The Ford Barn

40Coupe · 09-21-2012, 06:45 PM

and appreciate your advice!

I finished troubleshooting a stumble I have had at top of RPM range after tuning carbs (twin 97 on Offenhauser intake) and rebuilding original ’40 distributor. I assume this weak cylinder will solve my problems!

Engine is a 59 which received new rings in mid 90’s and put back together. Valve train was not inspected to best of my knowledge- a fair amount of miles logged on this engine. Car was my Father’s daily driver in the 60’s & now mine to care for. Cam is a “race cam”- I assume 3/4 Isky based on age and history bored .120 over.

Vacuum is 14-15” at idle with 2” quick fluctuations- steady at fast idle and 20”.

Spark plug wire check indicates #6 cylinder weak..

Compression check warm:

1- 105

2- 115

3- 110

4- 120

5- 120

6- 50

7- 135

8- 130

Squirt oil in cylinder and Sea Foam in valves no help- imagine that

.

Leak down: I can see both valves thru spark plug hole and stroked piston until both valves closed plus a tad rotation. Pressurized twice with 60psi air…quick leakage through exhaust pipe..intake silent.
No ticking at speed- assume lifter clearance is ok and cam not wiped. Valve movement appears significant.

Questions:

1) assume stumble/poor performance at load would be enhanced with a strong cylinder!

2) Is removal of intake and valve spring inspection the first move rather than pull head? Look for obvious issues and replace exhaust spring? Does/can lifter come out to remove spring?

3) Are mushroom valves/split bushings likely for this relatively large cam setup- (engine reportedly in Socal drag car prior to Dad’s purchase late 50’s)

4) Would vacuum smoothing at speed indicate worn guides (ref post on vacuum troubleshooting)? Leak down leakage appears very high.

5) Is a cracked seat/bad valve likely…crystal ball required

Thanks

Lane

09-21-2012, 06:45 PM	#1
40Coupe Junior Member Join Date: Apr 2011 Location: Livermore, Ca Posts: 23	Weak #6 cylinder and appreciate your advice! I finished troubleshooting a stumble I have had at top of RPM range after tuning carbs (twin 97 on Offenhauser intake) and rebuilding original ’40 distributor. I assume this weak cylinder will solve my problems! Engine is a 59 which received new rings in mid 90’s and put back together. Valve train was not inspected to best of my knowledge- a fair amount of miles logged on this engine. Car was my Father’s daily driver in the 60’s & now mine to care for. Cam is a “race cam”- I assume 3/4 Isky based on age and history bored .120 over. Vacuum is 14-15” at idle with 2” quick fluctuations- steady at fast idle and 20”. Spark plug wire check indicates #6 cylinder weak.. Compression check warm: 1- 105 2- 115 3- 110 4- 120 5- 120 6- 50 7- 135 8- 130 Squirt oil in cylinder and Sea Foam in valves no help- imagine that . Leak down: I can see both valves thru spark plug hole and stroked piston until both valves closed plus a tad rotation. Pressurized twice with 60psi air…quick leakage through exhaust pipe..intake silent. No ticking at speed- assume lifter clearance is ok and cam not wiped. Valve movement appears significant. Questions: 1) assume stumble/poor performance at load would be enhanced with a strong cylinder! 2) Is removal of intake and valve spring inspection the first move rather than pull head? Look for obvious issues and replace exhaust spring? Does/can lifter come out to remove spring? 3) Are mushroom valves/split bushings likely for this relatively large cam setup- (engine reportedly in Socal drag car prior to Dad’s purchase late 50’s) 4) Would vacuum smoothing at speed indicate worn guides (ref post on vacuum troubleshooting)? Leak down leakage appears very high. 5) Is a cracked seat/bad valve likely…crystal ball required Thanks Lane