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Grant piston ring end gap

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Ahmed Avatar
Ahmed Silver Member Ahmed EL Abasiry
Chestermere, Alberta, Canada   CAN
1958 MG MGA
1972 MG MGB
1979 MG MGB
Setup:

1) 18V ('73) block, bored +0.030"
2) Set of AE 0.030" pisotons
3) Set of Grant piston rings for 0.030" (Moss)

I'm checking the end gap on the rings (~ 1" or 2" below deck) and all are measuring 0.009". My understanding they should be between 0.012" to 0.022" per the factory manual.

Before I start filing them away to get the correct gap, I just would like to check to see if anyone used Grant rings before and got similar measurements and had to file them to get the right gap.

The side clearance came good at 0.0015"

Thanks..



"... the motor car, after woman, is the most fragile and capricious thing on earth." - London Daily Mail 1908



Edited 2 time(s). Last edit at 2017-12-06 09:37 PM by Ahmed.

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ingoldsb Avatar
ingoldsb Silver Member Terry Ingoldsby
Calgary, Alberta, Canada   CAN
1971 MG MGB
I recall that Hap posted something on this subject a while back. Try searching for a post by him on the subject.



Terry Ingoldsby
terry.ingoldsby@DCExperts.com

13401h Greg Mouritz
Mentone, Victoria, Australia   AUS
Hi Ahmed,

I rebuilt my engine a few months back with ACL/Repco pistons and had the same issue with the rings supplied.

Using a good quality fine hand file I opened the gaps up.

A couple of tips.
Only file one side (this ensures at least one side remains absolutely 100% square)
Shoot for the low end of the spec .012
At .012 any slight out of square will not be an issue provided the feeler gauge slips all the way thru the gap to the bore wall.
Take your time and don't try to file away to much material between each measurement check.
To remove .003 shouldn't take much effort.
I hold the file in my left hand and rub the ring up and down with my right hand whilst keeping the ring as square as possible.
Best done outside in good light where you can hold the file at eye level to ensure your remain square.
Remove sharp edge on gap ends with fine wet and dry sanding paper before assembly.long

Hope this helps.

Greg

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oleanderjoe Avatar
oleanderjoe Silver Member Joseph Baba
Fresno, Ca, USA   USA
Use the SPEC, Grant supplied with the rings. The Old shop manual gave a spec for the original "Cast Iron" rings, possibly newer technology will vary the spec. When in doubt or no spec available, = .003 per INCH of bore. If you are measuring .009 on all four, If it was me, I would call it good

Ahmed Avatar
Ahmed Silver Member Ahmed EL Abasiry
Chestermere, Alberta, Canada   CAN
1958 MG MGA
1972 MG MGB
1979 MG MGB
Thanks guys..

The specs which came in the package with the rings specifies 0.003" to 0.004" per every inch of bore diameter. So, for a 3.190" bore the end gap should be 9.57 to 12.76 thou. So, with the default gap out of the box, it is right on the lower limit.



"... the motor car, after woman, is the most fragile and capricious thing on earth." - London Daily Mail 1908

Basil Adams Avatar
About 12 miles from Sears Point, CA, USA   USA
.012-.013 is safe. .009 is very tight and you'd be at risk of rings expanding when hot and having the ends butt against each other and break. If you file (and I would) only file one side so that you always have one factory side to keep the angle correct. Best of luck. Basil 707.762.0974 basiladams@yahoo.com



Basil C. Adams
1956 MGA Coupe (Show Car)
1957 MGA Roadster (Driver)
1958 MGA Coupe (Racecar)
1959 MGA Coupe (unrestored)
1960 MGA Coupe (unrestored)
1960 MGA Roadster (Driver)
MKIII Elva Courier (E1056)
1967 427 Cobra
1972 Alfa Romeo Montreal
A coupla late MGBs
1960 Austin Healy BN7
More Cars than Brains

fast-MG.com Avatar
fast-MG.com Gold Member Dave Headley
Cortez, 4 corners, Colorado, USA   USA
Verify your bore size as 0.001" bore change equals over 0.003"(Pi x D) ring gap change. Also check the gap at several places in the bore which will indicate extent of bore taper.


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chris Avatar
chris Platinum Member Chris Roop
Pendleton, OR, USA   USA
A file should only be used in one direction on the work at hand.


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dickmoritz Avatar
dickmoritz Gold Member Dick Moritz
Philly 'burbs, PA, USA   USA
I agree with others. Rule of thumb is a minimum of 0.004 end gap per inch of bore. I agree with Basil that 0.009 is a little too tight. I recommend measuring your bores and pistons very carefully. Did your machine shop hone the cylinders and select-fit them to each individual piston? My first concern would be that they didn't allow sufficient piston-to-bore clearance. I very much like the Grant product, I use their rings all the time, and never have a problem with end gap or other issues of fitment.

Note that maximum end gap is, for all practical purposes, not a concern. Combustion gases migrate in behind the compression rings, pushing them outward to assure a good seal. Remember that the end gap will shrink as the ring expands from heat of combustion. So the prospects of combustion gases passing through the gap are inconsequential in a street engine.

I'd be more concerned with the bore size than the rings themselves...

Dick



Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

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Ahmed Avatar
Ahmed Silver Member Ahmed EL Abasiry
Chestermere, Alberta, Canada   CAN
1958 MG MGA
1972 MG MGB
1979 MG MGB
I did QC all the bores with a dial bore gauge after it came back from the machine shop. All bores were 3.191" top to bottom (they actually did a good job boring it out).

What I missed doing the first time around, is to have one ring installed on the piston before using it to square the new ring(s) being measured in the bore. This way it will guarantee the ring under testing is square and even inside because the piston will be square to the deck.

I will repeat the gap measurement again today, if it still comes to 9 thou, I will file them to 12 or 13 thou and call it done.



"... the motor car, after woman, is the most fragile and capricious thing on earth." - London Daily Mail 1908



Edited 3 time(s). Last edit at 2017-12-07 09:50 AM by Ahmed.

rocannon Avatar
rocannon Platinum Member Frank L
Inconveniently located in the wilderness, Oklahoma, USA   USA
1967 MG MGB GT "GT From Hell"
1980 MG MGB "Restored By Photoshop Inc."
Uh oh! eye popping smiley

In reply to # 3641384 by chris A file should only be used in one direction on the work at hand.



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ingoldsb Avatar
ingoldsb Silver Member Terry Ingoldsby
Calgary, Alberta, Canada   CAN
1971 MG MGB
Hap's posting on the subject was at http://www.mgexp.com/phorum/read.php?1,3372032,3372517#msg-3372517

Unfortunately, the link he provided seems to be dead.

https://www.hastingspistonrings.com/tech-tips-faqs/checking-compression-ring-gaps has a chart of recommended clearances for bore sizes. It sounds like 12 thousandths is the recommended minimum for the MGB's bore.



Terry Ingoldsby
terry.ingoldsby@DCExperts.com

fast-MG.com Avatar
fast-MG.com Gold Member Dave Headley
Cortez, 4 corners, Colorado, USA   USA
BTW, if you run the second ring gap at 150% of the top ring, it reduces ring flutter and improves high RPM sealing. Example, top ring at .012", second ring at .018". Many modern quality ring sets come this way. smoking smiley


Member Services:
Dave Headley, dba FAB-TEK offers full service race car parts and preperation for MGB & MGA race cars, SCCA and Vintage. Dave is a mechanical engineer and has raced MGBs since 1963.
dickmoritz Avatar
dickmoritz Gold Member Dick Moritz
Philly 'burbs, PA, USA   USA
Why would that be, Dave? Inquiring minds want to know...

Dick

In reply to # 3641442 by fast-MG.com BTW, if you run the second ring gap at 150% of the top ring, it reduces ring flutter and improves high RPM sealing. Example, top ring at .012", second ring at .018". Many modern quality ring sets come this way. smoking smiley



Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

fast-MG.com Avatar
fast-MG.com Gold Member Dave Headley
Cortez, 4 corners, Colorado, USA   USA
Dick, according theory, it reduces combustion gas pressure below the top ring during 3 of 4 cycles. This allows combustion pressure to push the top ring more firmly against the ring land improving stability and sealing. Proven years ago via testing. This technology originated with Mahle I believe.



Edited 1 time(s). Last edit at 2017-12-07 03:03 PM by fast-MG.com.


Member Services:
Dave Headley, dba FAB-TEK offers full service race car parts and preperation for MGB & MGA race cars, SCCA and Vintage. Dave is a mechanical engineer and has raced MGBs since 1963.
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