T120 rings in a +80 A10

[muskrat]

G'day Fellas.
My cafe is 72mm bore and needs new rings. +80's are rocking horse manure. Now T120 Trihard +40 are 72mm. Does anyone know if the radial thickness is the same? The height of the rings are the same 1/16, 1/16, 1/8.
Cheers

[Swarfcut]

 G'day Musky

    My 1989 AE Catalogue lists ring set R1150, to cover nominal bore of 70.998mm on the Triumph TR6 650cc engine from '54 to '71.

    Ring thickness is 0.0625" for both compression rings, 0.125" for oil ring, 1/16" and 1/8" respectively.

    Ring groove depth on the piston is indicated as 0.1000" (2.540mm) for all three grooves. Sadly there are no listings for BSA pistons in this publication. The ring groove depth and the radial thickness of the rings may or may not be the same thing, there is no clear guidance. 

 Cheers

 Swarfy.

[mikeb]

Musky your compatriots JP make a +80 A10 piston and rings.... no? I wouldn't either, but just saying

EDIT: i had similar thoughts re t120 rings when my JP's died, but with heavy heart and open wallet resleeved to IMD stds. too soft for your cafe, but no regrets here (and never JPs again over my dead body)

[groily]

(and never JPs again over my dead body)

What was it about them mike? Criticism of them crops up here and there, the rings in particular, but I have had a +20 8.5:1 pair for about 25K miles in an AMC and haven't had any problems. Weights were very close to originals in that case but I had the crank dynamically balanced anyway. Key thing seems to be to rebore with adequate skirt clearance. Have I just been lucky?
I went flat top IMDs on my A, and agree they're a very good bet. In other engines hereabouts it's Gandinis or AE / Hepolite - the hassle is limited choice nowadays unless we've stashed a few on a shelf over the years. Some engines are better served than others, that's for sure.

[mikeb]

Bill - i went against local wisdom and cautionary tales when installing the JPs (as they were the only +80s i could find). i can't exactly recall what the clearances were but i think 4 1/2?. but not enough: they seized on a hot day, up a hill, wide open trying a keep up a with a passing vincent. but that's how i ride.
i'm an office worker so really don't know, tho am told they have a higher expansion rate than standard and a higher failure rate to boot (eg a local story of one splitting in half). during their short lives they certianly let a lot of oil slip by to be burnt. the imds? none.
am i being unfair? possibly. i have since been told they shold be bored with a wider clearance. and noting the rings are more widely regarded as the inferior part.

for a final verdict, lets see if Musky fits JPs ...

[groily]

Thanks for that mike.
Maybe a thou more would be good - think at 72.5mm I had 5.25 thou but honestly can't remember for sure. I did run them in very carefully because I also heard their expansion rate was a bit more than normal.
Like with you, there was nothing else available in the size and comp ratio I wanted - and I don't think it has got any easier.

I was really pleased when I read about the IMDs on here - and the proof of the pudding has been in the eating. The current owner of the bike has done loadsamiles with loadsasmiles on them with low oil consumption. Which given that I didn't rebore, just honed, because the cylinders measured OK at half-way to the next oversize, has made me, and him, happy.

[muskrat]

"for a final verdict, lets see if Musky fits JPs ... "
G'day Mike. Not on your Nelly. The Cafe gets ridden hard so I don't want to strip her down again in a thousand miles.
I have a few T120 +40 rings earmarked on fleabay. GPM's for $160AU landed from US are on the short list.
Cheers