silver86

I did a compressions test this weekend with these results:

Cyl Psi Psi Cyl
1 130 141 2
3 141 150 4
5 139 151 6
7 131 130 8

Aside from the generally poor psi readings on every cylinder, could the increased pressure between cylinders 4 & 6 be caused by a leaking head gasket and thus the cylinders bleading additional pressure into one another?

C4Techie

Leaking head gaskets typically show LOW pressure between adjacent cylinders. My read is that THIS poor engine is just flat worn out.

Keystring

I would say no.

If the head gasket was leaking between cylinders, the pressure would be less, not more.

The pressure on those two cylinders actually looks good, but the remaining ones are a little low. At some point in the future you're probably going to need a ring job.

How many miles are on the engine? It may be due for a rebuild.

silver86

It has 134,000 on it, and it does need a rebuild. Dumping 10 psi from the Vortech huffer probably isn't helping. I don't drive it much (+/- 2000 miles/year) so I'm not in a great hurry to swap it out. It's not a race car, just wanted some more power for my weekend ride.

Bob CTS

Run the test again but this time squirt some oil in the cylinder before doing the test and repost your results, but I would agree with the others that it porbably is not a leaking head gasket.

Bob

89er

If it is not burning oil and has good oil pressure, I would do a valve job. That will probably give it another 100K.

silver86

Doesn't burn oil....oil pressure is good. I'm wondering if this could be a valve/lifter preload problem.....If I over did it on the preload, could the valves not be seating fully?

rick lambert

Absolutely, and the idea of squirting oil in the cylinders before testing again is to either confirm the rings are the problem or point toward a valve (head) problem.

silver86

Ah-ha! No it's coming in to focus. I know that I had set the pre-load on the driver's side using one method, and the passenger side looser, and tightened while the car was running (don't ask me why I did it two ways, I don't know).

The passenger side lifter were ticking, naturally, and I set the lash by listening for the tick to diminish.....So, there could massive lots of variations here.

C4Techie

The amount of lifter preload has nothing to do with cylinder compression pressures.

JAKE

[QUOTE=C4Techie;1558455182]The amount of lifter preload has nothing to do with cylinder compression pressures.[/QUOTE

I see it differently. Excessive preload can hold a valve off its seat, prevent the valve from sealing, cause a rough idle and will result in a lower reading on the compression gauge.

Wish I had a dollar for every post I've read where the lifter pre-load was set too tightly resulting in idle problems.

Jake

silver86

[QUOTE=JAKE;1558458168]
This is exactly where my line of thinking is taking me.....This would also lead to excessive crankcase pressure, even under low boost conditions leading my popped PCV incidences that led me to the compression test in the first place.

The method I used initially was to bring both valves to TDC on that cylinder, and set valve lash by tightening to eliminate up and down and rotational free movement of the pushrod. It should be said that I did not replace the original lifters, cam, or springs. I merely installed 1.6 ratio flat tappet rockers. On the passenger side, I initially set the lash, using the same process, to eliminate strictly the up and down movement in the rod. This led to ticking, and my resetting the lash while the car was running. Of course, it can be hard to hear which rocker is ticking with that blower on there.

Is there a better way?

C4Techie

What you describe is beyond preload. Preload is limited to the amount of lifter plunger travel. If the plunger is against the bottom of the lifter body, the preload is all used up. The valves will not close and the compression readings will be much lower than posted. Whether the lifters click because they are slightly loose, preloaded a half turn, 3/4 of a turn, etc, the compression pressure in the cylinder will not be affected by the amount of preload.

"This would also lead to excessive crankcase pressure" No it wouldn't. Even if the available preload was exceeded and some of the valves were hanging open, there is no connection between either the intake or the exhaust ports to the sump to allow the pressurization of the crankcase.

Dominic Sorresso

First, squirt the oil into the chamber and then check compression. If you need to reset valve lash, do it cold using the I-C/E-O method.
Intake closing, then set Exhaust valve, Exhaust Opening, then set Intake. this makes certain that lifter is on base circle of cam fpr the valve being set. May take a bit longer but I can set them and forget them like this.

coupeguy2001

change your intake gaskets for the excessive crankcase presure, and re-adjust your valves 1/2 turn after they stop clacking. Then for the bad compression, I have an 86 with 130,000 that I put aluminum heads on.
when I tore the old original cast iron heads apart, all of the exhaust valves had little pitts in them........alll of them seats too..... I can't believe how the valves were affected so much by unleaded gas, (not protecting them as leaded gas does).
I replaced all of the exhaust valves in the aluminum heads with stainless valves, and if I keep the car, I might just be able to tell if that's the answer.
I believe that your valves are pitted as well, and your compression is going out the tail pipe along with the exhaust.
Good luck

silver86

Thanks guys...some good info here.

JAKE

Well, I can see where this is going!

I'm not about to get into another one of those "I'm wrong but I can't admit it, so I'll change the the parameters a bit to make me "Right". (Self-Esteem issue)

This is so simplistics it doesn't warrant further debate. I can better spend my efforts helping others. Believe and do what you want; I'm outta here.

Jake

rick lambert

I'll go one further, ANYTIME a valve does not seat properly (hangs open) you WILL lose compression.....period,a burnt valve, carbon buildup on the valve or seat will cause the same affect.....thus the squirt of oil either points toward rings or valve problems. If the oil increases the cylinder pressure you have a ring problem...if it doesn't you need to look at the valve train. Blown head gaskets usually cause an engine to over heat, and usually with a compression test you have two ajacent cylinders with low pressure. The rule of thumb is compression should be around 10% of one another.

silver86

My project for this weekend. Thanks everyone for your good suggestion/recommendation/opinions. I'll post how the test comes out.

silver86

The result....rings.

Tested 3 cylinders:

Cylinder 2 142 143 w/oil
Cylinder 4 150 170 w/oil
Cylinder 7 135 150 w/oil

Didn't bother doing the rest. Instead, polished up my rims, and ran a can of Seafoam......