Amc 304 Oil Out Exhaust( Now Re-building)

Hey everbody, new to the forum but have had my 75 Cj5 304 for 10 years. Not sure it matters but it has an edlebrock intake and 4 barrel carb. As long as I have had it, it always seems to blow a little bit of oil out the exhaust, and after you have driven it a little hard there is some smoke coming out the exhaust. So I guess I should do a compression test and maybe a leak down test to see if its the heads or oil blowing by the rings? It also has a slight knocking noise when cold but don't really hear it much when it warms up. Any hints or other tests i should be checking out?

If it was more serious than head work can a 304 be rebuilt at home? I am pretty mechanical but just don't know how to tell if it needs serious machining. Thanks in Advance.

 

Welcome from Mississippi.
Worn rings, valve guides/seals. You could do a power balance test to see how the rpm may or may not drop. Little to no rpm drop points to a weak cylinder with low compression or erratic combustion. Do a wet compression test on low compression cylinders to see if you have leaky valves.

 

Are you sure it is oil? How is the engine oil consumption?

What color is the smoke? Is is worse after going downhill with the engine holding back?

 

Water (condensation in the exhaust pipes - normal) and carbon can be mistaken for oil. If it were oil, I would expect constant blue smoke, along with oil coming up the crankcase breather into the air cleaner. What color is the smoke? Oil is blue, water is white, and too-rich (gasoline) is black. What have you done to tune the carburetor to your engine?

Your two main indicators of engine condition are compression and oil pressure. At hot idle, full warmed up, you should have at least 10 psi of oil pressure, and more is better (very important). Compression check should be done routinely on an new-old car. Record the numbers and post them up here. A 304 in good condition should have about 150 psi on each cylinder, and less than plus-minus 10% variation, cylinder to cylinder. A leak-down test it better, but you need a compressor and more complicated equipment.

You can rebuild your engine at home. You'd have to send the block and heads out for machining, but you can do the assembly of new parts yourself. Evaluate the engine first though. Depending on what you find, we can discuss a rebuild further. To me, the knocking is more concerning than the "oil."

 

I will test the compression today. I do know that after I change the oil it gets black again pretty fast. Oil pressure gauge reads like 70 or so when you start it then once it warms up about at idle 20-40. I am not positive what color the smoke is. Will have to investigate more. Was never to concerning as its a second vehicle that gets driven a about 5 times a month. But I am wanting to maybe do some short camping road trips so efficient motor is on the top of the list. I also beIieve the carb is probably running to rich which probably isn't helping. Any good tutorials for holley 4bbl tuning? Thanks

 

Ok so Just got back from a 20 minute ride or so. Hot at idle oil pressure is just shy of 20, when driving its about 40psi hot. When letting it idle in the drive when i got back there is some white smoke coming out of oil breather tube and the exhaust just has a very small amount of white smoke. Will be doing the compression shortly.

 

The results are in, not the greatest news. Looking from the front on the engine L R

100 130

140 130

80-90 140-110

130 140
Front

So it looks like the motor is a little worn down. All the plugs are black and sooty but not wet. On the one cylinder (2nd back on left) I dribble a little oil in and the compression went up to 90. On the other the opposite cylinder once the motor stopped turning went from 140 down to 110. Looks like time for some rings? and head work? and bearing races?

 

Re the knock at start-up, what oil filter are you using? The Fram filter is well-known to allow too much drain back, and a slow rise of oil pressure at start-up. There is a lot if discussion of oil filters on the net... I typically use a Wix but right now I have a couple Delcos and a bunch of Purolators I bought on close-out.

 

It does have a fram on it, I will have to get a wix from Napa next time

 

Ok Update: On the cylinder that only had 80# compression I hooked to the leakdown tester first. Making sure on top dead center compression I am getting like 80% loss. You can feel it coming out of the oil fill, see light smoke coming out of carb, and hear air out the exhaust, and nothing bubbling in radiator. So looks like I have worn rings and some valve issues? Right? Thanks

 

Usually one low cylinder means a bad exhaust valve, but your numbers look like the engine is just tired. The one cylinder going down after adding oil does not make sense. I suspect that's a procedural error, not real. The pressure can only go up with oil on top of the rings. Leakdown around the rings will come out the crankcase, but you should not hear air out the exhaust unless the exhaust valve does not seal.

How much do you want to take on, and how much do you want to spend? The price difference between an exchange short block and doing the short block assembly yourself isn't huge. There's undoubtedly a local garage that will do the whole job for you. If you do the work yourself, the main saving will be yanking the motor and putting it back. However, many want to do the assembly work themselves because they do not trust the reman factory labor. If you have the short block, you bolt on the refurbished heads and external pieces, and put the engine back.

For the block, if you did it yourself, you'd buy a crank kit (reman crank and bearings) and have the block magnafluxed, washed and bored, and fit the pistons. New pistons are the most expensive item of a reman. Then you put it together.

Regarding the heads, you are pretty much at the mercy of the shop where the work will be done. They will wash and disassemble and tell you what's needed. 304 heads aren't rare, so don't do anything heroic to save them. Likely the shop will recommend replacing some parts and reconditioning the guides. You can fit inserts, or have the guides knurled to refurbish them.

 

How bad would it be to just ball hone and re-ring it just to get a little more out of it? The way I see it is if I do it and the compression isnt any better than I am not really out much besides a couple hundred bucks, I think I can pull the pistons without taking the motor out. In the process I can get a local shop to do any machine work on the heads.

 

An old-fashioned overhaul is typically rings, heads and rod bearings. Not common for modern engines with cast cranks. What you are suggesting is definitely a patch-up job ... how long do you plan to keep this Jeep? If you hone the cylinders and install cast-iron rings, you can get maybe 10K-20K miles before they wear out. Installing new rings in tapered bores wear them out quite quickly. Only cast iron type will seat in a tapered/out-of-round bore, and the constant flexing will fatigue them pretty quickly. But they are cheap, and you don't need new pistons. You can maybe reuse the rod bearings, depending on condition. Inspect and Plastigage. Low hot-idle oil pressure puts the rod bearings most at risk. These engines often have delaminating cam bearings, which you won't see without taking the engine out. If everything else looks great (oil pump, bearing clearance) and you still have low oil pressure, cam bearings are the #1 suspect. You're still going to have to spend a few hundred dollars on the heads. As I said, you are pretty much at the mercy of your shop.

 

White smoke from exhaust and breather, with a low cylinder = possibly just a head gasket? But timgr has good knowledge.

The thing with a partial rebuild is that you will keep finding a reason to spend a little more and a little more, or else waste whatever money you already put in.
And I have had the experience twice of doing a full rebuild, then having it be a loss because of machine-shop errors.

Might be a better bet to swap for a good used engine, if you can find one cheap?

 

What is the spec for a 304 compression wise per cylinder? Also what is good oil pressure for the engine? Thanks

 

What does the TSM say?

 

74 TSM ,,,
Compression
140 psi for the 304, 360, 401
Maximum variation between cylinders ,,, 20 psi
Oil pressure
13 psi at 600 rpm
37 psi at 1600 rpm
75 psi maximum

 

Trickey Tim.

 

Thanks guys, guess I need to decide what actions to take. Will I damage anything more by still driving it 6 miles to work every once in awhile?

 

Hey everyone, Starting pulling some parts off the motor to get a better look. Surprisingly the exhaust manifold bolts all came out with ease. On the pass. side head 2 rocker arm holders, on two different piston were broke. Not sure how that could of happened any clue? push rods do not look bent to the naked eye.

Should I be getting new rockers and holders for all the cylinders? Can the push rods be re-used if not bent? Another stupid question, I have not pulled out the lifters yet. (I know to keep them matched to where they came from. If the cam is ok can those be re-used or would a more performance minded cam and new lifters be a good idea? Thanks for reading all my issues.