Wrong Size Intake Manifold Bolt?
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Trailering
Joined: Nov 2019
Posts: 18
Likes: 1
Wrong Size Intake Manifold Bolt?
Hello all,
I've been noticing some smoke out of the exhaust on the driver's side of my '69 lately (stock 360), and through a bit of Googling, landed on the intake manifold bolts as a likely culprit. Turns out one of them was stripped, but when my replacement set came in (3/8-16), they just dropped straight through the threads. As long as the rain is stopping me from working on it, I figured I'd ask here: is there any other size I should look for? Or should I just assume this is the result of a previous owner's home repair job and go find a matching bolt?
I've been noticing some smoke out of the exhaust on the driver's side of my '69 lately (stock 360), and through a bit of Googling, landed on the intake manifold bolts as a likely culprit. Turns out one of them was stripped, but when my replacement set came in (3/8-16), they just dropped straight through the threads. As long as the rain is stopping me from working on it, I figured I'd ask here: is there any other size I should look for? Or should I just assume this is the result of a previous owner's home repair job and go find a matching bolt?
Cargo Master
Joined: Oct 2011
Posts: 2,241
Likes: 299
From: Kenner,La.
Intake bolts
ARP # 155-2102 are the correct bolts. 3/8”16. They are available on E bay. They torque to 30-35lbs. Import bolts are sometimes labeled wrong and not the grade they are advertised as.
Mountain Pass
Joined: Oct 2020
Posts: 214
Likes: 8
Always worrying when bolts just drops in and spins like that. One of two things - either the PO went up to 7/16" or the bolts that came were not long enough to make it through the manifold and into the block. Are the new bolts the same length as the ones that came out?
Geoff
Geoff
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Trailering
Joined: Nov 2019
Posts: 18
Likes: 1
New bolts are the same length, and looking at it this evening without any time pressure from a storm rolling in, it is the same thread, too (minus the packed in crud and couple of big burrs on the old one). Stopped and grabbed a 3/8 bolt at the hardware store too, just for a sanity check, and it was the same thing. Seems like my best bet to get it sorted is probably just drilling it out for a helicoil.
Mountain Pass
Joined: Oct 2020
Posts: 214
Likes: 8
This one is a head scratcher. If the bolts didn't break coming out, and the new ones are the same length and thread as the old ones, then why wouldn't the new ones bite? Maybe the upper threads in the hole got damaged when removing the bolts but maybe the deeper threads are intact? Have you tried an extra-long bolt to see if any part of the hole threads are good? I would also stick a long thin probe down one of these holes to see what kind of depth I'm working with. Sorry if this is stating the obvious, but I'm just trying to wrap my head around this.
Geoff
Geoff
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Trailering
Joined: Nov 2019
Posts: 18
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That sounds about right; I think the mangled section of the original bolt probably widened out the threads until it bottomed out, and it's able to skip because it's just engaging on the bottom thread(s). I can check with one of the good bolts when I get home, to satisfy your curiosity 
In any case, I'm probably grabbing a helicoil kit on the way home from work, and hopefully fixing it for good.
In any case, I'm probably grabbing a helicoil kit on the way home from work, and hopefully fixing it for good.
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