425 differences

Old August 15th, 2018, 12:08 PM
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425 differences

Is one way to tell if a block is a 39 or 45° cam bank angle by the size of the lifter bore? One has the same size lifter bore as a 455 correct and which one is that?
I have two blocks with no heads, one has a crank (steel?) I believe both or one has a small dimple near the front (drill spot) They both have the same size lifter bore at .842 (same as 455) Im just trying to figure what exactly I have.
I also included some pix. Is that dimple that some people talk about located next to oil fill tube hole?
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Last edited by scrappie; August 15th, 2018 at 01:16 PM.
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Old August 15th, 2018, 02:04 PM
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Look like 45* blocks to me, I have one of those same ones. That’s a good thing.
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Old August 15th, 2018, 02:08 PM
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I am not the expert, but I believe there wasn't a direct correlation with the cam angle and lifter size. I think there was some combination of Toronado vs 88 model and the 1967 model year that broke that correlation. I am the owner of a 1966 45 degree block.

Someone had suggested putting 12" pipes or dowels in two opposite lifter holes. Then put a sheet of cardboard (cut at a 90 degree angle) diagonally between the the two and see if the angles match. If they do, then it's a 45 degree block. You'd probably have to cut off a corner of the cardboard to make it work down by the lifters.

See this post for a further discussion:

https://classicoldsmobile.com/forums...ank-angle.html
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Old August 15th, 2018, 02:49 PM
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Originally Posted by sysmg View Post
I am not the expert, but I believe there wasn't a direct correlation with the cam angle and lifter size. I think there was some combination of Toronado vs 88 model and the 1967 model year that broke that correlation. I am the owner of a 1966 45 degree block.

Someone had suggested putting 12" pipes or dowels in two opposite lifter holes. Then put a sheet of cardboard (cut at a 90 degree angle) diagonally between the the two and see if the angles match. If they do, then it's a 45 degree block. You'd probably have to cut off a corner of the cardboard to make it work down by the lifters.

See this post for a further discussion:

https://classicoldsmobile.com/forums...ank-angle.html
Correct. At various times Olds has built examples of all four possible combinations (and at least three possible combinations on the 425 block). I got one of the Monedello lifter bore tools years ago. Slide it in the lifter bore. Put a square on the deck. If the tool is exactly perpendicular to the deck, it's 45 deg. The block from my 67 D88 is 0.842", 45°.
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Old August 15th, 2018, 05:49 PM
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Originally Posted by cutlassefi View Post
Look like 45* blocks to me, I have one of those same ones. That’s a good thing.
I was under the impression the 39 degree was more desirable? IDK
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Old August 15th, 2018, 07:11 PM
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Some years back someone posted the following pic showing two small lifter bore motors that purports to show how to tell the difference between those; supposedly on a 45 degree motor, there is lots of "meat" at the top of the lifter bore (as shown in RED), and very little at the bottom of the lifter bore (as shown in BLACK).

Seemed to make sense based on how the lifter bores would be drilled, but I can't swear by it. That said, based on this "method", I'd say you may have one of each.


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Old August 16th, 2018, 08:42 AM
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Originally Posted by scrappie View Post
I was under the impression the 39 degree was more desirable? IDK
Easier to get a cam, I am not aware of any other reason why 39 degrees is better.

However, there must have been a reason that they made the change. Does anyone know why they changed form 45 to 39 degrees?
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Old August 16th, 2018, 09:35 AM
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Originally Posted by sysmg View Post
Easier to get a cam, I am not aware of any other reason why 39 degrees is better.
Not anymore, you can get just about any cam for either combination.
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Old August 16th, 2018, 09:59 AM
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Originally Posted by sysmg View Post
However, there must have been a reason that they made the change. Does anyone know why they changed form 45 to 39 degrees?
I'm only speculating here, but if you look closely at the photos in Post #6, note that the small hole drilled into the lifter bore to reach the oil gallery is much closer to the top of the lifter bore on the 39 degree block. This means that a shorter drill bit could be used, which would likely be less prone to breakage on the machining line. That's the only advantage I can see. Going from 45 deg to 39 deg increases the angle between the pushrod and lifter, which increases side load on the lifter in the bore, which would be less desirable.
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Old August 23rd, 2018, 06:37 PM
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Originally Posted by cutlassefi View Post

Not anymore, you can get just about any cam for either combination.
Really? Even roller cams? Not ready to pull the trigger yet, but I've got a 45 degree 425 sitting around that I'd love to drop one into...
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Old August 24th, 2018, 02:35 PM
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Originally Posted by Bubba68CS View Post
Really? Even roller cams? Not ready to pull the trigger yet, but I've got a 45 degree 425 sitting around that I'd love to drop one into...
Yep, a 45* roller is no problem.
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