A tale of 2 pistons

We are lucky in the Western Canada and the US as we can avoid that crap, there are lots of ethanol free pumps. Not so easy in Eastern USA.
A list of 11,000 + stations with ethanol free fuel.
http://www.pure-gas.org/

Steves said:

When did you last wash the bike, any chance of water in the float bowl. I favour the running lean on that carb on the main jet theory, as some have said a localised blockage of some sort on that cylinder.

Been there done it with the water, albeit a monobloc.

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I try not to wash my motorcycles, I clean them, and I do it often enough so that I'm cleaning specific areas rather the entire machine. Lots of lint free cloths, misters, toothbrushes, Q-tips, Maguires/Mothers...a glass of nice rye...

My snow thrower sat for a season (no snow in New England...what a gift) and condensed water in its float bowel with no spring loaded drain (thanks EPA) so I know what you mean, but that issue was not aboard when I had my need for speed.

Fuel: Yes, more alcohol equals less heat content, higher octane rating with less power potential, It doesn't sound like a recipe for running lean, just less fast, not sure. I have 2 fuel injected motorcycles that should run all day with the throttles pinned, I can attest to blasts of 2-4 minutes after which Massachusetts begins to get small... The Norton was doing yeoman's service at 70 to 80 MPH for almost 15 miles; lasted about a minute at WOT. BTW it had nearly a full tank.

When I get this Norton back together and loosened-up I'm going to take it up to Dyno Dave's place and see if it can be tuned to run with WOT; with his instrumentation it should be easy to catch heat build-up before it produces bad results. I am convinced that my engine burnt up because I failed to make an adequate fuel supply available, another suggestion of starting with 260 mains is excellent, running on an eddy-current dyno is an excellent resource.

"It doesn't sound like a recipe for running lean, just less fast, not sure. "

You should reconsider that.

worntorn said:

Also a big difference in fuel flows between full tank and half full, less yet when nearly empty.
Who thinks of this in the heat of the moment?
I know I don't.
It would be good to make sure that fuel flow to the carbs is adequate for WOT with a low level of fuel in the tank.
Glen

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A good point, as the carbs are gravity fed. There would be less flow when tank is nearly empty with less weight of the fuel/gas on top when full. Another option open to you is to bore out the brass/ metal pipes that connect the gas pipe to the carb slightly bigger bore-I did this on my 750.

RoadScholar said:

When I get this Norton back together and loosened-up I'm going to take it up to Dyno Dave's place and see if it can be tuned to run with WOT; with his instrumentation it should be easy to catch heat build-up before it produces bad results. I am convinced that my engine burnt up because I failed to make an adequate fuel supply available, another suggestion of starting with 260 mains is excellent, running on an eddy-current dyno is an excellent resource.

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And should you require fuel on the way there is ethanol free gas available at 24 Plum Island Turnpike, Newbury Ma, 16 miles from Dave's house according to MapQuest.

worntorn said:

And should you require fuel on the way there is ethanol free gas available at 24 Plum Island Turnpike, Newbury Ma, 16 miles from Dave's house according to MapQuest.

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As it states always call first...In the winter they are often closed. That place is tiny.
Most airports in the east will NOT allow you to put gas in a over the road vehicle...bring a 5 gallon can...difficult on a bike...

I get my OPE(chainsaw/lawn mower/weed wacker) no-E fuel at Hampton Falls, NH airport 25 miles. Not bad only about $1 more than normal gas station price. Can't even get the car/motorcycle near the pumps. again gas can required or no sale. Airplane is OK

Salem Mass and Hafners in Haverhil has VP racing only $9.50/gal.
sorry not interested.

concours said:

"It doesn't sound like a recipe for running lean, just less fast, not sure. "

You should reconsider that.

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I have no problem with being incorrect on this, but I see greatly increased use of turbo chargers on new street cars to ring more power out of the alcohol laden fuel. I once considered converting a street car to run on methanol when my brother-in-law was running a saw mill that would supply me with a virtually unlimited source of saw dust, the issue was being able to utilize the methanol with any degree of efficiency; to do this a CR of 14:1, or better would be required; turbo charging solves this problem with variable boost and sophisticated engine management; the Norton engine has none of this, for all practical purposes.

So, can a Norton engine benefit more from E-10 with a higher CR, I don't know. I can appreciate that larger main jets may balance the energy equation and I'm going to take your advice and re-start my jetting with 260s and (carefully) work down from there. Dyno Dave's dynometer will be invaluable in making the final jetting assignments; I do want a Norton that can be run safely in the upper end of the tach; the person who buys it from me will, no doubt, test that, and because my sales come with a warrantee I want them to get real value, not headaches.

splatt said:

That's not a seizure, that's detonated it self to pieces,

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Precisely.

That is textbook detonation destruction. Moderate detonation over a long period of time. Generally, this is not caused by a lean condition, but advanced timing OR too much oil finding it's way into the combustion chamber. Motor oil reduces octane.

Why one side destroyed and the other not, is a question I'd try to answer first. On reassembly, check the timing individually on both cylinders.

pressureangle said:

splatt said:

That's not a seizure, that's detonated it self to pieces,

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Precisely.

That is textbook detonation destruction. Moderate detonation over a long period of time. Generally, this is not caused by a lean condition, but advanced timing OR too much oil finding it's way into the combustion chamber. Motor oil reduces octane.

Why one side destroyed and the other not, is a question I'd try to answer first. On reassembly, check the timing individually on both cylinders.

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I'm in agreement with detonation. The ignition system is inspired by a TriSpark with fires both cylinders at the same time, wasted spark, so, if the one piece forged crank (Falicon) was milled properly the timing on both sides would be the same.

Given that I had incorrectly set the deck height yielding lower compression I'd venture that you could be correct, but why such a dramatic difference between the two pistons; I'm thinking that I had an air leak on the left.

And here's another discovery: I sent the jug out for honing and measurement. The service found that the skirt clearance, using the "good" piston had grown from 5.3 thou to 6 thou, any one care to try and explain that, well beyond me. (not a collapsed piston????

Having the bore/piston wear by half a thou or more is not unusual - thats what 'running in' an engine is all about ?

Sounds like fuel flow is the hot favorite, and an air leak is an outside chance.
Never assume the ignition timing is the same both sides either, without actually checking it. ?
Although there should not be much scope for it to vary...
Have fun !

is the failed piston furthest from the fuel tap ?
losing the squish band wont help but like you say means the compression is probably low
piston clearance growing, if you cant measure it yourself you will never know what it really was to start with, pistons can change shape slightly after heat cycles and your cylinder has been through a shit load of stress so it also may have changed shape

If the bore still has honing marks, it hasn't worn much at all.

Eliminate the obvious left side fuel flow or air leak possibilities first. Measure the combustion chamber volume above the piston at TDC on both cylinders. Measure the squish clearance on both cylinders.

Even if your problem was overheating of the whole engine, because of retarded timing or under-jetting, one piston could fail before the other.
No two combustion chambers or inlet tracts or carburettors are exactly identical. It really isn't surprising when one side detonates (or seizes) before the other.

No two pistons are the same either, maybe in dimension but not in the structure, it could be just sheer bad luck in the that the piston had a hidden flaw. Considering the pistons were not that old, fatigue in the alloy can be ruled out, with the elimination of all the other possible causes it may have been a duff piston.

The same thing just happened at Bonneville with a carefully prepared 500 Norton twin. One petcock was turned on. They tried bumping up the timing advance a little. There was a lapse in power at top speed from fuel starvation. One piston burned a hole.

Pistons do loosen up a fraction of a thou on break in. This is from the heat cycle and pressure on the skirts as well as wearing off the high spots and seating in. Its unavoidable and it happens to all pistons. This is why many modern pistons use a black (usually molly) break in coating to get past the initial tight run in. If you could design a piston that expanded a fraction of a thou every few thousand miles - you would be a billionaire.

Note that it was the left side that destructed. This is the usual tendency with British twins because there is some passage of oil through the timing chest that helps cool the right piston. Even if you plug the timing breather holes the oil will still come through the hollow timing pinion shaft and a lowered oil return hole if you've done that. When I worked at a British shop in the 1970s it was standard practice to give the left cylinder up to about 1/2 thou more clearance than the right to avoid problems.

If I remember correctly, I think you said the pistons were forged ? Some cast pistons which have not been heat treated correctly can grow when run in a motor, however I don't think that was your problem. It is much more likely to be either a fuel starvation or an ignition system problem - both can give the same symptoms. If you are jetting your bike, it is always wise to have the main jets slightly over-rich. If you think about it, how often do you have the throttle wide open ? - and it is rare to do damage on part-throttle, because if the jetting is too lean the bike becomes a pig to ride. Whatever fuel you commonly use, the carbs should be jetted to suit it. However the most elusive thing is when the tank breather becomes blocked and a partial vacuum forms in the fuel tank. Often the breather is in the cap and sometimes the sealing washer can turn and shut it off.
If you are experienced and used to your bike, you should always know when it is running lean. If it is performing fantastically on full throttle or missing on part-throttle - watch out !

acotrel said:

If it is performing fantastically on full throttle or missing on part-throttle - watch out !

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When I was persuing the 100mph mark, after I fixed my bike's sloppy handling, I hit a wall where I couldn't accellerate past 85mph. I had 240 main jets, so switched to 220's which are the stock size for my bike and I zoomed past 85mph with no problem. Later, some people said I should have tried 230's first to try to stay on the richer side of the main jet size which still works. After reading this thread, I'm going to order 230 main jets to test in my bike this spring,... because the 220's are performing fantastically, so now I'm worried... :lol:

If the weather was particularly cold when you had the problem - that would not have helped. It is quite common for race bikes to go quicker when the weather is cold because the jetting leans off slightly and the motor will go faster just before it destroys itself. The trick is to maintain jetting lean - just short of the point where the motor self-destructs. If the black ring is still evident on the porcelain right down inside the spark plug, you should be OK. The trouble is that it is uncommon to do plug chops on a road bike. That sandy appearance on the plug was probably beads of aluminium - a very bad sign.
I think you are doing the right thing when you fit main jets one size larger than recommended. At worst, the motor will be only slightly sluggish when you use full throttle.

Its winter time.

Be sure to pay close attention to temperature when measuring piston/cylinder clearance. A cold winter shop is going to give a measurement anywhere from half a thou to a thou smaller than the same piston on a warm summer day. Iron cylinders about half that much. So a cold measurement can measure up to a 1/2 thou looser than when the parts are warm. Always make sure your machinist makes his measurements at a consistent room temp.

When you hear a little detonation at cruising speed you can back off - go home to adjust the jetting and check the timing. But when you're wide open with the wind screaming at over 100mph and you don't hear the detonation - that detonation just gets worse until the piston overheats and melts. That fuel starved piston never had a chance.

I thought engines performed better in cold weather (and damp) because the air is more dense and so dense air carries more fuel with it. (some gas turbine engines use water methanol to do this)

gripper said:

I thought engines performed better in cold weather (and damp) because the air is more dense and so dense air carries more fuel with it. (some gas turbine engines use water methanol to do this)

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Cold & dry is the most dense. Hot and humid is the least dense. And then there is altitude.

More dense air can carry more fuel but it takes an intervention. With a plain carburetor, as the intake air becomes cooler and drier, the AF mixture becomes leaner. Light aircraft have manual controls to richen and lean the mixture and most modern fuel injection adjust the fuel automatically.

Water injection for gas turbines is a whole different kettle of fish. Demineralized water was introduced in a liquid state where it rapidly flashes to a vapor state. From what I have been told, it is only used on extreme take off power requirements; its primary function was to reduce turbine temperatures.