Compression help - #6 is 60% of the rest.

[Guest Brian260ZT]

I had a buyer for my 260 that wanted a mechanical inspection. The shop did a compression check and found that #6 was at 70psi, where the rest of the cylinders are at ~130.

 

The car runs and drives just fine. I assume I've just lost a bit of power.

There is no smoke, no gas in the oil, no coolant leaking.

 

I plan on pulling the valve cover this weekend and look for a broken spring or stuck valve.

 

What else should I look for?

 

 

Thanks,

 

Brian

[texasz]

That's not too bad...mine are 120, 120, 120, 40, 120, 120

 

Pour just a little bit of oil in the cyl through the spark plug hole then do the compression test on that cyl again. If it jumps up quite a bit then the rings are bad in that cyl...this is my problem.

 

To "help" this you can run 'motor honey' in with the oil which will help to seal it up a bit but this is only a temporary helper...or a bandaid if you will. The engine will still have to be rebuilt.

 

Please do not use this technique to sell the car without telling the new owner the true condition of the engine! That's just plain deceptive and may come back to bite you.

[Guest Brian260ZT]

I would never sell a car w/o being fully honest.

 

I just hope it's something easy like a broken spring.

 

Thanks,

 

Brian

[Guest bastaad525]

yeah definately do the oil-in-the-sparkplug hole test, that will tell you if it's rings or valves.

 

it's not always indicative of a motor needing a rebuild. I had a valve that was sticking open ever so slightly, sprayed some marvel mystery oil down onto it while cranking the engine and afterwards it fixed itself and my compression came back up.

 

Though most people don't agree with 'fixes in a bottle' I have had good experiences with the stuff called Restore or Engine Restore, and oil additive you can get at Auto Zone etc. Yeah it's definately a bandaid fix but that's better than no fix... just to keep you going strong until you can rebuild or sell the car.

[Guest RubberBerner]

Or you could save yourself some time and do a leakdown test...

Kit costs anywhere from $35-$120, depending on brand. Basically it fills the cylinder with air, and you can narrow it down better examples:

air leaking out intake - Bad intake valve sealing

air leaking out exhaust-Bad exhaust valve leaking

air leaking out oil fill plug-bad rings...of course for this one the oil is usually easier, but if the rings on that cyl. are so bad that oil won't help seal it, this will tell you they're bad.

[preith]

Or you could save yourself some time and do a leakdown test...

Kit costs anywhere from $35-$120' date=' depending on brand. Basically it fills the cylinder with air, and you can narrow it down better examples:

air leaking out intake - Bad intake valve sealing

air leaking out exhaust-Bad exhaust valve leaking

air leaking out oil fill plug-bad rings...of course for this one the oil is usually easier, but if the rings on that cyl. are so bad that oil won't help seal it, this will tell you they're bad.[/quote']

 

Agreed. I bought a very nice leak down tester from Eastwood, made or sold by Total Seal, at a reasonable price. I now prefer this method over the compression test. On my motor I was surprised to see just how much air was leaking past the valves on certain cylinders. What made diagnosing easier was having both manifolds off, but I would imagine you could hear air coming out the intake pretty easily.

 

I like to pull the valve cover off, makes it easier to find TDC on each cylinder. Plus you can then tap the suspected valves to help them seat better, which it did for me.