Thanks for the offers and replies, gents.
Turns out the old head was pretty ugly, though it doesn't explain why I started burning coolant as the gasket looked good with no clear break. I think maybe the head just needed torquing down. It might have been loosened up when a muffler shop put on my new header, or maybe it is just a coincidence. I know the previous owner had the head gasket replaced once before.
Anyhow, there was a fair amount of scoring both on the pistons and head for cylinders 1 and 4. Something metal must have been in there in the past. I'll post pics later. It was working fine for two years, though, so I knew I could put it back on.
Valve seals looked surprisingly good, which was unexpected, since I have been blowing blue smoke on lift off for a year or two. They were still rubbery and flexible, with no clear break. When there is negative pressure in the head it just sucks oil through the valves and burns it. It doesn't happen with full or balanced throttle, just when lifting off and coasting. It looked like there was too much slop in the valve guides and so that was stretching the seals.
My mechanic buddy wanted to send me to a machinist, but the only one he trusted from many years of experience not to mess it up was away on holidays for a week. Then there would be turn around time, so I was looking to be off the road for two weeks. With FFO coming up that didn't seem feasible.
So I pushed him to try and put the guides in ourselves that I had bought. Despite putting them in the freezer to contract them, we broke the shoulder on two of them (they were probably about 1/1000" oversized). Now I was stuck: no head, no guides, no machinist.
I bought a used 1800 head and cam boxes from him and went from there, with springs and tappets already installed. It was a bit slow on one of the valves (intake #1) because it was just ever so slightly gummed up after sitting for years. We got it going and oiled up on a bench, plus more work to drill out a temp sensor. I took it home, installed my old cam shaft pulleys, decoked the existing valves, cleaned up the top of the head, put on new gaskets for the cam boxes, etc. I drained the old oil since with coolant in it it would be hard on bearings. With a new head gasket and Permatex copper gasket sealant I then fit it to the block with the help of a neighbour. It took two or three tries (finiciky with the dowels) to get it to sit right.
9 of 10 bolts torqued to spec 61 lbs. One of them seemed to start slipping -- it was good up to 57 lb/ft. I decided not to push it any further.
We turned it over by hand three times and it was all good. Everything was lined up properly (aux shaft, cam shafts, crank) and I didn't change anything on timing, so it should have been good to go.
I hooked everything back up this afternoon (carb stuff, rad) and went to fire it up. It was hesitant at first -- not unexpected given the oil we had put into the cylinder to lube everything up. It almost seemed to want to catch, but didn't. I had expected one big puff of smoke to clear the oil in the cylinders and then be off and running. I clearly flooded the engine and actually had gas pouring down the carb. I have NEVER had that before. That scares me because it reeks of an engine fire. I suspect maybe the carb float was stuck from having sat dry for a few days; the needle valve would thus stay open and fuel over-fiill the chamber, especially since I have an electric fuel pump that always runs when the ignition is on.
I called it a day and took my kids out to dinner. Tomorrow I will bang the side of the throttle body to see if I can unstick the float without having to fully open up the carb and am etting the battery recharge overnight on a trickly charger. I have a very busy weekend with both my girls in soccer tournaments and solo parenting as my wife is away on a vacation... I will try again tomorrow morning.
Once I get it going I will keep the engine as is for a bit. Clearly given the scoring I will need to get new pistons some time down the line. Maybe in a year or tow. Maybe I will get everything done at that time, using my new valves, springs, etc. and machining this newer head, and get Allison's MLS gasket.
Cheers,
phaetn
) while tightening. I suggest buying new head bolts because my 30+ year old ones were really brittle and broke off when I attempted to torque them to specs. The new ones from AR worked perfectly.
and the engine is a bit down on power from before, especially over 3500RPM. I think it's because of valve lash. There's also a slight leak at the downtube because he couldn't weld it all the way around. I might try to fill a small gap with JB Weld and let it cure overnight.