Tight piston to cylinder clearance

To be fair my 128,000 mile man is a gentle rider, always has been.
It is an astonishing distance for an original Commando.
I'm not quite so gentle, however with just 26,000 on the clock, decent maintenance ( on the bike) and other bikes to exercise, I'm thinking I'll be in an Urn before I wear this thing out.

Glen

The line2line coating is a graphite based lubricant. You can get it in different hardness's for different wear rates. There must be some abraidability or it will not "run in". I've been riding and rebuilding my Norton for over 30 years and I've worn out hepolites till they were smoking and rattling like a diesel. In 2009 I switched to forged lightweight pistons (40,000 miles so far). Any piston will wear out. The choice is if you want a tighter longer lasting piston or not. Let me think - for around $100 or so I can approx double the life of the pistons - or thrash it twice as hard and get about the same length of service.

jseng1 said:

Yes it will help in that situation but its never good to thrash a cold engine no matter what. On the other extreme - the coating could save your pistons when the motor is overheated to the point of seizure or melt down.

But its really just about running tighter clearances for those who want tighter longer lasting motors.

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Agreed in fact it takes about 10 miles to bring a Fast back upto working temperature.. other models may well take longer- airflow under fastback tank is very poor.. What prompts the question is that I am building an engine for hill climbing.. No more than a mile and its over !

Seems to me that Jim's reason for fitting the pistons tight in the bore is about the time taken to wear the bores until piston slap makes the situation untenable. The bores in my 850 motor are quite loose and because I use methanol fuel, the warm-up time prior to racing should be longer. It is something I don't worry much about - it will probably come at a price, if a piston cracks.

jseng1 said:

The line2line coating is a graphite based lubricant. You can get it in different hardness's for different wear rates. There must be some abraidability or it will not "run in". I've been riding and rebuilding my Norton for over 30 years and I've worn out hepolites till they were smoking and rattling like a diesel. In 2009 I switched to forged lightweight pistons (40,000 miles so far). Any piston will wear out. The choice is if you want a tighter longer lasting piston or not. Let me think - for around $100 or so I can approx double the life of the pistons - or thrash it twice as hard and get about the same length of service.

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Do any of the auto companies use coated pistons currently?

I think you’ll find that most automotive OEMs use coated pistons today.
But I think it’s mainly Teflon that’s used.

What prompts the question is that I am building an engine for hill climbing...

Say WHAT! oldmildew. This is my intentions too. Pave civilized or unpaved maniac type?

Commandos may not be the fastest nowadays but they are often still the quickest, even 20 yr ago before even more potent developments.



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jseng1 said:

. Any piston will wear out. The choice is if you want a tighter longer lasting piston or not. Let me think - for around $100 or so I can approx double the life of the pistons - or thrash it twice as hard and get about the same length of service.

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For me it's more like - Let me think, use proven setup that will outlast me or maybe spend a few bucks to coat and possibly see the engine self destruct before the next Visa bill comes in.
Someone here pointed out " the enemy of good is better", this often holds true.



Will be interested to see what experience shows up over time. The companies selling the coatings make them sound like a cure for everything including diabetes, but that is the norm for the Peddlar.

I don't like the fact that JE Pistons says no.

Are your pistons made by JE?



Glen

If I understood correctly Glen, JE said “no” to ceramic coating and anodising. Neither of which are what JS is talking about in this thread.

It’s strange that JE claim such doom and gloom from ceramic and anodising though, both are actuallly very common these days.

You ‘pays yer money and makes yer choice’ I guess.

I talked to CP Carillo about the line2line abradable coating. They would not recommend nor say anything negative, only that you are completely on your own should you choose to use it.
It was also suggested that the coatings in general are not needed for road applications.

I understand that the abradable coating being discussed is used to run forged pistons at tight clearances.
I'm just not sure why any road rider would think they need to run forged pistons, tight or loose.
Seems to me it's a race only thing.
So for the 2 racers here.....go for it!

Glen

I wouldn’t argue with your ‘standard is best’ approach to your Norton at all Glen. But I do sometimes struggle to understand how you can be the same bloke who hand built his own 1360cc ‘fire and brimstone’ hot-rod Egli Vincent !

I was an idiot!!

It is fun, but once was enough. It might have been the best approach, change up everything, hotrod everything, build it all for severe duty and hope like hell it holds together.
Very costly tho.

Ive come to the realization that a stock Norton with some hotrodded parts might be a bit of a ticking time bomb.
Your 920 Maney approach is likely best, especially if you add a TTi box. Again, very costly.
On the other hand a nicely setup (near)stock Norton is a pretty nice machine.

Glen

Here's the deal with pistons:

You can't get lightweight cast pistons - they don't exist and no one will make them unless you spend a fortune. If you want a modern design piston it has to be machined from a forged blank. That means using 2618 alloy or 4032 alloy. All the motorcycle racing pistons are 2618 alloy because it can survive higher temps and is less likely to break. The 2618 expands more than the 4032 alloy (4032 is more similar in expansion to cast piston material). The 4032 alloy is OK for the street and you can fit them with tighter cold clearances but you can't get them made for motorcycles as explained below.

I've had pistons made by JP Carrillo, Wisco and JE. Ross is another good option. Mahle has the best reputation and their piston coating is supposed to be good for 100,000 miles. Visit Mahle's website and see their videos. But they do not have forgings in the 4032 alloy in the Norton sizes. They would have to be made from billet at over $300 each dealer cost not including rings and pin. The last option for 4032 alloy is Wossner and I've been talking to them but now they say they need 24 pistons per size minimum order and the price is double the JE cost and I would not recommend 4032 alloy for racing.

So that leaves the heavy cast pistons, the modern lightweight 2618 alloy pistons or the triple expensive 4032 alloy pistons that have minimum quantity roadblocks and may not even be available.

Adding the coating to the JE pistons (which has been working out) is the best option to enable close tolerances with a 2618 alloy piston - This way you get the best of everything.

In the 1360 I have large lightweight CP Carillo forged (92 mm) running at 3.5 thou, no coating. This is at CPs spec. Cast iron liner, Al muff.
Seems pretty close for such a large cast piston. So far so good, but time will tell.
How does CP do it with such a tight clearance?

Glen

Thats a good question Glen. Have you had them at WOT for any length of time? Or are you giving them a nice long run in? If everything is good then maybe its your cylinder design.

Each motor has its own requirements. For example - I have been emailing a customer talking about clearances and he tells me that Triumphs need a thou or so more piston clearance than Norton's or they will seize (same brand of piston).

And when I worked at a Brit bike shop we had to give the Triumphs .006" clearance with cast pistons if they were going to go straight out and race. This wasn't guesswork - we knew what worked and what didn't because we saw what was happening with the piston skirts.

When you're talking jap bikes - JE recommends down to .0025" clearance with water cooled Nikasil coated alum cylinders.

Japanese two-stroke pistons are machine-made - spun-cast, then forged. They probably run at tight clearance in nikasil bores to stop the coating from being hammered. Mahle pistons are used in methanol-fuelled Jawa speedway motors. Methanol-fuelled motors usually run cooler than petrol-fuelled motors, so the clearances can be greater if the motor is not warmed-up properly. So a stronger piston is needed. A forged piston usually grows less and more evenly than a cast one because of the different grain flow in the aluminium. And the cast one is usually heavier.

acotrel said:

Japanese two-stroke pistons are machine-made - spun-cast, then forged. They probably run at tight clearance in nikasil bores to stop the coating from being hammered. Mahle pistons are used in methanol-fuelled Jawa speedway motors. Methanol-fuelled motors usually run cooler than petrol-fuelled motors, so the clearances can be greater if the motor is not warmed-up properly. So a stronger piston is needed. A forged piston usually grows less and more evenly than a cast one because of the different grain flow in the aluminium. And the cast one is usually heavier.

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T'other way round t'aint it?

Certainly with hypereutectic type cast the coefficient of thermal expansion is lower than with forged aluminum.

We run hypereutectic Omegas in standard Vincents at as low as .0025" Skirt clearance.
The nice thing there is that oil consumption drops to nothing. I used 8 Oz to go to Californa and back, 3,000 miles. The original setup (.008")was expected to consume 1 imperial gallon of oil for every 1500 miles, that's right in the rider's handbook as "normal"!

Glen

Still hard fact remains, if coating not be seen abraded some after run in, then its wasted money not doing anything but hollow bragging. JMS has not yet shown anything to support the claims its helpful on his engines, just un-touched do nothing black skirts. Its definitely a great feature, paid off in spades in Ms Peel engine done tigher than any JMS race builds can approach or stand very long so far. If skirt coat not worn away some its BS ignorance to claim if did anything but empty wallet and delay assembly. Yoose elite-ist builders need to pow wow more with the piston casters and coaters to see how to take advantage of coatings and not mis lead others to waste money better spent in proper clearance on obsolete air cooled, especially with pancake style crown wear prone slappers.

Most everyone only thinks TDC is the area of concern on piston slack slap crown stressing, but thats the 1st hottest-widest bore area during use, its the cooler tighter bottom bore reversals that rub pistons raw or seize them apart on way back up. Every see a piston with rod fracture near TDC or only about 1/2 way back up?

For those who missed it, here's the hard facts photo of a used piston with coated skirt after break in. This photo was already posted in this thread on page 1 (the very 1st post). The coating has burnished in to a perfect fit - just like its supposed to do. Photo provided by Yves.