I apologize for this: It is why I learned to use a micrometer. Typical ring clearance in the groove is .001 to .0025". If it exceeds this you should think about replacing the pistons. Inch oil rings for British twins typically measure .125". Ring groove clearance has not been an issue between different brands. Emgo made a run of 750 twin pistons with inch compression rings and a metric 3 piece oil ring. It is almost impossible to get a 3 piece inch oil ring anymore for our diameter pistons. The issue is someone installing Metric rings into an inch groove. Impossible you say, but I have already seen it done. Plus if the ring manufacturers stop making inch rings in our diameters because of lack of demand by current piston production I suspect they will stop making inch rings. Metric oil rings for these pistons are typically 3mm and they go into inch ring grooves with .010" clearance. Today, small production runs of boutique pistons by the likes of JE, Aries, etc. are supplied with Metric rings. Chrome is a one of several different coatings which allow steel rings to be used. Moly coatngs and Nitriding are others. Steel rings, like ductile iron, are not compatible with cast iron cylinders. Used without a coating they will wear the cast iron quickly. It is the ductile iron or the steel that give these rings better qualities, not the coatings. http://www.aa1car.com/library/ar293.htm Riken Piston rings has a very informative site. Especially look at the page on heat transfer. Most rings supplied for these old bikes are made from grey cast iron. john Hi, probably going to start a debate here, but I would like some clarification on ring gap standards. My T140 manual says piston ring gaps should be .008/.013".. Now I have being doing a little research (reason why later!) and on the Steadfast Cycles website they are selling ring sets with the following quotes... New industry standard for British motorcycles is to gap the rings at .020. All rings from USA (Hastings) are using this standard, as are JCC and Hepolite. New independant tests (in USA and England) show that any gap between .024 and .010 is efficient. There is also an article on the Institute of diagnostic engineers website (Ring gaps vs knowledge gaps) which goes into a lot of detail to back this up... 'it's the tangential load of the ring that matters, not the gap...etc....' My T140 is bored out to +40" and I have a new set of AE Hepolite rings which have a gap of .018 when inserted into the bores.Now if this 'new standard' is correct then I am guessing everythings fine. But talking to people is just giving me lots of different opinions, but no one with a Brit Bike I've spoken to has heard of this 'new standard'!!! Anyone spread any light on this????? thanks Jel''' Pete R - R.I.P. Offline BritBike Forum member Registered: 07/07, 2009, Posts: 3549 Loc: Vic. Australia 0.018" gap is no problem. If everything else fits well and ring pressure is OK,you'd notice very litle difference if the ring gap was 0.060". I think I've read that article you spoke of. Here's something else to look at,which will tell you to use about 30% bigger ring gap on the 2nd ring compared to the top ring gap.If you have 0.018" top gap,that's about 0.024" gap on the 2nd.Current thinking (since the mid-'80s) is that a bigger 2nd ring gap improves power and oil control. Read what Barry R has to say,about 1/4 way down the page 2ND RING GAP I believe the man has some credentials 0.0015" cylinder wear is nothing.I remember a T140 I did with 0.007" cylinder wear.That alone would have increased ring gap at the top of the cylinders by 0.022". I honed out 1/2 the taper and it ran fine.It doesn't see a lot of regular use,and it's been fine for more than 30 years. for 750 The "M" on the barrel no longer means anything.It's been bored twice since it was that size. Ideal piston clearance (brand new,by the manual) is 0.0037"-0.0047". You've got 0.0056" clearance,if you measured the pistons front to rear and 1/2" from the bottom.There not too tight,that's the main thing. Healy again reading from Hastings Technical data: bores from 2.9525" to 3.5424 use .010" to .020". This places your .018" within Hasting's recommendations. Remember these Hasting recommended figures are for an automotive engine which is liquid cooled and most likely has an engine management system. We have no such luxury. Air cooled engines can run hotter than an automotive engine. The hotter the engine runs the more ring gap that is required. A little bit of detonation, even when you cannot hear it, and that .018" starts to look pretty small. With the state of modern fuel, the inability for people to come to grips with being able to seat piston rings, and trends to run these engines at lower rpm's than they were designed to run at it is a pretty good chance the engine will suffer some detonate. While detonation was not typically a problem with fuel available 40 years ago, and riders didn't expect to putt around at 1500 rpm in high gear, problems with detonation was rare. In a perfect world things would be different. These engines were neither designed, or manufactured in a perfect world. They were not designed to be run on modern fuel or oils mandated by EPA to give automotive engines better fuel mileage. Ring end gap is there to keep the ends of the rings from butting up against each other as they heat up. If they touch they cause the ring to seize (micro-weld) to the cylinder wall. This starts all sorts of problems and given the right circumstances it can break the top of the piston off. Get some detonation and they heat up a lot. So in the imperfect world in which we use these engines having more gap is preferred to having less. 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 smile 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... Busted! There's no apostrophe in the plural of Vincent: "Vincents" is the correct form. The English Police 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. Sound O.K.? 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. Pete R - R.I.P. Offline BritBike Forum member Registered: 07/07, 2009, Posts: 3549 Loc: Vic. Australia I've got the clearance for these pistons in a TR6 listed as: Bottom of skirt 0.0033"-0.0043" Top of skirt 0.0088"-0.0098" You're as-new at the top,and 0.0017" looser than new at the bottom. I don't think you have anything to worry about. I have experienced exactly that situation with a Routt 750 barrel that I had helicoiled on my Triumph proddy racer because of head bolt/stud threads stripping. The symptoms were low compression and poor performance. Upon stripping down, I was advised by Triumph guru Terry Perna (brother of Marino Perna of MAP)to look for tell-tale smudge marks on the bore surface at the head bolt/stud locations. Sure enuff there they were with associated evidence of poor ring sealing. The barrel is now judged to be scrap the reason being that the helicoiled holes are too close to the bore resulting in distortion of the bore surface. OK, if the bore is round and not tapered, rings should seat instantly. Note I said should. Now not all rings are the same.. and Helpolites are not my favorites. There are many iterations on ring designs, but why use 40 year old technology when modern parts cost the same..? Ring school 101. The bottom ring normally called the oil ring. In reality it is the oil CONTROL ring, intended to leave just a thin coat of oil on the cylinder. It should be a 3 piece set up. If you have two or one piece oil rings, throw them away... rubbish.. Now a little trick with the 3 piece rings, take the thin rails and squeeze them,.. then note which way they curve.. you want them both to be the same way, so that they scrape on downward movement, sort of like this: ^ The middle ring is the OIL RING..! If your top two rings are the same, then throw them away... the middle ring should be tapered on the outside like this: / \ Only that bottom edge should contact the cylinder.. if you have FULL contact the ring is either worn out or it is a compression ring... throw them away... The top ring can be made of many materials and designs, usually they have a taper on the inside to promote compression sealing. The bore finish is not that important, only remember that the more coarse the finish the more the rings wear out during "break in." If the bore looks good, do not hone it again... that just wears the rings out... There are many sources of quality modern rings... In the late 60 and early 70's Triumph experimented with smoother cylinder bore finishes and finally settled on 30ra to 50ra finish (150 to 220 grit). On a Triumph cylinder finish is a consideration, made more poignant with the introduction of modern oils in the late seventies. The Hepolite grey cast iron ring, utilizing two taper faced compression rings and a one piece oil ring have been a proven winner in the 650 models (the triple likes 3 piece oil ring and the T140 the two piece oil ring). Being taper faced it is important that the two top rings be placed with the "top" printed on the ring facing up. If either of these rings, especially the middle, are installed upside down the motor will "pump" oil into the combustion chamber. It is important not to damage the rings when placing them on the piston. It is easy, if the proper tools are not used, to bend the rings. Once bent, the rings will not seal against the cylinder. This will allow oil to be pumped into the combustion chamber. It can also lead to piston seizure. The grey cast iron ring has been around since the days of the first internal combustion engine are still used in many engines still in production today. Steel or ductile rings, which are not compatible with cast iron cylinders, must have a protective coating applied to their contact faces or they will wear out the cylinder. This means that the steel and ductile rings must be "broken-in" during production and be perfectly round when they are installed into the cylinder. It also means the cylinder bore must be prepared round and be able to stay round while the motor is being used. Doug you mentioned "dry" assembly. But there is more to it than "dry." After the cylinder is honed it must be washed in hot soapy water until all of the "swarf" (bits of cast iron and bits of stone from the hone) left by the honing process is removed from the cylinder. DO NOT WASH THE CYLINDER IN A SOLVENT. It will not properly clean the cylinder. When you are sure the cylinder is clean rub a lightly oiled lint free rag on the cylinder bore making sure that when you are finished, the white rag does not come out with any grey residue from the honing process! Failing to remove the swarf left from the honing will leave small bits of honing stone embedded in the cylinder wall. These stone bits will cut the pistons and the rings often leading to ring failure. We have all seen pistons with fine striations on the face of the pistons and rings. The dry assembly comes when you do the final assembly and you lightly oil the thrust faces of the piston with MOTOR oil, but leave the rings themselves dry. You oiled the cylinder when you wiped it down after honing so the rings are not rubbing on bare cast iron (which would damage the rings and lead to high oil consumption or piston seizure). Now most of us learned that you cannot use synthetic oil to break-in rings, but a lot of modern oils are more problematic when used for ring break-in than the old synthetics we used when these bikes were new. Doug, there is no one thing that makes you successful when trying to get a new set of rings to seat in your Triumph 650, but a lot of small details. Sometimes, even the "experts" fail to get a new set of rings to seat.. I would check to make sure I didn't bend the rings when you put them over the piston or installed one of the taper faced compression rings upside down before I panicked. john - Hepolite discovered that with modern machining techniques and machinery they could get the required extra clearance under the oil ring by keeping the face of the skirt nearly straight and making, what was called the "taper," in the last 1/4" of the top of the skirt. This has confused more than one Triumph mechanic when they read the Triumph specifications for piston "taper" and measure a new set of pistons and see only about 0.001" of "taper." The problem comes when some one without the proper equipment, or knowledge, takes measurements at the top of the skirt and sees 0.001" "taper" and what is really there is 0.005" or more. In what is the width of the micrometer face, the side of the piston curves in to create the needed clearance. The current crop of after market pistons (specifically JCC brand aka Emgo, Careful, Harris, etc) use the same aluminum, and physical design, as the original Hepolites. Thus the bottom and top clearances are the same as Triumph specified in there literature for the Hepolite pistons used since the mid-sixties. Where I have seen a lot of problems is with is old timers and people who read old service literature not understanding that Triumph pistons went through a change in the mid-sixties. Gone is the 0.0035" clearances used with the lo-ex pistons. This is where we get into trouble. The old timers, and those referring to older literature, often use .0035" specified for the early lo-ex (low expansion aluminum) 650 pistons. So we often end up with 0.0035" clearance where we need 0.004" to .007" specified for the later Hepolite, or JCC units. While we are on the same page with most of this I think you miss-read Mr. Hall's statement. I have to agree with Mr. Hall on this one. For a given piston diameter you will get approx. .003" change in ring end gap for each .001" increase or decrease in piston clearance. The clearance they developed for the 650 was 0.0045 to 0.0061" 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. 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 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. 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. Ray http://vintagemotorcyclepistons.co.uk/ http://www.classic-bike-shop.com/pistons--parts-20-c.asp