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Thursday, September 29, 2016
Problems found with the 79 Mustang Engine
So I paid a machine shop to do all the work of inspecting and assembling these heads, but the engine sat on the stand for 5 years not moving due to budget constraints and time it took to cut all the rust out and re-weld the 79 Mustang back together. That being said I can hardly go back on the machine shop for the issues I have found.
The Mustang had a popping and backfiring issue that just wouldn't go away when the engine was warmed up to normal operating temp. In fact it would get worse as it warmed up, however at idle it would purr like a kitten. What the heck is going on right, so I went though valve adjustments and I swapped plugs and even plug wires. There was improvements because I did find a bad plug wire but it did not totally fix the problem.
I ran compression tests and the engine came back with results within parameters, so the final test I did was a Cylinder leak down test. Now this problem has plagued me all summer long and I have burned through at least Sixty bucks worth of fuel. Now the cylinder leak down was 35%, which says on the gauge from harbor freight good but everywhere online says it needs to be under 20%. Now Hotrod says you can sometimes get the valve to re-seat if you use a plastic dead blow and beat on the top of the valve. Before you do this I would advise taking the roller rockers off. No way in hell would I beat on an aluminum roller rocker. I removed my roller rockers and tried to get them to seat further unfortunately I was only able to get the leak down from 35% to 25%. This is not good enough so I pulled the engine apart.
Clearly you can see some of these cylinder are not firing. Very unclean.
Next test after the heads were off was to fill the the valve ports with Carb cleaner and check for fluid leakage.
And here we found a leaky exhaust valve.