Snyder’s 6:1 head

[BRENT in 10-uh-C]

Originally Posted by Killerbee

Well I’m over it and too many other people have had the same issue. I shouldn’t have to resurface a new head. I would expect that from a swap meet head not a new one. Everything was properly prepped torqued warmed cooled retorqued with the same issue. The gasket seems to blow on different spots every time either it’ll leak coolant into the cylinder or blow exhaust out of the side obviously there is an issues with this head. I’m not doing it a fourth time.

I also get the part where you are "over it" but as an engine machinist speaking here, I will tell you that if the gasket is blowing in different spots, it is my opinion that the issue is NOT with the head. If the head has an issue where it is unlevel in a certain area, it will repeatedly fail in the same location. The same can be said with cylinder block's deck. Based on your responses above, it is my opinion that the issue is with the head gasket installation. If I could inspect the gasket, the fasteners, and the block, I could likely pinpoint it even further as to the culprit.


Now the next issue you have is really not the manufacturers fault however they will likely get the blame. As soon as the installed cylinder head came up to operating temperature a couple of times, the cast iron will move by nature as it "seasons". If you check it after that heat cycle time you will almost always find it will be unlevel. Ford's O.E. heads did/do the same thing until they have seasoned and new engine components also do the same.


Adding to the above, most modern machine shops do not have a good way to support a Model-A cylinder head to resurface it. I have shown this to people in my own shop where if a Model-A cylinder head is supported on a surfacer with 3 stands and checked with an indicator, it will show one measurement however to anchor the head to keep it stationary on the resurfacer, the head is generally anchored to the table with a bolt down thru a couple of spark plug holes. When the head is tightened enough to anchor it securely, it generally deflects the head anywhere from 0.005"-0.010 in the center. That is why you typically hear of heads being distorted right out of the box.


A Model-A head is that flimsy by its design which is why the tightening process is to be performed radially and in graduated fastener tightening increments. This is another reason why clean and lubed fastener threads are important, and another area where hobbyist mechanics tend to miss the mark. At minimum you need to have your present cylinder head checked by someone who has experience and knowledge on how to correctly resurface a Model-A head. I would expect that it will be 'warped' simply because it has been heat cycled.


And finally, about the ONLY way you can accurately check a cylinder block for a level deck is with a Machinist's Straight Edge or a long Machinist's Level. The minimum length is 18" and the edge must be precision ground. Most hobbyists do not have that level of equipment to check or verify the deck surface and so their readings are false.

[Nosetime]

I bought a Central Tools machinist straight edge on Amazon for less than $75. Could not have done my engine without it, probably won't use it again for a while, but glad to have it in the box.

[Railcarmover]

A torque spec is used on fasteners to remove any potential stretch from the fastener.In theory this insures the cylinder head is held in compression,unable to expand.How ever,since the assembly is subjected to a heat /cool cycle.deviation in the head occurs.As Brett stated,finding a perfectly straight head is tough and even if you do,during the torque procedure it is altered by the application of clamping force unequally,its why modern engine assembly use 'gang' wrenches,so all head fasteners are torqued simultaneously.

Examine the deck thoroughly treat potential water leak areas the way you would on a simple gasketed assembly, you can use a light amount of sealant in selected areas around the water ports.do not use sealant on the fire rings or where it can migrate to the fire ring..90 year old head studs fatigue,and lose their 'memory',when torqued they can still stretch.Re using cylinder head nuts give false torque readings due to thread galling.

Understanding the assembly from a machinists point of view both faces..the head and the deck..need to be true prior to assembly.From a mechanics point of view proper assembly insures both faces are held in compression evenly.The processes compliment each other,often the machinist is indicted for bad mechanic practice.

[johnneilson]

The torque question has been brought up, just like opinions, everyone has one.

So, here is mine;
Using studs with fine threads up top for the nuts the max is 55 ft#.
As an example, this is adequate to contain 14:1 CR and 7000+ rpm.
Using good quality studs and lubricating the nuts and washers during the torquing process.
To contain the cylinder pressures, a solid gasket is used, copper and copper oring wires in the deck. OHV design, without saying.

I say this because some motors that come my way have had all kinds of damage. Cracked heads, right down in between the center studs and both ends distorted.

Railcar and Brent are right, mechanics cause most of the issues and the manufacturers are blamed.

Without going too deep into the subject, metal, all metal has a yield point, this can be the studs, head and or the block deck. You are working on a marginal design at best and watching the details you can be successful.
Things to keep an eye on, studs, are they good quality? Have they been yielded previously? If so, they will never keep the clamping force.
The tork wrench, most good ones are +/- 10%, some beam style ones are good if +/- 25%.
Decking off the cylinder head to raise compression (reduce chamber volume) and then adding in a second gasket is going to ruin a good block deck. Why? because the gasket is a compressible material sandwiched between two surfaces that are not rigid enough to resist distortion. Not to mention removing material from the head that is too thin to begin with.

You may not agree, that is fine, in some cases, less is more.

Best, John

[40 Deluxe]

Over torqueing the studs will crush the gasket in the area near the stud, thus distorting the block and causing another blown gasket!

[Bruce of MN]

Sponsored Links (Register now to hide all advertisements)

I took my unused 6:1 head to my auto machine shop for a check and the guy was surprised on how flat it was, so I got a good one.