End gap for rings in 1.750" bore?

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67L36Driver said:
Got a pair of new rings and the end gap is .003"-.005" when squared in the bore. A dab tight?

I'm thinking around .008"-.010" would be a better safety margin for thermal expansion maybe?
Click to expand...

.008-.01 is what I go by but I only do occasional rebuilds. Never had a problem.
 
Untitled Document

This might give you an idea

This is also automotive guidelines, air-cooled runs a bit hotter, but the cyl is alum and will expand with the piston


do the math several times over, nothing worse than taking off too much.


luck,greg
 
Last edited:
Follow up:

Original compression was 115 psi with .078" gap. Butt gap rings with locator pin.

Piston, rings and cylinder assembled dry with .008" gap (notched rings) compression 130 psi. Sans base gasket .030" thick.

After a long fast idle and a few short cutting cycles compression improved to 140 psi.

All in all, an improvement well worth the 18 USD for two rings and the tinker time spent.

Subject powerhead is a Pioneer 1110 54 cc.
 
67L36Driver said:
Original compression was 115 psi with .078" gap. Butt gap rings with locator pin.

Piston, rings and cylinder assembled dry with .008" gap (notched rings) compression 130 psi. Sans base gasket .030" thick.

After a long fast idle and a few short cutting cycles compression improved to 140 psi.

All in all, an improvement well worth the 18 USD for two rings and the tinker time spent.

Subject powerhead is a Pioneer 1110 54 cc.
Click to expand...

Great numbers but help me out here a bit. If I understood your description, the original rings were butt end rings. .078 was the ring gap w/o accounting for the locator pin. Should one take into account the diameter of the ring pins when filing the rings? Your new rings were notched. Was it difficult to maintain the notch when filing? The ring pins must have reduced your effective ring end gap somewhat. Correct, or am I missing something? Just trying to understand the issues a little better.
Bob
 
redunshee said:
Great numbers but help me out here a bit. If I understood your description, the original rings were butt end rings. .078 was the ring gap w/o accounting for the locator pin. Should one take into account the diameter of the ring pins when filing the rings? Your new rings were notched. Was it difficult to maintain the notch when filing? The ring pins must have reduced your effective ring end gap somewhat. Correct, or am I missing something? Just trying to understand the issues a little better.
Bob
Click to expand...

Original rings were square end designed to but up against .0625" dia. locator pins. Hence the usual tolerance of .070"-.080 end gap. Homelite XL-12 and XL-101 uses the same style & size rings also.

Not being one to give away extra performance and efficiency, I found rings on ebay from "The Greek' with notched ends to fit the 1.750" bore x 1/16" thick. Didn't need to file them for locator pin clearence but needed to file the ends that clear the locator pin.

Now compression gases have to pass thru a .008" wide opening instead of an opening .078" wide. Good for an increase of 15 psi dry and 25 psi with oil coating.

Compression should climb even higher as the new rings wear in to conform to the cylinder.
 
67L36Driver said:
Original rings were square end designed to but up against .0625" dia. locator pins. Hence the usual tolerance of .070"-.080 end gap. Homelite XL-12 and XL-101 uses the same style & size rings also.

Not being one to give away extra performance and efficiency, I found rings on ebay from "The Greek' with notched ends to fit the 1.750" bore x 1/16" thick. Didn't need to file them for locator pin clearence but needed to file the ends that clear the locator pin.

Now compression gases have to pass thru a .008" wide opening instead of an opening .078" wide. Good for an increase of 15 psi dry and 25 psi with oil coating.

Compression should climb even higher as the new rings wear in to conform to the cylinder.
Click to expand...

What? How are the rings pinned on that Pioneer piston, I thought the pins were full diameter set straight into the groove?

I just did a Poulan 306, also with "Greek" Homelite Super XL-12 rings, but had to grind each to clear the pin. "The" (as in one pin for both rings) pin on that Poulan goes top down through both grooves, no stagger at all. So the new end grind is vertical on the back side of the ring only, not a side grind like a Stihl. I set the gaps at 0.010" first & it runs great at 106°F outside temp, even though it only picked up 20# with the new rings. Hope to get a few pounds more when the rings seat in.
 
Vertical pin set back against bottom of ring groove.

attachment.php
 
I like it, tho' we may never find out, I'd guess it'll open up to .009 or .010 when seated and I'll bet after an hour you'll get another

10#'s hot

was the cyl. good? Too late now but did you scuff it w/400 grit? (I've spun it on a batt drill)


luck,greg
 
greg409 said:
I like it, tho' we may never find out, I'd guess it'll open up to .009 or .010 when seated and I'll bet after an hour you'll get another

10#'s hot

was the cyl. good? Too late now but did you scuff it w/400 grit? (I've spun it on a batt drill)


luck,greg
Click to expand...

I'm gonna make a quick disclaimer for certain folks... if the bore is not magnetic, DO NOT HONE IT.

There.
 
True enough:

For those who may wonder WTF?

On certain occasions I've attached a strip of abrasive (120coarse -600very fine grit) to a slotted 1/4 shaft (think gun cleaning)

I'll run this thru' something I only want to break the glaze in

A tru' hone, on the other hand can be used with similiar abrasive grades, but the stones are spring loaded, hence it don't take much to ruin a plated surface.

I thank Promac610 for yanking me back to reality.

P.S. - 67L36driver, I had a friend "T-Bone" after H.S. with a '67 L68 - every option - bought it used $3700 (around 1969) IIRC, A doctor's wife owned it - "It was too dangerous"

luck,greg
 

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