Why do outboards just die?

[peacekeeper6]

what makes an outoard die? why does the compression get low even if it is meticulously maintained? i am getting my first outboard boat and this is one of my main concerns, the motor on it now has compression of 95-100 accross the board. its even which is good but why is it so low? maybe thats where its supposed to be? but my main questions is are outboard blocks and pistons and rings and thigns as durable as there I/O counterparts? usually when an I/O goes its the drive or the block cracks or gets water in it somehow through the risers and such.

 

[WillyBWright]

Re: outboards that die

Re: outboards that die

Sometimes low compression readings are caused by inaccurate compression testers. At work we have a shop tester, my tester, and the other mechanic's tester. They all show different compressions on the same motor. That's why the key is to have readings fairly consistent as opposed to meeting a benchmark reading. It's also why the factory service manuals don't publish target compressions.

Other times, low compression readings are caused by the kind of rings. In old Mercs that have been partially rebuilt, it's not uncommon for compression readings to vary. Original pistons have three conventional rings. New pistons use two of two kinds, a conventional on bottom and a keystone on top. Keystones are designed to seal best under the most stress and that stress only comes with combustion. Those typically read lower than the old pistons, but under combustion they would read higher if it could be tested that way. So even if the readings vary, each cylinder can be perfectly healthy.

Johnson/Evinrudes use similar rings, but I forget what they call them. Pressure-backed piston rings? They usually read in the low one hundreds. And then we have larger motors that are electric start that typically have higher compressions than pull start models. On a 100Hp I'd like to see readings in the low one hundreds. On an old 9.5Hp I wouldn't be likely to see over 80.

So it depends on wutcha got. What motor, what rings, and what tester.

As far as durability, how many early sixties sterndrives do you still see in service? Hardly any. But how many outboards of the same age are still perking along? Gazillions.

 

[peacekeeper6]

Re: outboards that die

Re: outboards that die

that is a very good point. I just am basing my numbers on the late (90)'s models. I just see so many people withh low compression OB and that is the first thing to go. I oculd be totally wrong, but that information apbout the testers adn rings is great information. THAT IS WHY I LOVE TO POST!! THANX!!

 

[tashasdaddy]

Re: outboards that die

Re: outboards that die

i think the reason you see so many, is that there are so many out there, and these are the ones, that have not had that meticulous care. you don't here about the good ones. someone mentioned the other day that the Johnson/evinrude forum had twice the post of the Mercury forum. they assumed that the Merc were more reliable than the J/E's. but when you look at what's posted you see a lot of questions, on the old J/E's 50's and 60's. you don't see those post in the Merc forum nearly as much. Why? there not as many around any more. merc was the new kid on the block back then.

 

[peacekeeper6]

Re: outboards that die

Re: outboards that die

another excellent point, hey tash are you currently on a rebuild? i have two i am about to do adn would like to get some on hands practice if your doing some stringers or floor or anything. or even on coating some boards.

 

[Dhadley]

Re: outboards that die

Re: outboards that die

Outboards don't "just die". If something goes wrong there's a reason. A damaged piston or a broken ring is not a cause -- it's a result. Outboards outlast IO's by far. 4 stroke motors, particularily IO's, need valve jobs and / or rebuilds far sooner than a 2 stroke outboard will if proper care is given to both.

Finding the cause of an outboard "failure" is the #1 overlooked part of a rebuild.

Recreational outboards that have "low" static compression probably have high port timing. That allows them to make more torque and still run on 87 octane. For example the 200 crossflow vs. a 200 looper. The looper will have lower static numbers but makes a ton more power.

Don't get hung up on numbers. As long as there is no more than 15 lbs difference it's OK.

 

[JB]

Re: outboards that die

Re: outboards that die

Just an old guy's opinion, but outboard engines don't just die. They are killed by abuse or neglect. Most of the time the abuse or neglect is unintentional, caused by ignorance.

Don't change the impeller each 2 years? Neglect.
Don't use the correct fuel mix? Abuse.
Don't use the correct spark plugs, correctly gapped? Abuse.
Don't take the engine out of service at the FIRST sign of trouble? Abuse.
Don't properly prepare the engine for storage? Neglect.
Crank the engine without cooling water? Abuse.
Don't have and use both the OEM Owner's Manual and Service Manual? Abuse.

I could go on for another page or two, but I think you have the idea.

 

[Silvertip]

Re: Why do outboards just die?

Two strokes are low compression engines by design. 6:1 give or take a little is very normal. I/O engines will run anywhere from 8:1 on up.

 

[dajohnson53]

Re: Why do outboards just die?

what makes an outoard die? why does the compression get low even if it is meticulously maintained? i am getting my first outboard boat and this is one of my main concerns, the motor on it now has compression of 95-100 accross the board. its even which is good but why is it so low? ....

95-100 can be considered good compression, and close to new depending on the outboard. Of course, it varies w/ technique and gauge, but my big V6 has compression in that range and I've been told by two different mechanics that it is normal for that type of engine in excellent shape.

 

[fishingdan]

Re: Why do outboards just die?

As mentioned, the testing technique can impact the results. For example, a cold engine will have lower compression than a warm engine. That is why one is looking for numbers in a normal range, but more importantly, the numbers should be about the same across all cylinders.

 

[Scaaty]

Re: Why do outboards just die?

Outboards die because they have stupid onwers...and it would be VERY helpful if you would specify WHAT outboard, and year you are referring too?
I have 60 year old under 10hp Johnny's here that I have made room in the casket for...

 

[kenmyfam]

Re: Why do outboards just die?

Lot of old outboards out there and still going strong !! Owner / operator neglect and /or abuse is a huge reason for problems.