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A leak down test will give you a ot more info - and allow you to pinpoint the source (or sources) of problems.

My eL-cheapo version is just a hose that screws into the spark plug hole and attaches to an air line. Position the cylinder being tested at TDC on compression and apply 60-80 psi via the hose. be careful - the engine can suddenly turn.

With the cylinder pressurized, listen at the exhaust pipe, intake, adjacent cylinders, oil fill, radiator and around the edges of the head. It is normal to hear some hissing past the rings (heard at the oil fill) but not at the other places. A real leak down tester has a pair of gauges to measure how well the cylinder will hold air. My version just allows you to look for problems.

BTW, was your compression test done with the throttle(s) propped wide open?
 

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Throttle(s) should be propped open, all spark plugs out and the battery must be fully charged. If the battery is weak the cranking speed will get slower & slower (especially if you left the spark plugs in) which could explain the low reading in #4.

Are you sure the tester was tightened fully into cylinder #2 & #3?
 

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To verify cam timing position the #1 piston at TDC on compression (the cam lobes for #1 will be pointing away from each other - i.e. the intake pointing right and the exhaust pointing left.) There should be a pointer on the bottom of the water pump and marks on the crank pulley. 'P' for TDC and 'F' for ignition timing.

However, as the pointer is adjustable it could be mis-adjusted. I like to get it close then use a drinking straw as a poor-man's dial indicator to make sure the piston is at the top of its stroke. The straw is stiff enough to work yet soft enough that it won't hurt anything internally. When you think the piston is at TDC, put the straw into the spark plug hole and move the crankshaft back & forth while watching the straw to see if, indeed, the piston is at the top of its stroke. When you are certain it is, see if you can find the marks on the crankshaft pulley.

Back to cam timing - with the #1 piston at TDC on compression, the cam's timing marks should align with marks on the back of the front cam caps (away from the timing chain side).

Having said (written) all that, it is unlikely that improper cam timing would cause one cylinder to read so low. Something is drastically wrong with that cylinder. Either a valve is not sealing, the head gasket has failed, rings are broken or the piston has a hole in it!

I suggest the leak down test. See my previous reply for my eL-cheapo version. That'll tell you where the problem(s) is (are).

And before you tear it apart, you might want to try re-torqueing the head. Can't hurt (but unlikely to affect a lasting repair...).
 

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Here's a picture of what the timing marks on the cranshaft pulley look like. This is on a pulley I cleaned and then highlighted the marks with a bit of silver paint. Otherwise, they are much harder to find. You'll probably need a small wire brush to clean off any crud first.
 

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I agree that it is most likely the head will be coming off sooner or later. I like to have a diagnosis first though. Sometimes taking things apart too soon makes that difficult or impossible. For example, if the head gasket has failed, removing the head will probably ruin the gasket making it difficult to 'prove' that was the problem.

However, being the frugal guy that I am (OK, cheap...) I don't like to waste a lot of money to make the diagnosis. Thus my eL-cheapo leak down tester should pinpoint the problem(s).

One other thing to try before tearing it apart is to peek into the #2 spark plug hole while turning the engine over. You will be able to get a glimpse of the valves as they open & close. If they don't - big problem! (bent/broken valves). If they do, see what the edges look like. Any chunks missing means burned valves (and probably seats, too).

Finally, if the valves move and aren't missing any pieces, try using a screwdriver levered against the camshaft (not on the machined lobes but against the rough casting of the camshaft) to open & close them a few times. Do this when the lobes for #2 are facing away from the engine. Pry the valves open and let them 'slam' shut. If there is carbon built up on the seats, that may knock it loose. Then crank the engine over for 10-30 seconds (spark plugs out) to blow out the crabon and re-do the compression test. Remember to keep the battery fully charged and prop the throttle wide open.
 
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