HI everyone I am buying a 99 sx 600 and I want to know what the compression is supposed to be so I can compression test it. ANyone know the answer to this?
super1c
Super Moderator
I cant give u a exact number but the important thing is that both cyllinders are the same. Most people have a tolerance of 10% difference. Every tester is different so u will get different numbers. I do a cold and warm test, and make sure you hold the throttle open and give a good 10 pulls. I would do the test then post back with the results.
sleddineinar
VIP Member
There more or less is no exact number... Because there differences in compression testers. But like Super1c said, the numbers should be close to each other. Follow the instructions on the tester. Post the numbers here and people will chime in.
THE pto side had exactly 100 psi the center had somewhere around 95 to 98 psi and the mag side had somewhere between 85 and 95 psi my compression tester does not show exact numbers its kinda old school Haha how do those numbers sound tho ?
sleddineinar
VIP Member
Seems low, but that could be the tester, but what flags it for me is that mag side is so much lower than the pto... I would say you should pull the head and jugs off and inspect everything for wear, including checking the tolerances and clearance between the pistons and the cylinder walls. At very least put new rings in.
I guess I didn't test it when it was warm if that makes a big difference or not I have no idea does it?
sleddineinar
VIP Member
I guess I always test warm and cold...
When you test warm does it change a whole lot?
What is the proper way to compression test a sled anyway how I did it was the engine was cold and I hand tightened the tester in each cylinder but left the spark plugs in the other two and pulled it over about 8 times with the throttle wide open is this wrong? I ask because I have seen it done with all the skthe plugs pulled and I just need to clearIfy if I am even doing It correctly to begin with
super1c
Super Moderator
All taking out the other plugs does is make it easier to pull, i guess in theroy it might make you pull faster helping increase the compression a tad. What i do is hit the kill switch so i dont start it by accident. No need to ground plugs, old wise tale that they need to be grounded. Pull all three plugs, tape the throttle down WOT. Then pull with good force 10 times and take a reading. Some say warm engine some say cold. My thought is just do it the same way each time so you can compare those numbers. If i was you, start fresh and do each cylinder 3 times. Then compare numbers. I do cold then warm and they are not that much different but each cylinder increases about the same amount from cold to warm. Like i said up top the number is not important its the difference. Hope this helps clear up a few things for ya.
super1c said:
Agreed. I would only add that as a precaution I remove the ignition key to ensure it isn't left on. You can damage the coils if the key is in the run position and the kill switch up with the plug wires not grounded.
The 15-40KV will find a ground eventually... usually through the coil body/tower even at cranking speeds.
Ok thanks a lot everyone