Date: Fri, 3 May 1996 17:23:08 +0100
From: Oliver Motz <omotz@ftk1.fernuni-hagen.de>
Hi Rick,
$200 for a pair of original Hepolite Pistons is O.K., because they are very rare and hard to get items these days. Since a few years Norton has let pistons made at Gandini/Italy, brand name is GPM. These pistons are made to the Norton Factory specifications and are as good as the Hepolites. They come in original Norton cardboard boxes with the original Norton spare parts nos. and are a bit cheaper than the Hepolites. You can only get std., +0.020", +0.040" and +0.060"sizes, no +0.010", +0.030" etc. sizes. Use the Norton specifications for the oversize bore to be on the save side. (Personally I have the barrel of my 750 honed to give a play of 8-9/100mm because 11/100mm given by Norton seems too large. There's an old rule thumb: give 1/100mm play for each 10mm diameter of piston plus 1/100mm play for security reasons, this equals for a 750 Norton piston with 73mm dia. 8 to 9mm play AND a smooth running in. Remember that I am German and we measure things in Millimetres (mm).)
When it was hard to get original pistons e.g. for BSAs we took stock GPM pistons which we altered be turning and milling. These pistons had no original spare part no. They were slightly heavier than the original pistons and they needed more play than the original ones because they expanded more.
Never use Norton pistons with the slots around the piston's crown!
Bye, Oliver (Norton 750 Cafe Racer)
35.2 Norton's Slotted Pistons.
Date: Fri, 10 May 1996 02:35:28 -0400
From: Mike Taglieri
In a message dated 96-05-09 00:59:54 EDT, you write:
>There has been a thread lately about being sure not to use slotted
pistons
>in our Commandos. I read them all, but wasn't too concerned until
I
>pulled my cylinders today.
>
>We're not talking like (gulp) slots under the oil rings...
>Are we? If so, who has those great Taiwanese pistons again?
There are good slots and bad slots (just like the witches in Oz). Hold your piston so you're looking through the bore for the wrist pin. If you see two little slots, one on each side, this is OK -- it's not the latest design, but it's in use on many bikes, including mine. The questionable pistons have a long slot connecting these two little slots, resulting in a huge, U-shaped slot, one on each side of the piston.
The purpose of this design was to let the oil scraped by the rings get back into the crankcase, but it removed nearly 50% of the metal holding the top of the piston on -- not exactly one of Norton's brighter moments. The Combat in '72 was apparently when they changed over to the two small slots instead of the big one.
The experts seem to suggest that you shouldn't buy a new piston with the big slot (probably not something one can do today, I hope), but if you ride prudently you can use up the ones you have. The Commando Service Notes say the problem with slotted pistons is generally "the top coming off the piston when the revs were kept up towards 7,000," but that "the slotted pistons are OK for the man who never goes over 5,000 RPM." The Tech Digest agrees, noting that that piston failure tends to occur in "in a HIGHLY enthusiastically ridden (i.e. overrevved) Commando."
If I had slotted pistons that were in good shape, I'd probably keep on using them after carefully checking for cracks, which tend to extend DOWN towards the bottom of the skirt, according to the Tech Digest. On both kinds of slots, radiusing the slot at the bottom can help. Also, you should notice that older and newer pistons take different kinds of oil rings that are not interchangeable (oil groove deeper on the new pistons). This changeover was apparently NOT made at the same time as the end of the slotted pistons, which would have made it just too easy for us, right?
The only Taiwanese parts I've used on my bike were head gaskets, and it was a memorable experience if not a particularly pleasant one. Whether new Taiwanese pistons are better than slotted pistons in good shape (or NOS) is a question I'll leave to wiser heads.
Mike Taglieri
Raul -- '72 Commando Interstate
Date: Fri, 10 May 1996 08:26:50 -0700 (PDT)
From: Tom Allen
Thanks for making that important but overlooked distinction. My experience with piston breakage was indeed with BAD slots and while being enthusiastically ridden at or near 7,000 RPM. Nevertheless It's not like I shouldn't have known better. When I had the motor apart to re-ring it I noticed that the oil ring grove was binding on the oil ring. So in a fit of parsimoneousness ( remember him) I carved the ring grooves out to fit. My rationale was "Oh, It won't get that many miles on it and I won't ride it that hard."
Ha! An Atlas is an awful lot of fun to ride hard on twisty mountain roads. They handle superbly and cry out for "more motor, more motor, more motor." So I gave it a Superblend bottom end, an SS cam, Combat head and 32 mm carbs and (having seen the error of my ways) a new set of pistons with holes, not slots.
Now, of course, It'll eat primary chains even faster.
Tom
Date: Mon, 16 Sep 96 16:07:00 PDT
From: Ken Dubey
> Where do the early (slotted) pistons come from, old stock?
Yes, all the "new" ones anyway. While rummaging around the shelves of the local MC salvage yard, I found several sets of these slotted pistons in different sizes, still in the original boxes. Someone said a while ago that these slots look like they were cut with a hacksaw and rat tail file, and that is the absolute truth, I could have done better work after sampling several bottles of Guiness, and working blindfolded.
Clerk sees me looking at them and says, "if you want to make your Commando really go, these are the pistons you want, they're high compression you know". To which I thought, "Go where? To the engine rebuild shop?"
Date: Tue, 17 Sep 1996 01:07:44 -0400
From: Mike Taglieri
>My street bike (`69 Commando) rarely sees beyond 4000 RPM and I don't
think
>I've ever taken it over 6000 (in it's current state of tune). With
a low
>compression head, 30mm carbs, stock cam and early (Atlas) style mufflers,
>there is not much point.
>Both bikes have later pistons. Where do the early (slotted) pistons
come
>from, old stock? I go through a set of pistons every 35,000 miles
or so.
>That only takes two or three years and the slotted ones have been
out of
>production since the 70's.
Obviously, NOS slotted pistons would not have the fatigue problems I mentioned a couple of days ago, so they should be safe for this kind of gentle riding, as the Tech Digest and Service Notes say. When I suggested using them as paperweights, I meant if you find slotted pistons in your engine and don't know their usage history before you owned the bike.
Mike Taglieri
Date: Mon, 27 May 96 23:01:11 EDT
From: Gregg Kricorissian
Mike wrote:
>I put the pistons in the bore FIRST, then attach them to the rods
as I
>installed the barrel, and I think this is easier.
I have to second Mike's suggestion: having tried both ways, the way he describes is a *lot* easier on a Norton engine, especially if you are kosher, and stagger the ring gaps the prescribed way.
The "traditional" way, you need to have two ring compressors. Unless you believe Haynes, our optimistic publisher, who shows two hose clamps being used. You'll have at least two problems:
1. It's a bugger to get the ring compressors liberated, once the pistons enter the bores
2. Your average Tridon hose clamp has a crimped part around its tightening screw, which will impede compressing the rings evenly. They either won't enter the bores, or you'll break a ring ... or both!
If you're going to try using hose clamps, please don't do it the way Hanynes shows. Instead, make a sleeve by cutting soome thin sheet metal just wide enough to cover the rings, and just long enough to go round the piston without overlapping. Pre-shape it by rolling it round to the right diameter. Then put them on the pistons, put your hose clamps on, not too tight, and pray. Use lots of lube, like cam lube, or (gasp) STP on the clamp sleeves, pistons and bores to ensure the rings can slip by. (This is about the only thing STP is good for, and only because it won't run off the surfaces) Better yet, try Mike's suggestion.
Of course, if you're working on a Royal Enfield or Matchless twin with their lightweight, separate left and right cylinders, you'll be able to install the pistons easily with one hand behind your back no matter which way you choose, because you don't have to juggle two pistons at once, along with a huge casting....
Hope this helps,
...Gregg
Date: Tue, 28 May 1996 09:31:13 +0000
From: Skip Schloss
While you guys are busy heating your pistons to expand them so the wrist pins will slip in, I am headed for the freezer to pour more margarita mix.
While in the freezer, I pick up my wrist pins. You'll discover that frozen wrist pins slip in as easily as heating the pistons, and are easier to handle. (What's really trick is to spray the pins with liquid assembly lube before you freeze 'em. That way, when you go to do the install, there's already a lubricant film on the pins. No muss, etc.)
Ditto bearings. Yes, heating cases helps, but freezing the bearing at the same time helps even more. (I understand some folks have cans of liquid nitrogen in their shops to aid the freezing/shrinking process. However, this voids the corollary advantage of having an excuse to go to the refrigerator.)
This also helps with really painful little details such as fitting Norton rocker arm spindles. Yes...you still have to heat the head, but the frozen spindle means you don't have to heat the head much, hence you reduce the chance of warping the gasket surface.
Voice from the other room: "Honey, why do you keep opening and closing the refrigerator?" "Why, darling, I'm just checking to see if my wristpins are frozen yet..."
Skip Schloss
Date: Tue, 28 May 1996 10:44:35 +0000
From: Skip Schloss
Ok, folks, since Mike brought up the subject of mounting cylinders over rings...let's talk about it.
I currently own three different kinds of ring compressors, none of which work particularly well, including some EXPENSIVE Snap-On compressors that are designed (but not WELL designed) to come off the bottom of the piston.
I remember (but only vaguely, since much of the past is shrouded in a strange purple haze) working on Volkswagens back in college (I was desperate for money and would do nearly anything, such as work on VWs) and we had a set of scissors-like compressors, which had a ratcheting device. You squeezed the handles, the rings compressed, and the gadget locked. Then when the cylinder was down over piston, the locking device could be released and the band around the rings released.
It worked great...but I've never seen another one since.
So how about it? You A&Ps out there, how is this done on Lycomings? How about you Porsche fanatics, what do you have hidden away for ring compressors?
I must admit that even with my three sets of ring compressors to choose from, we usually still adopt the two-person method of cylinder installation. One gal/guy lowers the cylinder, and the other guy/gal manually squeezes the rings into the bore.
There must be a better way...
(Certainly do wish we could get away with the new "plastic sleeve" approach for car engines. You just position the plastic funnel device under the piston, on the cylinder decks, and tap the piston down into the bore with a hammer handle. No compressor involved. SLICK.)
Now, I wonder if a plastic (Teflon?) sleeve could be made to fit around, say, a Norton piston. with a single hose clamp around it, and a slit vertically up the side to allow it to slip over the rod. You'd clamp it on the piston, the base of the sleeve could rest on the case, you'd tap the cylinder down over it, then release the hose clamp and slip the sleeve (more appropriately, the pair of sleeves) off the rods and be done with it.
Hmm.
Skip Schloss
Flying Fish Motorcycles
Whitefish, Montana
Date: Tue, 28 May 1996 22:47:15 -0400
From: Michael A.R. Partridge
I must admit that as an enthusiast, before I got into this business, I always installed Norton twin pistons by sticking them into the cylinder first by hand and then offering up the cases with the rods sticking out and slipping in the wrist pins. I did it with the cylinder barrel and cases lying horizontally on appropriately placed blocks of wood. It is a very easy way of doing it once you have had a bit of practice. Wrist pins are usually a sliding fit - gently warming the pistons up with a blow torch before offering up the rods works fine. If the pins are hard to slip in it is usually because one has been a bit rough getting the circlips out and this is easily corrected.
I must be getting old because when I first started working on these bikes in the 60's blow torches were something of a luxury and the standard way to warm the piston for easy wrist pin removal was to soak a rag in boiling water and place it on the piston crown. Silly or not, it worked. Let's hear less of this talk about using hose clips for ring clamps - doesn't do anything for the sale of our overpriced and highly profitable proper clamps!
Another matter - our biggest inhibitor to business growth has been our inability to hire enough parts sales personnel. Anyone interested (must be computer literate - I'm sure everyone reading this will be) in a rewarding career selling British parts should contact me by E-Mail. We pay strictly on Commission only so you earn what you are worth. I don't want to take up B-I space with this so if you are seriously interested - I will be pleased to provide more details directly. Consideration will be given to applicants from anywhere in the world - not just Canada.
Mike Partridge, Walridge Motors Limited.
Date: Wed, 29 May 1996 08:45:59 -0500
From: John Goodpaster
>So how about it? You A&Ps out there, how is this done on Lycomings?
>How about you Porsche fanatics, what do you have hidden away for ring
>compressors?
Never used compressors on aircraft engines. The pistons are huge (HD size ) since the cyl. are one for each piston I insert the piston assembly. in the bore and then install wrist pin. No circlips as there are end plugs of aluminium in place to keep the pin from drifting.
I also never lube the piston rings, I assembly. dry to keep the cyl. from getting glazed, Also do this with ALL motorcycle engines and get a good ring seating right away..................
bsajohn@pla-net.net
AHRMA