Dibbons
Well-Known Member
- Local time
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- Joined
- Nov 29, 2014
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- 5,098
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- Location
- La Paz, B.C.S., Mexico
This "hodgepodge" 340 is a complete engine I purchased some years ago (it was already .040 over and had 1.88" intake valves). I had a valve job performed, the crankshaft turned (.020" now), and I honed the cylinders, replaced the rings, bearings, camshaft, lifters, springs, retainers, oil pump, oil pump drive, water pump, fuel pump, oil pan (Kevko). The pistons were re-used and are flat with four small valve notches (photo #5).
I rebuilt the factory '72 Thermoquad listed for a 340 automatic of that year. Ran the motor at fast idle, and curb idle while still in the driveway during several sessions of camshaft break-in and carb "tuning". Had a vacuum leak which I believe was alleviated by changing the base plate carb gasket "sandwich" of an aluminum plate with a top and bottom gasket to the thicker one piece gasket. I estimate total run time was about an hour altogether (used at least two gallons of gasoline during this time).
Then I ran down the highway to the local gas station and back (about a 5 mile trip). On the way there, it was running OK, but on the way back after accelerating a little aggressively for just a few seconds it began to run pretty crappy (but it never stalled). I never noticed any smoke during initial start-up nor idling nor driving down to the station. Vacuum reading is around 15 inches mercury at idle.
So before looking into any more "tuning", I decided to pull the plugs and perform a compression test. The motor was still a little warm at the time and I did block the throttle wide open during the testing.
All eight plugs looked exactly the same: pretty darn black (photo #1). When the first six cylinders all came back at 130 psi I began to believe my compression tester needle would not climb higher than 130. But then the next cylinder read 150 psi and the last cylinder 105 psi. I squirted some oil in the "weak" cylinder and turned the motor over a few seconds. Then I performed another check on the weak cylinder and it read 130 psi (photo #2).
When honing the cylinders, I noticed one of the corner cylinders kept coming out with a different looking sheen/finish. I believe that cylinder had previously been sleeved. Now I can't remember if that was cylinder #1, #2, #7, or #8 (might be written down in my notes somewhere).
I never performed a cylinder leak down test before and don't know if that weak cylinder warrants that kind of looking into. I will mention that timing was off during start up and a did a lot of cranking and was afraid a cam lobe may turn out to be wiped out (I hope not).
And I will mention that my old compression gauge tester became junk when it began to blow the hose off. I tried to remedy that situation with worm clamps but to no avail (photo #3). I had to purchase another one (photo #4).
I rebuilt the factory '72 Thermoquad listed for a 340 automatic of that year. Ran the motor at fast idle, and curb idle while still in the driveway during several sessions of camshaft break-in and carb "tuning". Had a vacuum leak which I believe was alleviated by changing the base plate carb gasket "sandwich" of an aluminum plate with a top and bottom gasket to the thicker one piece gasket. I estimate total run time was about an hour altogether (used at least two gallons of gasoline during this time).
Then I ran down the highway to the local gas station and back (about a 5 mile trip). On the way there, it was running OK, but on the way back after accelerating a little aggressively for just a few seconds it began to run pretty crappy (but it never stalled). I never noticed any smoke during initial start-up nor idling nor driving down to the station. Vacuum reading is around 15 inches mercury at idle.
So before looking into any more "tuning", I decided to pull the plugs and perform a compression test. The motor was still a little warm at the time and I did block the throttle wide open during the testing.
All eight plugs looked exactly the same: pretty darn black (photo #1). When the first six cylinders all came back at 130 psi I began to believe my compression tester needle would not climb higher than 130. But then the next cylinder read 150 psi and the last cylinder 105 psi. I squirted some oil in the "weak" cylinder and turned the motor over a few seconds. Then I performed another check on the weak cylinder and it read 130 psi (photo #2).
When honing the cylinders, I noticed one of the corner cylinders kept coming out with a different looking sheen/finish. I believe that cylinder had previously been sleeved. Now I can't remember if that was cylinder #1, #2, #7, or #8 (might be written down in my notes somewhere).
I never performed a cylinder leak down test before and don't know if that weak cylinder warrants that kind of looking into. I will mention that timing was off during start up and a did a lot of cranking and was afraid a cam lobe may turn out to be wiped out (I hope not).
And I will mention that my old compression gauge tester became junk when it began to blow the hose off. I tried to remedy that situation with worm clamps but to no avail (photo #3). I had to purchase another one (photo #4).
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