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The truck needs a quart of oil every 200 or miles or less. It puts out a good puff of white smoke on startup and nothing visible as im running down the road. There is also visible oil in the air filter housing. It also seems to be getting poor gas mileage. My first thought goes to rings but the poor gas mileage has me thinking maybe its something related. I popped the PCV valve off and it the internal piece seems to be opening and closing just fine.
I know I should do a compression test but id also like to rule out anything else that might be the problem.
Also what should I be getting for compression numbers?
Well, I've got a '79 six cylinder and for compression I ranged between 120psi and 135psi. My I6 doesn't burn any oil, so I'm guessing the rings are in decent shape. The white smoke is characteristic of a head gasket... I had a blown head gasket that didn't belch white smoke... just some on startup, and barely noticeable while driving. You may have a similar thing? Not sure that'd explain the oil though.
Edit: oil in air filter housing is interesting. Is it possible you have a piston w/ blown rings causing excessive blowby and building high crankcase pressure?
The smoke on start up indicates bad valve stem seals and/or worn valve guides. The oil in the air filter housing indicates a lot of blowby, enough to overpower the PCV system.
Sounds like you're due for a rebuild.
A compression test is definitely in order.
Yeah, I'd agree. Now, what's an interesting note is that on my '79 it didn't show any significant pressure difference in a cylinder when I tested just recently for a blown head gasket. So it's not a 100% certain diagnosis.
When rebuilding the top end is it necessary to replace the pistons, or can a hone and new rings generally suffice? I've rebuilt lots of old Harley top ends but never pulled the head off any car/truck motor.
Well, it'll really depend on the shape of the pistons and the cylinder bores. If the cylinders are really egg shaped, you'll likely need to bore them out and then you'd need new pistons AND rings. If it's not too egg shaped/worn, new rings would be OK. I've heard that pistons from a 360 will fit if it's bored out.
Don't start fixing without checking what the problem is. Here is what you need to do:
1 - check sparkplugs for oil
2 - compression test
3 - take off valve cover and sight valve seals... replace if cracked/stiff/worn
I had a 6 cyl do exactly the same thing, used a bit of oil and puffed on start-up. Compression was fine but plugs a bit dark and... wait for it... all valve seals cracked and 2 or 3 were missing completely! Replacing them all stopped oil consumption and smoke on startup completely.
Ok, cool. Well, not cool, but that's good to know. So, the next thing to do would be a 'wet' compression test. That's where you put oil in each cylinder and run the compression test again. If the compression reading goes up, that means the piston rings are shot. If not, it's either the head gasket is leaking all around, or you have leakage past the valves.
Either way, i'm deducing your head gasket is blown between cylinder 1 and 2, and the rest of the cylinders are pretty low as well. I've heard that if it's below 100psi you need a rebuild on it.
Also, I believe the 'technical' way to do the compression test is just like you did, but you want to turn the engine over until the needle on the compression tester doesn't go up any more. It will just kind of 'bounce' back and forth as the engine is turning over. 6 seconds might be ok, but it's best to have a 2nd person tell you when the needle stops going up.
I'm getting both increased compression and no increase with the oil in each of the cylinders. I decided to pop the valve cover off to take a look in there and discovered several mysteries going on with the carb/intake. I've got a manual ordered and on the way but in the meantime I'm hoping you guys can help me clean up this mess. Here's a video.
So I picked up this mid 80's model 300 6 engine on Saturday. This engine came out of a running truck and has good compression. the plan is to swap this engine for the the current one in my 75 and possibly rebuild it once its out. I am in the process of removing all of the smog BS and the AC compressor. I currently have one bolt behind the fan pulley I need to get to in order to remove the AC compressor shelf. I have removed the 4 bolts holding the fan on and neither the fan or pulley are coming off.
can someone tell me the proper procedure for removing the fan and pulley before I start applying force?
