compression test
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Stevego
New Member
I thought the engine had to be warm?
Also do you remove both plugs at same time or one at a time? With both wires removed of course.
When I checked my boat the owner (who is a mechanic) did not bother grounding the plug wires, just left them hanging loose. I assume you only ground them to avoid electrical shock in case they come in cotact with water or other contact point?
So many different methods I read also... But Dr Honda is a Guru here so drink from his fountain of knowledge
Also do you remove both plugs at same time or one at a time? With both wires removed of course.
When I checked my boat the owner (who is a mechanic) did not bother grounding the plug wires, just left them hanging loose. I assume you only ground them to avoid electrical shock in case they come in cotact with water or other contact point?
So many different methods I read also... But Dr Honda is a Guru here so drink from his fountain of knowledge
Dr Honda
Well-Known Member
Never check compression on a warm engine. The problem is... after you have been running it... it could hide a problem becasue....
A) Parts are expanded, and will have less "Leak" to them
B) the sealing parts will be wet with fuel and oil... once again, helping the numbers.
I can verify that a cold rotax 2-stroke has no problems hitting 150 psi if it's in good condition.
As far as grounding the wires... yes and no, on your comment. Yes it will keep the mechanic from getting a shock... but more importantly, it's to keep the coil from burning. Every time the coil gets a fire signal from the CDI, a spark is made. If it can't fire that power to a plug (or ground post) it will still try to fire. So... it may find a path to ground via it's internal windings. (especially on an old coil) Then eventually, it will burn that path in the insulation, and over time, will kill the coil.
OK... will that happen the first time you forget to ground the wires?? probably not... but it's a good practice to get into.
The reason you don't see grounding posts on other water craft is because they can be cranked with the ignition off.
OK... last thing....
The absolutely proper way to check compression is to leave the other plugs in the engine. BUT.... I find that most water craft starters, and batteries aren't working at 100%, so you can get a more constant reading with all the plugs out.
This is a debated point, but if you are cranking slow for any reason... you won't get full pressure. I personally take the plugs out.
A) Parts are expanded, and will have less "Leak" to them
B) the sealing parts will be wet with fuel and oil... once again, helping the numbers.
I can verify that a cold rotax 2-stroke has no problems hitting 150 psi if it's in good condition.
As far as grounding the wires... yes and no, on your comment. Yes it will keep the mechanic from getting a shock... but more importantly, it's to keep the coil from burning. Every time the coil gets a fire signal from the CDI, a spark is made. If it can't fire that power to a plug (or ground post) it will still try to fire. So... it may find a path to ground via it's internal windings. (especially on an old coil) Then eventually, it will burn that path in the insulation, and over time, will kill the coil.
OK... will that happen the first time you forget to ground the wires?? probably not... but it's a good practice to get into.
The reason you don't see grounding posts on other water craft is because they can be cranked with the ignition off.
OK... last thing....
The absolutely proper way to check compression is to leave the other plugs in the engine. BUT.... I find that most water craft starters, and batteries aren't working at 100%, so you can get a more constant reading with all the plugs out.
This is a debated point, but if you are cranking slow for any reason... you won't get full pressure. I personally take the plugs out.
jdabrowski
New Member
97 xp
I lost about 7-8 mph on my top end...did a compression test and I am at 120/130...Top end rebuild?? or...?? Please help me
I lost about 7-8 mph on my top end...did a compression test and I am at 120/130...Top end rebuild?? or...?? Please help me
Dr Honda
Well-Known Member
Yup. Those numbers are low. Time for a top end.
jdabrowski
New Member
ok! I was told that was the problem, I just wanted to make sure. I found a guy who is/was seadoo tech, he is going to charge me roughly $300 for a rebuild..good deal?? And do you think that will get me my mph back?
jdabrowski
New Member
Well, I guess he just ordered 2 new ring kits and it going to replace the rings...so thats what he is charging me for
BoyzFunBoat
Member
How do you ground the plug wires? I have a ROTAX 947, 2-stroke direct injection (DI)
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