help with compression check pleeeze!

[section8]

hello guys. Thanks foer all the time you guys spend helping others! I hope i have some knowledge to help other boaters soon. but til then, can you guys help me? i think im doing a compression test wrong. i pulled all of my spark plug wires because my lanyard does nothing.i then pulled the top plug out and screwed in the guage. turned the key and watched the guage go up in segments of 20 or 30 psi til it stopped going up. then i put the plug back in the hole and moved down to the next plug. took it out put guage in, turn key, up up up so on down the other two plugs. i did this a couple of times to make sure the readings were right.the problem is my results were the top cylinder at 146 psi then the second at 143 and the third at 134 and the fourth at 127. I just had the motor put on and the marina i got it from said all were at 125 to 127. also i have some brown burnt oil spatter on the plugs and they are new! any help is sooooooo apreciated! oh yeah, if quadmaniac reads this. do you know the diameter of your new sporqster tach? thank you to all of you guys.....
Erik

 

[Bigprairie1]

Re: help with compression check pleeeze!

...well it looks like your results are ok, even better than the marinas compression test...whats wrong with that?
Maybe they averaged theirs down to be safe or conservative?
Was the motor warmed up when you did the compression test? Did you have the throttle wide open?
I believe these can affect the numbers somewhat....but youre numbers appear to be higher than you expected.
You can always try a different compression test gauge....such as a friction fit style, but you'll need a friend to give you a hand to do that test. Then compare results to your test with the screw in type gauge.

 

[section8]

Re: help with compression check pleeeze!

i have only been learning boats for two months and havent had the best of luck. the only thing is i have yet to hear of over 130psi and some other threads mention a 15 psi difference is when you worry and i have a 19 psi difference between the 127 and 146. hey any idea about the spark plugs? im sorry to be such a pest but the marine repair industry has no time for boat repairs let alone questions! you guys are really all i have to go on and you all kick so much butt. i have a seloc manual but you cant ask it questions and you all have more info than that book anyway so THANK YOU EVERYONE!!!!!

 

[baxtr]

Re: help with compression check pleeeze!

I think 10 percent difference is "allowed" between cylinders, you could try a decarb, maybe loosen up the rings a bit getting the compression closer. Here is a how to on iboats http://forums.iboats.com/showthread.php?t=158076

One thing, you mentioned that your lanyard wasn't working? so you just pulled the plug wires. If in fact your lanyard wasn't working to stop the spark, if you pull the plug wires you MUST ground them to the block. If they are still getting the electrical pulse due to a faulty lanyard, they can overvolt your powerpacks if they are not grounded, causing them to burn out and making you purchase new ones. It's not a guaranty that they will burn out at first crank, because I did the same thing before I knew and mine still work.

 

[eurolarva]

Re: help with compression check pleeeze!

Apart from grounding all the plug wires you also need to have all the plugs pulled during the compression test. Not just the plug on the cylinder you are testing. Correct results should be with a warm engine and the throttle at WOT.

 

[Bigprairie1]

Re: help with compression check pleeeze!

..baxtr is right about the compression differences....10% is considered a good rule of thumb difference between the min/max values measured.
150 psi is probably close to the original max. spec so your numbers aren't too far off that to begin with. However you have that one cylinder at 127 psi.
As for the spark plug...some discoloration is expected. You would have post a couple of photos of the plug(s) to get more feedback on it.
How does that motor run?

 

[baxtr]

Re: help with compression check pleeeze!

Thanks Eurolava, forgot to mention that. Also, testing on a warm motor may give you closer readings, if it is a stuck ring, it may only be stuck while cold, so you may get closer readings when warmed up.

 

[section8]

Re: help with compression check pleeeze!

thanx guys,big prairie asked how it runs. im not sure yet.you see, im new to boating this summer and i got me a seaswirl with a johnson motor and that lasted us a month. we bought a used force because they are cheap and we are not rich so i dont know how it should feel.the marina didnt hook our guages or stereo or vhf back up so i have no tach reading even tho its a 12 pole so i need a tach. the boat goes faster than before but i went from 90hp to 120hp. it goes maybe 4 to 5 mph faster but has poor acceleration. the motor is way lower than the old one so much that we cant trim it down all the way when trailered in the yard. it hits the ground before its at verticle.on the first time out it felt like it was misfiring here and there but yesterday it didnt do that i dont think.the top speed is about 35 with me and my wife and 3/4 tank'o'gas on a 17.5 ft open bow.heres the terrible part!!!!there is an exhaust leak in the midleg somewhere between the exaust down section and the shift linkage downshaftish part. the marina who installed it said it would take a little longer do to a gasket leak so they fixed it by drilling a 2" hole in front of the top carb and putting a bilge vent over it.THEN they glued and ziptied a piece of pvc to the front of the carb to connect it to the "vent" hole.maybe cleaner air in the upper carb is why i have better compression up the top 2 cylinders. i feel like im writing a book right now. haha.im gonna take the back of the midleg off today to look at it but is it a real pain to attach the boot to the pee holes? anyway thats how the engine runs and im gonna order a fuel diaphragm today.THANX anyones input is so helpful!!!

 

[section8]

Re: help with compression check pleeeze!

oh and thanx again for all the test info! ill try another comp test today with all the advice like warm engine and wot and grounded plugs etc. THANX
Erik

 

[QuadManiac]

Re: help with compression check pleeeze!

oh yeah, if quadmaniac reads this. do you know the diameter of your new sporqster tach?
Erik

hole size = 3 3/8" bezel diameter = 3 3/4"

 

[bowhuntrrl]

Re: help with compression check pleeeze!

You will need a 20 pole tach for a Force.

 

[QuadManiac]

Re: help with compression check pleeeze!

It's the TACHOMETER 8000 RPM MARINE 4-10-12-20 POLE - Mfg Part # 28-1401 , 23.99 from Sporqster.com

Good Luck

 

[section8]

Re: help with compression check pleeeze!

thanxs quad and everyone else. at the top of the thread i wrote my compression test results and then i used all the advice from you guys and they didnt change more than + 1 or 2 psi. ive used the boat 2 or 3 times since that and just did a compression test. i got 147, 147, 146, AND 40! not 140 but 40. the plug in that cylinder was the cleanest and one other cylinder had a black gooey plug face(surface gap)the other 2 plugs had just some greyish fluid on them and were kinda clean!Any ideas from you guys? should i not take it out tommorrow? its labor day and supposed to be real nice here.!?

 

[Nate3172]

Re: help with compression check pleeeze!

It sounds to me like your 4th cylinder with the 40 lbs of compression has some issues if the test was done correctly. I would pull that plug and shine a flashlight in the hole and try and see what that piston looks like. Or use a bore scope if you can get your hands on one. My guess is that the piston and rings are shot on that cylinder. You can rotate the flywheel by hand to bring that piston up in the bore to see the piston, but you can only see a little bit. I was able to see the failure on my engine this way, but it also had a chunk of ring stuck in the top of he piston so it was really easy to tell that cylinder was toast! If you can't see anything through the plug hole and you have no access to a bore scope, you may have to pull the head and inspect the cylinder that way.