Compression Test - Blown Head Gasket?

There was some smoke coming out of the valve cover breather only (not out of the tailpipe) so I did a compression test.

Since the pressure in the 5 & 7 cylinders did not increase with the wet test, should I assume the head gasket is at fault?

The TA Performance heads and engine rebuild have about 700 miles and 1,500 miles on them.

Once the head is off, what else should I look at for signs of damage or component failure?


CD=Cold Dry
CW=Cold Wet
WD=Warm Dry
WW=Warm Wet

 

Smoke out of a valve cover usually indicates a cracked piston or broken rings....

 

There is very likely to be a chunk of the headgasket missing between the 5 and 7 cylinders. It also could be a ring thing, but I’d be surprised on a fresh, but broken in, engine.

 

Sure looks like it by the numbers and positions.
Question is why?

 

My guess would be assembly error. As careful as I was, the engine was still in the '72 Riv and I may have unknowingly scraped the gasket with the head

 

Well that's not hard to do . Considering you had to hold a 70 LB cylinder head across the fender about 3.5 '.

 

Definitely going to ask friends for help this time! I'm just crossing my fingers to see obvious gasket damage and not a cracked piston

 

To assist installing a head while in the car, put a couple long studs in the block,it will position the gasket and make it easy to put the head on. Then put some head bolts in and remove the studs.

 

Never thought of that, great idea!

 

Excellent tip; thank you!

 

Did it a few times in the last 50 years.lol

 

IF the gasket popped between those two cylinders, you'll need to verify the flatness and smoothness of both the block and head. I'd also verify that the plug wires are properly routed--including being separated as much as practical. Cross-fire between 5&7 is as bad as it gets, worse than any other.

Last time I popped a gasket between the cylinders (#3 and #5, TBI SBC) the combustion heat blowtorched a gouge into both the head and the block.

 

Thanks Larry , went back and read. Yes he wrote TA about the heads. My bad, Yes Big weight savings.
Still a big car and reach across.
What's the weight of assembled 455 Aluminum TA heads, 40 to 45 LBS ? And cast iron 70 LBS or 75 ? I dont know, just guessing.. My memory is not as good as once was...
Larry that's a great idea using bolts like head studs, I guess you mean to line up the head so not to slide it across the gasket.

 

The wires for all cylinders are as far away from each other as I can keep them all the way up to the distributor...wire loom bracket on the valve covers and then separators before the distributor. To check flatness, is it as simple as just using a straight edge and the thinnest feeler gauge or should I rig up something where I can use a dial indicator?

I felt like one fully assembled iron head weighed as much as both assembled aluminum heads

 

If it is a blown gasket then with a Aluminum head you should get it cut even just .003" just to be sure things are right.

This finish needs to be mirror like to get the best head gasket life and to this end you should yank the head on the other bank of cylinders to do the same.
Try to find a shop that uses a old type stone/ wet mill, or a modern Dimond type mill.

After the mill your is done be sure you lightly roll over any sharp edges of the lip of the chambers that stick out passed the heads gasket fire ring thereby eliminating any chances for hot spot induced ping or knock.

 

What type of head gaskets did you use?

I’ll have to disagree with automatic head resurfacing. If it needs it, it needs it. If it doesn’t, it doesn’t. Back in my wrenching days, I replaced MANY head gaskets on all types of engines, AL heads, iron heads, AL blocks, iron blocks. 100’s of them. My back still hurts.

 

I used the felpro 1125 performance gasket; Cometic C5754-027 are the replacements.

I'm not sure the problem was the head gasket though...I don't see any obvious signs of failure (broken or missing material).

 

Smoke out of the crankcase is usually from excessive pressure build up.. you likely have a broken ring or a cracked piston. Keep digging.