I'm looking at buying a '90 ford f150 4x4 that has the 300 six with some engine problems. The owner says it was his grandfathers and it has 50,000 miles original on it, but it sat for three or four years after the grandfather died. Now one cylinder is only showing around 30 psi on a compression test, while the other 5 are normal. I'm not sure of their actual numbers. I am thinking the rings broke or something due to sitting, or low oil or something. Would it be possible to pull the pistons without pulling the engine or is that necessary? I would like to get it running asap even if that means there might be future repairs. I'm thinking if I can pull the piston, I can check the cylinder's dimensions. If it looks good, hone it with a hand drill, buy new rings, and put it back together.

What do you guys think? Is this feasible, or would I be better pulling the engine and starting from there, inspecting the whole thing.

thanks,
Joel

 

well... im sure its possible... but it would be a hell of a lot easier and faster to just pull the engine... mark everything you disconecct with corresponding numbers blah blah you know... doing it in the engine bay would be alot of hassle...and im pretty sure that the front suspension wouldnt help you out any while its in the way

 

Here's something to try. Sometimes when a motor has been sitting, the rings get stuck. Sounds like this may be the case. Over that much time, with the valves open, rust may have set up in that cylinder, or on the valve stems, keeping them from closing fully. You can try taking out the plugs, pour a liberal amount of Auto Trans Fluid in there and let it sit for a day or two. With the plug holes covered with ragsor something to minimize the mess, crank it over to blow out the excess fluid, then re-install the plugs and start it up. Let it run long enough to burn out the remaining fluid, circulate oil through the engine and onto the cylinder walls. Shut it down and check compression again. If it's OK, change oil & filter and maybe new plugs as well. If it doesn't work, you haven't lost anything but a little time and a bottle of ATF. As far as tearing down in the truck, it's such a pain that you're about as well off to pull it, put it on a stand and do it right. With that few miles, you're probably not going to be out much money unless there is significant rust(pitting) in the bores which is unlikely. You may want to remove the valve cover, turn it over and see it the valves seem to be returning to their normal closed positions. I the ones on that cylinder are not, then you may be able to remove the head, repair and replace without even getting into the shortblock.

 

If I did a job that way my back would kill me for a month. I have a bad back from doing jobs like that when I was young and thought I was bulletproof. Just remember back injuries, even ones that are "just a sore back", are cumulative and will eventually add up to trouble for the rest of your life.

I agree that pulling the engine to do the job would be easier and save time. In order to get the pan off you will have all but removed the engine anyway. Working on it while it's hanging or propped up doesn't sound great either. I also agree that having good look at the valve action might be in order and that trick with the ATF may be a good idea. With that low of mileage you could assume nothing is broken, but stuck sounds very likely.

 

I would have to agree. Sounds like stuck rings. Have you had the engine running, or did you just do a compression test? Try the ATF trick and get the thing running. It may only run on five for 15 minutes or more. Get it running and let it warm up. Those sticky rings might break free.

 

I went and looked at the truck. He has already pulled the head off, so not much testing can be done at this point. The truck was pretty banged up, so I decided it wasn't worth taking a chance on. Thanks for the replies.