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Old 10-03-2013, 07:43 AM   #1
Sugar Pig OP
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Motor destroyed-what happened?

Harley 1947 Sidevalve, single carb, single intake, single points ignition




Front cylinder



Rear cylinder



Front head



Rear Head


Front head again, notice dark spots on head gasket



Front spark plug on bottom, discoloration of front plug started almost immediately upon installation. Old plugs did not discolor but were autolights and are black so it might not be noticeable. These are d16 Champions.
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Old 10-03-2013, 08:10 AM   #2
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Can you post a pic of the spark plug electrodes? The exhaust valve in the upper picture looks like way too lean a mixture.
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Old 10-03-2013, 08:21 AM   #3
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Front is the one on the right.
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Old 10-03-2013, 08:23 AM   #4
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Quote:
Originally Posted by trumpet View Post
Can you post a pic of the spark plug electrodes? The exhaust valve in the upper picture looks like way too lean a mixture.
Single carb, single intake. Same mixture to both cylinders.
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Old 10-03-2013, 09:14 AM   #5
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Did something get into the front cylinder, or did the piston melt?

Pistons melt from a lean mixture or advanced ignition.

You can also have the pistons expand to a press fit in the cylinders, which makes them run REAL hot.

If the piston melted, maaybe it was an air leak at the head gasket causing a lean mixture.


Old Triumphs needed to have a loose fit between the iron jugs and the alloy pistons....
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Old 10-03-2013, 09:22 AM   #6
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Got hot for sure, enough to blue the plug. Hot from a leaky headgasket leaning out the mixture????

You can see where the headgasket has been leaking seemingly for a little while.You are right about the dark spots, I don't think you need to look any further into the cause.
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Old 10-03-2013, 09:37 AM   #7
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How long have you run this motor? (just buy it) no doubt overheat. Years ago I had a chick come in with a servicar that overheated like that....turned out she was trying to run it at 55 down the interstate.(she had just bought it)
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Old 10-03-2013, 10:22 AM   #8
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Intake manifold leak probably....way too lean and hot...
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Old 10-03-2013, 10:36 AM   #9
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Motor has 900 miles on it.

This did happen at its first prolonged (30 minute) trip at 60mph per GPS. This is a big twin though with a 23 tooth front and should easily be able to handle that speed.

I was also snap closing the throttle occasionally per the manual.
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Old 10-03-2013, 10:37 AM   #10
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Quote:
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Got hot for sure, enough to blue the plug. Hot from a leaky headgasket leaning out the mixture????

You can see where the headgasket has been leaking seemingly for a little while.You are right about the dark spots, I don't think you need to look any further into the cause.
The plug doesn't quite seem blued in real life but more like the cadmium cooked off. The finish is dulled like the cadmium is just gone.
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Old 10-03-2013, 10:40 AM   #11
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I would think you would hear the blown headgasket. I have blown them before and it was VERY loud, like a .22 gatling gun. That was a complete blow out where as this may possibly be a slight blow.

There is no evidence of a head gasket blowout with respect to the paint on the cylinders or adjacent items to the cylinder.
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Old 10-03-2013, 11:14 AM   #12
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is that a copper gasket or is it composite? if it is copper, did you anneal it before use?

The piston destruction is caused by too lean a mixture, as stated above, so if it is not from the carb, then either it is the wrong plug heat range or air passing a gasket.
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Old 10-03-2013, 11:15 AM   #13
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At 900 miles she still might have been a bit tight for a high speed run. Sometimes those plumber manifolds can be a bit tricky too. That's just one big bummer man.
I'm thinking the dark spots on the head gasket is a result of overheating. Late timing can cause that too, could you of pulled timing accidently?
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Old 10-03-2013, 11:15 AM   #14
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900 miles, did you re torque the head at 500?
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Old 10-03-2013, 11:56 AM   #15
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hmm

That exhuast valve for the rear cyl looks like it got pretty hot too, for only 900 miles. I would think something is up with the carb. Maybe it runs too lean at higher RPM.
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