Six7390gt

Leif,
All of the above are good suggestions for cleaning your threads. I'll add that I'd use a spiral flute tap, compressed air and brake clean to clean them. Once you have them clean, I would suggest using Nord Lock washers to maintain the torque on your intake fasteners. Before retiring I spec'd these extensively for industrial applications as I was designing high capacity offshore hoists and winches. I believe Nod Lock's patent may have expired, and you can now find copies called wedge lock washers. One of the Nord Lock reps brought in a junkers vibration testing machine for our Engineering group to see - and the Nord Locks are impressive at not letting fasteners vibrate loose. We had zero issues reported with them in the field, and they are reusable They're a bit more expensive than standard lock washers, but IIRC a 3/8" Nord Lock will still be well under a dollar. a video demonstration of the junkers vibration test performed by by Nord Lock:

scowser

You mention tightening the threads dry. But aren't torque specs set for "lightly oiled threads"? I've found that, if you do it dry, they tend to gall.

leif.anderson93

Gary,
I'd, actually, thought about Nord locks versus the plain, hardened steel washers that are one there now. Probably going to go that route. Thanks for helping me make the decision.

Vettrocious

Torque specs are set using the parts as they arrive in the lab “as manufactured”, in order that the torque spec be applicable to the actual assembly of the production vehicle. No one oiled anything for any test. It would have changed the results dramatically.

In this case, the torque testing was probably done without cleaning the heads, they probably had some machine oil in the threads remaining from manufacture, or maybe, if the engine plant cleaned them as part of manufacturing, soap residue from the part cleaning process, or maybe they were dry. The bolt also had a coating, but not just oil, The bolt might have had Phosphate coating, dipped in oil, or might have had phosphate and paint, then dipped in oil, or any one of ten other finishes, all of which varied by manufacturer.

The testing engineer knew all this, but did not care about any of it for purposes of the test. If bare steel galls against bare cast iron, so be it. In my experience, sometimes it chatters, (a precursor to galling), but not really the destructive process called galling. In any case, if it was going to gall or chatter in production assembly, it had to also do it during the test. The objective of the test was not to eliminate that galling for the test, it was to provide a practical specification for the plant to assemble the parts when they arrived from the supplier. So, we tested it as delivered to the lab.

We didn’t add oil, because, in production, the plant wasn’t going to add oil to make a nice slippery joint. The plant was going to tighten them as they arrived and the engineers’ job was to validate that real production, not create an ideal test.

This all matters because:

60 years later we can’t know what was tested to arrive at the production spec. My advice to use bare surfaces above was intended to remove the variables, and provide frictional surfaces on the bolt and head threads that would have about mean friction. When the bolt is tightened to the mean production spec it is then very likely to fall within the range of the production clamp-load, which is all that’s important for you when trying to keep the manifold sealed.

Vettrocious

Before you go to the trouble and expense to add Nord locks, I’d make sure that the bolt heads are actually turning in service, thus causing the reduction in load. If they’re not, the Nord locks do nothing.

67:72

Actually, any lubrication on the threads will tend to over-torque the fastener. If lube is used, the torque settings need to be lowered something like 20-30% - I forget the specific "rule".

slammin

I've always used clean dry threads when torqueing most bolts, especially lug nuts.

Vettrocious

There is no “rule”, it varies with every fastener and every joint. Only testing works. If you want a generalized rule, it’s that the slipperier the threads (and under head) the more clamp load results ata given torque. Conversely, high friction surfaces (such as bare zinc) result in lower clamp-load at the same torque. You can’t put a percentage on it.

R66

This may make this discussion a mute point, but experience has taught me to put a sealer (not LokTite or thread locker) on all head and intake bolts to prevent oil and water from wicking up around the bolts and appearing on the intake or contaminating the oil in the valve covers.

Regardless of the sealant, it lubricates and reduces the torque required to obtain the clamping force of the original specified torque value and thus gasket compression. As Vittrocious has stated, the exact change in torque applied should be determined by testing prior to the installation of the bolting. Testing generally includes clamping load, bolt stretch, and bolting material yield measurements, at least in the Nuclear industry.

Our application does not even come close to taking the bolting in any application to yield, thus stretching the bolts. Most bulk bolting comes with some lubricant on it to prevent rusting. I doubt GM removed the oil before installing the bolts on the engine assembly line. I don't know if GM used sealant on any bolting.

Hardened flat washers and lubrication are recommended under the bolt head for most bolting to obtain accurate bolt torques in structural applications. I use them on head bolts to prevent the cast iron from cracking which occurs quite commonly at the outer holds under the exhaust manifolds due to the friction between the bolt head and the cast iron during the torquing. I also use them on the intake bolting to prevent galling of the aluminum around the bolt head. It is just good practice in my opinion even though GM didn't spend the time and money.

Both head and intake gaskets are going to compress during the heat cycles of the engine and thus become thinner. The bolt does not stretch or loosen, it just looses clamping force due to the gasket compression. The GM Chassis / Overhaul Service Manuals require re torquing of head bolting due to the loss of clamping force. Aluminum manifolds expand and shrink (coefficient of expansion thing) more than cast iron and thus compress the gaskets more. After one or two retorques, the gaskets become thinner and harder and thus do not compress as much with each heat cycle. and eventually eliminated the need to retorque again.

Now, I don't know if sealant was used on your bolting, but if you are adding sealant, I would clean the bolting only and install new sealant of the same type for installation - just personal opinion. I would not worry about cleaning the hole - just personal opinion. The last thing I would consider is using a thread locker (LokTite) on the bolting as the bond will be broken when you do the required retorque - fact. Any retorque will be inaccurate as you have to break the bond between the bolt threads and cast iron theads - personal opinion. This assumes you are using a torque wrench to tighten all bolting in the correct sequence, if not, wrench tight the bolts and have a beverage - personal opinion.

Ron

leif.anderson93

Ron,
After much reading (and, a lot of great info here) here's what I did last night. I removed the carburetor and ignition coil to get best access to the intake manifold bolts. When I had the heads off in 2019 for a valve job (and some other stuff), I had applied a sealant to the bolts for the exact reasons you state. That was 27000 miles ago and I had never gone back (after several heat cycles) and re-torqued everything...shame on me. Well, all the bolts had lost their clamp because of gasket compression not bolt loosening. Most of the bolts took a quarter turn of the torque wrench (some a bit more) to return initial torque to 30 lb ft. I re-torqued all 12 intake manifold bolts, re-installed the carburetor and took her for a 10 mile drive. She run's flawlessly.
I'm going to run her like this and see how it goes. Thank you for your insight along with Mike and everyone else.

Six7390gt

https://www.engineeringtoolbox.com/t...ts-d_1693.html

R66

Leif,
In order to verify I am correct, I would have to ask my wife's approval, but I think you are on the right path. 50 years ago, I would rip the heads off and reinstall them in less than 8 hours. These cars were daily drivers and we didn't get hung up on bolt cleanliness or torque except for head bolts, rod bolts, and main bolts. Never had a rebuild fail with that BUBBA head job.
We just have too much time on our minds and love in our hearts for these "Damned Old Chevies" and treat them better than we treat our wives.
I think you did the right thing, but no warranty implied.
Ron

CCrane65

I bet you can get a thread chaser from O'Reilly Auto on loan.

DansYellow66

I tend to use a pretty thick gasket stack on various areas of my cars - extra thick cork/steel reinforced valve cover gaskets sometimes for rocker clearance, double oil pan gaskets due to full windage trays, highly compressible intake gaskets, etc. My hemi takes a lot of care with gaskets. Changing the intake gaskets takes typically at least 10 rounds of re-torquing before they stay at torque (many small dia bolts in vertical plane with .060 gaskets). The oil pan has a full perimeter flange windage tray so two gaskets are involved and several rounds of retorquing over the first few weeks. I use steel reinforced cork gaskets on the valve cover that after changing probably take 15-20 re-tightening rounds over 3 months before the gaskets reach their equilibrium. I can torque them initially and go back 15 minutes later and the nuts on the studs are not even finger tight. I’ve used stud and nut kits in most places. I retorqued the L72 intake on my 427 last fall 4 or 5 times before the bolt torque and gaskets reached a state of equilibrium. Most gaskets shrink and take some retorquing unless they are metal shim gaskets. I think this is a lot more common than bolts backing up.

boxster99t

. Ehhh, what did he say? It was on mute

It's a moot point, and now even my comment is moot. (Just one of my grammatical pet peeves, as a retired lawyer, is hearing or reading someone use the word mute for moot).

scowser

Thank-you for the link. It's very interesting and incredibly detailed.

Another question now arises. When we see the torque specs for a particuler fastener, are these the specs for a dry installation or for lightly oiled threads? Most torque charts I've seen don't mention lubrication but I have seen them where they say specifically that they are for "lightly oiled threads".

jim lockwood

And, just to put a finer point on the matter, "moot" means "debatable", not "silent".

Skip Fix

I'll throw this out in favor of a chaser vs a tap. I have multiple taps that are supposed to be the same size that are in fact a little different in OD some make tighter some make looser threads as they CUT, as well as individual bolt can be different depending on how the threads are made. ARPs are generally going to be tighter that even grade 8 hardware store bolts ion the same hole, much less a grade 3 or grade 5! So using a tap has the potential to cut more metal off and remove thread surface area.

Many torque specs are set and specify what torque with what thread prep agent. be it loctite , oil, dry. ARP gives different specs for motor oil vs their lube. holes -like head bolts in some engines that go into water jackets require a sealant-ARP makes their own for their bolts vs a permatex sealer.

kenba

Funny how some of us seem to want to over think a simple problem.. Buy a tap run it down about half way. blow air in the hole & tap to the bottom. Remove tap blow out again & reinstall the bolt.

67:72

I believe the issue here is that the hole is a through-hole to the inside of the valve train area. Blowing air would force any debris into the engine & oil.

Coat the chase/tap with grease to catch debris and then follow up with a kerosene or similar solvent to clean the threads for sealant and remove remaining grime.