Britbike forum Forums British Motorcycle specific Brands Triumph bulletin board Request Advice on New Low Comp Pistons for T120

I put new rings into my 70 T120 about 3 years ago, after it developed a push rod tube leak following a complete engine rebuild a year or two before that. It was bored 0.020" over during the initial rebuild. It only had about 3K miles on it from the original rebuild. So when I pulled the barrels, the bores looked perfect with some remaining cross hatching evident. They measured within spec using my somewhat mediocre bore gauge and micrometer. So I put it all back together using new Hastings rings, but didn't hone the cylinders, thinking I didn't need to. That was a mistake - I probably should just have re-used the old rings which were seated and performed a thorough honing. So it went together well, with no leaks anywhere. However, the right cylinder burns oil. When I follow my daughter riding it, there is blue smoke on the right cylinder, which is also low on compression. The bike starts and runs perfectly, and she has put about another 2k miles on it since the top end. So I am planning to do the top end again now, and would like some advice.

I won't know until I pull things the wear on the bore, but I am hoping they will still be in tolerance for +0.020". I am considering installing the low compression pistons that TRV7 and others have tried with good success for the low octane fuel of today. I have attached a file of a snip of the Bonneville Shop offering. Would these be the correct pistons for my engine? Would anyone recommend using the supplied rings, or should I purchase the Hepolite rings that are available - and would they be compatible with these pistons? If my bore is worn much, I might have to send it out for a 0.040" over, which I would hope to avoid, but it will depend on the wear.

I considered just sending the barrels out to F&G to let them do the work and fit new pistons if needed, but they are booked solid and are not taking on new work. Looking on the F&G website and their installation guides, they recommend using a 220 grit for honing (this time - I plan to hone the bores correctly before installation!!). However, most advice I have read over the years advise using 180 or even 150 stones. I purchased a Lysle bore honer, which comes with 220 grit stones. Should I use something coarser?

I feel like a bit of an idiot, not having taken the time to do the job right last time. This time around, I am better informed, and will take my time. It seems like the perfect time to go to the LC pistons. The other option, again assuming the bores are still good, would be to keep the current pistons, do a good honing job and just put in new rings again. It is also possible I broke or distorted one of the rings on the original install. I will know better once I have it apart. But I am still strategizing a bit, and plan to go with the LC pistons.

Thanks in advance for any advice or other tips.

Hello; an opinion without seeing anything from here is that with all those few km I do not think that you need to go over to 0.040. I had mine with 0.040 and at least (many km with the speedometer cable worn or without it) 120000km with plenty of abuse by the PO etc and still is good.
Anyway; the normal situation is to re use the pistons; hone the cylinders and change the rings.
I see many problem slugging the engines; mostly with Harley D. but baby sitting the engines and riding constantly at low RPM do not help to seat the rings.

I'd avoid "Hepolite" rings - they are actually Wassell rings. In the US, there are several manufacturers & retailers of top quality Triumph engine parts, why not use one of them? The Bonneville Shop seems a good place to ask

I rarely go on here but just did, and a few things:

I would not advise to "avoid" Hepolite rings as they are now made by Federal Mogul in England and are very high quality. There are no other rings I have seen for a Triumph that are as technologically advanced. Maybe some people don't need that but they are very nice. The only reason you should avoid them is if you prefer simple cast rings that seat quicker or you don't plan to ride much.

The 650 low compression Triumph pistons are now being sold by Hepolite, and I have some in stock.

They are not on my website because due to ring shortages they are on back order from Wassell, but I have some .020 and .060.
They seem to be about .0015" bigger than the standard .020", so they may be okay to hone for them and run if your bore is straight.

If you want to send the cylinder out to me send an email and I may be able to do it.
My mother had a stroke and I have been taking care of her, as well as having way too many jobs in my shop. Now catching up but still behind.
Hope this helps out, Dan
Franz and Grubb Engine

Hi RickT120, Reinstalling cylinders using old rings works really well, so long as old rings working well. DO NOT REMOVE RINGS!! Just blow them off with compressed air. Oil & install.

At this point you have 2 choices. Reuse pistons, hone & new rings.

Or… Low compression pistons. I personally installed LF Harris 7.1 pistons & rings. Rings came with pistons. .0045” clearance 220 finish hone. Torco TBO 40w break in oil.

The pistons I used start out as iron head pistons. The “factory” machines the edge of iron head piston to make it alloy head piston.

On the dyno lower compression will reduce power. In real life riding power loss is not noticeable. It makes the easiest starting & sweetest running motor ever. If speed is your goal use 9.0.

The 69 Bonnie has covered over 10k miles now. Zero oil consumption.

I would take Dan up on his offer & send cyl to F&G. If he could hone slightly larger piston to fit, that would be ideal.

I don’t know who is making Wassell pistons. Or LF Harris pistons. I checked Harris web site recently. Looks like they’ve dropped the 7.1 alloy head pistons.

I’ll personally not do any high compression pistons again. The low compression runs so good.

The ones I’ve fitted are a fair amount lighter. This moves balance factor higher. The smooth spot will move about 600-1500 rpm higher. Depending on how smooth motor is now you may notice this or not.

The ‘69 Bonnie was dynamic balanced to 68% ( light version flywheel). Was horrible shaker. Now smoothest Triumuph I’ve ridden.

If Money is object, just hone & ring.

I always, always use break in oil. Afraid not to. Seen so many failures without it. I think F&G sells it now. Or Summit Racing on line. They even have 20-50 break in. I won’t use 30w. My oil light winked on at idle using that. Just relating my experiences.
Don

Federal Mogul bought out the Associated Engineering (AE) group some years ago.
AE owned Hepworth and Grandage (Hepolite ), Wellworthy Ltd (Wellworthy pistons--mainly diesels--- and Wellseal) and Glacier Metal Bearings among a lot of other companies.
I started my career at the AE Group R&D Center near Coventry.
Great memories and happy days!

Unless something has changed since J Healy told us, Wassell is selling Taiwanese JCC pistons under the Hepolite brand and Harris, Emgo and Cyclecraft are also putting JCC pistons into their own branded boxes.

They’re good pistons.

Hello Dan,
Are you sure about the "made in England" Federal Mogul rings? AFAIK, Federal Mogul use the Goetze brand for rings, and though they were making in Germany once upon a time, I think they may now made in India, and are exactly as shown on your website. Just to make matters muddier, I think Federal Mogul also still have the AE brand name. Velocette sell the Nural pistons (again, Fedreral Mogul) along with the Goetze rings to the UK dealer market.
Certainly, I have no problem with the Goetze rings!
Mick.
PS, I hope it works out with your mother, strokes are a cruel thing.

Federal Mogul is a huge International company, its owns many old trademarks and is free to apply them to whatever it wants on the aftermarket. So if they have a ring factory in the UK they are free to apply the Goetze trademark for the aftermarket. When selling to the OEM's then different rules apply, they can only sell parts made the OEM approved route, but for aftermarket they can make them where they want or buy them in and apply any trademark they own.

Not sure where Velocette stand in the OEM/aftermarket. AFAIK the Routt type barrels etc that they sell are produced exclusively to them. I have had Goetze and AE labelled rings from them, visually identical. No help to the OP, they only sell 9:1 for 650's

As a more direct answer to the OP, F W Thornton HERE have 7.5:1, you'ld have to check with them for the manufacturer, could be PHC (Peter Hepworth Components?), and there is Red Lizard Motorcycles HERE that have 7.5:1 from Gandini and 7:1 from JP in Oz. I have used PHC 8.5:1 pistons in an iron T110, the only ones I could find with the correct dome shape to get squish, and the only ones I have had with direct experience. And before anyone chirps in about using alloy head pistons in an iron head, I know.

Thanks to all for the advice. As always, I am learning a lot on this forum. Dan, I sent a PM to you.

I will keep this thread updated as the project moves along, and report on how the new pistons turn out once the job is done.

Mick- the Goetze rings and the new Hepolite rings are very similar but the Hepolite rings have pvd chrome on the top and oil rings. These rings will probably outlast any cylinder they are put in and may be overkill but I have had good results with them. Also having personally gapped thousands of Triumph 650 rings, I am very familiar with each manufacturers quality. These use a more expensive process than the Goetze, and I was informed by Wassell that they were made in England. I have zero reason to question that. I believe the pistons are JCC.
Also for everyone's info here Hastings has told me they discontinued Triumph motorcycle rings, although there are still lots of sets on shelves out there.

Hello Dan,
Good information, you would know on the quality front! Long may Wassel use good rings, some of their other products are, shall we say, a little more suspect, which was why my doubts.
Thanks,
Mick.

...Hi Dandruff; in the past the "chrome" rings did not worked any good in old pre units may be now yes? With these new rings what is the honing grit intended? Do not seems necessary the 150-220 ones.

- As all you know Federal Mogul is the one that fabricates Champion since long time ago...

Thanks

Chrome faced rings will be ok with proper cylinder preperation and the break in...

MAP offers forged 7.5 pistons with a tight quench. Nitrided stainless top ring and cast Napier second ring...3 piece oil ring...They are about $300
Certainly the pistons Dan recomended are more than adequate for most riders..