Trying to find a definitive answer to a question about which head bolts on a nailhead go into a water jacket in the block. I am working on a '61 401 for my brother and trying to track down a coolant leak that just appeared when I drove the car Sunday. My brother just bought this car and the previous owner recently installed A/C on it and had to pull a couple head bolts for the compressor mount. As best I can find in some google searching, seems there are at least three head bolts that go into coolant passages. I just need to verify to make sure I may be tracking down the right issue and am running out of time to get this done, finish buffing the car, and also possibly look over another car for the road trip to St. Louis this weekend... In looking at everything last night, I didn't see any other obvious places for the coolant to be coming from. So, I am asking the experts here that are all-knowing. I have never worked on a nailhead before, so this is all new to me. I just suspect one of the bolts is leaking from what I know about other engines I have built where I had to seal head bolts... Thanks in advance. Best I can figure, 11,1, and 5 head bolts in the image below are the ones that go into water jacket? However, what I think I am seeing is 8 leaking. I know this is a torque sequence, but the labels work well for trying to make my point...
I thought all of them went into a water jacket on Nailheads. I have one at home with the heads off. If no one else has the answer i will look at the block and check for you tonight.
Not an answer to your question, but how much less of the bolt threads are engaged in the block due to adding that air compressor mount? The rear of that mount (bolt #5 on the torqueing diagram) looks like it is pretty thick. If you have to remove those head bolts to seal them, I'd take a close look at thread depth. It'd be a shame to tear a few spirals of threads out of the block due to shallow head bolt engagement. Maybe consider a couple of proper length studs in those locations?
Hmm...that makes more sense to me that they would. I think the reality is that I will pull both bolts and seal them both this evening. As much as anything, I am somewhat curious since I didn't find much when searching. If we don't get an answer today, I might be able to answer it in the morning. Thanks for the offer Jason!
Yep, that was my thought too until I realized that there were bosses that stood up on the head and the bracket was basically a hollow stamping if that makes sense. But, I agree that I wanted to verify the thread engagement...especially before checking the torque...
So...best I can tell, both of the bolts that go through this bracket go into water jackets in the block. And, the front one was wet all the way up and not torqued to 70 ft-lbs. So, praying that pulling them out, cleaning them up, adding some liquid Teflon thread sealer, and torquing them to the correct torque solves my problem. They did have plenty of thread engagement (likely about 5/8”-3/4”). Thanks for all the input. If I had more than a couple days to fix this, I would find some bolts with studs to do this like @jaracer shows. But, this should get it fixed for now considering my timeline.
I cant remember exactly but I believe both of the front two head bolts on a 401 with AC are longer. I had to get some shorter bolts like they have toward the rear when I took the AC bracket off when I was getting the motor ready for my 34. I could probably measure the bolt lengths they are on my work bench somewhere.
From GM Service Manual: Sounds like all bolts should have sealer. I would be more inclined toward Permatek
On my 62 401 Nailhead the 2 front bolts on both sides are about an 1" longer to allow for the diecast brackets for the generator and aircon. @Canuck that is a big range in torque settings from the GM service manual. I would like something a bit more definite. Also not real happy removing head bolts to remove a generator bracket.
I checked on a 61 364 I have on my engine stand, and only the front middle 2 (either#1 or # 11 /#5 depending on side) goes thru into the water jacket. Later motors (63 up) use 1/4" longer bolts on #5 and #8 to mount the A/C / Alternator bracket. If your engine has not been apart, maybe the thin steel head gaskets have rusted thru?
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