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FXD doesn't have much compression, rear cyl...

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Old Jul 27, 2010 | 05:45 AM
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Red face FXD doesn't have much compression, rear cyl...
That's what a customer said when he dropped his bike off Saturday at the shop.


So, Monday I run a compression check and get 0 psi in the rear and only 35 psi in the front cylinder.

I pull the rear head and think I know why there's no compression......

So I cal the customer and leave a message to call me back........

I can't wait to here the explanation for this one, rotflol!!!
 
Attached Thumbnails FXD doesn't have much compression, rear cyl...-shovelhead-2.jpg   FXD doesn't have much compression, rear cyl...-shovelhead-1.jpg  
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Old Jul 27, 2010 | 06:21 AM
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Probably something like ""It was running fine, but just not right. I took care if it and only rode it on sunny sundays, changed oils regularly""

Wow that is not good.
 
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Old Jul 27, 2010 | 08:50 AM
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Originally Posted by sniper77
That's what a customer said when he dropped his bike off Saturday at the shop.


So, Monday I run a compression check and get 0 psi in the rear and only 35 psi in the front cylinder.

I pull the rear head and think I know why there's no compression......

So I cal the customer and leave a message to call me back........

I can't wait to here the explanation for this one, rotflol!!!
Inconel valves, at least on the exhaust side, might be in order for this guy.
 
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Old Jul 27, 2010 | 08:57 AM
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What the heck would cause that?
 
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Old Jul 27, 2010 | 09:28 AM
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Originally Posted by Cblast
What the heck would cause that?
Heat. Just a guess, but I'd say the exhaust valve 'tuliped' from the heat.

Total guess from here.
 
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Old Jul 27, 2010 | 10:00 AM
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Having never taken a Harley motor apart I have to admit I don't know what the problem is. It appears that the close-up is of the actually of the intake valve and except for being able to see the valve seat I don't see a burned valve, cracked head or anything obvious. I'm assuming the valve is supposed to be concave, which isn't unusual for some engines. When you added oil to the cylinder I'm assuming the pressure didn't increase. Sorry for my inexperience but I would like to know what is wrong.
 
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Old Jul 27, 2010 | 10:09 AM
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Greetings,
Did the owner say: "It was running great but only got around 35 MPG and I read somewhere on the interwebs that if I dropped the main jet 7 sizes it would get better gas milage......"

Is that a crack between the valve seat and edge of head?
 
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Old Jul 27, 2010 | 10:15 AM
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Originally Posted by JohnAE
Having never taken a Harley motor apart I have to admit I don't know what the problem is. It appears that the close-up is of the actually of the intake valve and except for being able to see the valve seat I don't see a burned valve, cracked head or anything obvious. I'm assuming the valve is supposed to be concave, which isn't unusual for some engines. When you added oil to the cylinder I'm assuming the pressure didn't increase. Sorry for my inexperience but I would like to know what is wrong.
The exhaust valve is always the smaller of the two. The intake valve has to be bigger because the air/fuel charge doesn't get a lot of help going into the cyclinder but the exhaust gases have a lot of help leaving.

The intake valve has the benefit of the much cooler air/fuel charge entering the chamber while it's open. The exhaust valves get most of the abuse because they're actually open when the hot gases are leaving the combustion chamber while the intake valve is (mostly) closed. Which is why some manufacturers (Ford on its FI 460 in the old days and some other models) use inconel exhaust valves.

I know Manley makes inconel exhaust valves for a Harley and (I think) Ferrea does too.
 
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Old Jul 27, 2010 | 10:18 AM
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Did you take one of the spark plugs out or did the owner forget to put one in? No way you'd run a compression check with only one plug in the head, right?
 
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Old Jul 27, 2010 | 11:28 AM
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Is carbon on the seat causing it to be held open....or is the valve effed?
 
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