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Piston ring gap

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Piston ring gap #1
Mitchman2 Mitchell Andrus Mills River, NC, USA Sign in to contact	Topic Creator (OP) Dec 9, 2016 01:43 PM Joined 9 years ago 3,100 Posts

I'm getting parts lined up for re-assembly and I need a gut-check on the piston rings.

Cylinders/pistons are +.040 and are in perfect shape.

I got a set of .040 rings from Moss, (Devon) and I'm getting a gap of .012 to .014 in a 60* shop, 1" from the top of the bore. In the WSM, they spec a gap of .008 to .010

Should I look for a set that I can grind a bit, is there such a thing for our engines (better made)? Or, am I being a little too cautious. I'm more used to working on high compression engines where this could be a point of failure. (Chev small blocks, etc.)

Thanks.

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Re: Piston ring gap #2
LaVerne LaVerne Downey Fruita, CO, USA Sign in to contact 1954 MG TF "Green Hornet" 1969 MG MGB "The Beater" 1979 Triumph TR8 "Turd 8"	Dec 9, 2016 02:16 PM Top Contributor Joined 16 years ago 15,545 Posts

The workshop manual is using the stock bore size. Use this chart to calculate the desired gap

TSringgaps.jpg 28.7 KB

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Re: Piston ring gap #3
Mitchman2 Mitchell Andrus Mills River, NC, USA Sign in to contact	Topic Creator (OP) Dec 9, 2016 03:12 PM Joined 9 years ago 3,100 Posts

LaVerne, thanks. Maths... I'd forgotten this step. I think I'm in the right ballpark.

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Re: Piston ring gap #4
fast-MG.com Dave Headley Cortez, 4 corners, Colorado, USA Sign in to contact	Dec 10, 2016 08:39 AM Top Contributor Joined 15 years ago 9,605 Posts

Keep in mind that a bore that is +.001" over nominal will produce a ring gap that is more than .003" bigger.

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about 2 weeks and 2 days later...

Re: Piston ring gap #5
DaveA David Ahrendt Lenoir, NC, USA Sign in to contact	Dec 27, 2016 06:52 AM Joined 13 years ago 332 Posts

Hi Mitch,

I'm just starting reassembly of the TC engine with +.020 pistons. Do you remember what you ended up with for a gap on the oil rings?
Moss supplied Grant rings and the oil rings have a gap of just about .004 and LaVerne's chart calls for a min. of .015". I think I'm going to have to borrow or buy a ring filer.
I don't I want to try to manually remove .011.

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Re: Piston ring gap #6
Mitchman2 Mitchell Andrus Mills River, NC, USA Sign in to contact	Topic Creator (OP) Dec 27, 2016 08:37 PM Joined 9 years ago 3,100 Posts

In reply to # 3419050 by DaveA Hi Mitch,

I'm just starting reassembly of the TC engine with +.020 pistons. Do you remember what you ended up with for a gap on the oil rings?
Moss supplied Grant rings and the oil rings have a gap of just about .004 and LaVerne's chart calls for a min. of .015". I think I'm going to have to borrow or buy a ring filer.
I don't I want to try to manually remove .011.

Hi Dave,

I didn't measure each ring, I only laid #1 in at 1" below the top. I figured a matched set were all the same.

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Re: Piston ring gap #7
DaveA David Ahrendt Lenoir, NC, USA Sign in to contact	Dec 27, 2016 09:43 PM Joined 13 years ago 332 Posts

Mitch,

I ended up measuring about 10-11 thou for the first ring and about 12 for the second ring. I'm unsure about the one-piece oil ring. I measure a gap of only about 4 thousand which seems small but I've never used a one piece oil ring before.
I've got to drop some stuff at the machine shop tomorrow so I'll ask him about it then.

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