valve adjustement increasing compression

[Andre Guay]

Hi, I had my 1982 sc for tree years and had the compression test done before I bought it.

According to the specialist?, the engine showed normal wear for his age and nothing abnormal based on the readings.

The compression read 135psi on all except #1 and #5 wich were at 130psi.


The engine have been running strong since...

But now it is a bit rough when cold and there is a bit of oil leak (a drop here and there) wich had me check for causes. I ended up on some data and now I wonder what is a proper compression readind?.

Could a valves adjustement help increasing the compression (I heard it haven't been done by the previous owner for quite a while). Or is this a sign of a costly rebuilt?.

Thanks

[javadog]

Andre,

It's more important for the compression numbers to be even, than to have a specific number. There are too many variables in the way the test can be done to quote you an absolute value.

If the engine runs well and doesn't exhibit any other signs of impending doom, such as very high oil consumption or smoking when driving, I wouldn't worry about it.

I would suggest you have the valves adjusted, both for the valves sake and to keep an eye on the head studs. After the valve adjustment, check for vacuum leaks and have your CO checked and adjusted. New filters and plugs might also be a good idea, if they haven't been done in a while.

JR

[Nine9six]

Originally posted by javadog
Andre,

It's more important for the compression numbers to be even, than to have a specific number. There are too many variables in the way the test can be done to quote you an absolute value.

If the engine runs well and doesn't exhibit any other signs of impending doom, such as very high oil consumption or smoking when driving, I wouldn't worry about it.

I would suggest you have the valves adjusted, both for the valves sake and to keep an eye on the head studs. After the valve adjustment, check for vacuum leaks and have your CO checked and adjusted. New filters and plugs might also be a good idea, if they haven't been done in a while.

JR

What JR said...
Depending on the mileage of your car, I would also look into a set of plug wires, rotor cap, and rotor, to go along with JR's recommendation of new filters and plugs.

[Early_S_Man]

Andre,

Your mean compression is 133.3 psi, so your numbers are quite even across the board. Nothing to be concerned about, really.

If the compression test was done cold, they might improve a bit if done hot, but it still isn't a concern if the engine is running well and not burning or leaking any significant oil.

I suggest a valve adjustment and check of the compresssion while hot, then a leakdown test ... just to be sure. Be sure to have the lower 12 Dilivar cylinder head studs checked for tightness and to see if any are broken.

Good luck!

[Zeke]

I hope you are not saying that you haven't adjusted the valves in 3 years. If so, you need to perform a comprehensive tune up and then see if the car still runs rough. A lot can deteriorate in 3 years, high milage or not. See some recent threads about the spark plug wires. If you search any tune up topic using Early_S _Man as the author, you will have all the info you need.

[Andre Guay]

Thanks everyone, the job is being done as we speak (major service) and you answered my question concerning the way compression reading should be analysed.

[Rodsrsr]

If the valves are out of adjustment, they may not be closing all the way, which would result in a loss of compression.