iflyfisher
Full Access Member
- Joined
- Oct 22, 2023
- Posts
- 105
- Reaction score
- 213
- Location
- So Utah
- First Name
- Ken
- Truck Year
- 1973
- Truck Model
- K20
- Engine Size
- 350
I am losing my head(s)!!
I finally got to checking the compression this morning. I took the truck out for a short run to warm it up then pulled the plugs. This is the first time I had pulled the plugs since putting a bit of time on the engine. I pulled 1, 3, and 5 and each of the plugs had a nice light tan color. I pulled 7, and it was black and sooty. I thought, "ah...ohh." I switched over to the other side. Plugs for 2, 4, and 8 again looked great. But 6 was black. I checked the compression and all the cylinders where the plugs looked good had compression between 148 and 150. Numbers 6 and 7 were 85 and 45, respectively. I have my Dad's old logs, which has an entry for 1975 at 20,390 miles, and the compression figures for all cylinders were between 140 and 148. So 48 years and 80000 miles, and the compression is relatively unchanged for 6 of the 8 cylinders. Given most of the cylinders show no decline in compression, I suspect valves rather than rings. Guess this answers the question of my original post. I probably should have checked compression first thing. But the other things I did were likely needed anyway, plus I learned a few new things.
Time to spray some penetrating oil on the exhaust manifold and head bolts then read up on how to pull the heads. It doesn't seem complicated as long as the bolts cooperate. Also, I will need to find a shop to seat the valves for me. One question I do have is do I replace all the valves while the heads are off? Maybe the answer is to wait and see what the others look like.
One more thing I haven't done before!
Ken
I finally got to checking the compression this morning. I took the truck out for a short run to warm it up then pulled the plugs. This is the first time I had pulled the plugs since putting a bit of time on the engine. I pulled 1, 3, and 5 and each of the plugs had a nice light tan color. I pulled 7, and it was black and sooty. I thought, "ah...ohh." I switched over to the other side. Plugs for 2, 4, and 8 again looked great. But 6 was black. I checked the compression and all the cylinders where the plugs looked good had compression between 148 and 150. Numbers 6 and 7 were 85 and 45, respectively. I have my Dad's old logs, which has an entry for 1975 at 20,390 miles, and the compression figures for all cylinders were between 140 and 148. So 48 years and 80000 miles, and the compression is relatively unchanged for 6 of the 8 cylinders. Given most of the cylinders show no decline in compression, I suspect valves rather than rings. Guess this answers the question of my original post. I probably should have checked compression first thing. But the other things I did were likely needed anyway, plus I learned a few new things.
Time to spray some penetrating oil on the exhaust manifold and head bolts then read up on how to pull the heads. It doesn't seem complicated as long as the bolts cooperate. Also, I will need to find a shop to seat the valves for me. One question I do have is do I replace all the valves while the heads are off? Maybe the answer is to wait and see what the others look like.
One more thing I haven't done before!
Ken