The cranking compression of the Mach Z 1000 SDI can change by as much as 20 - 25 psi when the static compression ratio changes by 1 point. Since the Mach Z compression ratio as shipped from the factory may vary 1 point (11.7:1 to 12.7:1), the cranking compressions vary from roughly 145 to 165.

There are several ways of doing a compression test to help determine the state of the rings, regardless if your gauge is accurate or not. I would use a gauge that screws into the spark plug threads as some gauges don't. You take both plugs out so the engine turns over easier. The throttle is held wide open (use a ty-rap if alone) to allow the maximum airflow to the cylinders. If you don't have the throttle open, your reading will be somewhat lower than actual compression. Make sure your kill switch is active to keep engine from starting. I also make sure the parking brake is set or sled track is off the ground. Pull the engine over five times. Make sure you do the same for both cylinders. Record the readings from both cylinders. If the readings between cylinders are different by more than 5% of highest reading you probably have issues with the lower cylinder.

Next install the spark plugs, turn off kill switch and then start the engine. Let engine run until the sled is at operating temperature. In the case of the 1000 SDI, run until temp gauge needle starts to move. Shut off engine, remove both plugs, make sure kill switch is active and check compression of both cylinders with hot engine. If the difference in compression between this hot test and the previous cold test is 7lbs or more, that is an indicator that you need new rings. If the hot to cold compression difference is 10lbs or greater, it is usually an indicator that new pistons are needed as well. Hope this helps.

The second way of doing the compression test is to start out with the same cold test as above but instead of running engine hot just squirt some of your 2 stroke oil into cylinder through spark plug hole. If the before and after readings are different by more than 5% of highest reading then you probably have ring issues.

 

Thanks for the reply Bluemax. I was thinking that maybe I would have to remove a fuse or relay for the fuel pump but I guess the kill switch will ensure no fuel delivery.

Also, I've read about grounding the plug wires when doing the test, is this a requirement?

Appreciate your help.

 

sled on a stand or not, parking brake or not, if you have both plugs out it won't start. the little bit of cranking to check compression shouldn't flood the engine so killing the kill switch or fuel pumps I don't think will do anything. I would just leave the plug wires in a area where they wont ground.

 

Very true. The Mach Z 1000 SDI is a little odd in that as soon as you pull on rope the ECU is activated and so are the fuel pumps even if kill switch is active. There is also a flooded engine special procedure that kills both the ignition and fuel injection. To activate this flooded engine procedure have the tether attatched, kill switch activated and throttle held wide open. The ECU knows these parameters and shuts both ignition and fuel injection off. I like to add those saftey items in case someone forgets a couple of steps. One of my first mistakes (many moons ago) on a snowmobile was flooding engine. I held throttle wide open and pulled start rope to get sled to start.

Lucky for me the sleds were a lot slower back then and I had plenty of snow to land in.