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Chris Collins
02-20-2006, 10:51 AM
This weekend my mechanic performed a leak-down test on the Avanti. Seven of the cylinders turned out real good (94 or higher with 100 being perfect). The #5 cylinder would not read at all, the air was just blowing out the exhaust. Our first guess (and hope) is that there's a bit of carbon that broke loose and is blocking open the valve. Neither of us recall the car "missing" previously. Been a couple of years since the car was on the road versus merely running in his shop, so we figure the first thing would be to drive it and see if it blows itself out. The old trick of dribbling water down the carb to break up carbon also comes to mind.

Anyone had success with the water technique or some other remedy to try before opening things up?

Thanks in advance...

Chris Collins
63 Avanti R-2
66 Cruiser

DEEPNHOCK
02-20-2006, 11:25 AM
The water trick works very well, but only on a hot engine.
Theory is you take the 17:1 expansion rate of water mist to steam and use that to blast the carbon loose.
But....
You aren't going to get any heat built into a dead cylinder (or combustion), and washing down a cylinder with water isn't a good thing.
Have you pulled the valve cover off yet?
Might just be a 'stuck' valve.
If the engine sat around for a long time and one valve happend to be open where it stopped... It could have a touch of corrosion in between the valve stem and valve guide, causing it to stick open.
Two ideas...
1) Try stuffing about 18" of nylon rope in the spark plug hole and hand crank the engine over until the rope is squished against the cylinder head. The rope should be fat enough to comprtably fit through the plug hole. Tie a knot on one end so you don't accidentally stuff it all in there[:0]. Hand crank the engine around and see if the piston will pop the valve back up. But you need some oil on the valve stem and guide right away, so....
You still should pull the valve cover off...squirt some oil right on the valve stem (if you can).
Sometimes just squirting the oil and tapping on the valve will pop it loose. Just don't smack it real hard and knock the keepers out. You should crank the engine so that piston is all the way up...just in case... Or, to be triple safe, stuff about 18" of nylon rope in the spark plug hole and hand crank the engine over until the rope is squished against the cylinder head. This will not allow the valve to fall down. I've had this happen before and that trick worked ok. (and is free;))
Hope the info helps.
Jeff[8D]




quote:Originally posted by Chris Collins

This weekend my mechanic performed a leak-down test on the Avanti. Seven of the cylinders turned out real good (94 or higher with 100 being perfect). The #5 cylinder would not read at all, the air was just blowing out the exhaust. Our first guess (and hope) is that there's a bit of carbon that broke loose and is blocking open the valve. Neither of us recall the car "missing" previously. Been a couple of years since the car was on the road versus merely running in his shop, so we figure the first thing would be to drive it and see if it blows itself out. The old trick of dribbling water down the carb to break up carbon also comes to mind.

Anyone had success with the water technique or some other remedy to try before opening things up?

Thanks in advance...

Chris Collins
63 Avanti R-2
66 Cruiser

Mike Van Veghten
02-20-2006, 03:06 PM
Could also be as simple as a valve adjustment. If Like Jeff said...could be a valve is not closing, but because of a poor adjustment, that's all it might take.
Always look into the "whole" system for problems like this.

I dought that any junk is stuck...though I guess it does happen, I look at the "stuck" or not properly adjusted valve, weak spring, frozen rocker arm, etc., etc.

Let us know what you find.

Mike

Chris Collins
02-26-2006, 09:58 PM
Thanks for the suggestions on this topic. Spoke with Dan Miller this PM. He pulled the valve cover off, and the #5 exhaust valve works freely, but was adjusted way too tight. He re-set the adjustment, and it failed the leak-down test again, so he thinks the valve may be burnt. He is going to check the valve adjustments on the passenger side as a precaution, and run the car to see how well it drives. If the driveability is OK, I may leave it be until repainting the car. Somewhere along the line my engine bay got painted black, so repainting the car properly likely will entail pulling out the engine; that would be the easier time to do a valve job if needed.



Chris Collins
63 Avanti R-2
66 Cruiser

Dick Steinkamp
02-26-2006, 10:45 PM
quote:Originally posted by Chris Collins

Thanks for the suggestions on this topic. Spoke with Dan Miller this PM. He pulled the valve cover off, and the #5 exhaust valve works freely, but was adjusted way too tight.



If the car was driven any distance with the valve adjusted tight, it could have easily burned the valve.

-Dick-