Oh and I was expecting more exotic stuff on break in. Like using the hone in the barrels to accomplish shaping the piston to get those tighter tolerances withour problem. How that could be done, I can only imagine. Careful heating and monitoring of the barrel before startup? The careful controlled cooling of the same, while still getting compression behind the ring. Like doing it on a dyno. Basically doing in situ what Irving was suggesting doing with a file. If it is possible, I do not know.
I agree that oil control seems to an issue, without the Hepolite rings.
Irving suggested chamfering the piston edge. I mentioned this before and no one has picked it up.
Oh btw, both Irving and Ricardo fancied chrome rings. Ricardo mentioned that the solution to the problem of getting them to seat, or it taking so long, was to use an additive. He never mentions what that would be. I find that intriguing. That he would say that and never reveal it.
Last edited by btour; 09/25/102:30 pm.
Bob, Lifetime bike: '71 T120R, bought in '71 at Ken Heanes, England.
B, i did pick up on that chamfering of the piston. Ted Hubbard always did that. I just dont think with the newer style rings its as necessary to do. John, are the JCC rings located in the same location as the old hepolites?
Rob I am sending down a Hepolite and JCC 650 piston to your dad's shop for you to measure. Remember we are talking about a Triumph 650.
Now remember when this thread started Yellow-cad asked this question:
The manual shows correct piston clearance to be 8 1/2 to 10 1/2 for the skirt top and 4 1/2 to 6 for the bottom. If the piston measures the same at the top and bottom of the skirt, what is the best clearance?
This is a fair question because both Hepolite and the JCC piston has approximately 0.001" difference from the bottom of the skirt to a point about 3/8" below the top of the skirt. This contradicts the information in the shop manual. I tried to answer this in one of my first posts. This change made by Hepolite to the design of this 650 piston goes back more than 25 years.
Yes, the 750 twin Hepolite and JCC pistons have the taper you indicated in a previous post. But as I have said many times, even though they look similar, these are not the same motors. For that matter neither is a 750 long rod.
Any one reading this, please understand that in no way am I saying that rob, doesn't do exceptional work on these motors. The Hall family has a long and very successful racing history. Just that rob's experience and this discussion would be better suited for the competition forum.
John, are the JCC rings located in the same location as the old Hepolites?
No, and this has always been a concern for me. The standard JCC top ring location is just about the same. But unlike Hepolite, who change the dome curvature to compensate for the increased radius of an oversize piston, JCC doesn't.
The top compression ring gets closer and closer to the top of the crown with each oversize. I have brought this to their attention, but the practice continues. It is so bad that at .100" oversize the what was .0.100" on a Hepolite is about 0.040" on a large oversize JCC.
While this is commonly done to help remove heat from the top of the piston, the ring runs much hotter. This means the typical .003" to .004" factor for ring gap for each inch of bore must be changed. KB, who locate their top ring very close to the top, specify .0065" per inch of bore.
It is interesting to note that Hepolite now supply their 650 piston rings with the .0065" factor for each inch of bore, or approximately 0.018" end gap. I know, this makes you shudder, but it is a different world when dealing with the variations of retail customers and their driving habits.
edited to make better sense, or please the english police
Quick side trip here, but what about the old practice of using slipper gauges to measure clearance.
Any chance of accuracy?
While I used the feeler gauge and fish scale method of setting pistons clearance doing Indian cylinders at Andrew's Motorcycle Sales in 1959 I wouldn't trade my micrometers and dial indicator bore gauges for a million bucks.
When we lapped Indian big ends with a hand lap we would check the clearance by cleaning the honing paste from the parts, assemble them with all of the loose rollers, and when they stopped "climbing" or "un-screwing" when we rotated the rod on the pin we knew that we had the right clearance.
Later when I started to do Vincent's we got high tech and would use trigonometry of sorts. We would measure the rod rock just under the small end of the rod. At 0.018" we were ready for the street, but if we were racing we went up to 0.0022 to .0024" of rock. While I still occasionally double check my work by rocking the rod (old habits are hard to break), today, when I am looking for 0.0009" clearance, I do my measuring with a rod bore gauge and micrometer.
edited - those english police are after me again...
I asked a question on the other piston thread about how the engine was run in but no response. I wonder if a lot of the piston seizures seen on this forum are from internet style running in techniques, ie, those which don't involve much running in? Dave
Thanks guys. I did weed out through all of this that the .005 clearance I have now between a set of JCC pistons that measure 2.852 and my 2.857 bores is OK for what I want and that is a dependable street bike that lasts a lot of non-lugging miles. I will cross-hatch the honing that removes the glaze and I should be in business. In previous times I have held die clearances to .0002 but right now I'm only working out of garage like lots of people so as long as things stay together and run fine, I'm happy. Thanks for all the help on this issue.
1970 Triumph Bonneville 1973 Commando Interstate 1971 OSSA MAR
For anyone who's interested here are the Triumph recommendations for running in circa 1967. This is for a complete new engine but would apply to a completely new top end, I would say.
A low constant speed would take a considerable mileage to break the engine in therefore the ideal method is to progressively increase the load and the length of time the load is maintained. these machines will travel at 50mph with a very small throttle opening when new but a large throttle opening other than for a very short time may cause damage.
Shift gear frequently neither pulling hard in a low gear nor revolving fast in a low gear. It is difficult to quote a set mileage but provided running in is done intelligently it should be possible to use maximum performance after 1500 miles. Whenever maximum performance is used it is a good plan to snap the thottle shut for a moment occasionally as this sucks oil up into the cylinders.
The old Pitman Triumph book recommends a similar procedure: 1/4 throttle up to 250 miles (if you think that is small my bike holds 70mph on this throttle opening, not that I am recommending this speed in the first miles). 250-500 miles 1/3, then 1/2, 3/4, etc until full throttle at 1500. If you don't do it then the engine will never develop its full power, so it says.
I tried all this on a complete top end and on inspection afterwards the pistons looked just the same as when they went in. I know a lot of people would say this is all wrong but it worked for me.
To run in like this you have to use the same specs for honing and clearance, some api se or sf mineral oil or some specific running in oil and change it at 250, 500 and 1000 miles. Retorquing the head a couple of times is also required.
Ok, you can all go back to thrashing the bollocks off your bikes now
I will cross-hatch the honing that removes the glaze and I should be in business.
Perhaps this goes without saying, but be sure you wash the cylinder bores with HOT, soapy water after honing.....the sure way to get rid of the honing grit embedded in the cylinder walls...if you don't do this important step, you may find yourself de-glazing once again...
'77 T140J "Vintage Bike". What's in your garage?
"The paying customer is always right."
Fitting round pegs into square holes since 1961...
Having just re-read this thread -- yes, all of it, I'd like to offer some measurements for comment by the experts regarding my 1964 TR6. My piston clearance seems a bit more than the gist of what I read here, yet agrees fairly well with the service manual.
Bore size per service manual: 2.7948/2.7953 (but you all knew that) My bore size: 2.79600 (+/- .0002 depending on where measured)
This is the original cylinder block from this engine. The bike sat for many years, and the rings were stuck in the grooves on one piston. I was able to get them out with no damage to the piston.
My pistons are original to this engine (made by Triumph, and are pre-Hepolite as per John Healy's remarks). They are marked in raised letters E3000 on one side, and LO-EX AM-4 on the other side, near the gudgeon bore. I measure them as having .0035 taper from bottom of skirt to just under the oil ring groove, when measuring perpendicular to the gudgeon. Measurements are 2.7900 bottom of skirt, and 2.7865 top of skirt.
This gives me .0095 clearance at top of skirt (Service manual spec is .0106/.0085), and .006 at bottom of skirt (Service manual spec is .0061/.0046.
I plan to hone lightly with 180 grit stone, re-use the pistons, with new cast iron rings, and assemble per John Healy's "dry" method.
I'm a bit troubled by the numbers in another quote from John in a different thread which, again, are tighter than stated in the Service manual? (click here for full text) . . .
Originally Posted By: John Healy
Triumph used a lo-ex aluminum alloy when they made their pistons. In and around 1966ish they stopped making their own pistons and bought them in from Hepolite. Hepolite did not use a lo-ex aluminum alloy.
Thus us old timers were used to 0.0035" piston clearance required by Triumph when they made the pistons for the 650. Then, with the introduction of the Hepolite pistons we had to get used to the 0.0045" to .007" recommended pistons clearance on this model. The Triumph lo-ex pistons have "lo-ex" embossed into the casting either side of the piston pin hole.
'64 TR6R Plus some Twins from other countries (U.S., Germany, Japan)
Re: What is the correct piston clearance?
#455012 09/19/1210:59 pm09/19/1210:59 pm
Thanks, Pete. Coming from you, that means a lot. Just curious, where did you get those specs? They agree with what John said earlier, yet are different from the 1964 manual. Did they revise it later? I know John has said in the past that the old Triumph manuals often had mistakes.
'64 TR6R Plus some Twins from other countries (U.S., Germany, Japan)