New AN barrel & Emglo Pistons

Mr. Rick said:

If anyone has a set of 750 Emglo +.020s I'm very interested, assuming they come with pins, clips and Hastings (or equivalent) rings; they are more likely to be closer in weight to the standard pistons that the engine was balanced with.

I did a search on eBay for: norton commando 750 piston set .020

There are at least 5 sets on eBAy now which all appear to be EMGO with Hastings rings; here's one of them:
http://www.ebay.com/itm/Norton-750-Comm ... hb&vxp=mtr
This guy is in MIchigan

Here's another set closer to you (Acushnet, MA): http://www.ebay.com/itm/Norton-Atlas-75 ... BA&vxp=mtr

Click to expand...

Thank you Mr. Rick. I purchased the set from Acushnet, MA, I appreciate the lead; I'll put the +.040s in inventory, unless someone could use them (good price).

I am not going to open a ticket with AN. I'm sure that they would do something, but I'd have to send the barrel I have back, they'd want to go over it, they might find that they have a "precision" error, where all there 750 barrels have some kind of tweak, maybe not, can't say for sure, but I do know that such an engagement would take time, a resource that I have wasted too much of at this point.

With all the concern and worrying I have done over this motorcycle I suspect that, when finished, cocked and locked, that it will start itself and take me for a ride...

I'm pleased to have been helpful, and I can relate to the concept of keeping the job moving forward.
I might suggest you send the pistons along to the folks doing the oversize bore, let them make a good match.
A further suggestion is to at least contact AN and tell them what you found? Those barrels are so far out of spec that they wd surely want to hear of it, even if you're not sending it back. Maybe rescue the next customer, the poor sap who was just about to receive the same version of the item that they sent to you...

Not sure in three pages of threads the actual bore size has been mentioned, only the piston size. Whats the bore size and the method used to obtain it.

FOUR THOUSANDTHS taper?!?! :evil:

I understand about keping the project rolling, but take pictures of your measuring tools, in situ, send it to them.

Ok, dumb question time...

How is it possible to unintentionally machine the bores with such a taper?

Is that correct. New cylinders from AN which have a .004" tapers bore?
Is that both bores?
I would be sending them right back if that is the case.

They are both out the same?

very hard to comprehend
(1) how they could bore it like this
(2) how the machinist didnt know
(3) how it got out the door

Fast Eddie said:

Ok, dumb question time...

How is it possible to unintentionally machine the bores with such a taper?

Click to expand...

I don't have a lot of experience here, but I'll pass it on anyhow.

A few years back, I did my best at getting some taper in a Commando cylinder by honing with more dwell towards one end of the bore than at the other. As I recall, it was very difficult to get more than .001" - .0015" of consistent taper this way. I only tried this because owner of the engine I was building wanted to try tapered bores. It's something that was normal practice some years back for at least one NASCAR engine builder, but I don't know if anyone does it now.

I've also bored Commando cylinders in my lathe using a faceplate fixture to hold them, and a very sturdy boring bar bolted to the cross slide. I noticed that the bores came out slightly tapered, but I could straighten them out by careful honing. I didn't worry too much about it at the time, but I think it might be a case of the lathe spindle and the bed ways not being precisely aligned. It could also be a case of wear at the area of the ways next to the spindle, because that's where most of my work is done. That might allow the carriage to be deflected slightly by the pressure on the boring bar as it got closer to the face plate, and so cutting a smaller diameter bore. It doesn't take much wear on the ways to get a significant change at the end of the boring bar.

I do most of my boring now on the mill, and have had no problem with taper in the bores. I suppose you could get the same problem with taper from uneven wear on the mill spindle, or on a conventional boring bar.

Back when I was actively building Rotax singles for road racing, I used cylinders from Ron Wood that had been sleeved, bored, and honed by a Southern California shop (that also sleeved 850 Commando cylinders to 920). I noticed that they usually had tapered bores, being tighter at the bottom. I don't recall exactly how much now, but it was significant enough that I noticed. They seemed to work fine, so I didn't worry about it much. This particular shop used a mill for both boring the cylinder for the sleeve, and boring the sleeve. I always assumed they got the taper from uneven honing, but it could also have been from the boring process.

After doing a lot of final honing by hand, I have learned that I have to stop and measure periodically if I want to avoid tapered bores. It's very easy to allow the hone to spend more time at one end of the bore than at the other. Still, I'm only talking about a difference in bore of .0005" or so. I used to have a shop nearby that was willing to finish hone Commando cylinders on their automatic Sunnen machine, after I made a base plate fixture so they could bolt them to their machine bed. They did absolutely perfect bores, and I was very disappointed when they went out of business.

Ken

https://s19.postimg.org/510aptxo3/Choked_cylinder.jpg


Common to have intentionally tapered cylinders on air cooled aircraft cylinders. Why not motorcycles?

Is the taper there to compensate with the heat gradient from top to bottom ? The problem I can see with excessive bore clearance is piston slap, especially with Nikasil coated bores and cast pistons. Normally the piston fit is not the main factor affecting compression - that is why we have piston rings.

acotrel said:

Is the taper there to compensate with the heat gradient from top to bottom ? The problem I can see with excessive bore clearance is piston slap, especially with Nikasil coated bores and cast pistons. Normally the piston fit is not the main factor affecting compression - that is why we have piston rings.

Click to expand...

Exactly. The thinking is the greater heat near the head will make the cylinder wall parallel when running.

Running a bore gauge into the jug it becomes quite obvious when you leave the constant section.

JimNH said:

https://s19.postimg.org/510aptxo3/Choked_cylinder.jpg


Common to have intentionally tapered cylinders on air cooled aircraft cylinders. Why not motorcycles?

Click to expand...

Doesn't sound like that good an idea.

Comments on this subject from an aircraft engine rebuilding facility, Chuck Ney Enterprises

"The Case For Straight Bore Cylinders

To the best of my knowledge, there is no other piston engine on the planet that is built with an intentional taper in the cylinder bore (choke). If you believe the story "cylinders get hotter on top and swell to a straight bore" you likely still believe in Santa, too. For the last ten years, we have refused to traumatize the poor cylinder with "CHOKE" in the bore, and for a simple reason explained here.
Using 5th grade geometry, the circumference of a circle is found by multiplying its diameter by pi (3.142...). Since an engine's piston rings follow the circumference of the cylinder, this means that the ring gap must change by pi times the cylinder diameter change due to choke. Using a standard aircraft cylinder with a .010 inch choke will require at least a .032 inch ring gap just to keep the ring ends from touching, or "bottoming out". This additional gap is just more space to lose compression through and increase blow-by.
While talking about compression, the top ring can not properly seat since it must flex .032 inch for every time the piston goes up and back. The top ring has now become a broaching tool, trying to scrape the taper out of the top of the cylinder, damaging both ring and the top of cylinder bore. My experience, measured both in cylinders (over 100,000) and years (over 30), has always found the same wear pattern: a ledge just above the top ring travel. In some cases this ledge exceeds .020 inch in height!
We now use only good 1st run, crack-fee cylinders, grind the barrel STRAIGHT, and install new valve guides and seats. These cylinders are then finished to the most reasonable oversize (.005,.010,.or 015) and given new rings and matching pistons. This results in a bullet-proof cylinder that makes 7 to 10% more measurable horsepower with a 15 to 45 degrees cooler CHT. Reliability is improved as more than 99% of these choke-free cylinders achieving factory TBO - and beyond. This simple fact is used by fleet operators who have received extensions to the FAA required TBO limits for their commercial operations. Additional advantages include reduced vibration and up to 25 hrs operation per quart of oil consumption.
This is real-world proof of 5th grade math. Would you now rather run your piston in a funnel or a true cylinder like the rest of the internal combustion engine world?
We use these cylinders in all engines rebuilt here. We also have been machining and line-boring crankcases since 1969. Although unique in how we handle cylinders, if plagiarism is the most sincere form of flattery, we are nearly flattered to death. Nearly every crankcase overhaul shop, including the factories use the techniques and approved procedures I pioneered several years ago. Why bother going to these copy-cats? Come to the original thinker, Chuck Ney, to have your next engine rebuilt. Join our hundreds of satisfied customers."

Ken

Comments on this subject from an aircraft engine rebuilding facility, Chuck Ney Enterprises

"The Case For Straight Bore Cylinders

To the best of my knowledge, there is no other piston engine on the planet that is built with an intentional taper in the cylinder bore (choke). If you believe the story "cylinders get hotter on top and swell to a straight bore" you likely still believe in Santa, too. For the last ten years, we have refused to traumatize the poor cylinder with "CHOKE" in the bore, and for a simple reason explained here.
Using 5th grade geometry, the circumference of a circle is found by multiplying its diameter by pi (3.142...). Since an engine's piston rings follow the circumference of the cylinder, this means that the ring gap must change by pi times the cylinder diameter change due to choke. Using a standard aircraft cylinder with a .010 inch choke will require at least a .032 inch ring gap just to keep the ring ends from touching, or "bottoming out". This additional gap is just more space to lose compression through and increase blow-by.
While talking about compression, the top ring can not properly seat since it must flex .032 inch for every time the piston goes up and back. The top ring has now become a broaching tool, trying to scrape the taper out of the top of the cylinder, damaging both ring and the top of cylinder bore. My experience, measured both in cylinders (over 100,000) and years (over 30), has always found the same wear pattern: a ledge just above the top ring travel. In some cases this ledge exceeds .020 inch in height!
We now use only good 1st run, crack-fee cylinders, grind the barrel STRAIGHT, and install new valve guides and seats. These cylinders are then finished to the most reasonable oversize (.005,.010,.or 015) and given new rings and matching pistons. This results in a bullet-proof cylinder that makes 7 to 10% more measurable horsepower with a 15 to 45 degrees cooler CHT. Reliability is improved as more than 99% of these choke-free cylinders achieving factory TBO - and beyond. This simple fact is used by fleet operators who have received extensions to the FAA required TBO limits for their commercial operations. Additional advantages include reduced vibration and up to 25 hrs operation per quart of oil consumption.
This is real-world proof of 5th grade math. Would you now rather run your piston in a funnel or a true cylinder like the rest of the internal combustion engine world?

Ken[/quote]

That guy has his opinion but here is a quote from Victor Engines, A premiere rebuilder:

Cylinder Overhaul and Exchange for Lycoming and Continental Motors Engines

Aircraft cylinders can be efficiently rebuilt and reused if properly inspected, properly machined and the necessary parts are replaced to provide for extended service life.

To rebuild a cylinder assembly that has had cylinder barrel wear or corrosion the steel barrel can be re-machined to restore it to factory new limits for piston to barrel dimensions. In order to accomplish this the cylinder barrel will be first measured and NDT tested to determine if there is enough material left in the cylinder barrel to allow for re-machining. Re-machining of the cylinder barrels is controlled using a “Power-By-Victor” precision honing machine that will provide for the proper taper and finish size of the barrel for optimum engine performance.

Machining the cylinder barrel for proper taper or “choke” is critical for efficient engine performance and lifetime of aircraft cylinders. As an aircraft cylinder expands under normal operation the upper portion of the cylinder barrel will expand greater than the lower portion of the barrel. When this occurs, loss of engine power, excessive oil consumption and blow by can occur even on a new cylinder. To correct for this anticipated and known expansion, Victor Aviation can re-machine the cylinder with a taper that will offset for the expected expansion of the barrel allowing for parallel bore dimensions when the cylinder is operated at temperature. With over 36 years of aircraft cylinder and engine overhaul experience, “Power-By-Victor” technicians know the exact dimensions necessary to machine the proper cylinder taper dimensions for your particular engine application.

When you consider that the factory new cylinders are choked the words of one rebuilder who may not have the correct machinery to properly machine the correct choke don't carry much weight.

Even the huge radial engines by Pratt&Whitney and Wright have choked barrels.

It's probably much more practical on an aircraft cylinder as it's a stand alone round unit with a the head screwed and shrunk on and has no direct attachment to any adjacent cylinder.

Aircraft engines generally have rather loose clearances due the extreme temperature differences. Consider one can go from max power shortly followed by a power-off glide with lots of cooling air rushing by.

So, the builder you quote may have something but it's not supported by many others.

Who in all of Norton-doom would request tapered bore, especially in obsolete friction prone long strokes, sheeze.

http://www.modelenginenews.org/rsch/build.html
The late George Aldrich convinced me to taper cylinder bores. The bottom should be from .0005 to .001 in. larger in dia. than the top (.0005 for ½ A engines). You simply spend more time lapping the bottom of a bore than the top to produce a tapered bore. Taper the piston about .0002 also. Tapering puts the closest fit at the top of the stroke were the combustion pressures are highest. The piston should just go tight (zero clearance) at the top of its travel. A tapered piston then fits like a keystone. The loose fit at the bottom will reduce friction and make the engine easier to start.

A taper is also a real advantage when fitting a piston. Finish the tapered bore first and then lap the piston until it will just enter the tapered bore. You then know that about another .0005 to .0010 in. of piston diameter reduction is necessary. Lap a little (10 sec.) and then try the piston in the bore. You can gage progress by cleaning both parts and determining how far the piston enters the bore. Quit lapping when the piston is a push fit at the top of the stroke. Before I started tapering the bores, I could not gage how the lapping was progressing and thus made a lot of pistons that were too small.

https://www.avweb.com/news/maint/182902-1.html
The bore is not precisely cylindrical—it is tapered in the top two inches of piston ring travel, usually by .003" to .007". This choke is used to compensate for the fact that when the cylinder is at operating temperature, the top of the barrel is considerably hotter than its base, and therefore it expands more. If the cylinder were not adequately choked at room temperature, the piston-to-cylinder clearance at top-dead-center would become loose and sloppy as the cylinder heats up, and the rings would flex excessively.

http://www.aircraft-specialties.com/cyl ... 5006-a20p/
Choked barrel
Optimal barrel choke allows rings and pistons to work properly at normal operating .
Improves performance and reduces ring and piston wear.


http://www.datwiki.net/page.php?id=1715 ... 20cylinder)&searching=yes
A cylinder of a reciprocating engine ground in such a way that its diameter at the top of the barrel is slightly smaller than the diameter in the center of the barrel. The large mass of metal in the cylinder head absorbs enough heat to cause the top end of the barrel to expand enough more than the remainder of the barrel that, at the normal operating temperature, the diameter of choke-ground cylinders becomes uniform throughout.

Interested with all the above theory and speculation what Andover Norton has to say about the above, if I have missed it in the thread please excuse me.
Either:
They were machined that way intentionally or
There is a fault with the machining and therefore quality control.

If it was the 2nd option I would have thought that they would need to know and might be able to do something about it, they would certainly need to address the situation with their suppliers.

If they were machined that way intentionally then, whats the fuss!

I hope Im not being too much of a killjoy but one of the things I have found since my son and I started racing is that you can go round in circles with advice, finally vanishing up your own backside!

I am none the wiser having read this post if the barrels are correct or not, if I was building a new motor and need new barrels do I buy the Andover Norton ones or not. I think I would have to go with the known and trusted experts but would very much like to know what the seller says.

Plenty of different opinions on choked bores here, so anyone doing their own boring and honing can digest it all and make their own decision.

I think the key difference here between the discussion of choked bores in airplane engines and the bores in new Norton cylinders is that the drawings and specs for the airplane engines include the amount of choke required. The Norton specs for their cylinders, unless they have been recently changed, do not. They specify uniform bore diameters, within their given tolerance limits. If the engine designers wanted them to be tapered, it would be in the specs.

Still, as several listers have pointed out, the question of why these particular cylinders are tapered would be best answered by AN. We'd all be interested in what they have to say.

Ken

Gentlemen,

Sorry we haven't replied earlier, but my attention was drawn to the thread only this morning and, it being a typical Monday in the shop, I was busy till after 6pm.

I have briefly discussed the issue with our technical buyer Ashley who overlooks the cylinder barrel manufacture. Our finidings & questions are:

- As I understand it Rocky Cycle intended to install used pistons in a new barrel;
- As I would expect these, having had wear & tear already, are undersize.

Our barrels are made to have a bore of 73.0mm (750cc), and the GPM pistons we sell are undersize to give enough clearance if put into these barrels. We normally go for 9-11/100mm on a road engine. Race engines depending on rider and spec.

As many have indicated, it would be hard to get a CNC machine to a taper unintentionally – oversize yes, undersize yes, not square to the crankcase surface yes, but 0.004’’ of taper we believe is practically impossible unless intentionally programmed to do so.

It seems that Rocky Point were originally measuring the skirt clearance at the top of the bore and looking to put pistons from a failed engine back in it. If the piston was TDC, and the skirt clearance was measured and then measured at the bottom of the bore that would indicate a taper of nearly 0.008-10’’ when you look at the figures William has obtained. With this amount of error the hone tool would have missed some of the bore.

As yet, there is no mention what they have used to measure the bore. We suspect they haven’t and just used an old piston and some feeler gauges.

I have sold quite a lot of our barrels into the German market (where I run the Norton Motors GmbH) with my friend Rudi, master toolmaker, doing his own reboring and honing in-house and always quite open in critizising what he thinks should be done better, yet to complain about our barrels even though he is my biggest customer for them.

Rudi also insists on using our GPM pistones, but that is another story. If the worn pistons Rocky Point first intended to use were undersize I'd have used new ones that I'd expect to go straight in, giving the correct tolerance.

Why Rocky Point did not contact us I also do not know. If I find goods not up to spec or expectation I tend to talk to the supplier about it whom I'd then expect to put things right. If the barrel was really tapered, which for above reasons we doubt, we'd have exchanged it immediately and then tried to find out how this was possible- if indeed it was.

If you have technical questions about manufacture of our parts may I suggest you contact our Ashley under ashley.cutler@andover-norton.co.uk

Regards,
Joe Seifert
Director, Andover Norton
MD, Norton Motors GmbH

PM sent.

No feeler gauges were mistreated or injured during the measuring process, because none were used!. No used pistons were considered for this project. A bore gauge calibrated to .0005 increments and a micrometer were used.

I may have been able to use the barrel as it was delivered, but it would have been outclassed by the rest of the work; I always aim for perfection and accept amazing or stunning as the final result, if perfection alludes me.

I have no beef with AN, and 'am happy that they exist, and quite impressed with their spares list.

If the cost of shipping it back is to costly, maybe have an AN agent nearest you confirm your findings and report back to head office