reboring cylinder

I am reboring the cylinder of a 750 Commando.
As per the pistons (new Hepolite) i am going with the size + 0,60.
Is there anyone who can tell me the correct size of the rebore of the cylinder?
Ciao.
Piero

The left and right pistons each should be measured by the machinist and the cylinder should be bored to allow about .0045 inch clearance for each piston



Tim Kraakevik
kraakevik@voyager.net

Are your cylinder so bad that you need to bore to +.060?

That's a big overbore. If owners paid more attention$ to valve issues you'd see alot less overbores I.M.O.

pete.v said:

Are your cylinder so bad that you need to bore to +.060?

Click to expand...

Yes, is very spoiled and must be rebored +0,60.
How much clearance should be given?.
I bought new Epolite pistons and the third groves rings seem to me to be a real crap!.

Ciao.

Piero

Can i use the new Hepolite pistons with the GPM / Hastings / other rings?
What do you recommend to mount?
Ciao.
Piero

Torontonian said:

That's a big overbore. If owners paid more attention$ to valve issues you'd see alot less overbores I.M.O.

Click to expand...

That's him told then!
very helpful
JohnT

Though my rebore is only .020" oversize, a clearance of .0045" has worked well with no issues in 8000 mi. I can say with certainty that .035" is not enough (had a seizure at 1000 mi). I don't know what Hepolite is supplying for rings these days, as I recall mine did not come with rings. The oil control ring I'm using is called an 'apex' ring it is a three piece affair with an expander and two thin scrapers that lock on to that. Very effective.

Wassell has bought Hepolite Branding and the pistons are made in Taiwan by JCC and the fit Hastings rings and stuff them in a Hepolite box, not a bad combination but not what the name on the box would suggest, such is the way of brandmarks today.

Correct me if I'm wrong, but is it not best to get the rebore done with the pistons and rings provided to the engineer so they can bore, honed and be checked to ensure a perfect fit as the job is being done.

Madnorton said:

Correct me if I'm wrong, but is it not best to get the rebore done with the pistons and rings provided to the engineer so they can bore, honed and be checked to ensure a perfect fit as the job is being done.

Click to expand...

Yes, but I don't see anyone suggesting otherwise although rings really don't enter into the clearance equation

pierodn said:

Can i use the new Hepolite pistons with the GPM / Hastings / other rings?
What do you recommend to mount?
Ciao.
Piero

Click to expand...

I had problems with smoking after re boring my T140 and fitting rings supplied with the JCC pistons I bought, I hunted out some genuine old stock Hepolite rings , fitted them and the smoking stopped immediately.
When I rebore my Commando in the winter, I will fit the JCC pistons and NOS Hepolite rings that I got in my store.
way to go !
sam

trident sam said:

I had problems with smoking after re boring my T140 and fitting rings supplied with the JCC pistons I bought, I hunted out some genuine old stock Hepolite rings , fitted them and the smoking stopped immediately.

Click to expand...

I purchased a set of pistons with rings from Domiracer(yes, I know). They came with 0ne piece oil rings. I am assuming that the pistons are JCC. They came with NO documentation

I dont want to use the one piece oil ring. I have an set of NOS "apex type 3 piece" oil rings. genuine AE rings.

when attempting to fit the AE oil rings to the alleged JCC pistons, I discovered the depth of the oil ring groove was shallow by about 20 thou. the thin top and bottom oil rings stand proud of the piston and will not go into the bore. I need to deepen the ring groove by about 15/20 thou it seems. andf yes, the rings were fitted correctly. I had an engine reconditioner look at this and the grooves are indeed shallow. The engine bloke says the pistons are quite usable as far as sizes go except for the oil ring groove. they are a about a bit smaller than old hepolite pistons above the top ring groove but he says they are still OK to use.

have I got JCC pistons or something really nasty.

has anyone else run across this.

Kind regards to all Bradley

When I was working at a small shop a few years ago, as I recall Hepolite pistons were still made in England and those that were supplied with rings for Triumphs had a one piece oil control ring as original and those supplied as Norton pistons came with the three piece apex type oil control ring also as original. There was quite a bit in price differance between Tai and Hepolite and a lot of customers chose the Tai but I don't remember if any customers opted for AE rings over the those supplied with the Tai pistons. If so I don't recall any fitting problems.

trident sam said:

I had problems with smoking after re boring my T140 and fitting rings supplied with the JCC pistons I bought, I hunted out some genuine old stock Hepolite rings , fitted them and the smoking stopped immediately.

Click to expand...

hello Biscuit.
thanks for that, very helpful. Mate, the trouble is the pistons from DomiRacer had no paperwork. I dont know what the hell I got here. Hell could be anything.
I dont want to go through Sam's experience though.
the amount the rings stand proud is about the thickness of the rail. the rail clips in perfectly by itself. the engine bloke tells me fpr longest life and cylinder lubrication and oil scraping function, use the NOS AE rings.

What do you fellas reckon. Has the engine bloke got it wrong. he has a lot of British motorcycle experience. Dont mean he is right though.
he also said its no trouble for him to deepen the grooves, would'nt cost much .

i am at a bit of a puzzle on how to proceed here.

deepen the groove of pistons of unknown source and use my NOS AE rings. this is what the engine man said, but one should listen to other opinions.

Or scrap these unknown brand and get a known proven brand. thats the main trouble. Has anyone run pistons from DomiRacer that came with no documentation, where the oil control ring does not fit "apex type" . ( this was before my conversion to Andover purchases only.)

Hey Piero, not trying to hijack your thread here but some of the stuff be relevant.
kind regards Bradley

Well,
Is better to mount one piece oil control ring as original (GPM Pistons) or the three piece apex type oil cont?
The two rings of the third groove that came with the Hepolite Pistons are too malleable and distort too easily, to me they seem like a great crap.
Ciao .

Piero

Instead, the EMGO pistons i bought (seems equal or perhaps the same as the Hepolite) arrived with rings that look best and the third groove is a single piece on the internal spring seems more solid and easy to assemble.
What do you think?

Ciao .

Piero

Talking only pistons, JCC, Craft Cycle, Wassell Hepolite and Emgo pistons are all made at the JCC factory in Taiwan. In Triumphs at least they take the same clearances as original Hepolites eg 4.5 thou as the material they are made from is very close.

Hi Piero, I had used many JCC pistons(and all that big family: emgo etc) they are very good IF used with three pieces oil ring, at the start I had used the one supplied in the box (the one piece) and bad luck with them (smoke), now I still used them (from Carl Hockanson, as he supplied them with good three piece oil ring (may be hastings??), and they are cheap..........my two cents

One pc. oil rings gave me hard time with a Trident rebuild. Back to conventional three pc. for me.