Topic: No starter or kick, can I check compression by hand?

[daewon774]

I have a CB650 missing some parts.  I'd like to check the compression on this engine (sold as a parts bike, now a project).

Tell me if I did this wrong, I first wanted to see if the engine turns over so I took a wrench to the rotor (behind the stator cover on the left side) and turned.  It turned over fine, but I'm not sure this is a proper way to test if the engine is turning over (aka not seized).

So, now that I 'think' the engine is turning over, I'd like to check compression.  Can I do the same thing, take a compression tester, throw it in, then turn the rotor a few times to get a reading?  Carb is off, so throttle doesn't have to be held open

[Gordon]

If the engine turns, then it's not seized, but I don't think you're going to be able to turn it fast enough by hand to get a good compression reading. 

[daewon774]

If the engine turns, then it's not seized, but I don't think you're going to be able to turn it fast enough by hand to get a good compression reading. 

is it speed of the pistons turning thats important?  I thought I just want to make sure the pistons/seals/rings are compressing gas sufficiently in a given volume.  Does speed matter for this?

[BVCB650]

If the engine turns, then it's not seized, but I don't think you're going to be able to turn it fast enough by hand to get a good compression reading. 

is it speed of the pistons turning thats important?  I thought I just want to make sure the pistons/seals/rings are compressing gas sufficiently in a given volume.  Does speed matter for this?

Put a 15/16" socket mounted on a 1/2 inch drive drill. Take the RIGHT side cover off, and have at it.

[razor02097]

you will NOT be able to measure compression without a start device.  Try a leakdown test instead.  You don't need to use a start device.

[BVCB650]

you will NOT be able to measure compression without a start device.  Try a leakdown test instead.  You don't need to use a start device.

But that won't tell him what may be wrong, for example bad rings.

[750goes]

Yes it will

[BVCB650]

Yes it will

No it won't!! It may tell if there is a leak or not, but not the source. Only way to do that is to circulate oil to the rings manually. Why guess the valves are leaking without verifying the valves or rings??? Or, it could be the cam lobes are worn, or the cam chain is worn or off a notch or two. Huh?

[TwoTired]

Using a leakdown tester pressurizes the combustion chamber.  If the rings leak you hear it in the engine breather.  If an exhaust valve leaks, you hear the leak in the exhaust.  If the intake valve leaks you hear it in the intake.

With only a compression gauge you rely on perfect ring and valve seal get any reading at all (and none are perfect).  If they do leak (likely) then it is a ratio of how much is lost vs what was built up over time.  I can't think any meaningful info can be gleaned with this approach.

Doing a compression test by turning it over by hand will NOT tell you condition of rings or valves.  It might tell you if you have a holed piston, and broken/bent/ burned valve.  But, only expect to isolate catastrophic failures and you don't need any gauge for that.  Just put your finger over the spark plug hole and see if the compression stroke pushes it off the hole evenly for each cylinder.

[BVCB650]

Using a leakdown tester pressurizes the combustion chamber.  If the rings leak you hear it in the engine breather.  If an exhaust valve leaks, you hear the leak in the exhaust.  If the intake valve leaks you hear it in the intake.

With only a compression gauge you rely on perfect ring and valve seal get any reading at all (and none are perfect).  If they do leak (likely) then it is a ratio of how much is lost vs what was built up over time.  I can't think any meaningful info can be gleaned with this approach.

Doing a compression test by turning it over by hand will NOT tell you condition of rings or valves.  It might tell you if you have a holed piston, and broken/bent/ burned valve.  But, only expect to isolate catastrophic failures and you don't need any gauge for that.  Just put your finger over the spark plug hole and see if the compression stroke pushes it off the hole evenly for each cylinder.

All true IF he is a competent mechanic, which apparently he is not. Took the wrong side cover off, and we don't know which way the engine was rotated. I don't understand why he doesn't hook up a good battery and turn the engine over with the starter.

[daewon774]

Using a leakdown tester pressurizes the combustion chamber.  If the rings leak you hear it in the engine breather.  If an exhaust valve leaks, you hear the leak in the exhaust.  If the intake valve leaks you hear it in the intake.

With only a compression gauge you rely on perfect ring and valve seal get any reading at all (and none are perfect).  If they do leak (likely) then it is a ratio of how much is lost vs what was built up over time.  I can't think any meaningful info can be gleaned with this approach.

Doing a compression test by turning it over by hand will NOT tell you condition of rings or valves.  It might tell you if you have a holed piston, and broken/bent/ burned valve.  But, only expect to isolate catastrophic failures and you don't need any gauge for that.  Just put your finger over the spark plug hole and see if the compression stroke pushes it off the hole evenly for each cylinder.

All true IF he is a competent mechanic, which apparently he is not. Took the wrong side cover off, and we don't know which way the engine was rotated. I don't understand why he doesn't hook up a good battery and turn the engine over with the starter.

Didn't get that information until now about the cover.  It's the reason why I came on here in the first place to ask you all.  I didn't know I was going to be flamed for asking questions.

I also don't have a stator on this bike or a R/R.  All parts missing when I bought this as a parts bike. 

[BVCB650]

A missing stator doesn't have anything to do with being able to turn the engine over. In the future, more info would be nice, like what parts are missing etc. But to help you out, I did mention a way for you to turn the engine over in my first post. As always, it is wise to don thick skin.

[daewon774]

A missing stator doesn't have anything to do with being able to turn the engine over. In the future, more info would be nice, like what parts are missing etc. But to help you out, I did mention a way for you to turn the engine over in my first post. As always, it is wise to don thick skin.

You just asked why I didn't turn it over with a starter, and it's a 650 which doesn't have any type of kick start.  The topic title says I don't have a starter.  And to add to that, I don't have other parts. 

All I was asking was how I can check compression by hand without the starter.  You gave me an answer, I appreciate it.  I'm going to try the 1/2 drive drill.  No need to get hostile when you don't read through the entire post.

[BVCB650]

I'm not hostile at all. I did not read the lack of a starter in your title. My bad. You may want to use an adjustable drill motor to get the rpms down though. Also, it may be helpful if you pulled the plugs out of the cylinders that you aren't testing so the engine will turn over easier.

[MRieck]

A missing stator doesn't have anything to do with being able to turn the engine over. In the future, more info would be nice, like what parts are missing etc. But to help you out, I did mention a way for you to turn the engine over in my first post. As always, it is wise to don thick skin.

You just asked why I didn't turn it over with a starter, and it's a 650 which doesn't have any type of kick start.  The topic title says I don't have a starter.  And to add to that, I don't have other parts.  

All I was asking was how I can check compression by hand without the starter.  You gave me an answer, I appreciate it.  I'm going to try the 1/2 drive drill.  No need to get hostile when you don't read through the entire post.

PM me if you need some advice etc....I live in Ashland MA

[daewon774]

I'm not hostile at all. I did not read the lack of a starter in your title. My bad. You may want to use an adjustable drill motor to get the rpms down though. Also, it may be helpful if you pulled the plugs out of the cylinders that you aren't testing so the engine will turn over easier.

cool thanks, I honestly didn't know that speed was a factor when checking compression.  For some reason I just thought if there was movement from the pistons that, if the seals were good, the compression would still show.  I'll update this weekend on the drill method.

[the technological J]

easy guys i think we're a step away from name calling (seen it on other threads)..
but scwabling (skwable, scuable?) bickering aside
 you might find the downloading manuals handy thier at the top of the thread page from what i under stand if u determine u have low compresion and u put some oil in the cylinder and it raises u have a bad ring if not it may be a hole in the piston or a valve. if u have the time and are not in a rush to get the engine running pull the head... theres nothing like hands on experience with these old bikes

[BVCB650]

easy guys i think we're a step away from name calling (seen it on other threads)..
but scwabling (skwable, scuable?) bickering aside
 you might find the downloading manuals handy thier at the top of the thread page from what i under stand if u determine u have low compresion and u put some oil in the cylinder and it raises u have a bad ring if not it may be a hole in the piston or a valve. if u have the time and are not in a rush to get the engine running pull the head... theres nothing like hands on experience with these old bikes

We're all good. I suggested oil on the rings if there is a low number in a cylinder or 2 to further diagnose the issue. A number of things can cause a lower reading, but in the end, it is what is acceptable to determine the health of the engine that is desireable. First things first.

[74cb750]

check your pm's, as I 'm driving down to Newton, Ma today to see my kid.
I'll bring a starter if you want.
peace,
michel

[razor02097]

If you use a driver make sure its not an impact type.  Don't want to booger up threads or break bolts