I'm in the process of rebuilding my 273 HP. I'm confused on where to measure ring gap in the cylinder bore. The factory service manual says to measure 2 inches above the bottom of the cylinder, but I've read other articles that says to measure 1- 1 1/2 inch below the top. When I measure according to FSM the gap is within specs, but when I measure 1 1/2 below top, the gap is at .020 to .021 on compression ring and the oil rails are over .055. Any clarification would be greatly appreciated.
where to measure 273 ring gap in cylinder bore
- Thread starter GLW
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67Dart273
Well-Known Member
Actually I'd check TDC, bottom, and center. The thing is, you want adequate gap at the SMALLEST part of the cylinder. What you are trying to do with gap, is when the rings are hot, they will not butt ends and compress and damage/ break, etc.
A lot of taper is a bad thing. A new set of rings is like putting lipstick on a pig.
Professor Fate
Push the button, Max...
This^^. Yes, if you're seeing that much variance from top to bottom, you need to check your cylinder taper- on a true cylinder there should not be any difference in end gap wherever you measure it. It should be the same all the way down the cylinder.
If you must, then measure it at the point that you get the lowest measurement, as 67Dart273 said.
If you must, then measure it at the point that you get the lowest measurement, as 67Dart273 said.
Just re-ringing an old motor or has it been bored and honed to fit new pistons ?
Just got it back from machine shop. It was bored to .040 and heads reworked. Compression ring end gap Measured .020 at about 1 1/2 inch down from the top, it measured .017 at 2 inches from the bottom. Is that to much taper?
Ironracer
Gearhead
What? That Don't sound Right, not at all! Maybe a Machinist Member can hop on. But to my knowledge, there should not be that much taper in a fresh bore... @RustyRatRod
Professor Fate
Push the button, Max...
I'm not going to try to do the math to figure the circumferential difference in relation to end gap and taper at a given cylinder length- just measure the bore at top and bottom and see if it falls within spec. The number should be in the FSM. The machine shop should have given you the final dimensions after cylinder prep... Heck, it should have been matched to your pistons.
Yeah taper is not a good thing, especially in a fresh bore. That means someone didn't do their job right.
Professor Fate
Push the button, Max...
Make SURE you're measuring your ring gap(s) with the ring square in the bore- generally you use the piston top (upside down piston) to locate the ring in your intended location in the bore- then measure the gap. The more out of square the ring is, the more inaccurate of a gap measurement you will get.
FSM says anything over .010 taper has to be bored. They did measured my new egge hp piston
I did use a two barrel piston to locate ring, I will remeasure Monday just to make sure.
Professor Fate
Push the button, Max...
So, you disagree with what? That you want me to do the math that you can easily determine? That the spec is in the FSM? Or that the machine shop should have done the finish hone to match your piston size and ring material? (And without substantial taper, I might add.)
I must be hitting button by accident. I’m not disagreeing with anything.
.010 TAPER is a TON. I believe that's a misprint.
Ironracer
Gearhead
Smaller Bore, but Max for my Ironhead is .003.
Ironracer
Gearhead
Gotta be... that's crazy. Is that a FSM, or one of them crazy parts store books? I've ran into bad info with the latter...
The fsm I down loaded from the internet. It uses that spec in a couple different places in the manual and for all engins 273-383. Seems like it would be an error to me or I’m reading it incorrectly, which is very possible
Yea though I would try to find one and check it.
Homemade and handy. I had to come up with that also. HP pistons don't work to square the rings.
Cool.
Dale Davies
Well-Known Member
Has the block been bored or honed for rering freshen? A bored cylinder should have no taper and the ring gap the same top.or bottom. A rering where you cut the ridge off the top above where the top ring travels to, and then hone the cylinders will have taper and out of round. The most wear will be about 1" down from the deck surface. Put the ring in at about that point and square it to the bore. Then use a light from the bottom and watch for light around the ring between it and the cylinder bore. May be light on the major and to lesser extent minor thrust sides of the bore. Check end gap there. Then push the ring down to about 2" from the bottom of the cylinder, square the ring and check the gap again. This will be less gap as there should be minimal wear.
If there is light in places between the ring and cylinder wall or more than say 0.005" gap change between the top and bottom, the block should be bored and new pistons and rings purchased to fit. Machinist will hone for proper piston fit.
Factory wear limit is .005" taper which equates to +.015" end gap , at .003" end gap increase per .001" wear , factory spec means .030" end gap is the wear limit . I rebuilt the standard bore 340 in my cuda in 2000 with .003 taper and .025 end gap and just a light hone , now 40,000 miles later no smoke , no oil use and still runs strong. You are overthinking it , put it together and run it.
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