Compression check

[Guest]

I have a 352 HP and I notice a little blue smoke on the right side of exhaust how do I do a compression check to see if it is the valves or the rings and also what would be a good preeuer on each cylinder

[JBird]

RE: Compression check

>I have a 352 HP and I notice a little blue smoke on the
>right side of exhaust how do I do a compression check to see
>if it is the valves or the rings and also what would be a
>good preeuer on each cylinder


Straight out of the book.

At Sea Level, 180 +- 20 for a 352 with 9.6:1 compression for a NEW engine. In reality, 120 to 140 works well and shows signs of wear but not to the point of needing an overhaul.

Valve guides and seals often puff when you rev the engine and back off quickly or when you shift with a manual trans. They also cause blue smoke when you first start up in the morning. This is because oil from the rocker area drips down the valve stems into the cylinders overnight and the exhaust turns blue until it burns out of the cylinders.

[JohnG]

RE: Compression check

how much oil are you consuming? (how many miles per quart?)

[Guest]

RE: Compression check

Interesting, I ran a compression check of my 352 last weekend and had the following results with the motor.

Highest was 160, lowest was 140, the majority of them ran around 150 to 152. We then squirted in oil, a friend told us that would tell us something if we saw a large bump. We didn't see much of a jump at all. The guy that gave me the TBird told me the car and motor has 77k original miles on it.

B

[JohnG]

RE: Compression check

a jump in readings after putting some oil in would tell you that the rings were leaking compression. The oil temporarily seals them. That pretty much would then isolate the valves.

You can also buy or borrow a piece of equipment called a "leakdown tester". You position the cylinder at bottom dead center on the stroke leaving both valves closed. You then screw an air fitting into the sparkplug hole and attach a gauge and an air source to the fitting. The gauge tells you what percentage air you are leaking. You also can listen to the air escaping and tell if it is going past the rings or by the valves.

[KULTULZ]

A Suggestion

A quicker method to determine if rings or valve seals is reading the spark plugs (and this is assuming the road draft/PCV Sytem is fully operational). If black and wet (all or some cylinders), it will indicate bad oil rings. If brownish and dry in appearance, it will usually indicate valve seals (or possibly dyes used in the gasoline).

It is possible to have good compression and still have a failed oil ring. The valve stem seals are of a nylon material (umbrella type) and can usually be inspected by looking into the valve spring. Most likely you will notice deterioation after all of these years. They can be replaced on the car (and if deterioating, pieces will find themselves being drawn into the oil pan creating another set of problems).

Below is a fairly good chart describing plug reading;

http://www.centuryperformance.com/spark2.asp

[JohnG]

RE: A Suggestion

I looked at the spark plug chart you provided the url to and saw plugs consistent with what I had seen for many years and would take as good indicators of the conditions listed.

Strangely, after buying a 58 Tbird 3 years ago, on the one hand I was using a quart per 125 miles but on the other hand had clean, excellent looking plugs. Compression readings were all in the 135 to 145 range. It also smoked increasingly.

After ruling out any leaks, I hauled the motor out and took it apart last winter. All oil rings were terribly worn (vertical dimension), between .010 and .015". Three top oil rings were broken in half. About half of the valve guides were worn past spec. All evidence and paperwork indicated that the motor had 150,000 miles on it. The cam and lifters had been replaced but the rest was all original and very worn.

From all this I should have seen plugs that looked poor in various ways but never did. I don't have an explanation.

John
'58 Hardtop

[KULTULZ]

RE: A Suggestion

>Strangely, after buying a 58 Tbird 3 years ago, on the one
>hand I was using a quart per 125 miles but on the other hand
>had clean, excellent looking plugs. Compression readings
>were all in the 135 to 145 range. It also smoked
>increasingly.
>
>After ruling out any leaks, I hauled the motor out and took
>it apart last winter. All oil rings were terribly worn
>(vertical dimension), between .010 and .015". Three top oil
>rings were broken in half. About half of the valve guides
>were worn past spec.

>From all this I should have seen plugs that looked poor in
>various ways but never did. I don't have an explanation.

Interesting John...

Was the ignition points or had it been upgraded?

[JohnG]

RE: A Suggestion

just points... the coil was a little better than stock.

If you go to the following url and go about 1/3 of the way down, you will find a picture of a compression ring. It is WORN!

[http://www.squarebirds.org/users/johng/OCC.htm]

But the plugs always looked good... Back in the 70s I used to look at plugs on cars with oil problems and there would be so many deposits that you could barely find the electrode. This car should have had plugs that looked the same... dunno why not...

John