A tale of 2 pistons

Best to run with both taps open if going full bore.

The Harley flat trackers had big problems with fuel starvation and seizure/melted pistons several decades ago.
The creation of the Pingel high flow fuel tap was a response to that problem.

There is a tremendous amount of fuel being burned at 105 MPH. A single tap would be struggling to keep up.
As fuel level in the tank drops, so does fuel flow. Also any obstruction, ie gunk on the tap screen or the Carb inlet screens, slows down the flow even more.
A friend melted a piston in his Vincent a couple of years ago. He was cruising along at 70 MPH on the I-5. He had a single tap open, which normally would have been adequate, however he later discovered that the tap screen was nearly plugged.
This caused lean running and melted the piston.
Just like Sir Eddie's Rocket, except in slo-mo!

Re- Why don't both pistons melt at the same time? I wonder about that too. If your fuel plumbing is such that the open tap supplies a double banjo on one Carb which in turn supplies the other Carb, then the first Carb likely gets the best of a meagre flow with the other Carb getting the remainder.

Glen

The Blacksmith's 12 Days of Christmas


ON The first day of Christmas, my Blacksmith gave to me, a cartridge in a bare tree.

ON The second day of Christmas, my Blacksmith gave to me, two pairs of tongs and a cartridge in a bare tree.

ON The third day of Christmas, my Blacksmith gave to me, 3 Betty Lamps, two pairs of tongs and a cartridge in a bare tree.

ON The fourth day of Christmas, my Blacksmith gave to me, four tons of coal, three Betty Lamps, two pairs of tongs and a cartridge in a bare tree.

ON The fifth day of Christmas, my Blacksmith gave to me, FIVE SPATULASSSS. Four tons of coal, three Betty Lamps, two pairs of tongs and a cartridge in a bare tree.

ON The sixth day of Christmas, my Blacksmith gave to me, six chunks of babbit ,FIVE SPATULASSSS. Four tons of coal, three Betty Lamps, two pairs of tongs and a cartridge in a bare tree.

ON The seventh day of Christmas, my Blacksmith gave to me, seven brand new swedge blocks, six chunks of babbit, FIVE SPATULASSSS. Four tons of coal, three Betty Lamps, two pairs of tongs and a cartridge in a bare tree.

ON The eighth day of Christmas, my Blacksmith gave to me, eight hand forged punches, seven brand new swedge blocks, six chunks of babbit, FIVE SPATULASSSS. Four tons of coal, three Betty Lamps, two pairs of tongs and a cartridge in a bare tree.

ON The ninth day of Christmas, my Blacksmith gave to me, nine Mouse Hole anvils, eight hand forged punches, seven brand new swedge blocks, six chunks of babbit, FIVE SPATULASSSS. Four tons of coal, three Betty Lamps, two pairs of tongs and a cartridge in a bare tree.

ON The tenth day of Christmas, my Blacksmith gave to me, Ten Hammer handles, nine Mouse Hole anvils, eight hand forged punches, seven brand new swedge blocks, six chunks of babbit, FIVE SPATULASSSS. Four tons of coal, three Betty Lamps, two pairs of tongs and a cartridge in a bare tree.

ON The eleventh day of Christmas, my Blacksmith gave to me, eleven hand forged trivets, Ten Hammer handles, nine Mouse Hole anvils, eight hand forged punches, seven brand new swedge blocks, six chunks of babbit, FIVE SPATULASSSS. Four tons of coal, three Betty Lamps, two pairs of tongs and a cartridge in a bare tree.

ON The twelfth day of Christmas, my Blacksmith gave to me, twelve scrolls with collars, eleven hand forged trivets, Ten Hammer handles, nine Mouse Hole anvils, eight hand forged punches, seven brand new swedge blocks, six chunks of babbit, FIVE SPATULASSSS. Four tons of coal, thre-ee Betty Lamps, two pairs of tongs and a caaartriidge in a bare tree.

RoadScholar said:

Bernhard said:

Check the flow from the tap on reserve, there may be muck or other in the bottom of the tank :shock:

Sorry the mice got at your piston :!:


I suggest that when you reassemble the bike and get it running you check the ignition timing on both cylinders, and on a dark night use a color tune to check the mixture .

Click to expand...

Before I removed the tank I drained the fuel from both taps; I got a steady stream from a 1/4" ID line, it took about 10 to 12 minutes to drain a gallon from each tap. I do wonder with the reserve closed if there was an air bubble between the left carb and the reserve tap preventing full fuel flow?? Don't know.

Click to expand...

You need to test how fast fuel flows all the way to both float bowl drain plugs at the same time.

Late to this party but Splatt called it right IMHO:

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

Click to expand...

Hole in piston crown right at spark plug, subsequent damaged all stems from that first event. Seen it before. HTH
Cheers, Martin

230 main + cold dense air + at sea level + sustained maximum output = too lean

Try using 260's to start with, chop/check if you must, but just right from what I've observed. JMWO :mrgreen:

Have you checked to see if there might be something blocking the main jet on the side that seized ? And if it was extremely cold on the way home, that would not help. The other thing is that the petrol tank breather might be blocked. The sandy appearance of the valve sounds as though it was running very lean. If you motor was quite tight, it would be easier to get a seizure if it leans off. In an old motor, all you should get is a burnt piston or valve.

"I turned the reserve tap on as soon as I noticed the power loss; "

Your bike set up standard? Main on the right? Reserve on the left? On just the main tap, left carb is last in line, receives the least head pressure (already a trivial amount), and thus less flow. At sustained WOT, it matters. JMWO

sportsroof said:

Late to this party but Splatt called it right IMHO:

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

Click to expand...

Hole in piston crown right at spark plug, subsequent damaged all stems from that first event. Seen it before. HTH
Cheers, Martin

Click to expand...

First: Fuel flow, I think this what got the events started. I had the right side tap on and the right side is the one that looked like nothing had happened. If I had both taps on I don't think the damage would have happened.

Second: Detonation, No holed piston, it was a forged slug; had it been a cast example I suspect that I would be looking for a complete replacement engine. As the mixture leaned out I'm fairly sure, now, that detonation is what broke the piston edge around the intake valve relief.

I just got back from a local machine shop; looks like the bad bore will be restorable with just a hone, I have my hopes up on this. Worst case I go for the next larger overbore. I'll be sending the head out to Jim for his evaluation and to do any repairs. So in any case I should be up and running before the Spring riding season gets under way.

Look on the dyno data sheet for the EGT of each side. You say it was similar jetting to combat. I don't recall an ignition being declared or compression ratio or cam. What is the exhaust system? lack of back pressure alters mixture requirement plenty. There must be a dozen different peashooter internals and at least several interstate mufflers. Most people seem to be fixated on fuel flow... how did you high speed synchronize the R&L carbs...brake dyno? at 45+hp until heat soak... EGT???? a mismatch might easily cook one side before the other. The side that is pulling harder=(hotter) more BTU if not temp. An air cooled can alway make more power to 1400+deg but you probably won't finish a lap at daytona. I'd be a coward over 1325.

One can run on the highway for months/years at 8-16hp and never get to the grenade zone until one day....speed test... ka pow
been there done that
This is my thought process for a cooked engine.

dynodave said:

Look on the dyno data sheet for the EGT of each side. You say it was similar jetting to combat. I don't recall an ignition being declared or compression ratio or cam. What is the exhaust system? lack of back pressure alters mixture requirement plenty. There must be a dozen different peashooter internals and at least several interstate mufflers. Most people seem to be fixated on fuel flow... how did you high speed synchronize the R&L carbs...brake dyno? at 45+hp until heat soak... EGT???? a mismatch might easily cook one side before the other. The side that is pulling harder=(hotter) more BTU if not temp. An air cooled can alway make more power to 1400+deg but you probably won't finish a lap at daytona. I'd be a coward over 1325.

One can run on the highway for months/years at 8-16hp and never get to the grenade zone until one day....speed test... ka pow
been there done that
This is my thought process for a cooked engine.

Click to expand...

The ignition is a TriSpark (current generation), the timing was set at 28 degrees at 3500 RPM, The cam is a WebCams 12, The carbs were synchronized with a Twin-Max electronic vacuum/tranducer meter at idle and at 3000 RPM, admittedly unloaded. The exhaust is a combination of 1 3/8" headers from Commando Specialties, the peashooters where from an EPCO design. The carbs (32mm Amals) were new with chrome slides, the main jets are 230 and the cutaway is a #3 with needles set in the mid position. The counter shaft has a 20 tooth gear, the primary is a Maney belt with a slightly different ratio than stock. The compression ratio would have been below stock, as the deck height was (incorrectly) set at flush with the jug.

I'm sure that the problem could have been spotted while being strapped to an eddy current dyno with dual EGT feeds, If you are gracious enough to (still) offer me a run on your dyno I won't hesitate the second time around with this engine.

RoadScholar said:

dynodave said:

Look on the dyno data sheet for the EGT of each side. You say it was similar jetting to combat. I don't recall an ignition being declared or compression ratio or cam. What is the exhaust system? lack of back pressure alters mixture requirement plenty. There must be a dozen different peashooter internals and at least several interstate mufflers. Most people seem to be fixated on fuel flow... how did you high speed synchronize the R&L carbs...brake dyno? at 45+hp until heat soak... EGT???? a mismatch might easily cook one side before the other. The side that is pulling harder=(hotter) more BTU if not temp. An air cooled can alway make more power to 1400+deg but you probably won't finish a lap at daytona. I'd be a coward over 1325.

One can run on the highway for months/years at 8-16hp and never get to the grenade zone until one day....speed test... ka pow
been there done that
This is my thought process for a cooked engine.

Click to expand...

The ignition is a TriSpark (current generation), the timing was set at 28 degrees at 3500 RPM, The cam is a WebCams 12, The carbs were synchronized with a Twin-Max electronic vacuum/tranducer meter at idle and at 3000 RPM, admittedly unloaded. The exhaust is a combination of 1 3/8" headers from Commando Specialties, the peashooters where from an EPCO design. The carbs (32mm Amals) were new with chrome slides, the main jets are 230 and the cutaway is a #3 with needles set in the mid position. The counter shaft has a 20 tooth gear, the primary is a Maney belt with a slightly different ratio than stock. The compression ratio would have been below stock, as the deck height was (incorrectly) set at flush with the jug.

I'm sure that the problem could have been spotted while being strapped to an eddy current dyno with dual EGT feeds, If you are gracious enough to (still) offer me a run on your dyno I won't hesitate the second time around with this engine.

Click to expand...

I guess I will look to find a dyno guy that knows classics and isnt half an island away when I get my new motor in...

"The ignition is a TriSpark (current generation), the timing was set at 28 degrees at 3500 RPM"


any Idea what the advance curve yeilds at kamikaze speed? 5700+? 6000? @105?
If you don't know... bring it along to a tech session and I can run it on the distributor machine. coils and all.
If the lay of the pipes are fairly stock I have stock dyno pipes with holes for the TC.

dynodave said:

"The ignition is a TriSpark (current generation), the timing was set at 28 degrees at 3500 RPM"


any Idea what the advance curve yeilds at kamikaze speed? 5700+? 6000? @105?
If you don't know... bring it along to a tech session and I can run it on the distributor machine. coils and all.
If the lay of the pipes are fairly stock I have stock dyno pipes with holes for the TC.

Click to expand...

The Tri-Spark advance curve is compared to others in the following thread:

commando-timing-advance-curves-compiled-t6451.html

Thanks Dave, I'll bring it up as soon as it gets some decent break-in miles. I have decided to go back to the standard rod length with some above board cast pistons. I plan on carefully measuring the above deck height of the pistons relative to the depth of the squash band in the head; I' m sure that you'll get a few calls/visits from me to check my work. I want to end up with a Commando that will hold full throttle as long as I have the balls to keep it that way... Just to know that my 40 to 70 MPH back road sorties are doing the engine a favor...

Triton Thrasher said:

RoadScholar said:

Bernhard said:

Check the flow from the tap on reserve, there may be muck or other in the bottom of the tank :shock:
Sorry the mice got at your piston :!:
I suggest that when you reassemble the bike and get it running you check the ignition timing on both cylinders, and on a dark night use a color tune to check the mixture .

Click to expand...

Before I removed the tank I drained the fuel from both taps; I got a steady stream from a 1/4" ID line, it took about 10 to 12 minutes to drain a gallon from each tap. I do wonder with the reserve closed if there was an air bubble between the left carb and the reserve tap preventing full fuel flow?? Don't know.

Click to expand...

You need to test how fast fuel flows all the way to both float bowl drain plugs at the same time.

Click to expand...

I have no doubt that you did, but that was THEN are you 100% sure that you have NO issues inside the Gas tank :?:
The reason I brought this up is because every bike I have owned that had a steel gas/petrol tank (but Never alloy) have at one time or another cause me problems, for example a couple of months ago I couldn’t get any flow on reserve, so I removed the pipe and switched on the reserve and got next to no flow the cause was a previous owner had lined the tank with something that had started to peel off and clog up the bottom of the tap. After thought cleaning out there were brown flakes that seemed to have come off like orange peel- I expect I will have to do it again ….. soon.

[/quote] I have no doubt that you did, but that was THEN are you 100% sure that you have NO issues inside the Gas tank :?:
The reason I brought this up is because every bike I have owned that had a steel gas/petrol tank (but Never alloy) have at one time or another cause me problems, for example a couple of months ago I couldn’t get any flow on reserve, so I removed the pipe and switched on the reserve and got next to no flow the cause was a previous owner had lined the tank with something that had started to peel off and clog up the bottom of the tap. After thought cleaning out there were brown flakes that seemed to have come off like orange peel- I expect I will have to do it again ….. soon.[/quote]

The tank is metal and was sealed (Caswell) while it was off being painted. The fuel was always mixed with Startron and the banjo filters never showed even a speck of debris. My motorcycles are stored indoors, out of direct sun light and are held at temperatures that do not vary much. I run each motorcycle every 7 to 14 days (3 seasons) for a minimum of 20 miles when the ambient temp is above 60 degrees, generally; Winter time the pod hibernates with stabilized fuel, battery tenders and light weight covers. I could go on.

Oddly the only motorcycle that I had that had fuel tank issues was an Ducati Hypermotard, the plastic they produced the tank with grew over an inch port and starboard and about 1/2" vertically.

"Winter time the pod hibernates....." :mrgreen:

Sounds like you have a pretty strict maintenance regimen going there, more than adequate.

The single tap on is the likely culprit, but we'll never know for sure.

A couple of years ago on an isolated stretch I did a speed run on the Vincent. It wouldn't crack the ton. Normally it pulls to 115 at sea level. Looked down and noticed that only one tap was on. Tried again with both taps and got 115.

I wonder how close things were from melting on the first run, maybe a few more seconds at full throttle?
With one tap on it ran smoothly but just wouldn't pull at the top.


Glen

Sorry to hear of your misfortune. The photo of the good piston is absolutely beautiful (photo below). Nothing wrong there. No signs of rocking or scuffing. So you can rest assured that your bore clearance was correct. But you must have had a fuel mix or delivery problem with the piston that melted. Its what happens when the fuel is too lean on one side at WOT. It was probably because of only one fuel tap being open. As it is Amals can barely pass enough fuel on a good running motor at WOT. The Randy Jones Norton 750 set the speed record at Bonneville in production class on a stock looking bike with hot rod internals. The Amals would not pass enough fuel through the bowls even after setting the floats so high that the carbs were leaking at idle. He had to switch to Alky Amals to get enough fuel at sustained WOT.

Check the fuel flow through the bowls with a measuring cup. Get bowls with the plug at the bottom, remove the bowl plugs and measure the amount of flow through each carb in one minute. You must have at least 6 ounces through each bowl and preferably 8 to be sure (with a full tank of gas). You can also run both bowls at once to check petcock delivery. If thats not the problem then look for an air leak. If you can't find an air leak then you might want to take a close look at the carbs and if there's a problem - switch them or try another brand.

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

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.

Let's also not lose sight of the fact that today's ethanol fortified fuel has less heat energy per volume than the fuel back when these bikes were in their day. So, just as a matter of course, we should be fueling (jetting) 5-10% richer than yesteryears setups as a baseline, just to be where we used to be. JMWO :wink: