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MG TD TF 1500 - Piston ring gap

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.
MAndrus

I had a similar problem with another car from the 50's. Bore is 54.5 mm.
The spec said 0.1 to 0.15 mm. I got many problems with this gap and new rings : abundant white smoke, water on exhaust : impossible to drive. I tool the head off 5 time. I tool the engine off 3 times. Eventually the manufacturer of the rings explained that 0.1 to 0.15 was the spec for the metal of the 50's but today's material expands more and he recommended a gap of 0.2 to 0.4 mm.
So youre situation may be normal but I would check this with the ring manufacturer before getting into troubles.

Laurent.


LC Laurent31

A common end gap 'rule of thumb' is .0045" per inch of cylinder bore. (2.618"+.040") * .0045= .012". The WSM spec is .006" to .010". Sounds like you're in the ballpark at ~.3mm as Laurent was told. Contact Devon and see what they say. Bud
Bud Krueger

Sorry.... inches. .010" to .014"

Bud, thanks. I'd forgotten to double check with maths.

Looks like I'm in the right range then.
MAndrus



Last time I called Moss technical (2015) about piston rings, they said all of their rings were coming from Hastings. They had previously bought theirs from Deves, but could not renew their contract.

The problem I experienced was that the Hasting compression rings that came from Moss with new .040" pistons were too thin for the new piston groove they fit in. I measured the thickness of the Hastings rings and they were not correct(too thin by .002"). Moss refunded my money but did not get me a set of correct rings. I had to order a correct set from Deves direct from their company. I highly recommend you check your piston/ring clearance in the piston groove.

Note: the Hastings internet catalog lists the correct ring specifications under the MG TD page. The Hastings representative said that Moss had contracted for a special ring for their specific piston application. I did not get in between their argument, but at the time I wondered how many customers might be affected by this discrepancy.
Richard Cameron

Personally, I prefer Deves rings. My Deves catalog shows the following for Compression Ring Gap:

Cylinder dia: 60.00 to 89.99 mm.:

Norm. Gap: 0.20-.035mm/.008-.014 in.

Max. Gap: 0.20-0.60mm/.008-.024 in.

Bud
Bud Krueger

Richard and Bud, good info. thanks.
MAndrus

I installed Deves rings in my recent rebuild. They required no filing right from the company. I had the old 4 ring style pistons. Also 40 over. Be careful as they are very brittle. I broke one. Deves was good enough to send me a replacement no charge.
Good luck on your rebuild.
Sandy
smb brainsky

This thread was discussed between 09/12/2016 and 11/12/2016

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