Block Notching?
Dr. Detroit
Joined: Mar 2012
Posts: 10,095
Likes: 4,022
From: New Braunfels Texas
It is a common practice to notch a Mark 4 or Gen 5/6 block.
Prussina Blue the block or Dy-Kem.................mount a head gasket to the block......and scribe. Boom....there you go.
Mount the same gasket to the head and do the same thing. As long as you are inside the fire ring, you are fine. The need to do this goes away at over 4.500 bore......a 502 has a very small notch at 4.370 bore.
You can relieve it as far down as about half down the piston crown just above the top ring land.
No fear here.....just a steady hand and premium carbide bits from McMaster Carr. I like to use a large flute medium tree then finish with a tootsie roll style sanding roll.
Same way with the heads....just pay attention and blend, blend, blend.....removing as little as possible as you go until you are either confident, or the desired result is obtained.
Have fun
Jebby
Prussina Blue the block or Dy-Kem.................mount a head gasket to the block......and scribe. Boom....there you go.
Mount the same gasket to the head and do the same thing. As long as you are inside the fire ring, you are fine. The need to do this goes away at over 4.500 bore......a 502 has a very small notch at 4.370 bore.
You can relieve it as far down as about half down the piston crown just above the top ring land.
No fear here.....just a steady hand and premium carbide bits from McMaster Carr. I like to use a large flute medium tree then finish with a tootsie roll style sanding roll.
Same way with the heads....just pay attention and blend, blend, blend.....removing as little as possible as you go until you are either confident, or the desired result is obtained.
Have fun
Jebby
Dr. Detroit
Joined: Mar 2012
Posts: 10,095
Likes: 4,022
From: New Braunfels Texas
When you get it all scribed.....bolt the head on, flip it over and shine a light bore......and you will see why notching is a good thing.
In fact.......scribe and relieve the block first and bolt the head on with Dy-Kem and scribe the bore to your head.....this is a better way to do it......
Jebby
Last edited by Jebbysan; May 19, 2018 at 03:11 PM.
Dr. Detroit
Joined: Mar 2012
Posts: 10,095
Likes: 4,022
From: New Braunfels Texas
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Thread Starter
Safety Car
Joined: Aug 2000
Posts: 3,909
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From: Clymer PA
Milan454:
I have a bunch of questions so I apologize ahead of time. Do you have some closer pictures of the notching? Did you notch the exhaust side as well? Do you think it is more effective to notch the block like that or perhaps use more of a tapered/ramped notching? Thank you to everyone for the information thus far.
I have a bunch of questions so I apologize ahead of time. Do you have some closer pictures of the notching? Did you notch the exhaust side as well? Do you think it is more effective to notch the block like that or perhaps use more of a tapered/ramped notching? Thank you to everyone for the information thus far.
Race Director
Joined: Jul 2015
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From: SW Florida.
That notch was done by GM on the line as block was machined. A 45 degree taper done with small sanding drum would be optimal. Only intake side really benefits from notching. They say worth 30 hp on 4.25 bore.
Instructor
Joined: Sep 2017
Posts: 169
Likes: 20
From: Westlake Ohio
Hence, Derek beat me to it. Intake valve only. It has to do with the size of the valve and the angle of the valve stem. A gentle angle is better than the step the factory creates. Think of the modification this way. The Mtg. Would do anything to save a nickle if this didn't work they would gladly save the effort. By the way, I enjoy the questions. They help keep me sharp��
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From: Corsicana, Tx
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Yes do it...BUT....make sure you have the pistons in hand you plan to use to be sure the ring lands haven't been moved from what was in it previously. If using same pistons you're good.
Offset dowels do similar things...I've used them too...but make sure to watch valve pockets in pistons when you start scootin' things.
Also very common to "offset" bore the cylinders on BBC (and others) to move the entire cylinder over a little. Real handy when rules say you can't do things like put the relief in the top of the bore.
JIM
Offset dowels do similar things...I've used them too...but make sure to watch valve pockets in pistons when you start scootin' things.
Also very common to "offset" bore the cylinders on BBC (and others) to move the entire cylinder over a little. Real handy when rules say you can't do things like put the relief in the top of the bore.
JIM
Thread Starter
Safety Car
Joined: Aug 2000
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From: Clymer PA
Jim:
Is there any benefit to using both block notching and offset dowel pins or is it best to just go one route or the other? The block has carbon lines where the fire ring stopped and also on the deck surface where the head gasket was. Can I go off of that or should I wait till I get my pistons (I will be using different ones) and check to make sure it will be the same? I read that you should measure about 1/16" up from where the fire ring stops and stop there with the notching....does that sound about right? I have a tendency to overthink things so I apologize for the seemingly endless questions.
Is there any benefit to using both block notching and offset dowel pins or is it best to just go one route or the other? The block has carbon lines where the fire ring stopped and also on the deck surface where the head gasket was. Can I go off of that or should I wait till I get my pistons (I will be using different ones) and check to make sure it will be the same? I read that you should measure about 1/16" up from where the fire ring stops and stop there with the notching....does that sound about right? I have a tendency to overthink things so I apologize for the seemingly endless questions.
Last edited by bence13_33; Jun 9, 2018 at 03:25 PM.
Race Director
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From: Corsicana, Tx
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You could do both...won't hurt things at all...just need to watch relationship of everything else as you move things. Getting valve away from the wall is similar to what you see when they test a cylinder head with a 4.250 bore vs a 4.500. Not that extreme..but getting the wall away from the valve helps.
Try to watch the chamber so you aren't creating a dead space on the other side.
I'd have the pistons in hand and measure things before grinding. Make sure you have the gaskets also. Some have different shapes. 1/16" is .0625"....I wouldn't go any closer than that. You want to make sure gasket doesn't get toasted on the edge.
If you're ordering pistons..you could have a larger valve notch made or have them move it over some to keep it away from valve.
JIM
Try to watch the chamber so you aren't creating a dead space on the other side.
I'd have the pistons in hand and measure things before grinding. Make sure you have the gaskets also. Some have different shapes. 1/16" is .0625"....I wouldn't go any closer than that. You want to make sure gasket doesn't get toasted on the edge.
If you're ordering pistons..you could have a larger valve notch made or have them move it over some to keep it away from valve.
JIM
Thread Starter
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Joined: Aug 2000
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From: Clymer PA
Jim:
Thanks Jim. I'm trying to visualize exactly how to install the offset dowel pins and how they work. The offset pins push the manifold towards the lifter valley and moves the intake valve away from the cylinder wall? Does that bring the head gasket into the bore? Is there a standard offset for the pins or is it something I need to measure? I do plan to order pistons, do you have any recommendations? Thanks again.
Thanks Jim. I'm trying to visualize exactly how to install the offset dowel pins and how they work. The offset pins push the manifold towards the lifter valley and moves the intake valve away from the cylinder wall? Does that bring the head gasket into the bore? Is there a standard offset for the pins or is it something I need to measure? I do plan to order pistons, do you have any recommendations? Thanks again.