Compression?

[BlueGhost93]

Hi guys. Im wondering what the compression should be on a 1988 Johnson VRO 40? I was going to pick one up today but I got the feeling compression is low on it so we are going to check. What should be optimal and whats just "ok" but still fine? Ive noticed a lot of ouboards around me have low compression.

Thanks!

 

[boobie]

Get a good gauge, go check the compression an get back to us. There are no specs for compression.

 

[1983 ercoa 21']

A ball park would be in the neighborhood of 100 to 120 and there shouldn't be any more than 10% between cylinders

 

[BlueGhost93]

Both are at 95. Like exactly. He seems to think that's fine im thinking that's low... If I get it I need this outboard to last me at least a year or more.lol

 

[Bosunsmate]

hard to say, ive had motors with 96/100 and they have done me well.
If the price is sharp then those numbers wouldnt stop me, id try and have a look at the cylinder walls

 

[Bosunsmate]

hard to say, ive had motors with 96/100 and they have done me well.
If the price is sharp then those numbers wouldnt stop me, id try and have a look at the cylinder walls

 

[Bosunsmate]

hard to say, ive had motors with 96/100 and they have done me well.
If the price is sharp then those numbers wouldnt stop me, id try and have a look at the cylinder walls

 

[BlueGhost93]

Huh posted three times? Haha

Yea hmm try and peek in the plug hole? He fired it up and it sounds awesome. Pretty smooth. Has a new controller with it. I can get it for $800.

Would there be higher compression on a cold start or after the engine has been warmed up?

EDIT: It comes with this controller
http://galleryplus.ebayimg.com/ws/web/200567260355_1_0_1/1000x1000.jpg

 

[Bosunsmate]

Yeah if theres light behind you you can often see the cylinder walls quite well and look for any gouging.
If a motors running ok i try and do the compression test when its warmed up as the oil is doing its job better then too, filling in tiny voids etc

 

[1983 ercoa 21']

I wouldn't be scared of 95 at all considering the year of the motor when the factory reduced compression because of fuel. I'm not sure where you are from which makes a difference in what things sell for but the price don't seem out of line

 

[BlueGhost93]

Im in San Diego. Where prices are ridiculous haha. Ok ill take a look at the cylinder walls and if they look ok I think ill get it. The fact the compression is the same makes me think its just a low compression motor.

 

[bonz_d]

Just for referance, Have a 1975 Johnson 50hp that is pulling 148# on both, a 1983 60hp Johnson that has 142 and 146# and a 1987 Johmson VRO 50hp that has 145 on both. The 60hp is the one I use on my boat. The 1975 I've been trying to sell and the 1987 is waiting for a new lower unit.

 

[BlueGhost93]

Well hmm... IDK what to think. From what ive googled a lot of late 80's early 90's motors seem to have lower compression for some reason. I cant afford to pick up a engine that's not good

 

[boobie]

If you do get it, do a good de-carb on it. That may help the compression.

 

[BlueGhost93]

Ok just picked it up. Suggestions on how to decarb it? Its pretty dang clean under the hood for a saltwater motor. What I find interesting is it has 2 **** spots. It has a tube coming from under the hood that sprays almost right away then it has a double hole on the shaft that must spray once its warmed up.

 

[Bosunsmate]

yes thats the thermostat relief hole.
you might want to check out this link on a service bulletin on telltales
http://forums.iboats.com/forum/engi...aq/228380-johnson-evinrude-adding-a-tell-tale
Ive a 82 60hp compressions 98 102 and it goes like wildfire

 

[metriccrescentwrench]

.... From what ive googled a lot of late 80's early 90's motors seem to have lower compression for some reason. ....

I don't know anything about that particular engine, but in the late 80s OMC started going away from crossflow engines to "loop charged" engines. Many (maybe all, I'm not sure about this) of their loopers have an idle relief port which bleeds off a bit of compression at cranking speeds (but has essentially no effect at running speeds) - thus lower compression readings for loopers. I looked at the online parts diagram and it appears this engine is in fact a looper, so if all of the above holds true 95 psi is probably right in the ballpark for that engine.

 

[Bosunsmate]

Metric.
Just wondering what this idle compression relief port is, how does it work and also not be effective at running speeds?
Ive a 1982 60hp thats a looper currently with the head off so im curious to know what i could be looking at in there.
thanks

 

[racerone]

You will not find that wee hole drilled in the cylinder wall on an 82 motor !!!---That hole bleeds of compression at low speeds .---Starts exhaust a wee bit early for quiter running.----At higher throttle settings there is not enuff time for any significant loss of compression.----Simple really.

 

[Bosunsmate]

You will not find that wee hole drilled in the cylinder wall on an 82 motor !!!---That hole bleeds of compression at low speeds .---Starts exhaust a wee bit early for quiter running.----At higher throttle settings there is not enuff time for any significant loss of compression.----Simple really.

Thanks, so if i find a hole i know im in trouble!