If there is a crack in the exhaust maniold of a classic without any emission control devices what -beside more noise- can be caused by it?
Oliver
Oliver
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Re: General question - crack exhaust manifold - consequences?
Oliver------
There are at least two problems associated with a cracked exhaust manifold:
1) Increased noise, as you have mentioned;
2) Exhaust gas leakage into the engine compartment and, from there, into the passenger compartment. This represents the BIG problem. I've had this occur, myself (although not on a Corvette) and I can tell you that a lot of exhaust gas will get into the passenger compartment, even on a relatively well-sealed, modern car (which old Corvettes definitely were not). YOU DO NOT WANT ANY EXHAUST GAS IN THE PASSENGER COMPARTMENT.
In Appreciation of John Hinckley -
Re: General question - crack exhaust manifold - consequences?
Oliver, what Joe Lucia advised is spot on! But, often a cracked exhaust manifold can be repaired by a competent welder. So, if this is in reference to one of the manifolds on your car, don't despair. You may be able to 'save' the original part without have to replace it and pay the freight & duty consequences...Comment
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Re: General question - crack exhaust manifold - consequences?
In addition to the serious negative consequences Joe mentions, depending on the size and location of the crack items adjacent to the crack may be heated to the point of combustion. Plain English: It might catch fire.
I would rate this as a negative consequence. Depending on the type of cars you are used to driving you may feel differently.
Now let me see, where did I put that "burning shoe" Award.
TerryComment
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Re: General question - crack exhaust manifold - consequences?
My first car was a 50 Chevy coupe that I had a succession of Chevy V8 engines in. Being young and of meager means, I used the early log style exhaust manifolds that came with the first engine (55 in 1956) as the driver side had a clearance problem around the steering box. The pipe had to be welded (brazed) to the two bolt flange at about a 60 degree angle. That brazed joint worked well with the 55 engine, and then again with a 56 Vette engine (9.5 to 1), but when a put in a near new 58 fuelie engine (10.5 to 1) my troubles began. Apparently the flange got very hot with the extra heat generated by a fuelie engine at 7000 RPM, and it warped and would blow out the gasket. As long as I whistled around town below say 5500 RPM I was fine, but when I went out in the country to prove my valor in a drag race - well I'd blow out the flange gasket. I then would ride around that way with a spitting flange until I could garage the car to fix it (in the winter). Sometimes I would try a temporary fix with an exhaust sealer, but that would last only until the next time I punched it. I never (knock on wood) got sick, but I did notice the engine would be down on power. Thought it was my imagination, but I see the same sutuation happens with race cars when they break a header.
Stu FoxComment
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Re: General question - crack exhaust manifold - consequences?
I think I would find a capable welder ... if the manifold were removed. But since this hasn't been done in the last 40+ years I fear the bolts to break. I'm going to give QuikSteel xtreme a try. If not successful I'll start to spray WD40 on the bolts for several weeks.
OliverComment
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Re: General question - crack exhaust manifold - consequences?
Oliver, don't use WD 40. It's a great product but it's not a penetrant oil. You can probably get Kroil (Aerokroil) shipped to you, but I don't know about some of the others like PB Blaster. There may be something available to you locally that you can use, although Kroil is a superior product.
PaulComment
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Re: General question - crack exhaust manifold - consequences?
Oliver-----
Have you tried to remove the bolts? Very often, these exhaust manifold bolts will come out with very little difficulty. In fact, sometimes you'll find them to actually be loose. I would not apply a lot of torque, though, if you do find them difficult. ALWAYS replace the bolts upon re-installation.
While the manifold-to-cylinder head bolts usually come out without problems, the same is definitely not true of the manifold-to-exhaust pipe STUDS. These are almost always extremely difficult to remove. That's why I only use stainless steel replacements for these studs. These will seize, too, but you'll never need to replace them so you'll never have to remove them.In Appreciation of John HinckleyComment
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Re: General question - crack exhaust manifold - consequences?
ATF mixed is what I have used for years to penetrate.
As far as welding your manifold I would suggest that you bolt it to a head that is not in use. This will keep the crack in check as it cools.
It will warp to much when heated and unbolted during welding. you can paint and let things take place to hide the weld if it works.
I use emery cloth after grinding the weld and put the rough side against the surface, then tap it with a hammer to get the original texture back.
Only problem is that cast iron that gets red hot over and over will have a lot of carbon and will be really be hard to weld.
I actually hate welding cact as it will crack when cooling so it needs to be red hot when welded to eliminate cracks, then peened with a sharp peening hammer as its cooling to stretch the molicules in the metal.
Have it welded thick so you can grind the peening out.
At best works 1/2 the time on exhaust.
DOMComment
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Re: General question - crack exhaust manifold - consequences?
@Joe: I had the car at a shop specialized in US cars and they initially wanted to replace the exhaust manifold gaskets but then decided to leave it due to the high risk of cracking the bolts. Hence I never tried it by myself.
Since the penetration oils recommended here are not available in Germany I had a look what the guys in UK use or have at hand. There was a test and a mix of 50% ATF and 50% aceton yielded the best results followed by Kroil and slightly behind Liquid Wrench. WD40 was last.
There are a many other products available here - I have to check what's best - or use the mixture above.
OliverComment
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Re: General question - crack exhaust manifold - consequences?
Oliver-----
These engines did not originally use exhaust manifold gaskets. So, any gaskets found there were added. If the manifold surface is flat and true, no gaskets are necessary. If the manifold surface is not flat and true, the best plan is to have a machine shop machine it flat and true.
If you try removing the bolts using moderate torque, you may find that no penetrating oil is required. It's extremely unlikely that the bolts are going to be so hardened and brittle that they crack like an eggshell. However, if you wish to try using the penetrant first, it's certainly not going to hurt anything.In Appreciation of John HinckleyComment
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Re: General question - crack exhaust manifold - consequences?
Hi Oliver,
In addition to the above, a leak in one of my manifolds caused several plastic parts to melt, ie: washer bottles and extensions. I did have the manifold repaired by having it welded. The welder opened the crack into a large "V" cut, then proceeded to fill the "V", using a nickel welding rod. He actually did most of the repair from the inside, making it almost impossible for the judges to see (it was never discovered). One successful story!
Second story, another vehicle (64 T Bird) same issue cracked manifold, several bolts broke off, just as you suspect! Which led to a complete engine rebuild......
Best of luck!
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Re: General question - crack exhaust manifold - consequences?
Getting penetrant to the threads of the exhaust manifold bolts is not so easy. I see most people putting the penetrant on the bolt heads, and I would suggest that is counterproductive. Putting the penetrant on the bolt head only will make the socket slip on the head, and it is unlikely unless the engine is lying on its side that the penetrant will reach the thread. The interface between the manifold and head is where the penetrant needs to go, but whether that seal will allow it to pass is another matter. It certainly can't hurt if placed at the interface of manifold to head.TerryComment
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Re: General question - crack exhaust manifold - consequences?
Yes, as Paul Jordan said, WD-40 is NOT a penetrating oil. If/when you decide to remove the exhaust manifold, the LIBERAL use of a good penetrating oil, say, a day before you put a wrench on the bolts is well advised.
Next, a trick taught to me by an ex-Navy mechanic is to first get the bolt 'moving' before you really torque away on it. By that he meant you put the wrench on the bolt and move it gently but firmly in BOTH directions (tighten and loosen) until you sense it has broken loose and will now move just a bit.
When that happens, now begin to loosen the bolt and when/if you hit a stubborn spot, again, move in both directions until the bolt breaks past the stubborn point. Then, once the bolt is turning consistently in the direction of removal, now speed up and apply more force to the fastener.
I used to snap/crack stubborn bolts and this method has reduced that to almost zero for me...Comment
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Re: General question - crack exhaust manifold - consequences?
As mentioned before, I'm going to use QuikSteel extreme first. If this doesn't help I mix this ATF/Acetone and apply it on the interface, too, for a certain periode. Then I try my best
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