Head Removal: Tips 'n Tricks
- Thread starter '29 Pickup
- Start date
'29 Pickup
Member
Is there a way of being able to mark the positions of each stud on a steel plate ready for drilling without having a head gasket available as a template to mark it up with accurately. The gasket I want isn't available here and I'm not ready to make my big order in the US....(small orders work out way too expensive for international shipping per item).
alexiskai
Well-known member
Use bluing to mark the tops of the studs and then put the plate on top.
https://en.wikipedia.org/wiki/Engineer's_blue
'29 Pickup
Member
Would the plate rest flat on all the studs at the same time? (excluding the water inlet studs of course).
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alexiskai
Well-known member
Probably not, you’d probably have to do multiple passes. It’s not a great solution, I was just trying to offer an idea that would work within your stated constraints.
'29 Pickup
Member
Thanks
I think it really needs the gasket to do it spot on.
This is why I didn't like the plate and bolt idea from the get go....too fiddly.
But I think it is probably the best approach.
1crosscut
Well-known member
No actually I have not seen that happen but I think that it is a possibility.
It just doesn't seem to me (perhaps I'm the only one) to be a sound way to remove a stuck head.
alexiskai
Well-known member
What I'll say in its defense is:
1. It is by far the most recommended solution every time this problem comes up, by people who say it worked for them, so from an empirical standpoint it seems to be reliable.
2. 90% of stuck heads aren't literally fused to the block, they're just heavily gummed up and you don't have a good way to grip them from the outside. The force required to remove them is not large if applied effectively, and that's what the rope trick does.
katy
Well-known member
For the "rope trick", never heard of using the starter, used a socket and breaker bar, gently on the crank (ratchet) nut.
I know there's a lot of people who cringe at the rope method, but it's actually quite safe.
Here's how it is done (fast forward to about 7:30)- https://www.youtube.com/watch?v=du1AZS5y3r8
Here's the full explanation of how and why the rope trick works so well- https://www.youtube.com/watch?v=4M7o5v_exXE
Easy, safe.
Big hammer
Well-known member
Thank you ;-)
johnbuckley
Well-known member
When rebuilding is there an engineering reason for not replacing the studs with bolts, like modern car? This would surely make life easier for the next person to remove the head.
alexiskai
Well-known member
Studs provide much more consistent clamp force. Since the A head already doesn’t have as many fasteners as it should, switching to bolts would increase the risk of head gasket failure.
Afordman31
Well-known member
Pictured are of the one I made to remove stuck and not stuck Model A heads.
I have used this on a couple of heads and have loaned it out to others with great success removing the head. The chain is hooked to bolts that go thru two old Model A spark plugs with the porcelain removed. The bolts pictured in the plate are half inch diameter with a nut on the back side. The bolts set on the head studs. It takes two wrenches one to hold the bolt and another to tighten against the bottom side of the plate thus lifting the head. A spare head was used to lay out the head stud pattern.
I have used this on a couple of heads and have loaned it out to others with great success removing the head. The chain is hooked to bolts that go thru two old Model A spark plugs with the porcelain removed. The bolts pictured in the plate are half inch diameter with a nut on the back side. The bolts set on the head studs. It takes two wrenches one to hold the bolt and another to tighten against the bottom side of the plate thus lifting the head. A spare head was used to lay out the head stud pattern.
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johnbuckley
Well-known member
Why? If the nuts/heads of the bolts are the same dimension, and the diameter of the bolts/studs are unchanged , I can't understand why it should make any difference... though presumably it does
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alexiskai
Well-known member
Why? If the nuts/heads of the bolts are the same dimension, and the diameter of the bolts/studs are unchanged , I can't understand why it should make any difference... though presumably it does
To understand why, we have to think about the nature of the materials being used.
When you fasten a cylinder head to a block, particularly with flathead engines, your main objective is to create a perfect seal around the combustion chamber. After ignition, the expanding combustion gases will try to escape the chamber. We want to force them to push against the piston, which means we need to seal off other avenues of escape.
Head gaskets are weak and fragile things relative to the other materials in the engine, so the combustion gases will try to displace the gasket and escape into the water jacket. The only way to prevent that is to make it impossible for the gasket to be displaced. To do that, you have to clamp the gasket between the block and the head in such a way that the force on every point in the gasket is as strong as possible.
Cast iron is a very strong, rigid material, so we can put clamping force on the gasket by placing fasteners at key points around the head and tightening those fasteners down. The cast iron in the head will take the clamp load applied by the fastener to a very small area (the area under the bolt head/nut) and distribute it across a wide surface. This lets us use a small number of bolted joints to apply clamping force evenly across the surface of the gasket. By tightening the fastener above a certain threshold, we prevent the gasket from being displaced, which would induce head gasket failure.
However, cast iron is not infinitely rigid. If you apply too much clamping force, it will flex/warp around the bolted joint. Some parts of the mating surfaces will deform toward each other and other parts will deform away from each other. In any spot where the head and block deform away from each other, the clamp load on the gasket will be decreased. This introduces the risk of head gasket failure again.
Therefore the clamping force applied by the cylinder head fasteners must be inside a particular range. Not so light that the combustion gases can overcome the force and displace the gasket, but not so heavy that the mating surfaces become distorted, disrupting the gasket seal and allowing displacement.
We now come back to your original question of bolts vs studs. On a Model A, the threads in the block are 7/16-14, coarse pitch, while the threads at the top of the stud are 7/16-20, fine pitch. The block threads are also class 3 fit. Class 3 joints have very close tolerances. You will notice when threading in a cylinder head stud by hand, there is a fair amount of friction in the turning even though there is no load on the stud.
If you were to use bolts to seal the head to the block, and particularly if you did it without lubrication, a very high proportion of the torque applied in the tightening would be used simply to overcome friction in the joint. The pitch is coarse, so a given amount of rotation on a bolt tightens the joint more than the same rotation on a head nut, and the tolerances are very close. Furthermore, these engines are 90 years old, so the threads are likely already torn up a little bit from prior wear and tear.
It has been clearly established in engineering science that the more friction there is in a bolted joint, the more variance there will be in the exact value of the friction. So across the 14 fasteners in the cylinder head, you might get friction resistance that varied by 20%, 30%, or even 40%. If you are applying identical torque on each fastener, this means the actual tightening force on those fasteners will vary by up to 40% as well.
This is the key reason that bolts are not suitable for this application. It is not possible to ensure that the clamp load on all the bolts will be within that critical range I talked about earlier, where the gasket is clamped tightly enough that it can't be displaced, but not so tightly that the block or head deform.
'29 Pickup
Member
Do you consider copper spray on the gasket to be unnecessary snake oil or useful to help get a good seal?
alexiskai
Well-known member
The purpose of copper spray is to compensate for small imperfections in the finish of the mating surface. If one or both components are being assembled without having just been professionally surfaced, using copper gasket spray on that side of the gasket may improve the seal.
So for example when I put a brand new head on an engine, if the block hasn't just been decked, I would do a light coat of copper spray on the side of the gasket that goes against the block, but not on the side facing the head.
(Unless the manufacturer of the head specified that you should do that. Always follow vendor instructions.)
Copper spray will not correct for a warped surface.
'29 Pickup
Member
Is there any benefit to using copper spray if both surfaces have just been decked, as an extra safety precaution or is it counterproductive?
alexiskai
Well-known member
I don't have a strong opinion on that one. I do know the 509G gasket is reputed to work well without sealant, and folks say that the only result of applying copper spray there is to make it harder to scrape the gasket off when you change it.
For the older style copper gaskets, accounts vary. Traditionally you would apply some kind of sealer to the gasket. Could be anything from silver paint to axle grease.
The goal is always to compensate for imperfections in the surface. Sometimes people talk about adhering the gasket to the surface, or keeping it from shifting when the head is tightened down. None of these treatments will keep a gasket from displacing under combustion pressure if the clamp load and surface flatness are inadequate.