Dead cylinder on new engine ( what in the he// happened? )

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duster360

duster360

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Just broke in this fresh build. I have one cylinder that has not fired yet. The spark plug looks like I just pulled it out of the box. I do know that the plug is firing. Did a leakdown test and it sounds like the exhaust valve is not sealing for reason. I know I will have to remove the head to see exactly what happened, but just curious until I get around to it. The cam from what I can tell is not wiped out. Both valves are opening and the adjustment has not changed. This engine has only about 30 minutes run time in the garage, that it.
What do you think happened?
 
valve job sunk valve too far and stem height was not checked ..allowing lifter to hold valve open slightly..... or debris in engine..or single pushrod different length..
 
You ran an engine THIRTY MINUTES and didn't realize it wasn't hitting on all 8??????

If something damaged that valve it's too late now.

If it ain't closin' it has notin' ta do wid' da cam no' bein' wipe'd out.

Can you move the valve? You using custom length pushrods? adjustable pushrods? adjustable rockers?
 
67Dart273 said:
You ran an engine THIRTY MINUTES and didn't realize it wasn't hitting on all 8??????

If something damaged that valve it's too late now.

If it ain't closin' it has notin' ta do wid' da cam no' bein' wipe'd out.

Can you move the valve? You using custom length pushrods? adjustable pushrods? adjustable rockers?
Click to expand...

It didn't sem to be just right but I didn't want to shut it down to early and lose the cam.
I have smith brothers custom pushrods non adjustable.
Hughes adjustable rockers.

When you say move the valve, what exactly do you mean?
 
When I did the leakdown test I heard no air coming from the carb side, sounded like it was going into the header tube.
 
Can you manually depress the valve, and does it seem free? This might give you a clue as to whether it's lack of valve clearance, or a bent valve, etc.

With adjustable rockers, you should be able to back off the adjustment and get it to close
 
Is there a chance you had some VTP contact and bent the valve stem. Pull the cover and see if it appears lower than the rest using a straight edge.
 
I would suggest that you remove the rocker arms and do another cylinder leak test if the valves are now closed then there is no problem with the valves sealing you need to check the lifter and the valve adjustment but this will keep you from pulling the head off again
 
I will check these things shortly. Just throwing this out there but when I finished the breakin I had to remove all the valve springs and install the in the inner springs. I had the piston at top dead center with 80 psi of air pressure and the valves stayed up while I had the springs removed.
 
hemi446 said:
I would suggest that you remove the rocker arms and do another cylinder leak test if the valves are now closed then there is no problem with the valves sealing you need to check the lifter and the valve adjustment but this will keep you from pulling the head off again
Click to expand...

I will back the adjustment off on that cylinder and see what happens.
 
I gonna be pissed and happy at the same time if I just got the valve too tight.
 
Haven't started it yet, but the exhaust valve was too tight and the valve was always open causing the misfire. I will be starting it shortly and repost the news.
 
Well.... We're waiting.....

[ame="http://www.youtube.com/watch?v=Z0YIJQ1jgEI"]Caddyshack - Well? We're Waiting - YouTube[/ame]
 
You might have got really lucky on that one.
Hope so anyway.
 
I was going to guess valve a little to tight. Have seen this before. If it was not leaking when you added inner valve spring, Id guess you will be all set
 
The suspense is killing us.........................................what did you find????
 
Snake said:
LMAO your the man krazykuda
Click to expand...


Thanks. I love good "soundbits" from movies etc, that fit the situation...


[ame="http://www.youtube.com/watch?v=jGQ-ISsDm8M"]Where are the white women at? - YouTube[/ame]
 
We'll I got it started and it is still missing. Same cylinder, dam dam dam. I can tell the cylinder has never fired. Leakdown test showed that the valve adjustment made a huge difference. Did a compression test on that cylinder and it has 170 psi. I did the dollar bill test suggested rustyratrod and it was definitly trying to pull it in the exhaust.
 
With 170 on the comp test you might be looking at a different reason for the miss.
Check for spark on that plug wire and try using a different plug. (seen em not fire right out of the box)
It couldn't have 170 with a bent valve so probably assume the valves are ok for now.

Is it possible you have two wires switched?
 
Checked the wires multiple times. Put a different plug in. Turned the engine over with the plug out and I could see it sparking.
 
duster360 said:
Checked the wires multiple times. Put a different plug in. Turned the engine over with the plug out and I could see it sparking.
Click to expand...

Which cylinder is this happening on? It's very easy to get 5 and 7 backwards. I'm not doubting you checked it, just throwing it out there.
 
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