Compression Test
 

Hi everyone!

I know it's been a while, hope everyone is doing well.
I have a question:
I want to do a compression test but haven't seen any procedure anywhere. I know it's pretty straightforward I suppose but if I don't ask this question, I know there will be something I should have done. :roll: I'm thinking the only thing I need to do is disconnect the fuel line but other than that, I'm not sure. Does the throttle need to be wide open or anything like that?

Re: Compression Test
 

I believe it's explained and showed with pictures in service manual... The procedure is explained also!
Good luck!

Re: Compression Test
 

Throttle should be wide open. :) :cool:

Re: Compression Test
 

Hey thanks Blaine :tup:

My main computer is down for the moment, can't download stuff in the library. When it rains it pours kind of deal. :roll:

Re: Compression Test
 

Hello Way,
I'm also interested in it, could you please inform us about the actual measured compression ratio.
If you find any trick, please share it :-)
Thanks! :-)

Re: Compression Test
 

If memory serves correctly today the compression ratio is 9 To 1. 9x14.7 would be approx 132 lbs per square inch of pressure. If your compression is within 10% of that figure you are probably doing fine.
If you have or can borrow a compression tester it would be best to have one that reads up to 250 PSI. It will likely read most accurately in the middle of it's range.

Re: Compression Test
 

Hi trionyx, nice to meet you.

I will definitely post up what I did. I'm not sure whether I'm dealing with a bad oil pump or not, but the valves started making some noise the other day at the end of a 40 mile ride and the motor seemed hot. When I say started making noise, I mean like they started really clattering. I'm hoping maybe it's an overdue valve adjustment as there was oil in the sight glass, although it was to the L side.

I have an Isuzu Amigo which requires valve adjustments too and I know I had to do that before I did a compression test so I figure I have to do the same with the GZ.

Hopefully I can get online with my own computer soon, maybe later tonight (hopefully.)

Re: Compression Test
 

Before anything else, Way, top off the oil. A cheap, short-term solution would be to use a slightly thicker oil until the repair or replacement is absolutely necessary.

These things can vary in temp from day to day. The only way to know if it's really hot is to either scan it with a gauge. Either that, or you'll smell the cooking carbon and you might experience that tangy taste of metal on your tongue. That's a sensation I have, anyway....

A quick valve clearance check wouldn't take long either, just so you know for sure.

Re: Compression Test
 

Hi Jonathan, thanks. I didn't smell any carbon or have a metallic taste but it was definitely hotter than it usually is. What concerns me is how within a matter of miles the valves got so loud. I'm going to change out the oil anyway so that sounds like a good idea. Just wondering what an acceptable thicker oil viscosity is?

Well I checked the valve adjustment yesterday evening. Valves were loose as all get out, which is the opposite of what I understand to be normal wear? Usually when they wear, the adjustment gets tight right? Hope that isn't a bad omen...

I used a #2 square drive screw for the adjusters, and set them to .013 for the exhaust and .008 for the intake. I figured since valves wear to a tighter clearance, maybe that would give extra time between adjustments. I also don't own a 22 mm socket but I did have a 7/8" socket that fit real close. Not that I'm ever recommending using an SAE in place of a metric but sometimes you got to do what you got to do.

Now I might as well clear the air, admit it and get it over with:

I am an idiot.

I'm hoping that admitting this is the first step to a cure.

For some weird reason I figured I'd save time finding top dead center by using a pencil to know when the piston was on the upstroke. I know in hindsight that I just simply needed to put my finger over the spark plug hole to find the compression stroke and then watch for the mark on the crank to match the mark on the cover as stated in Jonathan180iq's how-to. But no, apparently my iq is not that high. :tongue:

So, anyway as the piston moved up I thought I heard a faint crunch but as it was getting dark and I was in a hurry I just took the pencil out and set about adjusting the valves. (It was in TDC for compression though as I confirmed, feeling the compression with my finger). So anyway, it got dark and I just put everything back together lightly, to keep moisture out until this morning. When I came out this morning and took the bike apart again, I happened to notice that the end of the pencil that USED to have the eraser, had a fresh break in it, the eraser nowhere to be seen. Now my IQ is barely high enough for me to remember I had the eraser side down because I figured I didn't want to risk the tip breaking off inside the cylinder head. So it seems, I broke the non-magnetic eraser part off in the cylinder. :cuss: I brought the piston to the bottom of its stroke so I could maybe see more of the inside of the cylinder but the spark plug hole is too small to really be able to get enough light in there to see if the eraser is indeed in there. I thought about putting some gum on the end of a thin dowel I have and try to fish around, but again the spark plug hole is too narrow for me to get anything in there enough to try. I was thinking maybe I could use a piece of wire or something but I'm thinking I'd probably just make things worse.

So anyway it appears I'm going to have to pull the cylinder head to clear it out. I figured I'd let you all know so you don't think I abandoned the thread. :roll:

Re: Compression Test
 

Sounds like you will be getting your learning curve increased whether you want it or not. Best of luck and do keep us in the loop.