Sport Jet 175 xr2 - low compression in one cylinder

[rossman21]

I just purchased a 1997 Sea Rayder with the Sport Jet 175 xr2 engine. These are the results of my compression test:
Port side 120 125 120
Starboard side 115 120 105

Engine seems to run great - should I be worried about the one cylinder with the 105 reading?
Is there anything I can do to increase the compression in this cylinder?

 

[Dukedog]

if your mechanically inclined ya might wanna pull tha head an take a peek at tha hole and piston.. could be tha start of something serious or jus a little excess wear.. would at least get a bore scope in it.... jmo.

 

[Scott Danforth]

Is there anything I can do to increase the compression in this cylinder?

start saving for a reman

 

[racerone]

In the big picture a head gasket is cheap.-------Pull the head and have a look in there.----These engines live a tough life in the hands of joy riders.

 

[Scott Danforth]

In the big picture a head gasket is cheap.-------Pull the head and have a look in there.----These engines live a tough life in the hands of joy riders.

thought the sportjet was a merc power head - no head gaskets

 

[Dave1027]

How about try a piston soak with powertune? Might free up the rings?

 

[rossman21]

How about try a piston soak with powertune? Might free up the rings?

I believe the instructions say to spray powertune through the carburetors. In this case, to soak the piston, should i spray powertune directly through the spark plug hole?

 

[Dave1027]

I believe the instructions say to spray powertune through the carburetors. In this case, to soak the piston, should i spray powertune directly through the spark plug hoIe?

Yes, in the spark plug hole. I'd tilt the motor up fully and turn/tilt it so the offending cylinder is as close to level as possible. Get the piston towards the top of it's stroke so the powertune doesn't just run into the ports. Then spray some powertune in and let it sit over night. Then spray some more in the morning. Then spin the motor over to expel all excess powertune. Then try another compression test.

 

[racerone]

???----It is a V-6 power head.---Also indicated with 6 compression values posted.-----And those have always used head gaskets !!!!!

 

[rossman21]

Yes, in the spark plug hole. I'd tilt the motor up fully and turn/tilt it so the offending cylinder is as close to level as possible. Get the piston towards the top of it's stroke so the powertune doesn't just run into the ports. Then spray some powertune in and let it sit over night. Then spray some more in the morning. Then spin the motor over to expel all excess powertune. Then try another compression test.

Thank you for your suggestion. I do not think I will be able to change (level) the piston. The pistons run parallel to the ground - the piston tops are vertical. If I understand what you are suggesting correctly, I would have to remove the motor and hang it sideways for a day - I don't think i can do that.

 

[QBhoy]

Run the engine up again and try the test again. See what happens. Did you test this after it was ran ? If so..was it ran on hose on trailer ? If so..did you turn the water off before stopping engine ?

Thank you for your suggestion. I do not think I will be able to change (level) the piston. The pistons run parallel to the ground - the piston tops are vertical. If I understand what you are suggesting correctly, I would have to remove the motor and hang it sideways for a day - I don't think i can do that.

 

[racerone]

????------This is a V-6 outboard powerhead.----Mounted as an inboard motor.------Mounted on top of a jet drive pump !!!-----It can not be tilted up and turned to fiddle with power tune or other potions !!

 

[rossman21]

I ran the compression test on a cold engine. I removed all 6 spark plugs and did a compression test on each cylinder without water running. Is this correct?

 

[racerone]

That will give you excellent and meaningful test values.

 

[QBhoy]

I ran the compression test on a cold engine. I removed all 6 spark plugs and did a compression test on each cylinder without water running. Is this correct?

I think you need to run the engine up to temperature then do a test.
You’ll know already, I’d think…that these things need to be started and stopped in a certain way, when on the trailer. Start the engine first, then turn hose on. To stop…turn hose off first, then stop engine. Otherwise you risk taking water into the engine, if hose is on and it’s not running with exhaust pressure, keeping the water from coming in. That’s why I had asked previously around it really. In case it had affected things.
So all that said…run the thing up to a decent temperature, then do the test again straight after. Otherwise your engine isn’t in a normal state of operation. As in everything all expanded, rings getting oil and things all making a seal, then in turn compression. See how you get on. Likely you’ll find all is well.

 

[rossman21]

I think you need to run the engine up to temperature then do a test.
You’ll know already, I’d think…that these things need to be started and stopped in a certain way, when on the trailer. Start the engine first, then turn hose on. To stop…turn hose off first, then stop engine. Otherwise you risk taking water into the engine, if hose is on and it’s not running with exhaust pressure, keeping the water from coming in. That’s why I had asked previously around it really. In case it had affected things.
So all that said…run the thing up to a decent temperature, then do the test again straight after. Otherwise your engine isn’t in a normal state of operation. As in everything all expanded, rings getting oil and things all making a seal, then in turn compression. See how you get on. Likely you’ll find all is well.

QBhoy - thank you for this explanation. I run the engine up to temperature then remove the spark plugs. Then run compression tests in each cylinder without the water running. Here is my question - won't the engine be much hotter on the first cylinder tested and much colder by the time I get to the 6th cylinder?

 

[QBhoy]

QBhoy - thank you for this explanation. I run the engine up to temperature then remove the spark plugs. Then run compression tests in each cylinder without the water running. Here is my question - won't the engine be much hotter on the first cylinder tested and much colder by the time I get to the 6th cylinder?

Probably…but be just fine to get you a more realistic result of her health. And crucially, she’ll have oil around about her and letting the rings do what they are meant to. These things need a film of oil around the bores and rings to give their best. Everything all expanded and tight. See what you get then.

 

[Dukedog]

???----It is a V-6 power head.---Also indicated with 6 compression values posted.-----And those have always used head gaskets !!!!!

JAN..
the SJ V6 powerheads (175, 210, 240) all went ta o ring in 2000 along with production 2.5 V6's...

doubt that any kinda "additive" is gonna help.. right now its jus showin' "weak".. may/may not be any damage.. it needs ta be LOOKED at to determine which it is... then you can devise a plan of what ta do... if not ya risk destroyin' tha other five along with a lot of other stuff.. no mater what ya do, unless you have tha ability to take it apart, reassemble, it can get very expensive.. good luck with whatever ya decide.....................

 

[racerone]

It was posted as a 1997 model.

 

[Dukedog]

It is a V-6 power head.---Also indicated with 6 compression values posted.-----And those have always used head gaskets !!!!!

this statement kinda says "all" v6's.. ta me anyway.. sorry if i misinterpreted.