Johnson AD-12 7.5 HP Piston Ring End Gap etc.

[aquasonic]

In search of the ring gap end clearance for the Johnson AD-12. It may be the same for all OMC 7.5 HP from 1950-1958, but I’m not sure about that.

Also, I’ve seen some filing the ends down by dragging a doubled over piece of sandpaper through the ring as it’s held pinched together. Others use flat files or ring grinder machines. No machine here, so what hand filing procedure/technique is best?

Are piston ring compressor and installer pliers helpful?

Thanks for any help.

[fleetwin]

The ring end gap spec for your 7.5hp is: .007-017″. Something is wrong if new OEM rings need “filing”, wrong part number, improperly bored oversize, etc. Again, I am referring to OEM rings, follow whatever instructions are included with aftermarket rings.
I would not use any type of piston ring compressor on this engine, you don’t want to chance misaligning the rings over the piston alignment pins. I would just use my fingers to compress the rings on this little engine, perhaps with the help of an assistant, I’m available (on vacation) next week….D

[aquasonic]

Thank you fleetwin. I have OMC rings, and by the way, they are getting hard to find and very pricey. I was “lucky” to buy them at about 1/2 of what some vendors charge. If no filing is required, that will be the best outcome. I did do a relatively light honing, so hopefully the new rings work out.

Once checked for end gap, getting the rings and pistons into the bore will not be an issue, as I’ve done it several times. I do really appreciate the offer for help though. How about using the ring pliers for installation? In the past, I’ve just used my fingers to open the rings. I don’t know if there are better results with the pliers. I do have a talent for breaking the old rings when removing them.

[Mumbles]

Like fleetwin says, I wouldn’t use any kind of ring compressor on them as it would be to easy to snap an end off if the ring isn’t lined up perfectly with the locating pin. I like to install them one ring at a time. Once the bottom ring is in the hole, the next ring is put on the piston and so on until all three are in.

[labrador-guy]

I have found that some after market rings need to be checked for end gap and be sure there is clearance around the locating pins. If you have to file your rings for any reason what I do is put a small point file in my vice. And gently squeeze the ring on the file and move it up and down. It doesn’t take much filing so go EASY!

dale

[fleetwin]

Sorry, didn’t read your post correctly Aqua….The pliers you are referring to are for spreading the rings open in order to get them on the pistons…. Sure, they are a good idea provided they are small enough to fit the relatively thin/small rings without slipping off….D

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