Burning oil

My 170 has been smoking, and burning oil for a while now, but its to the point that I have to clean the plugs every few hundred miles. The carbon actually closes the gap and cause the cylinders to misfire. For the last few months I have been thinking that the rings were shot, and the engine needs a rebuild. I figured I'm not lucky enough to just need valve seals. When I cleaned the plugs last I decided to do a compression test and found the following. Dry-135,145,150,150,150, 150. Wet-195, 185,185,185,185,185. I know that the raised numbers after adding oil is a sign of bad rings, but I feel like the dry readings aren't that bad especially the last 4. I am contemplating just taking the head off, doing a valve job, and replacing the seals. Anyone have any advice? Thanks

I agree, ~145 isn't bad and all within 10%. A valve job, maybe worn valve guides and maybe a look at the jetting/carb. Is it running rich? How often and how much oil are you adding?

Seth, I recently discovered that the distributor had slipped a little, and the timing was retarded(it's so hard to get it tight even with a distributor wrench, the vacuum advance doesn't allow much movement of the offset wrench) I corrected that and the power went way up, in fact I have to keep looking at the speedometer when I'm on the interstate, and it doesn't take nearly as much throttle when pulling out. I also thought maybe some of the carbon on the plugs was caused by fuel mixture, so I adjusted the mixture screw using a vacume guage. It is running great, but still burning oil. I would say it goes through a quart every 200-300 miles. Thanks

Yeah, that's pretty bad. Badly worn valve guides perhaps. You've got descent compression.

You gonna try and change the seals by putting air into the cylinders to keep the valve from falling down while you get the rocker arms out of the way then compress the spring to get the seal off?

Thanks for the info. I was thinking about doing it that way, but I think I'm going to just use it for the rest of the summer/fall then pull the head off this winter and just have a machine shop do a valve job, guides, seals, and resurface it if necessary.

if your pulling the head anyways, why not just hone the cylinders and install new rings? never did a 170 but would think it could be done in the van.

To do that the rods would have to be taken off the crank, which would require the oil pan to come back off, which would require the engine crossmember to come back off, which would require supporting the engine in place from inside the cab with Jack stands, and straps. At that point I would be better off pulling the engine and rebuilding the entire thing. I'm trying to avoid that. I just had all of that apart to replace the rear main seal, and clutch about a year ago. I probably should have done rings and home then.

Pulling the head and doing a valve job is a good plan imo. You'll see in there and if you do the valve job and still have a problem you've already taken care of the head. I bet it'll fix you up though. How's your oil pressure?

If when you pull the head it still has a steel head gasket make sure they mill .025-030" off the head to compensate for the thickness of the new felpro gaskets, .046-050" compressed vs .020" for the steel shim gasket. If it has a composite gasket and it's a fomoco gasket have them mill ~.020". But it never hurts to measure and having the head off is the perfect time to do it. It's a bit of work but then you know for sure.

Thanks, that's great to know about the gaskets

Those "umbrella seals" on the valves are notorious. They are probably chunks of hardened rock-like rubber in your oil pan by now. I found a rebuilt head on ebay for $150 and it solved all my problems, including the broken/rusted exhaust manifold bolts.

I'm thinking you are right about the seals. They are 50 plus years old and have been sitting dry for most of that time.That's a good idea. I will have to check around for a rebuilt head. It will probably be cheaper, and save time. Fortunately I'm good on the exhaust manifold bolts, I just replaced the manifold a few months ago. Thanks.

You can always just pop new seals in. You hold the valve up with either compressed air in the spark plug hole or feed twine in the cylinder through the plug hole and then raise the piston to the top. The rope holds the valve up while you undo the keepers and put on the new umbrella. Lots of room to work on these heads and you can do it in the rain.