low compression (30 psi) on ALL cylinders... what the ...?!

frank Jacobs

frank Jacobs

Daily Driver
Hi,

I think I have a big problem..

Just a short introduction: X1/9 1977, 1300, as I posted before (2 weeks earlier) I had problems with starting the car, which got worse and worse voer a few weeks, until I couln't get it started anymore. But Once it WAS running, it was pretty much OK, no loss of power funny noises etc! Also spark is OK, fuel is OK.

As recommended by some of you, I checked both timing and compression, which I believed wouldn't be a problem as the car was running fine.. Timing was OK, both pully mark/cam-mark and ignition timing.

However... I have extremely low measures on all cylinders. about 30-35 psi, which gets about 40 when I poor in some oil.. To me blowing the headcasket for all cyliners sounds impossible.. Still, cranked it >5 times as you should, I used the compression gauge before when I bought it only 6 months ago, does not seem to loose pressure (not leaking), drivebelt is present, cylinders are moving up an down, I can't figure out what's wrong..

I should mention that I replaced the headcasket 6 months ago, had the head flattened, new casket etc, and did about 3000 km since then..

I could really use some help, so every suggestion is welcome!

Best regards,

Frank Jacobs
 
I would suspect valve timing...

If you got any reading on the compression gauge at all, then the pistons are moving up and down and the valves are opening and closing. It sounds like that is occurring for all cylinders. Possibilities:

Timing belt has slipped, or if you are running a phenolic cam pulley, it's died and slipped.

Head gasket may be blown across all cylinders, or at least between 1-2 and 3-4, but that's pretty unlikely, they usually go between 2-3 cuz it's thinnest there. Check your ignition timing carefully to make sure it has not slipped and overly advanced, burning your head gasket.

Head bolts all tight?

Burned exhaust valves. Ugly.

Try a leakdown tester as the first diagnostic step. If the leakdown percentage is low (say, less than 10%), I would bet timing/pulley belt slip. If it's higher, that points to actual sealing problems (head gasket/head bolts/valves).

Hope this helps, let us know what you find.

Pete
 
leak down test

Hi Pete, thanks for your input.

First of all, I checked the timing by looking at the timing marks only, I have no timing light to check it otherwise. They seem to be ok to me, at least as I aligned them after the head removal 6 months ago. When the cam mark aligns with the upper arrow on the drivebelt casket, the pully mark aligns with the 0' mark on the lower drive belt cover. At this position, the rotor in the distributer connects to cylinder 4. This sounds OK, right?

Secondly, I tightened the bolts to specs, but have not checked them after that.

Finally, I guess with a leakdown test you apply pressure to the cylinder through the sparkplugwhole right? I don't have the tools fro that, I'm affraid.. WOuld there be any other way to pin point the problem?

Frank
 
hmm how did the cylinder walls look? were they scored? might have some bad rings? altho bent valves might be a cause

or valve clearance might be keeping the valves open way longer than it should be
 
Leakdown tester

Frank,

If your timing marks are good, then the valve timing is probably ok. A leakdown tester won't pinpoint the problem, it will just show that the combustion chamber is not sealing. There might be a lot of causes for that, Thai hit on one (bent valves) that I had not considered - I forgot the 1300 was an interference motor.

Leakdown testers are not complicated or expensive. I built one out of 2 air compressor gauges for about $50. You can buy them for about $65 also. The way they work is to pump air in the spark plug hole (you want the piston down when you do this or it might turn the motor on you) and measure the amount of pressure being input (from air compressor) versus the amount of air leaking out of the combustion chamber. If you use 100PSI, then it's easy to read leakdown on the 2nd gauge as a percentage (1st gauge says 100psi, 2nd says 90psi, you have 10% leakdown). The two gauges are separated by a sized orifice (usually .040 inches if I recall).

Like I said, they won't pinpoint your problem, but they will tell you if it's time to tear into the motor.

Pete
 
Valves

Valves should be OK, had the head pressure-tested 6 months ago, was still OK, not too much leaking through the valves. Also, has NOT been out of timing, so that pretty much rules out bend valves, right?

Frank
 
General Q.

Can it actually RUN on cylinders with only 35 psi?? I should underline that once the car was running, it was running pretty good.. And that's how I put the car in its place where it is now. running fine... I know this only complicates things.

Previously I mentioned that quite some fuel has mixed with the oil, due to the continuous cranking. Could it be that this has worn the pistonrings/headgasket?

Best,
Frank
 
Can you try another compression tester?

Maybe your tester is not functioning properly?

Always start with the simplest explanation and work toward the most outlandish. Ockham's Razor says so. :)

Good luck Frank.
 
I wouldn't say that bent valves are ruled out...

You say you did not have bent valves 6 months ago, but on the other hand, the car was running 6 months ago, so something has changed. Have you had a high-RPM overrev? Possibly a missed gearshift? In these cases the valves can float and smack the piston, bending them.

It is also possible that the cranking has washed down the cylinder walls and messed with the ring seal, but if you only saw a few lbs of improvement with oil down the sparkplug hole, I wouldn't consider that a realistic possibility.

If the engine got progressively harder to start/run over a period of several weeks, I'm leaning towards burned exhaust valves, possibly as a result of out-of-spec valve clearance.

Another more remote possibility is wiped-out cam lobes, but I doubt all 4 cylinders would go at once. Ditto for weakened or broken valvesprings. You can pop off the cam cover with just a few bolts to observe if the valve action appears functional, that'd be my next step in the absence of a leak-down tester. You can also verify cam phasing by dropping a screwdriver down a spark plug hole and watching it go up and down, along with the valve action. Turn the engine over only by hand if you do this.

And as Jim says, it might be cheap insurance to try a different compression tester. But if you were already having problems with the car...

Pete
 
ok

Thanks Pete,

I will check the things you recommend and will check the compression gauge on another car tomorrow. that will at least show whether my equipment is fine. I will keep you updated.

best,

Frank
 
Valve clearance.

Now we are getting somewhere. I suspect that the valve clearance is low or non existant, this would cause the valves to burn and slowly loose power.

Will an engine start at let us say 60 PSI compression, yes. Can you load it, no. I suspect that you will have to pull the head, check the valve guides as they too can be worn. Repair and replace as nessessary.

TonyK.
 
You must log in or register to reply here.
Back
Top