JC Commando pistons

I'm just in the process of fitting a pair of plus 0.020" JCC pistons to my 750. The quality looks good though the surface finish on the skirts is not as fine as the original AP product. This could be an advantage as I envisage this holding a film of oil in use.

If you search JCC pistons, there is a wealth of info including many awards. They probably make more pistons than any other company.

Measuring the ring gaps reveals a gap of between 0.009" and 0.015" and I have heard of members of the American Norton forum fitting other ring sets. Total seal supply high spec ring sets for about £45

I would be suprised if a company producing millions of pistons would compromise their product with inferior rings. I'll let you know in about 6 months.

Likewise.....

I've just fitted a pair of +40 JC hepolites. Fingers crossed all goes well.

Will update thread as information arrives.

Ben

For those who want pistons with rings that work I'd recommend Andover Norton's GPM pistons. We have used them in many engines over the years, including racing ones, and they very simply do their job. Probably less exciting than experimenting with unproven Chinese products, though. Available in STD, +.020", +.040", +.060" for 850s and 750s, with the additional +.030" variety for 750s. Your local friendly probably does not stock and recommend them because he makes much more on the "alternative" offerings.

I paid £106 for my JCC pistons on ebay. Thorntons In Shrewsbuy quoted me £89 +vat each for Gandini pistons. How much are yours Joe? My previous pistons fitted in 1975 with the dreaded slotted oil ring cost me about £25. (that was a weeks wages as a trainee AC in the RAF)

Incidently, the bike cost me £350. Who knows how much I have spent on it in 37 years.

David previously wrote:

My previous pistons fitted in 1975 with the dreaded slotted oil ring cost me about £25.

Did they break?

David,

For me the question of cost is secondary to quality. I know the Gandini pistons work even under great stress with no problems and simply don't have the time to rebuild my engine again and again. Which, incidently, is not a cheap exercise when pistons fail. So I tend to use something experience has shown to work.

Too simple? Yes, I probably am.... but I prefer riding to doing jobs twice.

Oddly enough, the only pistons I have had fail over the years have been genuine Hepolites. A variety of failures, one even having the top come off only 200 miles into running in after a rebore. Don't like Hepolites! However, I have used Taiwanese pistons in a BSA A7 very successfully and have trouble-free GMPs in my Atlas (the original Hepolite split in half).

The first GPM pistons were cheap and cheerful and reputedly sourced from Italy. They were vastly heavier than equivalent sized Hepolites, which could upset the engine balance. Also they had rings that were not marked 'TOP'. Consequently, many people fitted them upside down and then wondered why their engines smoked worse than the pistons they had replaced.

A good many people, who fitted the early GPM pistons, later claimed that they had distorted after hard use. The comment, generally being, they were fine if not taken above 5000rpm.

I was quite surprised, on a recent visit to AN, to see them on sale there but was assured that the latest versions were vastly better and that rings were now clearly marked.

On a connected note.......I notice that the Yanks are always banging on about fitting new pistons and rings un-oiled and then running themdry at firststart-up. Apparently, this knocks hundreds of miles off the running-in period. Personally, I would not dare to try this after a rebore as the inner cylinder surface always looks so rough.

Has anyone got experience of such practice?

The production of cylinder bores which give good oil consumption and long life is a complex business and beyond the capabilities of many of those who undertake rebores. There are 3 stages in the process, the initial boring, which needs great care to ensure roundness and non waviness, honing to give the crosshatch pattern and finally plateau honing to ensure easy running in and long life.

Research by Mahle showed that' for good oil control, the crosshatch angle should be 60deg. This ensures that oil can be moved up and down the crosshatch channels without excessive amounts entering the combustion chamber. It also reduces the risk of the piston rings being damaged.

Plateau honing is carried out to remove the undesirable sharp peaks on the liner surface. Some engine suppliers used diamond hones. These give a more consistent finish than do the Silicon carbide ones but produce undesirable levels of work hardening. Clean cooling fluid/ lubricant is essential.

Plateau honing should be carried out to produce a surface finish with a value of the surface finish parameter, Rku, of about -1.5.

Do all this and running in will be easy and oil consumption low.

This contribution is based upon studies carried out in conjunction with the Universities of Birmingham, Coventry and GKN Sheepbridge-Stokes

I hear tall stories about GPM pistons all the time. Amazing, then, that the man who rebuilds more Commando engines in Germany than anybody else- my friend Rudi Kolano- and who insists on putting a few more horses into them then when they left the factory, whether the customer wants it or not, has been using our GPM pistons for many years.

I can assure you at least our race engines rev 7000+ regularly, have GPM pistons, but those pistons have never failed in many a season.

May I offer the idea that incompetent mechanics, encountering problems with their workmanship, tend to blame components that their customer isn't sure about and which may have failed due to something totally unconnected to the component itself?

As for our road engines not being treated to revs over 5.000, I can well believe that in England, having seen the style of riding of most classic bike owners over there, but rest asured an engine built by Rudi would not even survive the test ride if the pistons gave up at over 5.000rpm.

As for prices, look at the Andover Norton homepage.

Joe previously wrote:

As for our road engines not being treated to revs over 5.000, I can well believe that in England, having seen the style of riding of most classic bike owners over there

Not all English classic owners have forgotten how to ride a bike!

Alan,

There are always exceptions to the general rule, but with traffic and speed trap density in England plus the general attitude of thankfulness the bike runs at all- I really have no other explanation for the continued existence of the workshops of certain "Norton specialists" in England- chances are that over here twistgrips get used with less reluctance.

My slotted pistons did not break despite being regularly thrashed, one of the previous ones had a crack from the slot to the bottom of the skirt as a result of the previous owner setting the ignition timing so far advanced that the pipes glowed red on start. The two pistons I replaced are in excellent condition after about 60,000 miles but the bores were totally shagged out and the top ring on each was broken.

The Norton specialists you mention Joe, are there to cater for the owner that wants to ride a Norton but does not have the mechanical nous to maintain or repair his steed. Whilst with modern modifications to Commandos they can be made almost maintenance free, you don't see many BMW or Jag owners with their heads under the bonnet at weekends

I had a GPM piston that cracked from the gudgeon pin to the crown - within the first couple of thousand miles. Has anyone an explanation? It had not nipped up (I only found out because I had to strip the engine after big end failure).

On the topic of honing - one interesting snippet gleaned from the random material on the internet was the recommendation that, after honing, the bores should not just be wiped clean with solvents etc - but washed with soapy water and a scrubbing brush to make absolutely certain that no carborundum was left. Plateau honing and careful cleaning afterwards is apparently one of the reasons why modern engines often go for well over 100,000 -200,000 miles without a rebore.

What caused the big end failure? Obviously, with the big end failing (again: through what?) the conrods would then at least be loose and could possible not run parallel to the bores, thus putting an angled load on the pistons. I ask because all the GPM pistons we have used in the last 10 yearsnever gave any problems in use, be it 750/850 Commando or Dommi.

I can't know - old age, excess wear, poor oil filtration, too much bearing clearance followed by oil film failure under pressure of high revs. I never thought to associate the piston crack with the big end failure. The 'death rattle' appeared suddenly towards the end of a couple of miles full bore high rev 'thrash' (though I should have realised the bearings were on their way out when I put the new pistons in - I could not find top dead centre as easily as I thought I should). Once the rattle started I rode home (maybe changed 20 miles) without any particular noise until the revs went up, so the oil film must have been breaking up under high loads due to the excess clearance.

Anyway - if the big end failure did cause the piston crack, maybe I can rest assured the pistons are now safe. I don't intend to removed the block out of pure curiosity!

I can't know - old age, excess wear, poor oil filtration, too much bearing clearance followed by oil film failure under pressure of high revs. I never thought to associate the piston crack with the big end failure. The 'death rattle' appeared suddenly towards the end of a couple of miles full bore high rev 'thrash' (though I should have realised the bearings were on their way out when I put the new pistons in - I could not find top dead centre as easily as I thought I should). Once the rattle started I rode home (maybe changed 20 miles) without any particular noise until the revs went up, so the oil film must have been breaking up under high loads due to the excess clearance.

Anyway - if the big end failure did cause the piston crack, maybe I can rest assured the pistons are now safe. I don't intend to removed the block out of pure curiosity!

Hello and to add my 2 cents worth.

I have used JCC pistons in 5 engines now, after researching this brand on several forums and calls to reputable rebuilders here in the USA.

I have not had any issues with them. These have been from .020 to .060 over.

I do fit other rings. I have been using Total Seal rings. These do seem to require a "dry fit" if you will. Simply wipe the bore with light oil and then polish with paper towel to get the excess oil off. Lightly oil the skirts with your break in oil. I fit them with a .004 clearance if I do the break in and .0045 if someone else is doing the initial break in.

After initial run in the compression readings are in the 145 to 150 psi range

I am now trying a set of Hastings rings on a .060 rebore as the price is easier on the pocket book, by about half. I don't think that for the average rider the extra sealing performance and cost of the Total Seal product to be cost effective. We will see.

For what its worth

.

Hi Mark,

My rebuild is a couple of months away from engine start but the engine is more or less complete. Do you have issues or concerns with the rings that come supplied with the JCC pistons?

Previously wrote:

Hi Folks.

Anybody had any experiance with the new Hepolite pistons made by JC in Tiawan. I'm sure they will be fine but just because they have Hepolite on whats the quality like?

Cheers Tony

To Mark Zenor,

I was wondering if you had any experience with the rings supplied with the JCC pistons that detered you from using them. My engine is back together but as you may have seen in my "750 strip" thread, the re-assembly has taken a backward step while I prepare a frame that is straight.

Dave E

Previously tony_harris wrote:

Hi Folks.

Anybody had any experiance with the new Hepolite pistons made by JC in Tiawan. I'm sure they will be fine but just because they have Hepolite on whats the quality like?

Cheers Tony

much delayed reply, sorry i just saw your post today

quality fine, wrong circlips supplied, they were a bit slack weren't they?

never mind correct ones onlt cost £1 for the four from andover

charles