Hi All,

Well I found my mis-fire in cylinder 5, it was a blown head gasket. The head gaskets were last replaced by me in June of 2018, 20k miles ago. Elring gaskets with ARP studs.
Check out the picture. Something blew right through the metal ring and the top of the head gasket.
- Engine has not overheated. I have the in-line mod and temps never go over 200f
- Right before this happened, I got a 'trans overheat' light whilst going up a mountain highway in Western Carolina. Never saw this before and had to look it up.
- After getting home, less than a week later I got the mis-fire in cylinder 5

So this is my current theory: I have a clogged cat that created too much back pressure that blew out the head gasket. I say this because the drivers cat is right next to the transmission pan, and cylinder 5 is the closest to the cat through the header.

Would love some thoughts on what could blow a hg like this, and whether the clogged cat could be a viable cause.

Thanks,
Jamie

Blown HG on cylinder 5. Blown area is top of HG.

 

That sucks. Is your liners moving up and down any ticking ??

 

Nope, no ticking and no indication of liners moving.

 

Maybe something in the torque sequence didn't sit right?? It seems pretty strange that combustion pressure would do this, although a plugged cat makes a lot of sense. I would think you might have seen additional codes prior to a catastrophic event however. Something caused the gases to channel out through the gasket but at least you have a smoking gun, now to figure out the cause.

 

Yea. I'm stumped. Previous HG failures were all related to an overheat. Not this one though. And where it blew is odd.
I ordered the parts I need for the HG job and new cats/downpipe. Hopefully this $500 will get me a few more years out of her.

Was talking to a local indy mechanic about this, and he told me that he had a car in last week where the back pressure from clogged cats destroyed both turbos on a Mercedes.

 

I was going to ask about a previous overheat. Did you have the heads milled after the last one, specifically that head? Maybe there's an inconsistency that led to venting.

 

I did. Sent them out for a clean and decking.

 

That looks like burn through,not water or liner related,but rather running lean and getting detention. Low octane bad fuel can do it too.

 

My guess was heads not flat also, but now I am going to go with torque inconsistency. I got about halfway through torqueing the studs on an engine and stopped, did not like the way they felt.

The LR head bolts are NOT torque to yield, torque to yield bolts have a necked down portion on the shank, the LR bolts don't. They are torque to angle. The purpose of that is create a specified gasket compression and thereby pressure capability. The angle translates in to a linear compression dimension. The instructions on the ARP studs are torque to force, that introduces variance in the gasket compression dimension and thereby pressure capability. Torque is a factor of thread and flange friction, which is a factor of the stretch force. On top of that, LR did not make the bolt holes deep enough, only 1 thread clearance when fully tight. The studs are screwed all the way to the bottom (or in my case, I left them 1 turn loose so they were not on the bottom). So if during torquing the stud turns instead of the nut, it puts that force on the bottom of the bolt hole. That can be an issue.

Studs are used on top fuel or other high boost applications. Top fuel is for quick changes.

Also, when we design machines we leave 3-4 threads clearance at the bottom of the hole to allow for manufacturing tolerances. LR left 1. This can be an issue if your heads are cut, I use ARP hardened washers under the bolt head if the heads have been cut. Back to the studs, if you run the stud to the bottom of the hole, then it turns, what happens in the hole?

On a block with no known cracking issues I would not worry about studs, but the LR block concerns me due to the thin wall casting. My BIL also has a block that studs pulled out the threads.

I have done a dozen HG jobs, never had a problem with LR head bolts, but I always chase the bolts holes, and lubricate the threads and the flange surface with grease.

Counterpoint: J. E. Robinson likes the use of studs.

https://robisonservice.blogspot.com/...rover-v8s.html

I respect their blog immensely, they provide an lifetime of service experience to their analysis.

I provide the perspective of a engineering degree and a career in design and maintenance engineering on multi million dollar equipment combined with my LR experience. He has done 10x the number of HG I have.

You decide which way to go.

 

I've used studs on the majority of the trucks I've owned..Have put way more than 20k onto studded motors, I consider it a "fix" to the motor.

However....
I "race" MINI Coopers.

They don't blow head gaskets very often, but we do burn through pistons!

Usually by high load knocking.

Sounds like you may had some preignition on that cylinder causing a hot spot, maybe a not so great injector leaning out that cylinder and while you're running up the mountain started eating away at the head gasket, heating up and warping the metal, and ultimately blowing the head gasket.