Thoughts please regarding installing new rings in 1964 3hp johnson.

[Monte NZ]

I am wondering what could be the result of installing new rings after a light hone. The compression is 60psi on both cylinders and I’m

wondering how much the compression may improve. Its worth mentioning that there is a distinct rattle at low speed, which makes me wonder if it’s a wristpin rattle.

Attached is a video clip of the motor idling………hopefully you can hear the rattle.

https://photos.app.goo.gl/4by48cvJXpgBUWCy6

Thanks again for your help.

Monte NZ

[billw]

Cell phone video is never as good as one’s ears, so I can’t really tell you what I hear. A couple of classic problems would be a coil lamination hitting the flywheel or an improperly fastened gas tank and/or support ring. If you remove the flywheel and apply Magic Marker to the face of the coil laminations, then run again and inspect, you can see if the coils have been rubbing. I wouldn’t really be automatically aghast at 60 psi. When the engine is at its lowest possible idle speed, where does the mag control lever point to? On a very good running three, it will actually point to “idle,” and not half way to “start.”

Long live American manufacturing!

[fleetwin]

Like Bill says, tough to judge based on audio.  I have never seen one of these engines with a worn wrist pin though.  Usually, the wear will be on the crank end of the rods reulting from water or not enough oil in the mix.  You can check for slop by gently rocking the flywheel back and forth with the head off checking for lost motion when the pistons move.  I’m thinking the noise is more likely from the mag plate or cover hardware.  These engines have a wavy washer sandwiched between the mag plate and aluminum retainer to provide stiffness so the mag with not move on its own while the engine is running.  Once these wave washers get worn, the mag can wobble a bit, allowing the coils to rub on the flywheel.

I probably wouldn’t trust the 60PSI compression reading, compression gages are usually inaccurate when used on these small combustion chambers.  I would hesitate to pull this powerhead apart unless you can really see an issue with rings/pistons/cylinders.  70PSI readings seem normal for these little guys.  If you decide to pull it apart, you should take time to inspect and measure everything closely.  New rings aren’t going to help worn/rusted cylinders much.

PS:  I listened to that video again, and didn’t hear anything unusual, the engine seems to idle nicely, I would leave it alone unless I’m not hearing the noise you are concerned about.

• This reply was modified 1 year, 3 months ago by fleetwin.

[Fastwin18]

If your cylinders are worn then don’t expect miracles when changing the rings.

I’ve just changed the rings on my TD20 and the compression went up from 55 to 67. Mind you, the 55 was dry after sitting 40+ years unused. 67 is with oil and new head gasket.

[The Boat House]

What result are you looking to achieve? You don’t mention a running
or starting issues. Replacing just the rings in an attempt to push a
needle farther on a gauge can result in other unintended issued with
little rewarded in the end. As far as your knock I would suggest check
for any ware in the rods or wrist pin by watching the pistons after
removing the exhaust cover, thereby avoiding the possibility of a broken
head bolt.
Tubs

[crosbyman]

run it till it croaks  then the autopsy will be easier …. a used PH can  revive it.   nice piant job !

Joining AOMCI has priviledges 🙂

[need2fish]

IMHO – if it runs well @ full throttle and half decent at idle, then leave it. Once you open up the crankcase, you’ll want to change bushings, then you’re in for a head gasket. There may be crankcase leakage through the top and bottom crankshaft seals. As you replace those you’ll see how bad the driveshaft receiver is and you’ll want to replace the crankshaft, then you’ll find a bit of play in the rod ends.

And…. and …. and .

PS – that’s all generic op-ed, not necessarily your situation.

[Dave Morrison]

I’ve got 5 of these Ev/Johnson 3 hp from 1952 to 1964 and none of them have more than 70 psi and several have 60, and they all run fine. The trick is to get the throttle down to Idle when the motor is actually idling. Some do . Some don’t. OMC Engine Tuner ( or similar) will usually get these idling better after 1 treatment.
So, I wouldn’t worry too much about the 60 psi .

[billw]

I often have better luck dialing in the low speed mixture adjustment at maybe 1000 RPM. At that speed, minor changes are more quickly noticed. When I do it that way, it seems to result in a more stable low idle.

Long live American manufacturing!

[The Boat House]

The carburetor should also be considered
when low speed running is an issue. While
dirt can often be the cause, a vacuum leak
should be investigated. Wear around the
throttle shaft can have a negative affect
on low speed running. As these are great
motors, many have experienced extensive
use, creating this issue in varying degrees.
Tubs.

https://youtu.be/thtxPPgjA5g

[Author]

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