Compression tested my 73 Newport and it’s rough. Is it worth trying to get it started or just rebuild the motor first?

L

Lordofthepings777

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FYI motor is 400CI 6.6L

Bought this thing a few weeks ago as a project car, but couldn’t get it started. Spent $ and time on new parts all over, and finally decided a compression test was due.

Unfortunately, almost every cylinder read 75PSI, mind you this wasn’t a wet test, but still disappointing. 5 cylinders are reading 75PSI, and 3 reading ~50PSI.

keeping that in mind, what would you guys suggest? Is there any benefit to attempting to get this motor to run before taking it apart? Or is it worth a complete rebuild and refresh then attempting to get it running.

Keep in mind I’ve already spent 2 weeks trying to get it to run, and nothing has come of it.
 
Have you checked the timing chain? I assume you have checked to be sure that you have both spark and fuel. Check for spark by pulling the coil wire from the distributor and prop it about 1/8" from the block, the wire should shoot a a spark to the block as the engine is cranked. If you do not have spark, check the ballast resistor by using a voltmeter to be sure you have a completed circuit thru the resistor. Next, check to be sure you have voltage to the coil. If you have spark, put about 3 oz of fuel down the carb throat and see if the engine fires. If this vehicle sat for a long time, the fuel tank is probably full of degraded fuel. Disconnect the input side of the fuel pump and run a line to a small gas can to draw fresh fuel. You can check the timing chain for excessive slop by turning the engine by hand using a socket attached to the large nut on the harmonic balancer nut. Turn the engine over until the timing mark is lined up TDC with the mark on the harmonic balancer. Remove the distributor cap so that you can see the rotor. Now have a helper rock the crankshaft back and forth and note how many degrees of movement that it takes to get the rotor to move. If it takes 15 degrees or more of crank movement to move the rotor the timing chain is shot and needs to be replaced. Check these things and report back.

Dave
 
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Wont start like that. The timing chain is the first stop. Jumped teeth, valves not in sync with pistons, won't build any compression. All 8 low tells you to start there. Unless bent valves on all 8 cylinders.
 
Compared to the 9.2+CR engines prior to the 8.2CR engines like you have, the 75psi would automatically mean it was completely worn out, especially the compression ring and cylinder walls. But seems like the specs for the 8.2CR motors was 90psi+? The issue would be why the several cylinders are at 50psi, to me.

If you want to "do something", the starting place would be the timing chain set. The second place would be a full valve job. Of course, if you want "the full meal deal" pull the engine and put it on a quality engine stand. That would certainly make things easier to deal with!

Please keep us posted on your progress,
CBODY67
 
What parts did you replace? When a motor sits for a long time, there is no real way of knowing it's condition except for performing some tests. The advice above is good. Make sure you have spark and fresh fuel and check the timing. With an old motor that has been sitting and not started for a while, I like to take out the plugs and squirt some oil in the cylinders. Good luck.
 
57fury440 said:
What parts did you replace? When a motor sits for a long time, there is no real way of knowing its condition except for performing some tests. The advice above is good. Make sure you have spark and fresh fuel and check the timing. With an old motor that has been sitting and not started for a while, I like to take out the plugs and squirt some oil in the cylinders. Good luck.
Click to expand...
I replaced the battery, starter, repaired/rebuilt the carb, changed the fuel filter and the fuel pump, and not to mention the distributor is new along with the wires and plugs.

Oh and the car did sit for about 30 years…
 
Make sure when you do a full (all cylinders) compression test that the throttle is wide open and all the other spark plugs are removed so the engine spins over free and as fast as possible and put's the least strain on your starter motor and battery.
Then if your compression is still low squirt some oil into the cylinders and redo the compression test, if it comes up a bit with the oil squirt your rings are worn.

.
 
Lordofthepings777 said:
Oh and the car did sit for about 30 years…
Click to expand...
The very first thing you should of done was the compression test before spending all the money on other parts, not that they weren't probably needed but what is your budget going to allow? Better off spending the money on a bore scope to have a look see if there is rust on the cylinder walls.

.
 
Lordofthepings777 said:
Oh and the car did sit for about 30 years…
Click to expand...

If it sat that long the rings are defiantly setup a little (or a lot) in the pistons. I would start by removing all the stark plugs and squirt some auto trans fluid or mystery oil in each cylinder and letting it set for a day. After sitting for a day, pull the valve covers and crank the engine over and check that all the valves are closing. An engine that sat that long could have valves sticking. If you can get it running the heat might loosen up the rings. If all the valves are closing reinstall the valve covers. Check your base timing and try to get it running.
 
Battery cables need to be good, the power needs to make a full circle from battery positive to battery negative posts.
 
Throwing this out there because I do not know, would a slow/slower turning motor yield lower compression numbers? Anyone know?
 
You want a fully charged battery for the test. If it still spins slowly check all the connections and at the starter as well.
 
I run a battery charger on the battery while doing a compression test. Keeps the crank rpm even.
 
The motor should run with those slow cranking numbers if the chain is good, and the starter spins it a 200 rpm or more.
But it's probably going to burn enough oil to see smoke out the tail pipe.
 
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