old evenrude 18hp speedwin engine compression

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lancsjohn

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Hi does anyone know what the cylinder compression should be in psi using a tester on hand start engine please, I have starting problem wonder if I have crankcase seal problems.
My best cylinder pressure only appears to be 90 psi is this enough?
 
What is the model number?
Any idea of the year?

Workshop manuals available here
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"Artificial intelligence is no match for natural stupidity"
 
You need to call evinrude. I have a Bukh DV10. When I try to hand crank the engine it takes all my strength to get the piston over TDC unless I take 30 seconds or so of steady pull to get it over. The faster I try and crank the engine the harder it becomes.
Don't suppose that helps you in any way but I had problems a few weeks back where I thought I had enough compression but clearly didn't so had to fix it.
 
This is a two stroke? If it is you will not get anything like the 130 - 150 psi pressures you'll get with a four stroke.

My 6hp evinrude will just about get up to 100psi.

Crankshaft seals will not affect the reading. All that will are the piston rings and the bore wear. Bad seals will affect the starting though.

You can identify the year from the model (not serial) number. This website
http://www.storesonline.com/site/573683/page/599222 Will identify the year from the number. Note different systems before or after 1980.

If you think it is a compression problem allow a little oil to run around the rings and then try to start it.

The iBoats forums are good for advice on outboards. http://forums.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=forum&f=28 will take you to the Evinrude pages but be sure to quote the exact model details including year and model number
 
Cylinder pressures per se are not a very good indication. If the two cylinders give a similar result that is better than if they vary.
Handpulling, especially on a 2 stroke, is unlikely to create the cylinder pressures that occur during normal running.
Even 90 psi is not a disaster on a 4 cylinder 4 stroke car engine being cranked by the starter motor, 50 or 60 psi would warrant being worried.
It all depends on the designed compresssion ratio, the cranking speed, the valve overlap (or 2 stroke equivalent) and in the case of a 2 stroke the crankcase volume and particularly the cranking speed.
 
[ QUOTE ]
. I have a Bukh DV10. When I try to hand crank the engine it takes all my strength to get the piston over TDC unless I take 30 seconds or so of steady pull to get it over.

[/ QUOTE ]

Yes but the Bukh is a diesel with compression ratio of probably 18:1, while the Evinrude is a 2 stroke petrol engine unlikely to have more than around 7:1 compression.

The problem with the Evinrude is far more likely to be the crankcase seals are worn, reducing induction efficiency. The 2T creates a partial vacuum in the crncase to suck the fuel/air mix in via the transfer port as the piston rises. The descending piston the compresses the crankcase volume, so that when the induction ports open the mixture blows in to the combustion chamber removing the exhaust gases from the previous cycle more efficiently. If crankcase seals are leaking insufficient mixture is drawn in, and insufficient pressure is created to blow the mixture into the combustion chamber. The first noticeable effect is poor starting as they begin to fail.
 
Rule of thumb, if an outboard doesn,t want to know after 3/4 pulls sumats up.VicS is spot on ref crank seals,might affect starting also idling. Compression ain,t the be all and end all. Likely the seals have gone "hard" Use this routine 1, check for decent spark , 2, clean out carb bowl.3, preferably strip and clean all carb and jets. If all of the aforementioned are "tickity boo " /forums/images/graemlins/grin.gifyou should get some action.Don,t know if you,ve tried new plugs but at least get one plug that you know is ok to test the spark. To just fire her up don,t worry about what grade as long as you have the correct reach. 2 stokes will fire and run with quite a bit of cylinder,piston,ring wear although obviously not pefectly. Can you feel any compression if you turn her over with your fingerstuck in the plug hole? If you,ve got none at all it is well worn. Good Luck! /forums/images/graemlins/grin.gif
 
Early '63 long shaft, same as my old one, now long dead but IIRC 90 PSI on hand pulling is good. My 25hp still gives ~90 PSI on pulling over. I found two starting problems, one was the lower sparkplug tended to foul if the engine was run at low revs for extended periods and the other was gumming of the carb.
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hammer.thumb.gif
"Artificial intelligence is no match for natural stupidity"
 
i agree with the others - 90 psi is plenty. look elsewhere for your starting problem. Bad timing, blocked jets. Hope it's not the crankshaft seal because they are a pain to replace
 
It's over 10 years since it last run but it appears to have been well oiled defore it was stored. I have checked the water impeller which is OK and inspected the bores rings look OK through the side cover plates. The insulation around the two ignition coils was cracked so I have covered with slicone and will recheck the timing, I did have a spark on both plugs but it was difficult to watch two at once I suspect I may be getting two sparks per rev. at each plug as if the coils leads are shorting to both plugs, so I have marked the flywheel with chalk at the piston top centre reference position and will try to check plugs again.
many thanks for all the advice John
 
Some twin cylinder evinrudes have two coils with the sparks acting together. A 'wasted spark', it doesnt cause a problem as there is nothing to ignite when the other cylinder does.
 
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