Sorry non Mav/Comet related. I picked up a 69 F100 390 C6 on eBay and recently brought it home. I performed a dry compression test on it ranging from 124 to 150 on all cylinders except the #2 cylinder which showed 45 psi. I added a little oil to it and it bumped up to 58 psi. I also added oil to the #1 cylinder and that got bumped up to 175 from 150. My gut is telling me the valves since there is not much of a change with the wet compression check. The compression check was done with all the plugs out, fully charged battery and at WOT. What do you guys think I should do next. This is going to be a beater truck so I'm not looking to dump too much $$ into it. The engine is a truck 390 with probably low conpression and in unknown condition.
Valve seats are probably gone since it didn't come with hardened seats. Do a cylinder leak down test and see if you have air coming out of the intake or exhaust.
I've got the D2TE-AA heads which would have came with the hardened seats from the factory but I still think it's the heads. I'll see if I can get my hands on a leak down test.
They say around here that they cant find the 390s. Better save it for later after you use it. The Intake should weight a half a ton to pull by yourself! Then the Heads will be easy to remove. The Exhaust Studs will break ,and expensve exh. manifolds will leak,Shave the manifolds if needed. Use Brass Exhaust Manifold Studs when possible. My Fred Jones short block was awsome in the 1976 F100 with C6. Check the Rings and Cylinders.
Could be deposit related too. Old mechanics trick to help clean up an old engine. 1. preferably install a set of old plugs first.. then run the rpms up to about 3,000-4,000 rpm and pour cheap type-F transmission fluid down the carbs primaries until it starts bogging down. Keep the rpm up as best you can and continue to pour in for another 8-10 seconds or so while avoiding killing it completely. Then stop pouring and let is smooth back out just long enough to gain back rpm up to the same 3,000-4,000.. then pour quickly over about a 3-4 second timeframe to completely bog the motor down till it dies. Let is sit overnight.. or about 10-12 hours. Fire it back up and watch the smoke show begin. 2. After the motor has cleaned back up and reached full operating temps you do the same exact thing as above with WATER. But this time you are not trying to kill the motor as you did in that last step. Only need to do it for about 30-60 seconds at most and you don't want to get carried away with sudden large gulps that almost kill the motor for fear of washing all the protective oil and fuel film off the parts..scuffing the pistons and cylinder walls. Vary the rpm between about 3,000-3,500 and pour enough to bog it down a little, is all. You're essentially steam cleaning the engine at this point. Change the plugs(preferably to a step or two hotter to help combat fouling from blowby), change the oil.. and run it. Some engines won't clean up as well as others and takes a couple of cycles of the above routine to get the compression back up again. I learned this from a very old mechanic buddy of my uncles and have successfully used it dozens of times through the years. Seen a few times where it didn't make a huge difference but never once saw a situation where it was worse afterwards either. Easy low budget stuff like this is fun too.. kinda like a science experiment of sorts.
Sounds like "seafoam." After further inspection the block is .030 over. Can't seem to get one head off however. Valves look decent, as does the piston tops. The other side has the low pressure on one of the cylinders.
Tried the light under the valve with no light coming through. Heads didn't look too bad from the outside. Bottom end was rebuilt at some point so it's .030 over. Found this tag on the block.
Truck was on non op for at least 3-4 years, I found a set of rebuilt heads at a local machine shop for a good price. Now I'm considering changing the stock cam for a small RV cam. Just a little over stock, nothing over 210ish duration at o50. And under 500 lift.
