Piston #8 - missing in action
Thread Starter
Racer
Joined: Apr 2011
Posts: 471
Likes: 3
Piston #8 - missing in action
It seems piston #8 is not working in my SB... when I remove spark plug no difference at all... is there any troubleshooting guide I can follow in order to understand what's wrong? The car had in the past problems of timing, which I solved, but now I realized I'm missing one piston...
Drifting
Joined: Aug 2004
Posts: 1,883
Likes: 124
From: Lubbock TX
You're not missing a piston, you're missing compression on one cylinder...I think.
When you pull the plug, do you get a squirt of air out of the plug hole as the engine is running - should be a rapid puff-puff-puff?
With no compression, you have valve(s) that are adjusted wrong, the piston is forcing the air/fuel mix either back out through the intake valve or out a slightly open exhaust valve...or both.
If you had a missing piston, it would shake your teeth out from being so far out of balance and that plug would be drenched in oil slung onto it by the crankshaft.
When you pull the plug, do you get a squirt of air out of the plug hole as the engine is running - should be a rapid puff-puff-puff?
With no compression, you have valve(s) that are adjusted wrong, the piston is forcing the air/fuel mix either back out through the intake valve or out a slightly open exhaust valve...or both.
If you had a missing piston, it would shake your teeth out from being so far out of balance and that plug would be drenched in oil slung onto it by the crankshaft.
Thread Starter
Racer
Joined: Apr 2011
Posts: 471
Likes: 3
You're not missing a piston, you're missing compression on one cylinder...I think.
When you pull the plug, do you get a squirt of air out of the plug hole as the engine is running - should be a rapid puff-puff-puff?
With no compression, you have valve(s) that are adjusted wrong, the piston is forcing the air/fuel mix either back out through the intake valve or out a slightly open exhaust valve...or both.
If you had a missing piston, it would shake your teeth out from being so far out of balance and that plug would be drenched in oil slung onto it by the crankshaft.
When you pull the plug, do you get a squirt of air out of the plug hole as the engine is running - should be a rapid puff-puff-puff?
With no compression, you have valve(s) that are adjusted wrong, the piston is forcing the air/fuel mix either back out through the intake valve or out a slightly open exhaust valve...or both.
If you had a missing piston, it would shake your teeth out from being so far out of balance and that plug would be drenched in oil slung onto it by the crankshaft.
Drifting
Joined: Apr 2008
Posts: 1,305
Likes: 2
From: Lewisburg WV
thegazman
We all knew what you meant. Do what MDJ21 suggested, pull the valve cover and make sure your valves are working properly. Could be a camshaft, lifter, pushrod, etc. problem.
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Racer
Joined: Dec 2009
Posts: 308
Likes: 2
From: South Italy
Do you have heater? The plug it's to close the exaust.
For the compression tester:
http://www.summitracing.com/search/P...ression+tester
Where do you live in Europe?
For the compression tester:
http://www.summitracing.com/search/P...ression+tester
Where do you live in Europe?
Melting Slicks
Joined: Oct 2002
Posts: 2,317
Likes: 111
From: St Louis MO
It's possible that spark plug wires for #8 and #4 were swapped which led to very late timing on #8 - this would cause it to run very hot, melt the boot and probably do more damage. Please verify that you had the correct firing order... 18436572.
Thread Starter
Racer
Joined: Apr 2011
Posts: 471
Likes: 3
Firing order is ok, a week ago I had timing issue, 2 degree retarded, but I fixed when it started to overheat the temp...
Thread Starter
Racer
Joined: Apr 2011
Posts: 471
Likes: 3
Do you have heater? The plug it's to close the exaust.
For the compression tester:
http://www.summitracing.com/search/P...ression+tester
Where do you live in Europe?
For the compression tester:
http://www.summitracing.com/search/P...ression+tester
Where do you live in Europe?
Race Director
Joined: May 2005
Posts: 10,674
Likes: 122
From: Millington Illinois
St. Jude Donor '08-'09
Last edited by 63mako; Mar 16, 2012 at 10:40 AM.
Racer
Joined: Dec 2009
Posts: 308
Likes: 2
From: South Italy
Thread Starter
Racer
Joined: Apr 2011
Posts: 471
Likes: 3
This is more than likely your whole problem. Retarded timing causes the cylinder to fire late (as the valve exhaust opens). I have seen headers glowing orange from incorrect timing. You cooked your wire and/or boot and spark is arcing to the header or nonexistant and are getting no spark to the #8 cylinder. It can also burn exhaust valves if not caught and can blow the head gasket between # 4 - #6 or #3 - #5 due to the exhaust ports being siamesed at the center cylinders and the excessive, cocentrated exhaust heat causing uneven head expansion. If the plug wire is the only problem consider yourself lucky. Replace plug wire and see if the prfoblem is resolved. If not, investigate further.
Race Director
Joined: May 2005
Posts: 10,674
Likes: 122
From: Millington Illinois
St. Jude Donor '08-'09
Good. It is probably just a cooked wire/boot. It does not take long to get the header glowing orange right where it attaches to the head with retarted timing. It is thin material and the exhaust valve is open during plug firing even if timing is just a little retarted. A couple miles will do it. Spark takes the path of least resistance. The plug is a resistor with a gap. Arc from the boot to the header is the path of least resistance.
