Exhaust bolt sealant

[Megiddo]

I was changing my header gaskets today to get rid of a small exhaust "tick".  I was very surprised when I pulled out one of the header bolts and a stream of coolant came gushing out.  Apparently, when I had my engine and heads rebuilt last year the machinist ran a little deep when chasing the threads on the head.  Anyway, can I use RTV on that as a thread sealant or do I need to do something more involved?

Thanks,

Tom

[mat in tn]

try whatever. but you need new heads

[Gary Lewis]

I wouldn't use RTV.  Instead I'd use a thread sealer, like Loctite 56747 PST.

Had the same issue on a 351M and that's what I used.  Worked well.

[Gary Lewis]

mat in tn wrote

try whatever. but you need new heads

I disagree.  As said, I had the same issue on a 351M where someone drilled too far in to install a helicoil.  The Loctite PST did the trick.  And, as Bill/85lebaront2 pointed out to me back then, the 383 in my SuperBee came from the factory that way.

[mat in tn]

I have not found a need to drill when chasing threads. it's more likely a crack. it's true that you can seal threads that enter a coolant passage. outer head bolts for example. but when it's a fault I don't trust it.

[Gary Lewis]

In my case the PO wasn't chasing threads.  He was drilling out the hole to tap and install a helicoil and somehow went too far.  And in that case there isn't anything wrong with the head.

But I agree that if it is a crack then the head is bad as it'll probably continue to crack.  So I recommend that Tom checks to see if his head has been drilled too far or if it is cracked.  I'd think that would be easy to ascertain by sliding a drill bit in to see how far it goes in comparison to the other holes.

[Megiddo]

I'll try that, but the volume of fluid that came out made me think it was more than a crack. I think its drilled too deep.  I don't know if my header bolts vs. the original manifold studs could have contributed.  My machinist did do some extra work on the head as a different bolt hole had been drilled crooked for an easy out and had half a bolt "keyed" into the head with half an easy out.  He then ran a tap through the the rest of the holes to make sure the threads were solid

Will the locktite sealant make it difficult to get the bolt out next time?  I don't plan on taking the headers off in the near future, but I seem to be good at twisting bolts off.

[Megiddo]

The hole in question is about 3/8 inch deeper than the rest.  I'll try the sealant.  Thanks.

[Gary Lewis]

That sealant won't make it very difficult to get the bolts out.  It is kind of a cream and sets up a bit, but not hard by any stretch.  I use it on lots of things and really like it.

[mat in tn]

3/8" deeper is significant, that is easily the casting thickness behind the bolt. that sounds like they drilled too far for certain. in this specific bolt position, is it possible to use a stud with a nut to tighten instead of a bolt? I know header bolts with reduced heads are the norm but some positions are tighter than others.  in fact, fords factory mustang headers are clearance'd so full-size bolts can be used. I know they don't flow as much but they fit so much better

[Megiddo]

I don't think I could get a stud and nut in there.  I'm using the bolts with reduced 3/8 inch heads and can just get a wrench on them.

[Megiddo]

What would be the advantage to a stud with a nut over the bolt?  

[grumpin]

I’m thinking it will stay in there and not leak if you need to pull the manifold or headers.

[mat in tn]

bingo!

[Megiddo]

I used some of the locktite sealant Gary recommended.  I haven't driven far, but have had the motor up to normal temp.  So far so good.  I'll just plan on changing anti freeze every time I take the headers off.  Hopefully I'll have to change the antifreeze more often than I have to remove the headers.

[Gary Lewis]

I think you'll like that sealant.  And especially if you put a stainless nut on a stainless bolt.  I had a new, dry stainless nut seize on a new, dry stainless bolt before I started using that stuff.  I never put stainless on stainless w/o the stuff now.

[Megiddo]

Good to know.  My bolts are just plain the black oxide coated ones.  I would try a stainless stud as was recommended, but I couldn't get a nut on it unless I did something weird with a spacer sleeve or something like that.