All Small Six Big external coolant leak on new head gasket

This relates to all small sixes
DannyG said:
As others have stated, if the head bolts are too long, they will bottom out and give you a false torque reading while the head remains untorqued.
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It's got ARP head studs. Checked the length by marking the bottom ~3 threads of the studs with a paint marker before we dropped the head on. The painted threads weren't visible with the head on. These use hardened, kinda thick washers under the nuts, so I'm certain we're not bottoming out on the available thread.
 
End of Saturday update.
As a reminder, 9am next Saturday this thing needs to be doing laps in beautiful Buttonwillow, CA. Any and all options are filtered against a need to have this thing on a trailer by Thursday afternoon to pass tech on Friday to do laps on Saturday and Sunday.

So, head gasket is just straight blown. GM magic tablets seemed to seal it for a bit, but then it got back to bubbling a bit out the side once things got really hot. Also, definitely have combustion gasses pressurizing and heating the water. While breaking in the cam we could only run it about 5min at a time before it'd hit 210-220. The radiator would start puking at like 210, which tells me it's pressurizing like crazy to overcome the 20psi cap.

Next thing we're doing is to just hit it with Blue Devil headgasket in a bottle stuff. If that seals we'll just send it. It's suboptimal, but things just get weirder if we go further down the diagnostic and parts-swapping rabbit hole...

If the Blue Devil doesn't seal, then I've got a previous "race" head that's milled for compression I could swap in. It ended its last race with a blown HG or maybe a cracked block or something. It was running stupidly hot if we got above like 3500rpm, then the #1 rod went though the side of the block.

Tricky part is ^^^ that head was milled for compression with stock pistons. With my current 255 pistons it'd give like 10.4-10.5:1 static CR, but with the 274/274 108 LSA cam the dynamic CR should be around 9-9.1. Pretty aggressive, but I do have access to race gas (and octane booster). Doing just a head is attractive because we've got that down to about a 2 hour job.

Next next option is to swap to a backup craigslist-sourced bottom end that "was running". I can drop the shaved head on that and have decent compression, etc. It's just a lot of unknowns (literally) stacked atop each other. That's also an ~8 hour job.

I still have no obvious root cause, but the following are possibilities:
  • Head is not level. I think no because: It was milled, straight edge shows no warp, resurface-on-glass action showed no obvious warping/high spots.
  • Block deck is not level. Didn't have this one decked, so might be the case. I kinda think no because: I checked it with my straight edge and wasn't obviously off, but side-to-side is tough to gauge. Wouldn't trust it 100%
  • Head studs are stretching/yielding/otherwise not clamping. No indication other than poor HG sealing. If true this would explain like everything. I do have a different used set I could swap in.
  • FelPro made a bad batch or change to gaskets. Normally I'd be reluctant to even consider this, but I'm on a streak of like 4-5 failed FP gaskets at this point. Again, if true this explains everything. They're just way more available than Mahle or Victor Reinz. Anyone else recently have FP HG issues?
That's all I've got for now.
 
Weird Sh*t have you had the head/block cracked checked (zyglo).
Super cheap sorta works sometimes DIY check use a spark plug adapter to your air compressor. Use max pressurize one cylinder at a time and look for bubbles in the radiator
 
So if there are no cracks in the head or block. I once had a very weird thing happen on my 77 Maverick 250 not to long after I got it was very low mileage and only about 5-6 months old. Because of front end damage I had replaced the water pump with a rebuilt one, installed a new Radiator, and all new Hoses. Right away I started having issues if I drove it more than 62 MPH it would push the coolant out of the overflow tank and than quickly overheat. I couldn't see anything wrong externally and tests didn't show a problem. Finally I decided to pull off the water pump and look at it good. The Water Pumps Cast Impellor was completely gone. Put a new water pump on it this time and my over heating troubles went away. Yet all the engine overheating had done some damage to it and later on I needed to replace the head as the guides were really worn out from it running so hot and it was also cracked in the center too that just got worse with use. Best of luck on getting it ready to race.
 
mad_science said:
So, head gasket is just straight blown. GM magic tablets seemed to seal it for a bit, but then it got back to bubbling a bit out the side once things got really hot. Also, definitely have combustion gasses pressurizing and heating the water. While breaking in the cam we could only run it about 5min at a time before it'd hit 210-220. The radiator would start puking at like 210, which tells me it's pressurizing like crazy to overcome the 20psi cap.
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It looks to me that you are fighting detonation as one of the problems.
I would run a higher-octane fuel just to take that problem out of the equation.
 
For once I have a good update: It lives!

This morning instead of embracing the Blue Devil, decided to re-torque the head studs/nuts one more time, loosening and re-doing one at a time. Figured what the hell, it's free and we've got nothing to lose.

Set the wrench to 85 and did them all in the proper order, one at a time and it held.

It held all day today while debugging other stuff (fuel delivery and a blown rear main seal). But test drove it a bunch and temps are holding nice and low. No pressurization of the cooling, no water in oil, no water leaks at the HG.

I think from now on my spec for a FelPro HG with ARP studs is 85-90lbft. All along the symptoms matched under-torqued HG, so it's not that surprising that more clamping helped.

Now we need to see if this holds while we flog it for hours at a time on track. Full throttle 3500-5500rpm for hours at a time in 90 degree heat...what could possibly go wrong?
 
Going back 20+ yrs I remember a slight torque value variation when using ARP hardware AND their recommended lubricant. I do not remember if it was specific to the engine I was building or whether it was pertaining to the head or the mains when using their stud kits. Glad you got it to behave.
 
sixtseventwo4d said:
Going back 20+ yrs I remember a slight torque value variation when using ARP hardware AND their recommended lubricant. I do not remember if it was specific to the engine I was building or whether it was pertaining to the head or the mains when using their stud kits. Glad you got it to behave.
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I remember the same thing. The clamping force comes from the bolt stretching. A stronger bolt will take more torque to stretch it. However, I suppose a finer thread pitch could effectively increase the number read on the torque wrench.
On rod bolts a stretch gauge is preferred instead of a torque wrench.
 
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