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I've read thru several sources, and get confused by the actual compression specification for my T140V. Some sources say 7.9:1 others 8.5:1. The engine has Hepolite 19162 pistons. The Haynes manual refers to Low grade vs Hi grade specs. Is this referring to compression ratio and that the bike was available with different compression engines?
I ask because I may have to replace at least one of the pistons. I just can't get the top compression ring off one of them. If I need to replace, I'ld like to either replace one with an original Hepolite (if I can find one) or perhaps get a generic set of pistons sold on eBay for this model bike. Either way, I want to understand more of what I might be buying.
 

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I've read thru several sources, and get confused by the actual compression specification for my T140V. Some sources say 7.9:1 others 8.5:1.
I ask because I may have to replace at least one of the pistons. I just can't get the top compression ring off one of them.
The compression ratio varied,depending on model and market.The number you gave is supposedly 8.25:1.The lowest nominal compression was 7.9:1,and I think home market were 8.5:1.Unless you can find new old stock,you may have to settle for 8.6:1.

High and low grade only refers to a small difference in piston and cylinder diameter within a range of 0.0011",for selective fitting.

If need one piston,it's best to buy 2.They are more likely to be the same weight,or at least close enough that they can be balanced.They are more likely to give identical compression.

Have you tried heating the piston then quenching it in kerosene,or a mixture of kerosene/ATF to free the stuck ring?You may need to do it a few times.
 

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I'm sure the original pistons that would have been fitted to a T140 made between 1976 and whenever they changed to the 'E' models (1979?) were 8.6:1 comp. ratio. The very first T140s had 75mm bores giving 736cc, but these were soon changed to 76mm. The 75mm pistons may have been a different comp ratio - no idea about these. After the change to 'E' models, the comp ratio was lowered to 7.9:1.

It is confusing, because there are also 7.4:1 pistons (fitted to the TR7 Tiger Trail), and many of the pattern pistons (Emgo, Wassel 'Hepolite' etc) are sold as 8.5:1.

If its any help, I did a great deal of research into pistons during my recent-ish rebuild, and eventually concluded that the JCC Taiwanese pistons are actually as good as you'll get without paying 3 times their price for MAP forged pistons. Other forged ones (Italian and Australian) have very variable reviews and seemed a little risky to me, though some swear by them.

TMS is a very good parts supplier.
 

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I would urge caution when buying Hepolite Pistons and rings - if you can get old stock items then all well and good if they were actually made in the UK .

I fell foul of this when my T140E had it's first re-bore carried out - I bought a pair of Hepolite =020 pistons and rings from TMS & after rebuild the motor smoked heaps refer to link :
http://www.triumphrat.net/classic-vintage-and-veteran/198994-smoking-t140e-after-rebore.html.

I restrippd the engine and checked and double check to make sure the rings were fitted the correct way up but still no change .

The give away is the Hepolite pistons that have a stamp on the underside of the piston skirt JCC denotes that they were made in Taiwan see attached pic.

The cure in my case was to junk the hepolite rings and fit a set of Harris rings and the engine now runs fine .:)
 

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Discussion Starter #7
Thanks for the replies. I don't feel so bad now being confused about the compression ratio spec for this bike. I now realize that if I need to change one piston, it is very sensible in this case to change both as this is the only way to guarantee matching specs.
And good news...last night I managed to fracture off the stubborn ring. This after about a week of soaking in Chem-dip, ATF/Acetone, propane torches, and finally MEK-substitute. I made a drift out of a ground-down Masonry nail to knock out pieces starting at the ring gap. Took the devotion of a monk. I made a very very slight ding on the outside edge of the land, but I think the piston is totally re-useable.
Now to move on and find a set of replacement rings. Hastings, I suppose...?
 

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The best advice I could find was to use JCC pistons with Made In Japan Riken rings. I obtained these from Tri-Cor. A bit more expensive than the alternatives but supposed to be a lot better. My TR7 doesn't smoke at all (just as I'd expect, but not as some people experience it seems).
 
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