Dolmar 7910 ring end gap

[banditt007]

New 7910 OEM piston and cylinder. Out of good practice I'm going to check the ring end gap before installing. I see the FSM states a max of .020". But no insight for what it should be like when new. If .020 is the wear limit. Should I be concerned if it tested to .014"? I checked it really quick and will again but thats what I came up with. Perhaps the ring got bumped out of square with the bore. I'm just looking for an idea of whats good for this saw brand new. Thanks.

 

[alexcagle]

Interesting.
I've got two new 7300 series Dolmar OEM cylinder kits here, and are both .012" squared in the bore, positioned just above the intake port, and .014" about 1/2"from the top of the bore.
The flip side of too much gap;
I always thought thought they should be as close to touching as possible, but I just recently saw a case where @westcoaster90 had an OEM 371 Husqvarna cylinder that I sent him; which took a poop from a Golf brand piston kit I sent along with the cylinder. Turns out that on the ring; that the end gap was too close. The ring swelled, then hung on the exhaust port, which gouged it all the way up to the squish band. He had ported It, and It ran strong for about a day and a half. Then it sharted.

 

[Little Al]

The usual reckoning is 4/6 thou per inch of bore for air cooled motors

 

[alexcagle]

I can't spell that.lol
So on a 52mm bore converted to inches would be?

 

[cuinrearview]

I can't spell that.lol
So on a 52mm bore converted to inches would be?

Just over two inches

 

[Big_Wood]

Yep. Shaved the plating clean off above the exhaust port. Was beveled extra special because the cylinder was iffy to start with but the cylinder was not the problem.

This pic shows the chipped ring end from when they collided.

This pic shows the ring broken on exhaust port side

And here's the cylinder

Exhaust port looks sharp in the pic but it was beveled extra special because I had a hunch there was potential for this. Can see that the ring shaved the plating clean across the exhaust port and way up the center. Noticed the tight end gap but figured it would be ok as I had luck with golf in the past. Needless to say I'll never use one again. I mostly used it cause it came with the cylinder and the cylinder was questionable anyways. Was a strong runner though.

 

[blsnelling]

I've never seen a ring end gap issue with OEM parts.

 

[Big_Wood]

I've never seen a ring end gap issue with OEM parts.

i'm done with AM except maybe the odd meteor. got anymore OEM 372 top ends brad? i ported a big bore a while back and put about 100 tanks on it before i pulled it from a saw i sold. it's back on this saw now and going up for a shift on the hill with @Westboastfaller. he should be able to test it for me lol. i'm no fan of the chinsy chrome plating but it's been fine.

 

[alexcagle]

Looks like a healthy port job.
That sucks *** Dude.

 

[Little Al]

I can't spell that.lol
So on a 52mm bore converted to inches would be?

A gnats whisker over 2 inches.

 

[alexcagle]

That's what She said..... lol