[TR] TR4A - Head Gasket Blown Sanity Check

Guy Huggins guy.huggins at icloud.com
Wed Oct 6 08:42:12 MDT 2021

Greetings from Texas,

So there I was… about to take an evening drive, and the car wouldn't start.
I have been having some issues with this recently (suspect I have a parasitic drain), so I rolled-started the car down the driveway.  I remember it being a hard start, but the engine came to life.

As I drove down the street, the car was running very, very roughly.  When I turned onto the main road, I immediately pulled into a parking lot to check it out.  Then I saw it… clouds of steam coming from the tailpipes.  Dammit!!

I got back in the car and was in my garage in less than a minute.  Suspecting a catastrophic issue of coolant pouring into a cylinder, I dutifully pulled the plugs to perform a compression check with the engine still warm.  #3 plug was soaking wet.  All compressions looked good and held for over a minute, save #3, which was reading at 72 ‘ish.  Found the problem cylinder.

I recently pulled the head off, and sure enough, the gasket had been “pushed” into the water jacket space between #3 and #2.  A closer inspection revealed that none of the “fire rings” of the gasket were ever perfectly aligned over each cylinder, leading me to believe that maybe I did not get an appropriately sized 87mm gasket, or the torque-down didn’t go perfectly, maybe somehow skewing the gasket in the process.

The good news is that I got almost 10 years and 22K miles before this happened!!
I’m a little disappointed seeing how when I rebuilt the engine about 12 years ago, I had the block and the head mating surface machined to be flat.

Now to the sanity check items…

Fo8 Gaskets - I have refilled the water jacket, and it remained at the same level overnight. I assume they are still 100% sealed.  Is this a safe assumption?  Also, #2 liner is prouder of the block than the others (by feel), but I haven’t measured by how much yet.

Pistons & Liners - I poured 1/2 cup of fluid onto the top of each piston and it remained there for an hour until I removed it.  #2 did drain out more than the others, so I know it is not perfect, but none of them are completely fluid tight.  This tells me the pistons and rings are OK, confirming the last compression check numbers.  Is this reasonable?  
Also, what is the best why to clean carbon from the pistons?

Head - I am planning on cleaning it up and checking for it to be flat with a straight edge.  Is there anything I can do to check the valves while I have it off?  Again, the compression check suggests they are fine.  
Is there a safe way to clean off carbon deposits from the valves themselves?

Pushrods - If they are straight, I plan to reuse them

Replacing - I plan on replacing all gaskets and head studs.  I could use recommendations on the best 87mm head gasket out there.  The one that blew was a copper Payen gasket.  I also installed it with some copper gasket sealant (spray on), which I wonder about, as there are clear imprints and residue on the mating surfaces that I somehow have to clean without harming the surfaces. Any suggestions for this?

My working theory is that some serious detonation occurred in #3 on the roll start, and the gasket gave way to the weaker side, into the water jacket space.  Compression has historically been in the 160’s for each cylinder, 180’s when freshly rebuilt.  I can’t help but wonder if this is just too damn high, and the gasket’s fire rings are all out-of-round because of this, as opposed to my earlier thought about them being distorted due to the head being torqued down.

I have pictures to share if anyone would like to see them.

Thanks in advance for any thoughts and comments you share.


Guy D. Huggins
1965 Triumph TR4A
CTC 63569LO

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