbiker]

5 hours ago, canthai55 said:

I pointed out that the leakdown method provides more info.

If you take this as a criticism ...

  After the compression test shows complications, yes.

 

      Nope, I don't see that as criticism, it's all cool. Cheers.