BBC 4 Additional Head-Bolt Hole Blueprint Locations
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BBC 4 Additional Head-Bolt Hole Blueprint Locations

  1. #1
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    Default BBC 4 Additional Head-Bolt Hole Blueprint Locations

    Hello,

    I am looking for the blueprint dimensions to locate the four additional head bolt holes in the block and heads on a big block Chevy. I have searched every book that I have, including the Chevrolet Power: The official Factory Performance Guide! book. The Chevrolet Power book, as well as several other big block Chevy books, describes adding the “missing” head bolts to cylinders 2, 3, 6, and 7 of a production block, but none give the dimensions. In looking at the accompanying pictures in these books, it appears that the holes, which I have located at 7.20, .85 and 16.88, .85 are inline with the other head bolts located at 2.36, .85 and 12.04, .85. In my drawing, that places the “missing head bolts” inline in y axis and 4.840 (bore spacing) in the x axis. This location also places the bolt approximately centered in the port.

    In the past, I know factory aluminum heads have used this procedure, adding four 3/8-16UNC socket head cap screws. Some books recommend a 7/16-14UNC. I have been looking at my 188 heads and I can not tell if there is a water jacket in this location or not. Is this procedure only for the aluminum heads, or will it work with cast iron heads?

    The reason I am asking, I currently have my engine apart to investigate a water in the oil issue after an overheating issue while running at Aha Quin where I ended up with a blockage in the odd bank water jacket. I am running copper head gaskets with stainless steel o-rings. There is evidence of combustion gasses weeping in #3 towards the lifter valley, but no evidence of water leaking. I ran a compression test and all cylinders were within 5PSI, but the leak-down was at the low end of the acceptable range. It appears that this is resulting from lack of ring seal due to some corrosion pitting in the cylinders. Also, I was not able to do the leak-down test hot as the engine is not currently in a running condition right now.

    Even though my head gaskets were not actually leaking (yet), I would like the added clamping force that these bolts provide.

    Thank you in advance.
    Cheers,

    Joe
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  3. #2
    gn7
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    Quote Originally Posted by Flusher View Post
    Hello,

    I am looking for the blueprint dimensions to locate the four additional head bolt holes in the block and heads on a big block Chevy. I have searched every book that I have, including the Chevrolet Power: The official Factory Performance Guide! book. The Chevrolet Power book, as well as several other big block Chevy books, describes adding the “missing” head bolts to cylinders 2, 3, 6, and 7 of a production block, but none give the dimensions. In looking at the accompanying pictures in these books, it appears that the holes, which I have located at 7.20, .85 and 16.88, .85 are inline with the other head bolts located at 2.36, .85 and 12.04, .85. In my drawing, that places the “missing head bolts” inline in y axis and 4.840 (bore spacing) in the x axis. This location also places the bolt approximately centered in the port.

    In the past, I know factory aluminum heads have used this procedure, adding four 3/8-16UNC socket head cap screws. Some books recommend a 7/16-14UNC. I have been looking at my 188 heads and I can not tell if there is a water jacket in this location or not. Is this procedure only for the aluminum heads, or will it work with cast iron heads?

    The reason I am asking, I currently have my engine apart to investigate a water in the oil issue after an overheating issue while running at Aha Quin where I ended up with a blockage in the odd bank water jacket. I am running copper head gaskets with stainless steel o-rings. There is evidence of combustion gasses weeping in #3 towards the lifter valley, but no evidence of water leaking. I ran a compression test and all cylinders were within 5PSI, but the leak-down was at the low end of the acceptable range. It appears that this is resulting from lack of ring seal due to some corrosion pitting in the cylinders. Also, I was not able to do the leak-down test hot as the engine is not currently in a running condition right now.

    Even though my head gaskets were not actually leaking (yet), I would like the added clamping force that these bolts provide.

    Thank you in advance.
    Cheers,

    Joe
    I believe the drawing you posted is for a 8.1 BBC GEN VII block, not a MKIV GEN 5-6.
    The ADDED bolts for a MKIV block are not in alignment with any bolts in the standard deck. The top 4 bolts in that drawing are all in alignment.

    The added valley bolts for a MKIV deck line up with intake ports, not water jackets. I guess they could be added to existing iron heads although I don't think I would recommend it.

    The added bolts are NOT perpendicular to the deck, but are off by a few degrees.

    What makes you think you need to add the bolts? You running some high boost pressure or a ton of spray?





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    Reher Morrison makes this kit. But you have to know what your doing to install it and have access to the proper tools.
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    Thank you gn7 for your reply.

    The picture that I posted is one I created in SolidWorks based off of drawings in the Chevy Power: The Official Factory Performance Guide!, 7th ed., for bore spacing and dowel locations titled “Use the dowel-to-cylinder bore dimensions shown above to position the cylinder bores accurately in a Mark IV Bow Tie block with semi-finished cylinders” (p. 109) and "BASIC MARK IV BIG-BLOCK V8 ENGINE CYLINDER CASE DIMENSIONS (NOMINAL)” (p. 110, 111). The Gen VII would be dimensioned in millimeters.

    The head bolt holes that I am referring to that appear to be inline are illustrated in this picture from CHEVROLET POWER CATALOG, 6th ed., Figure 78, "Cylinder block modified for #128 Bow Tie cylinder heads has six head bolts around each cylinder bore. Additional head bolts (arrows) improve gasket seal.” (p. 6-23).

    My heads are shaped like the above head in your picture. They do not have the bosses (red arrows) cast in for adding the additional head bolt holes. Also, my block does not have the head hold-down bosses cast into the lifter valley.

    My heads have three intake-side steam holes (blue arrows & green circle) of which the heads in your picture only have two (blue arrows). The two steam holes in your picture are below to the first and third intake ports from the left. Per the lower head in your picture, the holes that I wish to add are located in the same intake ports as the bosses that are cast and machined (red arrows). While probing around inside of these steam holes with a wire, I can not tell where the water passage is and if it passes under the intake port where I want to put the additional head bolt holes and I do not have a junk set of heads that I can cut up to look at. I am just concerned that if I add these holes, I might inadvertently add water injection to these two ports.

    As to the why, I do plan on pushing it harder. I haven’t had a problem yet with this engine, but it is evident that there is weeping of combustion gasses past the o-ring and that there is uneven clamping in this area. Years ago, I used to wrench on what is now my boat for the previous owner, and I seem to recall, as does the original builder of the engine, that the block and heads had this modification done. However, neither I nor the original builder of the engine were part of it going together the last time and anything could have been done. I know for sure that the block and pistons are different now than the last time I was involved in it. Also, the heads do not have receiver grooves for the o-rings like I remember. That could be part of the problem with the uneven clamping.

    May I ask why you wouldn’t recommend adding these to iron heads?

    Unfortunately, a Dart block and aftermarket heads are not in my budget, so I will have to make due.

    Thanks again.

    Joe
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  7. #5
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    Quote Originally Posted by Hass828 View Post
    Reher Morrison makes this kit. But you have to know what your doing to install it and have access to the proper tools.
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    Thank you Hass, I was looking at that kit and even thinking about making something similar, but my head castings do not lend themselves to that configuration. Even if I was to locate the additional head bolts in the lifter valley in this manner, there would be no material under the intake ports to support the bolt head or provide an even clamping force.

    At the moment, I am lacking any good ideas for adding material to this area of the head. The head casting is thin where these head bolts would go. There isn’t enough material to machine a flat for a Reher Morrison-like bolt-on boss kit, which protrudes above the deck, to seat against and have a substantial amount of material left for a counterbore with sufficient material thickness to be useful.

    When you all were forced to run production parts, how much boost, cylinder pressure, or horsepower could you push before you experienced a gasket failure assuming that it was not from a tuning or mechanical error?

    Thanks again.

    Cheers,

    Joe

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    I don't have those extra bolts in my early Bowtie block and I run 12 psi of boost on pump gas and so far haven't had a problem.

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    I have the dimensions. Give me a few minutes, I'll post up a drawing.
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    Quote Originally Posted by Flusher View Post

    When you all were forced to run production parts, how much boost, cylinder pressure, or horsepower could you push before you experienced a gasket failure assuming that it was not from a tuning or mechanical error?

    Thanks again.

    Cheers,

    Joe
    This whole thing is confusing as hell!!!
    First the RM kit DOES NOT stick up above the deck. I have a similar kit and it is infact well below the deck. There is no need for it to be even with the deck, you aren't clamping against it like you do with the head/gasket/deck interface.

    With a o-ring copper head gasket arrangement you could make more than 900HP from 468 without the valley bolts.
    Its not a HP thing, its a cylinder pressure thing. There is a difference. Its called cubic inches!!!!
    Why don't you just say what the flock it is you running with these iron heads and what fuel and maybe somebody could tell you if you are wasting your time.



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    Quote Originally Posted by gn7 View Post
    What makes you think you need to add the bolts? You running some high boost pressure or a ton of spray?
    I made over 1000hp with a .060 over mark 4 block, without the extra head studs, blown alky deal with 10-15lbs, and MLS gaskets. alot of time and money to add a few holes, i am not saying its a bad idea, but maybe a little over kill..depending on what your doing, and it may be time to get an aftermarket block if your going big!

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    OK, here's the deal:
    This drawing has the bolt holes (I marked in red), just not in the right place. If we use "zero zero" as the reference point; going up, the distance to the two new holes is 1.53". From left to right, the first hole is shown on your drawing to be at 7.20". The correct dimension is 7.170". The next bolt hole is shown at 16.88". The correct dimension is 16.85". I have the drawing here, just can't seem to be able to convert it form a PDF so I can post it here. If you send me a fax # I can fax it for you. The bolts are at a 10* angle referenced from the deck.
    Last edited by scott foxwell; 08-13-2013 at 02:38 PM.
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    Usually about the same time you make enough cylinder pressure to need the extra bolts added from under the intake is the same point that you also start walking the main caps in a production block.
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    Quote Originally Posted by Hass828 View Post
    Usually about the same time you make enough cylinder pressure to need the extra bolts added from under the intake is the same point that you also start walking the main caps in a production block.
    Among other things. Cap walk tends to be RPM/stroke related, but even if the caps aren't walking, if you need the valley bolts with todays gaskets, you on the edge of failing a cylinder wall.



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  15. #13
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    You guys think that the only reason to increase cyl head clamping is to prevent a failure? You think there's 100% seal all the time?
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    Cap walk is sometimes the result of a poor tuneup,,, agree ?

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