It's been about 3 years now since I changed the headgasket on my car. Yesterday it decided to go again. The failure this time appears to be a water passage on the exhaust side of #3. The gasket appears to have come apart. There are witness marks in the gasket that look like it got hot. The temperature gauge never actually got hot but it could be due to the exhaust gasses creating some sort of air pocket. I was hoping to get some advice on contributing factors to my falures.
Relevant information:
L20b 0.5mm over
W53 head milled a bunch
Pontiac Fiero radiator (I think the thermostat housing is higher than the radiator tanks)
Radiator filler neck hose run to a reservoir
Weber DCOE 45s (the manifold does not have water passages)
Electric fan with thermostatic switch at about 165 degrees located in thermostat housing
In the pictures you can see the gasket falure location between 2 and 3 cylinder. Notice the discoloration of the gasket between the 2 cylinders.
Last edited by D52E on 25 Jul 2017 11:23, edited 4 times in total.
Could be the gasket quality but if it blew there before, I would look at the head not being perfectly flat. A high spot here would be all it takes.
It did blow on the block surface side so inspect the block for erosion. Are you using anti-freeze coolant????
Check the block bolt hole threads nearby. Are the head bolts bottoming out on debris in the hole and reading full torque but not clamping the head down?
L20B with un-milled closed chamber head is 9.8 compression. If it has been shaved it will be higher.
"Nissan 'shit the bed' when they made these, plain and simple." McShagger510 on flattop SUs
Head looks sorta semi-closed, plus they have a bunch of unshrouding around the valves.
Because when you spend a silly amount of money on a silly, trivial thing that will help you not one jot, you are demonstrating that you have a soul and a heart and that you are the sort of person who has no time for Which? magazine. – Jeremy Clarkson
I had a mystery head gasket failure once on my wagon - same spot. As it was an EFI conversion, and the day I diagnosed the blown head gasket, I was to be headed out from Vancouver to Edson to watch the Big Horn National Rally.
I picked up my buddy Malcome from work, stopped at Lordoc and picked up a new gasket and some paper towel and a 5l jug of oil. We hit my fathers place 10k down the road. Left the manifolds and all electrical on the head, just broke the exhaust connection and drained the rad. Placed the wood block down the timing chain. Lifted the head and changed the gasket in situ. As the motor was only a year old since rebuild, nothing was very stuck. But the failure was clearly in the exact same spot as yours. We cleaned it all up best we could with acetone and put the new head gasket on. Torqued the head and we flashed the motor before the block had cooled down. I often wondered if the heat effected that torque setting, but it wasn't exactly hot so I wasn't worried. Ran the motor till it was warm. Shut we down and we cleaned up. The system held pressure, so we Changed the oil/filter (I always keep a few Wix ones at home) and we were down the road less than 2 hours after driving into dads driveway.
This second gasket outlasted the motor to my knowledge as the car changed hands from me two years later and went through 3 more owners until the motor apparently outlasted the car.
Cause of the failure? I'm guessing in my case it was likely a dirty fingerprint on the block or gasket. It's the only head gasket failure I had on a motor I built, and there has been more than a few.
My advice would be to watch that track already worn in place on the head, and make sure it's also not or roses or cut into the block, and I'd think you would be good to go.
Byron
Love people and use things,
because the opposite never works.
Thanks for the feedback.
I am using antifreeze 50% mix in my car.
Visual inspection of the block looks OK. I will have to try and borrow a straight edge and check for warping.
The head was measured to be less than 0.003" variation in flatness in the center. I do believe the spec is 0.003". (the 0.002" feeler gauge would fit but the 0.003" would not fit).
I will chase the block threads and confirm the bolt length without washer before re-assembly.
Block and head will be carefully cleaned with scraper and acetone before re-assembly this following weekend.
I had a Fel-Pro leak water along the spark plug side but I think the head bolts didn't torque properly 'cause there were no imprints on the gasket for the water passage holes.
I too are using 280ZX turbo head bolts but since I don't know how many times the bolts had cycled, I purchased new from Nissan Parts Deal. The new bolts came with the part numbers associated with the turbo engine, but the long bolts do not have the circle on the head of the bolt but rather a 13 on the head. The short bolts do have a circle on the bolt head. Do you have the same?
Stock L bolts are totally reusable if not damaged. I see no advantage to stronger turbo bolts where the stock ones are more than adequate.
My L20B ('78 620) mysteriously blew between #3 the water jacket and out to the spark plug side. Cold, at night and the steam out the exhaust covered the street curb to curb. Water was spitting out above the starter. Left the manifolds and carb on, lifted enough to softly wire wheel both surfaces, $23 NAPA FelPro bolted together and worked perfectly.
"Nissan 'shit the bed' when they made these, plain and simple." McShagger510 on flattop SUs
Car is back together. Seemed to run ok on the test drive. I will report back if any issues come up.
I also checked the thermostat just in case. It is a 180F unit that opened at 192F (tested in pot of water on stove). I left it out for now. I will put a new one in when the weather gets colder.
I have an update. The car has not run quite right since the head gasket was replaced. The idle and off Idle have been a bit hesitant. I spent a couple hours today looking at it. The number two cylinder seemed to be running lean. I did the usual check for compression and found about 145 to 155 PSI on all cylinders. This seems a little bit low but I suspect my camshaft could be part of the reason.
Anyways I have weber DCOE 45 carburetors and I noticed that no amount of tuning would change the RPM at idle for cylinder number two. I proceeded to disassemble the carburetor to clean the idle circuit with no result. I kept looking around and scratching my head for a while. I ended up finding the PCV valve that is plumbed to runner number two had fallen apart and allowed a large vacuum leak. I speculate this could have created a lean condition contributing to high cylinder temperatures and damaging my head gasket originally.
