Jhiltonn

Hi, I'm hoping for some advice on this issue...

I removed my q-jet for rebuilding and I've drained the anti freeze to put on a new water pump and decided to reapaint my intake manifold and front block. I'm using the POR15 Chevy orange paint. After painting 2 coats, it's all nice and dry except a small section on the very outer edge near the middle section of the intake.

It's actually not on the intake, but in the tiny flat areas of the heads that show between the intake and the valve covers. You can see some RTV along that edge.

On the drivers side, right next to the embossed 3 on my cast iron intake#6263758 I noticed the intake manifold paint wasn't dry, as the rest of it was, and it looks swirled like its mixed with a tiny bit of antifreeze. So I tried to tighten the IM bolt and it wouldn't fully tighten, it just starts to tighten , about a half dozen turns, then the bolt head pops back a bit and it's loose again! So I turned it he bolt out and the bolt is fine, not broken off or anything, and the threads look good and sharp. So after trying several times to tighten and getting the same result, I figured the receiving threads must be stripped on the block, so I put some pipe sealant with PTFE on the bolt threads and re tightened it as much as possible, to just before it pops loose a bit. So if coolant is leaking up through the bolt hole, hopefully the sealant on the threads will keep it from coming thru again. I'd say the bolt has only about 10 lbs of pressure on it, at best.

I did drive the car a few hundred miles last summer with the same bolt being not tightened correctly, when I first noticed it not completely tight, and never saw any antifreeze on the intake, nor any milky white in my engine oil. Should I leave it alone or remove the IM and fix the problem?

What's involved with the solution? I don't have hundreds to spend now but I could reseat the IM if needed myself and my guess is that a helicoil procedure might be needed...??

Thanks!

CaseyJones

I would try a longer bolt first. Even if you had to use a washer or two to get the installed length right that might get you by for quite a while.

Vette-kid

Does that bolt match all the others? It sounds like it may be the wrong pitch, perhaps a close metric thread? If the bolt bites into the thread at all, it shouldn't break free that easily unless it is slightly undersize, or the thread are damaged. I would pull the bolt and check the thread and then check it against another bolt. maybe even try swapping it with another bolt from the intake and see if that threads in correctly.

Jeff_Keryk

Sounds like a cheapo non-rated fastener. Use a grade 5 or better.

thegazman

Something is stripped. Pull the bolt and look at it. If the bolt is not stripped, try Casey's suggestion: use a longer bolt to grab threads deeper in the head.

Tom454

This has been a source of frustration for me for many years. The 4 (two per side) end head intake blind bolt holes are about 7/8" thread engagement. The 8 (4 per side) center head intake "through" bolt holes are 1/2" thread engagement. These are open to the lifter valley (oil)... not the water passages. Intake bolt flange thickness is pretty reliably 1/2" thick. I just measured two 350 heads, and two 327 heads as well as 3 GM intake manifolds (1 aluminum Z28 and 2 factory cast iron). Typical intake bolt kits such as ARP 434-2101 provide 1" UHL (under head length) thread. If you install a washer or other item such as an engine lifting bracket or ignition wire support etc, the amount of available under head bolt thread is reduced. The intake gasket compressed thickness also comes into play, further reducing the bolt thread engagement. In the case of the center bolts, this lowers the 1/2" head thread engagement to 3/8" or possibly less. GM provided longer UHL bolts from the factory to take this into consideration. But... over the years... these old engines have been wrenched on by a lot of people. So... you never know what you have in terms of bolt/head thread engagement. The end result is that the center intake head threaded holes are very often helicoiled due to strippping. One of the 327 heads I am working on has one of the center intake bolt holes helicoiled. It is very likely that the threads in your head are "pulled" or stripped and need to be repaired with a thread insert. This will require pulling the intake. Take one last shot at it by trying a longer intake bolt...1/1/4" to 1-1/2" UHL. Don't try this on an end hole because it will bottom out in the head. If it won't tighten up, you will have to pull the intake and repair the head threads. I doubt the bolt is at fault although it's possible. It's almost always the head threads due to previous inadequate thread engagement.
FYI- the water passages are on the ends between the end bolt and the first center bolt.

I use the BB ARP 435-2101 1-1/4" UHL bolts (613-1250 bulk) instead of the SB ARP 434-2101 1" UHL for the center 8 bolts and for the end bolt situations where there are additional items sandwiched under the bolt head. Each case must be measured during assembly.

Jhiltonn

Thanks everyone for your responses and especially to Tom for the detailed response! Much appreciated! At least I know what my options are now.
Joe

doorgunner

As a last resort......insert a straight shank punch into the hole/mark the shank where it is flush with the top of the manifold (incuding flat wwashers-lockwashers-brackets-etc that you will need on THAT hole)

Measure the punch shank to the mark.....subtract 1/16"(subtract 1/8" if using lockwashers)....that will be the length of the bolt shank that you need for THAT hole (if the hole is open-ended---add 1/16" to the measured punch mark (add 1/8" if using lockwashers).

Use the punch-method for each bolt hole.

One other thing......some fastener venders stock close-tolerance bolts........they fit much snugger in worn bolt holes/cost more, but are worth it in circumstances like yours.

larrywalk

Be careful when using longer intake manifold bolts... Most of the central bolts, if too long, will contact the push rods!

7T1vette

If hole depth is less than bolt length, the threads will surely strip. Check hole depth and compare to bolt. If threads are stripped and the hole is 'shallow', a Heli-coil is not possible. You will have to use some other kind of insert, like a Keen-sert or similar thing that engages with the 'over-drilled' hole in a different manner.

Hopefully, you will NOT find that you have a cracked part.

Tom454

As noted above... the head center through hole threads should be 1/2". The head end blind hole threads should be 7/8" +/-.

Edit: helicoils do not require any of the original thread to be present. The hole is drilled clean and re-tapped for the inserts outer thread.

Tom454

Yes... good point. This can happen on the 3rd hole on the passenger side and the 4th hole on the drivers side. The rest will clear. The longest GM SBC intake bolt I have ever come across is 1.5" UHL. And this had a thick bracket mounted under the head of the bolt. Regardless, it has to be measured to be sure.

Jhiltonn

SUCCESS! I bought a grade 5, 3/8 16, 1.5" long bolt and it caught all the threads and tightened up nice and snug!

This was the 3rd bolt hole on the IM on the drivers side, counting from the front to back. The first 2 bolt holes are also attached to the front engine lift bracket, and the 3rd hole is right next to the carb.

Thanks everyone for their help! I put PTFE sealant on the bolt before installing.

Joe