Compression Test Results- Opinions?

Hi-

Just finished running a compression test on my car. By way of background, it's a '71 non-stage 455 with 70kmi original miles. Motor has never been apart. Sat for 20+ years before being started this year. Did all the right things (pre-lube, oil in spark plug holes, etc) before starting. Tom Telesco and Carl Rychlik checked it out and are of the opinion that the # 1 and 7 cylinders are dead, probably valve related. There is valve movement on these, and a fairly cursory look at valve springs doesn't reveal much in the way of signs of damage. The valve train doesn't clatter or otherwise make noise when it runs.

As I haven't done a compression test in a long, long time, let me state what I did to assure the technique was correct. I started and ran the car for about 10 to 15 minutes. I took a leisurely cruise around the block and returned home. I disabled the ignition system and loosened all the spark plugs. The primary butterfly was set in the open position. I screwed the tester (Sears) in each plug hole, spun the motor until the gage stopped increasing, then took a reading. I then took the tester off, squirted several drops of motor oil in the plug hole and repeated the test.

Here are the results:

Cylinder/No Oil/Oil
1/15/15
3/105/105
5/110/110
7/45/45

2/75/80
4/115/115
6/130/130
8/90/90

It would appear as though cylinder #1 might be a bit of a problem. ou: There doesn't seem to be a difference between oil/no oil, so perhaps rings are ok? The four corners of the motor have the lowest readings. Any significance to this? Oil system related problem?

So, what opinions do you have? What further tests should I run? Does the oil/no oil test on #1 mean anything with so low a pressure?

I look forward to hearing what you guys have to say!

Thanks

 

I'd agree, those look like dead cylinders. And some of the others aren't in prime condition, either...

Anyhow, oil or not, you're gonna have to tear into that motor if you want to fix the problem. Could be as simple as some valve seals, could have broken pistons. (Even when I had a busted piston, I still managed 35 PSI).

So you can either:
1) Take it out and apart right now, or
2) Just drive it until things get really bad.

-Bob C.

 

How much run time does the motor have on it after starting for the first time?

John

 

wow...do you feel a big miss in that thing when it's running?

Pull the heads and rebuild them...that will also give you a look at the pistons while you're there. Or you could wait until things get really bad if you don't want to tear into the motor until you are ready to.:gt: :ball:

Hope it's not anything too bad.:TU:

 

Thanks for the responses so far. :TU:

the motor has about 130 miles on it since it was started. There's also combined a couple of hours in tuning, etc. It does has a slight vibration at idle, but really not that bad. When I first started it it seemed to run just fine. Once it was timed, and the idle came down, it had a slight lope to it. It definitely does not seem as strong as it should. I think it would take plenty of go pedal and a good clutch dump to light 'em up. That ain't right. :gt:

Anyway, keep the thoughts coming. I know I'll be pulling heads, but I'm hoping I can limit it to that due to cash flow. Unless there's an overwhelming reason to yank the motor, I won't at this time. I'm hoping you guys can give me guidance as to whether or not I need to pull the whole thing.

Thanks

 

Run a leak down test on it before you tear into it to find where the problem is. The leak down will give a tell tale of where it is leaking when the compression test only tells you it is leaking. A penetrant can be used to free up rings on occasion but valve leakage it will need to come apart.

 

it's really not too hard to remove the intake and heads...even if it's something small, i really see no downside to going ahead and tearing down the top end to inspect things, put new parts in if needed, and getting new head gaskets along with replacing the other likely-leaking gaskets.o No:

 

Speedy-

I definitely agree that the heads will need to be rebuilt either way. I was just looking to see if anyone saw a major signal that the bottom end might be hurt too. I'm hoping not as I don't have the funds right now for a full rebuild. I will probably try to do most of the labor myself on disassembly/assembly. That being said, I'm thinking that if I end up with a bottom end issue that I can diagnose ahead of time I figure it's easier to disassemble the top of a yanked motor than one still in the car. I could be wrong, though.

Dennis-

What's the correct procedure for doing a leakdown test? Can you point me to a website that describes it? In the meantime I'm going to go look in my service manual and see what I can find there.

Thanks!

 

David-

I was writing my response as you were posting yours.

So it isn't that hard to take apart the top end? What about a cam swap? I'm thinking if I'm in there already... :Brow:

 

With the 4 corners low, I am wondering if you have a head gasket problem at the water jackets. Having not run in 20 years and aged coolant, it could have turned corrosive and ate away at the gasket. You are then leaking compression into the coolant. Any bubbles or vapor coming into the radiator? Just some thoughts.
Also, I have taken apart 71 350's that had the exhaust valves burned and cracked causing a compression leak. The 71 motors were a lot leaner running than 70 and older and the higher exhaust temps stressed the valves.
It may be worth removing the heads to get a look see and going from there. If you don't see piston damage or cylinder wall scoring, you may get away with just head work.
Just my opinion,
Mark

 

i've done it, and i'm no einstein.:laugh:

the water jacket idea is good one...and would mean nothing more than about $40-50 in gaskets.

btw, the cam swap doesn't entail much more once the heads and intake is off. the timing cover is an easy removal, but you'd want to be VERY wary of those bolts with the amount of time the car has been sitting. only othr concern is the cam bearings...beating the cam out with a chisel becuase bearings are shot isn't fun.:ball:

rob speaks the truth though...the timing cover will come off, and you'll see how leaky the front of the oilpan is...so you'll take it all the way off. then you'll want new valve springs with your cam...and once you got both the top and bottom open, it won't belong before you decide you need forged pistons and aluminum heads.p

 

Here is the problem area in the head gasket....I know this all too well:af:

 

Yikes! Adam, I followed your post (and Arcdevilz) when you were going through this. You both survived so I guess it's doable. I just hope I don't get a bad case of the "little bit more" syndrome as Speedy noted.

Oh well, I put 130 miles on it. At least I got some use before riping the top end apart. o No:

 

Ken, it;s not that baad really....

It took me close to 10 days from start to finish. The machine shop had a 3 day turn-around. So I got lucky there. The worst part is putting it back together trying to lift the damn head back into place without dropping them!

It just takes some time and a lot of knuckle busting and greased up showers and sinks:grin:

I had lots of fun doing mine though. I didn't throw a cam in mine, because I wasn't ready to pull the timing cover off. I didn't want to tackle too many things at once, especially since I was pretty much driving that thing all the time. It is sitting in the garage all the time now. I drive the irrigation van for daily stuff.

It's a mess when you get those things apart though! Jeez.....

 

What a good thing to look forward to though!!

 

Ken stop,
Dennis Halladay has it right!!!, do a leak down before you pull anything loose by some one that understands how to do the test "properly", you will have no guess work! it will tell where the problem lies, not trying to sound like a know it all guys but it is the RIGHT way to troubleshoot the motor, leave the shade tree stuff behind, there are way to many great tools at are disposal these days to aid in working on these great cars.

Bud.

 

Leak down test is done by pressurizing the cylinder with compressed air and measuring the air loss with a gage. The piston should be at top and rockers removed so valves are fully closed. I have a moroso single gage unit that I would loan if you promise to return it. If you pull apart without testing you may put fresh heads and gaskets on a junk shortblock and have to do the work all over again. Do yourself a favor and check properly or plan to do the whole engine not just the top half. Let me know on the leakage tester.

 

That pic is pretty much what I am talking about. Looks like a 455 too. Had that exact same thing on #1 in a 71 455 motor I had too. Those darn red gaskets just didn't hold up. The steel or metal composition ones from 70 and earlier were so much better. Guess the factory thought that with lower compression they didn't need the older gasket style. ou:
A leak down test is a great idea too. Anything you can do before you pull it apart will be a help.
Looks like you got your work cut out for you.
Good Luck,
Mark

 

71 455 it is:TU: Stupid thing was probably sitting for 5 years before I got a hold of it.