Pull the engine to replace the timing chain?

[John Mc]

Guys, question please and the archives pretty well tells me what to do, so I’m just confirming. My ‘77 Town Coupe needs a timing chain. 73,000 miles and it runs terribly with only 75-80lbs on each cylinder.
I’m thinking of removing the engine instead of just the chain replacement. Why?
First I think I’d be in traction after bending over that long, plus I would pull the pan clean the pump, replace core plugs, replace valve stem seals, paint and detail the block etc. all on a stand. I’d remove the trans too.
Good idea??

[Dan Szwarc]

I thought cylinder pressures should be in the 100-120 psi range. So... I'd agree with a rebuild.

Why not do the full wet and dry and leakdown cylinder tests and then report back? I hate rebuilding motors before their time as it's such a waste of money when it could be put off for many years if barely driven.

[1Bad55Chevy]

It probably just needs a valve job. Valve seals and seats will cause low compression. When you pull the oil fill cap off the valve cover when its running is there a lot of smoke and pressure coming out?

[John Mc]

I thought cylinder pressures should be in the 100-120 psi range. So... I'd agree with a rebuild.

Why not do the full wet and dry and leakdown cylinder tests and then report back? I hate rebuilding motors before their time as it's such a waste of money when it could be put off for many years if barely driven.

Yes pressure should be 140-160, so I’m way off. I would do a total rebuild, probably just clean and replace the valve stem seals, which are probably hard as wood at this point.
I

[John Mc]

It probably just needs a valve job. Valve seals and seats will cause low compression. When you pull the oil fill cap off the valve cover when its running is there a lot of smoke and pressure coming out?

Some blowby, but not bad, it just runs terribly, so bad I’m thinking it could only be a timing chain issue. Either it’s super loose or it has jumped. The car shakes violently at idle. Can’t think of another thing that could be the cause.

[Dan Szwarc]

Misfire is the first thing to check. Distributor play? Cross-firing spark plug wires? Carbon tracked dist. cap?

John, does your 77 have original style blue spark plug wires with the numbers? I have a used set somewhere I can send you.

[Lee]

A jumped timing chain could easily cause low compression. All the valve opening and closing intervals would be late. If you need it, I can get you the actual intake BTDC opening degrees, you can pull the passenger valve cover and check. But you can also get a rough idea but checking where the distributor rotor is pointing when you're on TDC. Given that all cylinders are low, that's my bet. Usually valves won't be equally bad, so you'll have high and low cylinders. Squirt some oil in each cylinder, and if they don't raise much, I'd say the timing chain is almost guaranteed.

If you are the type to pull the engine for a timing chain (I'm not making judgements!), you'll suddenly realize that you might as well replace the engine and tranny mounts, replace the radiator hoses, maybe new hydroboost lines, blast the exhaust manifolds, paint the engine bay, etc. etc. and pretty soon its a major project. Its happened to me.

[Dan Szwarc]

There are all kinds of tests to run with the motor in the car that can isolate leaky valves from bad rings to bad valve seals.

Put in a nice double roller timing chain while you’re in there.

[John Mc]

I started the car this morning to check the timing. The ignition timing is set at 8 degrees.
Interestingly the car ran pretty well with the vacuum that feeds the distributor blocked off. Once reconnected the rpm’s went up and the 460 ran ,much rougher. I assume then there is a bad vacuum leak somewhere?

[Dan Szwarc]

Check the vacuum advance on the distributor with your mouth or a vacuum tester. It may be that simple.

[John Mc]

I started the car this morning to check the timing. The ignition timing is set at 8 degrees.
Interestingly the car ran pretty well with the vacuum that feeds the distributor blocked off. Once reconnected the rpm’s went up and the 460 ran ,much rougher. I assume then there is a bad vacuum leak somewhere?

[John Mc]

Check the vacuum advance on the distributor with your mouth or a vacuum tester. It may be that simple.

It’s a new distributor and the vacuum system is spot on

[John Mc]

Misfire is the first thing to check. Distributor play? Cross-firing spark plug wires? Carbon tracked dist. cap?

John, does your 77 have original style blue spark plug wires with the numbers? I have a used set somewhere I can send you.

Thanks Dan, but I have installed all new Motorcraft wires and plugs

[Dan Szwarc]

You know, being n ew used to rule things out, but nowadays, I don't trust anything.

To isolate vacuum, do exactly that: Isolate each system. Door locks, headlamps, cruise control, HVAC.

What about the pickup in the distributor? Can you verify spark pulses at all cylinders when it's running rough?

[John Mc]

You know, being n ew used to rule things out, but nowadays, I don't trust anything.

To isolate vacuum, do exactly that: Isolate each system. Door locks, headlamps, cruise control, HVAC.

What about the pickup in the distributor? Can you verify spark pulses at all cylinders when it's running rough?

Yes, I need to do both of those items. Good hit Dan.