?????? Question Johnson QD-16

[Buccaneer]

#176222

Who knows, maybe it will be a good runner when back together.
Let us know what happens!
I’ve never researched rings for a Scott yet.
Possibly you could obtain some from this guy …….
http://pistonrings.net/

tinkerman wrote:

No sir that is the picture of a Scott Atwater model 497 …. May go ahead and clean the carb and fix the pull rope and see if it’ll start

Prepare to be boarded!

[wbeaton]

#176343

I think you are looking for a problem that may not exist. The fact that every motor reads 50 psi is a red flag. I have never seen a 1950’s OMC with compression below 60 psi that would run. In fact, 60 psi seems to be the basement of whether it will run or not. I’d prefer to see 70 psi or better. Every gauge reads differently, but the difference shouldn’t be that big. I suspect your gauge is reading low or not sealing properly. Either way, don’t start tearing things apart, yet. Start with the basics first.

Wayne
Upper Canada Chapter

uccaomci.com

[Mumbles]

#176353

What Wayne says, X 2.

[phil]

#176373

He wrote:

tinkerman wrote:

I have a 30 hp mariner on my boat that runs great and it shows 85 psi per cylinder so I’m thinking my gauge is ok.

http://www.omc-boats.org
http://www.aerocraft-boats.org

[wbeaton]

#176375

I missed the 85 psi part on the Mariner. However, 85 psi is still low for a motor of that horsepower and age. I still suspect the gauge.

Wayne
Upper Canada Chapter

uccaomci.com

[David Bartlett]

#176378

wbeaton wrote:

I missed the 85 psi part on the Mariner. However, 85 psi is still low for a motor of that horsepower and age. I still suspect the gauge.

Especially if it runs well.

David Bartlett
Pine Tree Boating Club Chapter

"I don't fully understand everything I know!"

[jeff-register]

#176386

Looks like you have the pistons out. Take a ring off & put it in the cylinder & measure the ring gap at the top of the bore, next do the bottom of the bore to check for cylinder taper.

[tinkerman]

#176404

No I didn’t take the pistons out yet, I was contemplating it. I think I’ll get a better compression gauge and see what happens. It makes sense if my mariner runs like a brand new engine then 85 is really low for that motor. It’s an 89 model. So maybe if the mariner is actually better compression than the gauge is showing (even 110-115) then maybe my vintage motors are closer to 80-90 which would be ok for an old motor. I wasn’t crazy about buying ANOTHER gauge but I think at this point I NEED to rule it out. Thanks for the advice

It's a jungle out there.