flathead front cylinder cold as bike is running

[tfburke3]

Reviving an old thread here: I recently picked up a 49 WL, and it's running on rear cylinder only. I tried different plugs, replaced coils and wires with Bulldog Bros (great guy to deal with btw), but still only rear firing. Is my next step the intake manifold? Any other rabbit holes to go down? Bike is a mostly-original, mostly-unrestored barn-find. It has all new wiring, coil, plugs, wires & battery, plus carb has been overhauled. Points/condenser are old.

I would start by inspecting point contacts and gap.If they are God the condenser is probably fine.If they are pitted start with new points and condenser,
Tom

[dukekleman]

Sure thing,
The engine will run on that cylinder at 20-25% leak, however it will exhibit combustion inefficiencies above that.

I have had success restoring higher leak rates on flatheads above the stated percentage values without dissembling the engine.

Please post the measured leak percentage and I'll be happy to help and advise based off that number.

Duke

[T. Cotten]

Sure thing,
The engine will run on that cylinder at 20-25% leak, however it will exhibit combustion inefficiencies above that.

I have had success restoring higher leak rates on flatheads above the stated percentage values without dissembling the engine".

Please post the measured leak percentage and I'll be happy to help and advise based off that number.

Duke

I really confess I've never ever performed a "leak-down test", Duke!

Because my gauges are all psi, not percentage. A quick web-search produced only flatulence, except for what I always did anyway! With air on the sparkplug:

• Leaking intake valves - Sound of air escaping at the carburetor
• Leaking exhaust valves - Sound of air escaping through the exhaust pipe.
• Leaking piston rings - Sound of air escaping through timing plug
• Leaking headgasket/sparkplug - Bubbles when snooped with soapy water

But I'll bite:
How did you restore "higher (I'm sure you meant lower) leak rates on flatheads above the stated percentage values without disassembling the engine"?

Thanks in advance!

....Cotten

[dukekleman]

Ok, what I mean by "Higher" is they leaked higher percentage than I stated meaning 25% and higher.
I Use engine tuner, Kroil and marvels mystery oil in conjunction with the leak down tool to achieve this successfully.
These particular scenarios were high leak engines due to carbon and/or rust.
Other mechanical failures scenarios obviously couldn't be fixed this way.

Hope this helps,
Duke

[T. Cotten]

Ok, what I mean by "Higher" is they leaked higher percentage than I stated meaning 25% and higher.
I Use engine tuner, Kroil and marvels mystery oil in conjunction with the leak down tool to achieve this successfully.
These particular scenarios were high leak engines due to carbon and/or rust.
Other mechanical failures scenarios obviously couldn't be fixed this way.

Hope this helps,
Duke

I love snake oils too, Duke!

But what exactly did the 'tool' do to fix it?

....Cotten

[dukekleman]

It forces the chemicals into areas not normally accessable by just pouring something into the cylinder and letting run past the stuck piston rings and into the crankcase.. I cycle the engine with the kicker pedal while applying 20 psi.
It works and is a mere band aid for motors that need proper rebuilding but don't get the rebuild.

[T. Cotten]

It forces the chemicals into areas not normally accessable by just pouring something into the cylinder and letting run past the stuck piston rings and into the crankcase.. I cycle the engine with the kicker pedal while applying 20 psi.
It works and is a mere band aid for motors that need proper rebuilding but don't get the rebuild.

But I thought the leak-down 'tool' read in percentage, Duke?

I'm starting to think I don't need one.

Just my hollowed-out sparkplug with a brazed hose barb.

....Cotten

[dukekleman]

A modern leak down tester is a dual gauge.
The old leak down testers were a single gauge and have to be used different.
A snap tool brand leak down tester has a pressure gauge on the left and a percentage gauge on the right. This eliminates the need to do math like other tool brands require

Hope this helps,
Duke

[T. Cotten]

Doubt I'll ever need one, Duke.

(But I'll keep a space open on the wall!)

Once I got out the speedwrench with a socket to fit the sprocket nut, stuck the clutch, and poured in diesel while I tried to spin it backwards and forth...

Messed the exhaust good when it started.

....Cotten

[SamJ]

Well the plot thickens: I swapped out spark plugs one more time to totally eliminate that as a cause and lo and behold the front cylinder is running fine, hotter even than the rear cylinder. Going to try a brand new set of plugs since I have kind of a mishmash of different used plugs. I have a pretty mean exhaust leak at both the front cylinder and at the muffler (it's pretty rusted out) so I figure I'll replace the exhaust to be safe.

[T. Cotten]

...and lo and behold the front cylinder is running fine, hotter even than the rear cylinder. Going to try a brand new set of plugs since I have kind of a mishmash of different used plugs. ...

How would any plug, Sam,...

Make a cylinder run cooler?

(Unless you put the dud back in.)

....Cotten

[SamJ]

I mean to say now that it's actually firing, it feels warmer than the rear cylinder. Exhaust too. Both clearly running, just thought the difference in heat was interesting. No idea what it means.

[T. Cotten]

A digital thermometer would put numbers on it, Sam..

Heat only comes from compression, combustion, and friction; If you feel the compression is the same, and the oiling is the same, then the combustion is different.

....Cotten

[rudy]

I had a intermittent loss of the front cylinder with a sticky front valve. Maybe a compression test is in order.
good luck, you'll figure it out.

[T. Cotten]

I had a intermittent loss of the front cylinder with a sticky front valve. Maybe a compression test is in order.
good luck, you'll figure it out.

Didn't it make an ugly noise, Rudy?

(Askin' for a friend...)

....Cotten
PS: Did you fix it with Marvel?



Had to ask.


(I'd try it. Or ATF to keep it out of the landfill.

Nothing to lose...)