ARP head studs came loose?
 

Hi guys and girls,

First thread, please be gentle. I've built my motor to find that after warming up the car starts burning coolant.

No discernible cross-contamination between oil and coolant, idles and revs nicely. On a whim I thought I'd check the head studs. Engine was assembled to the recommended 65ft.lb in 3 stages with Cometic head gasket using ARP lube. Machine shop skimmed the block and the head. Threads were cleaned with brake cleaner and a brush, and the studs ran smoothly into the block. Mating surfaces cleaned with acetone. Nevertheless, after an hour of running I found 3 studs around cylinder 2 that took an extra 1/8 - 1/4 turn to get back to 65ft.lb!!

What the hell could have caused this? I was careful during the build to the point I went back around probably 3 times and clicked the wrench to be sure I got all of the important fasteners.

I guess the important question is, what next? I suppose the head gasket is trash now, so I'll replace that, and I'll confirm that the head and block are flat before reassembly.

Pretty standard to re-torque head studs after first heat cycle; I have always done it on every rebuild. I don't think you have any issue there.

Re checking is pointless unless you loosen first and make one complete turn without stopping until torque is met. When you stop the nut needs to overcome the "stiction"(is that a word). I've never loosen again after first heat cycle.

Static friction is the word you’re looking for.

never had to retorque head studs, something’s definitely wrong with the assembly. Do yo have dowel pins in?

@curly Yep, dowel pins are in, and the head and gasket were definitely seated into them.
@Erat Noted, thanks. I'll be especially careful on re-installation.
@tomrev Interesting, I've read many differing opinions on the matter.

Head comes off tonight. Any tips on what I may be looking for?

My impression is that retorquing head bolts is something required for old cork/etc head gaskets, not MLS.

--Ian

Dont quote me on this but I've heard people torque them to close to 80 ftlbs with the cometic head gasket.

ARP is specific on the torque #'s, and point out they want you to use their lube when doing so. Oil, etc. on bolts, or studs/nuts will have a different "slip" factor, and can change the ultimate torque value by quite a bit. The finer pitch bolt threads on a ARP type stud require less torque than a courser, stock bolt to achieve the clamping force, so sometimes that confuses things when people are reading the factory specs. I guess you already have it off by now, but did you run a comp. test? As Erat said, I back off each nut ,just a half turn, one at a time in the bolt sequence, and re-torque after my first start up and run to temp. Anyway, hope you see something; nothing worse that not knowing why things went South. ( or maybe North in this case).

What method/sequence/steps did you use for torquing?

Did the studs get installed in the block dry (no lube) lots of people see the assembly lube and think it goes on all the threads.

None of the Miata head studs are into the water jacket are they? I can't remember. Been working on SBCs too much lately.

No

Most of us use a Mazda head gasket.

I prefer Honda gaskets on my BP but thats just me.

Interesting. I use durex gaskets on mine.

Raw dog checking in here. gaskets are sooo post aircooled VW.

So, the head is off, and unfortunately there are no clues there. Studs came out clean and smooth, no evidence of stripped threads on the studs or block. Pistons and chamber were quite oily, but I'll chalk that up to having crushed the turbo drain on the PS rack on installation and flooding the intake and exhaust with oil. Perhaps some oil was leaking into the cylinder via the head gasket, though the blue smoke cleared up immediately after fixing the drain. Anyway.

Torqued up in 3 stages (20, 40, 65 from memory) in an outward spiral per the ARP slip and FSM. Went with the Cometic because of the overbore (83.5). Put a little oil on the threads going into the block for some corrosion protection. Each stud farted the air out as it went down and I nipped each one up with an allen wrench. Liberal application of the included ARP lube on the upper threads, washer and shoulders.

The only thing I can think of, is I had a water port on the back of the head welded up, but the head was submerged in a bath for cooling and checked to be true at the time. Perhaps something shifted then relaxed again after heat-cycling causing the stud to "come loose". This was at the rear of the head though.

Read about the 80ft.lb thing at length. Definitely aware of the confusion surrounding that one.

I have a straight-edge coming in the next day or two. If things check out I'll whack it back together and send it. If not, I know a fabricator getting slapped.

Thanks for the feedback guys, this noob really appreciates it. This forum is fantastic.

Sounds like you did a careful, proper job on the install. Was your initial worry about the thing that it was definitely burning coolant? Only thing I do different, and it's super minor, is to use pipe sealer on the studs (into the block), and not tighten them all the way down, but let them stay a half turn or so loose. Seem to remember instructions from ARP, and Raceforce studs, or one of my engine builder mentors saying that helped, but now I don't remember exactly why, so can't say; I'v just done it that way ever since. I don't think I'v ever re-checked head nut torque and not had a few turn a little more, and this with engine running fine. Hope 2nd time's the charm!

Thanks for the insight @tomrev yep, this whole thing started from the lost coolant. I kept trying to convince myself that it's just condensation, high humidity, whatever. Glad i checked it out, as inconvenient as it is I'd hate to have caused more damage.

I have some liquid sealant, perhaps I'll give that a shot. I would have assumed that once the threads in the block are pulled up with torque from the nuts that slipping wouldn't be an issue. Then again, everything about this build is brand new to me. About the most technical job I'd performed on a car before this rebuild was a timing belt. Thanks again.

Well. Put in a new head gasket, and confirmed that the head and block were straight with a new straightedge. Couldn't even squeeze the 0.0025 feeler under at any point.

Buttoned the car up and she was idling great, no emissions, then the moment I hit the street, this started. Clouds that a vaping WRX driver would be jealous of.




A local mechanic was kind enough to lend me his hydrocarbon tester, which came up negative for a combustion leak into the coolant. I'm ringing around for a cooling system pressure tester, and I'll have leakdown and compression testers after Christmas.

Interesting thing though, during the hydrocarbon test there was no emissions from the tailpipe. Brought the car up to operating temp, still no emissions. Spark plugs look normal. Seems the issue only arises once at temp and the cooling system is pressurised.

My thinking leads me to a cracked CHRA. There's nowhere else for coolant and oil to mix, and it isn't mixing with the oil or vice-versa inside the motor.