Top speed with 18hp Evinrude on 14′ aluminum

[stephenspann27]

quote Chris_P:

Obviously those pistons were junk!

In the bore, are my eyes playing trick, or are there gouges out of them? Bottom of 4th pic. OR is that just heavy pitting?

No chunks missing,this is a fairly deep groove, but the rest of the scoring is light.

[stephenspann27]

You can see the rust rings the wristpin circlips lift in the bore, this was a salt water motor with a lot of damage, the head gasket was also leaking. This block is most likely junk. I had to build up with JB weld and file flat the midsection surface that the powerhead bolts to because so much material was missing. I probably picked one of the worst 18hp motors out there.

[stephenspann27]

Just for fun I checked the ring gap on the old motor:

Piston 1

ring 1 = .022

ring 2= larger than .035

ring 3 = larger than .035

Piston 2

ring 1 = .023

ring 2 = .018

ring 3 = .012

[wiscoboater]

Stephen….stop trying to talk yourself into a myth. The pistons , rings and bores are bad. Sugar coat it any way you want but the advise you have received here is from guys that have been there and done that hundreds of times. Frank, Chris and Fleetwin would not steer you wrong. When a motor is worn out… well… It’s worn out.

[stephenspann27]

Thanks wannabe, keep in mind the pics I posted are of my old powerhead. It does sound like my current powerhead could be bad as well, knowing the totally toasted one made 90 PSI, my "good" powerhead that made 100 PSI might be in bad shape as well.

[stephenspann27]

I found the ebay ad for the powerhead I have, the seller said it had 125psi top and bottom.

[jerry-ahrens]

You really have to watch the compression gauge closely, to see how fast they pump up while cranking. I had an 18 a little older than yours that had near 95 psi, but the pistons were scored from overheating. Its a good idea to pull the intake port covers and have a look before purchasing. These old engines would run so good for so long, that folks wouldn’t bother with impeller maintenance! Then one good over heat would spell the end for an otherwise good engine.

[stephenspann27]

quote Jerry Ahrens:

You really have to watch the compression gauge closely, to see how fast they pump up while cranking. I had an 18 a little older than yours that had near 95 psi, but the pistons were scored from overheating. Its a good idea to pull the intake port covers and have a look before purchasing. These old engines would run so good for so long, that folks wouldn’t bother with impeller maintenance! Then one good over heat would spell the end for an otherwise good engine.

When pulling the rope, if the rings/bore are good, should it only take about one pull to build max PSI?

[stephenspann27]

I found this on iboats, plan to try it:
"wot drop to idle and it wants to die points towards a loss in crankcase pressure…try this sequence, wot, quick drop to idle, quick snap to 1/2 throttle….if the engine won’t recover and dies this points towards leaking or loss of crankcase pressure in 2 strokes < this assumes the ignition and fuel delivery are ruled out >…causes?…crank seals, crankcase halves seam leaking, worn piston to cylinder tolerances, loss somewhere else."

[wiscoboater]

One other thing to think about Stephen. Just because it makes compression when doing the compression test, whats not being measured is "blow by". As was stated earlier in this thread, a leak down test will most likely reveal that it is not holding that cylinder pressure for the complete combustion stroke. That is where the significant power loss comes from. The pressure is leaking past the rings.

Also, be very careful when buying powerheads from Ebay. They show you a compression gauge pegged at say 120lbs. and state the power head "has great compression". Last winter I had a 66 FD 20 with 120 on top cylinder, 60 on the bottom. If i put about a teaspoon of 2 stroke oil in that bottom cylinder I could get it to read 95psi. on the gauge. You see where I’m going with this? Buyer beware.

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