Outboard Motor Repair Outboard Motor Repair  

Outboard Motors

Power Heads

Lower Units

Props

Repair Manuals

Controls, Steering

Trim/Tilt

Power Tilt/Trim

Parts

Outboard Motor Repair


Chrysler
Evinrude
Force
Honda
Johnson
Mariner
Mercury
Minn Kota
Nissan
OMC
Suzuki
Yamaha
2 Cycle Outboard Motors
2 Stroke Outboards
4 Cycle Outboards
4 Stroke Outboards
Aftermarket Outboard Parts
Boat Wont Plane
Bolts
Brackets
Carburetors
Cavitation
Choke
Coils
Compression
Condensors
Controls
Cooling
Cowling
Crankshafts
Cylinders
Diagrams
EFI
Electrical
Engine Cleaner
Engine Smoke
Exhaust
FICHT
Fins
Flywheel
Fouling
Fuel Pumps
Fuel Systems
Fuel Tanks
Gaskets
Gauges
Gear Cases
Generators
I/O
Idle
Ignition
Impellers
Inverters
Kill Switch
Leaks
Lower Units
Lubrication
Manuals
Oil
Oil Injection
Oil Mixture
Old Outboards
Outboard Engine Blocks
Outboard Inboard
Outboard Maintenance
Outboard Motor Prices
Outboard Propellers
Paint
Parts
Pistons
Power Loss
Power Packs
Powerheads
Primer Bulb
RPM
Repair Tools
Reverse
Running Lean
Running Rich
Runs Hot
Sea Drives
Sealants
Shafts
Shifter
Skegs
Spark Plugs
Specs
Spring Maintenance
Starter Motors
Starting Problems
Stators
Steering
Synthetic Oil
Tachometers
Tillers
Tilt Trim
Timing
Trim Tabs
Twin Outboards
V6
Voltmeter
Water Pumps
Winterization
Wiring
Year

How to test compression?

Somie I have a 98 Evinrude 250 (carb) and would like to test the compression on it. I bought a kit, that has the gauge, a rubber bung, and two sizes of screw-in adapters that would go where the sparkplugs were.
Should I run the engine before testing? I've a
2001-12-13
Somie Oh yeah, here are 2 pics of the rig taken last weekend.

(copy and paste into a new browser, Angelfire sux)
http://www.angelfire.com/ny/somie/PC090009.jpg

2001-12-13
Captn Dave Start and warm the engine up to operating temperature. Shut down and remove all the plugs. I've heard about reconnecting the plugs to the wires to avoid damage to the coils. I'm not sure about this but it can't hurt. Put the gauge with correct threaded adapter to fit your spark plug hole into the first cylinder you're going to check. I never heard about disconnecting the fuel lines and since all the plugs are out you don't have to worry about the engine starting. Turn the key and crank the engine over several times. Record the pressure and go on to the next cylinder. All cylinders should be within 15 lbs of each other. Good luck. And let us know what the results are.
Dave
2001-12-13
Ross J Somie, I believe that you must have the leads all connected and the spark plugs earthed whilst doing the compression check otherwise the power pack/s may fail. I guess disconnecting the power pack whilst spinning the motor over with the starter would overcome this problem. If the motor is warm you won't need to oil the bore as the fuel or oil would have done this for you. I would leave the fuel lines in situ when testing compression. Hope this helps some
Ross
2001-12-13
SeaDawg Somie, got another couple of suggestions, if you have time to do it.

Just for kicks, check the compression with the throttle at idle, and also at wide open throttle. I've noticed in the past it is higher at WOT (wide open throttle), and have never hear

2001-12-13
Somie Thanks for the tips!
Right now I'm relocating the fuel/water separator to the stern and replacing the inline fuel filter, so when that's completed, the fun will begin.
Will post results.
2001-12-13
petryshyn HI

You guys are all right!

>crack the plugs and re-snug(prevent thread damage)
>warm up engine
>remove all plugs
>ground plug leads to block
>crank engine over with wide open throttle
>crank equal number of hits per cylinder(5-7 hits minimum)
>don't use WD-40, as it will increase your readings and give you a false sense of security
>generic spec = 10% variation from highest to lowest cylinder

just my .02 cents worth..good luck!

2001-12-13
Somie Unfortunately, I was unable to perform the test today, One thing i want to completely understand though, is to make sure the spark plugs are earthed? That means running a wire fron the leads to the block of the motor..?
I'll also look into the manual to see about disconnecting the powerpack.

I don't think the starter will engage if in gear, so that'll mean no WOT test (for now at least)

2001-12-14
johnkc somie, I believe that you have an ignition safety switch ,just pull the lanyard and the ign will not spark, hence no damage to ign components 2001-12-14
Ross J Somie, Johnkc makes a lot of sence. it was my advise that the power pack be disconnected so if the kill switch would prevent a spark then it should be safe to do compression test that way. Obviously no good for testing for a spark however.
Ross
2001-12-14
SeaDawg Somie, you should still be able to use the ignition starter switch at your motor, even with the boat in gear. You just need to connect it so that you get 12 volts to the + side of the starter.

Just make sure you DON'T connect the starter switch from the positive 12 volts to the negative (ground) side of the solenoid, or you will create a direct short and burn up the test switch. And probably make a big arc or two.

You should be able to look at the wires and see which one is the "hot" wire there.

If you are uncomfortable using the starter switch, get any of your electrician friends to help you, if you show them this e-mail, thay should be able to help you, even if they know little about boat motors.

Just 2 more cents worth!!!

2001-12-14
Somie Season's greetings to all. Well due to my ISp screwup and going to orland for a few days, I finally have the results to post.
Here is a diagram of the cylinders (looking at engine from back) and their average PSI after 3 cranks each (at idle). Oh yeah, I disconnected the power pack.
100
2001-12-30
rtrent Normally the shifter has a "button" to permit accelerating throttle without engaging into forward or reverse gear. You would use this to "juice" it when starting so you can rev the engine without it in gear. Use this to go to WOT without prop spinning. Engine won't crank with shifter in gear. You must check compression with WOT. Using oil in cylinder is part of troubleshooting AFTER you determine that a cylinder has low compression. You spray a couple squirts of oil in and recheck compression. If compression is higher with oil, low compression problem is caused by bad rings. 2001-12-30

If you would like to post your own question for the experts just click on
the Boating Forums tab at the top of the page or click here!

Disclaimer: iboats.com provides this content for the education and benefit of all boating enthusiasts.
We cannot, however, take responsibility for individual postings, nor can we verify the accuracy of any posting.
Please use any information provided from individuals with great care and read any applicable manuals or safety instructions.
Also, if you determine that a posting is inaccurate or offensive in any manner, please use the Contact Us email form found below.

If you would like to post your own question for the experts just click on the Boating Forums tab at the top of the page!


Outboard Motors

Power Heads

Lower Units

Props

Repair Manuals

Controls, Steering

Trim/Tilt

Power Tilt/Trim

Parts

Outboard Repairs | Boats | Outboard Motors | Boat Dealers
Boat Covers | Boat Propellers | Boat Repair | Marine Engines | Outboard Forum Directory
Terms of Use | Privacy Practices | Legal Notices

1-800-869-1686 (Toll Free)
001-801-571-0071 (International Calls)
Copyright © 1999-2009 iboats, inc. All rights reserved.