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 Bearing Spacers For 3" Journal Crank in 3.25" ?
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Douglas Willinger
Sitting Bull

USA
140 Posts

Posted - 01 Aug 2018 :  01:15:32 AM  Show Profile  Reply with Quote

Are there any examples of people building Pontiac engines with a 3.25" main journal block with bearing spacers allowing use of a 3" main crankshaft?

I note 4.35" (Eagle), 4,375 and 4.65" (Molnar) stroke aftermarket forged crankshafts with the 3" main journals only.

Such bearing spacers would thus provide a greater array of stroke length choices for the larger journal blocks, and also allow the lesser friction of the smaller journal which would be useful say with the need to use a 421, 428 or 455 block for the sake of keeping a project vehicle numbers matching. For instance, if rebuilding a 1971 or 1972 455 HO, get the advantages of the smaller journal while retaining a matching vin number block.

Another idea would be an even smaller main journal crankshaft, in either a 3.25 or 3" main journal block. For instance, the 2.623" of the 3.75' stroke 1957 347 cid, and 1958 370 cid, or the 2.5" of the 3.25" stroke 1955 287 cid and 1956 cid 317 Pontiac engines.

Where can one obtain such bearing spacers?



tjs44
Crazy Horse

USA
533 Posts

Posted - 01 Aug 2018 :  10:52:44 AM  Show Profile  Reply with Quote
There is a issue with the thrust bearing.People have been going the other way for years with a bearing spacer,never heard of anyone going the other way.Tom
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Douglas Willinger
Sitting Bull

USA
140 Posts

Posted - 07 Aug 2018 :  10:32:49 PM  Show Profile  Reply with Quote
When I eventually restore a 1971 or 1972 455HO, I would like to use such bearing spacers to use a 3" journal aftermarket forged crankshaft for the reduced friction, if not also the somewhat lengthier 4.375" stroke offered my MOLNAR. Seems to me that the 4.375" choice would give a bit more torque over a 4.21" or 4.25" while avoiding the added side loading of a 4.5".

So far I have not found any accounts of Pontiac engine builds regarding either the 3" crankshaft into a 3.25" block via such bearing spacers, nor the 4.375" MOLNAR (or 4.35" Eagle)stroke crankshafts- both of which AFAIK come only in a 3" journal crankshaft.
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tjs44
Crazy Horse

USA
533 Posts

Posted - 08 Aug 2018 :  11:01:26 AM  Show Profile  Reply with Quote
I have never know anyone to waste the time and money to do it.The thrust on the crank would need to be welded.Tom
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Douglas Willinger
Sitting Bull

USA
140 Posts

Posted - 08 Aug 2018 :  12:48:58 PM  Show Profile  Reply with Quote
quote:
Originally posted by tjs44

I have never know anyone to waste the time and money to do it.The thrust on the crank would need to be welded.Tom



IIRC Nunzi offered such spacers.
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Steve C.
Chief PONTIAC

1884 Posts

Posted - 08 Aug 2018 :  1:59:00 PM  Show Profile  Reply with Quote
"The thrust on the crank would need to be welded."

Been there, done that. Many years ago in conjunction with putting a 455 crank into my numbers matching 400 block. This years ago before these aftermarket cranks were available. Who ever is doing the work had better know what they are doing ! At the 600+ HP level after some use my set up resulted in a cracked crank and block damage. My origional numbers matching block ended up being toast.


.

Edited by - Steve C. on 08 Aug 2018 2:01:39 PM
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Corncob2061
Cochise

USA
268 Posts

Posted - 08 Aug 2018 :  6:50:19 PM  Show Profile  Reply with Quote
I think in addition to Nunzi, Program engineering made a spacer for a while to put the 3 inch crank in a 3.25 engines.

I can not see it being worth doing either, at least not for less friction. 3.25 was ok for the SD421 nascar engines, we ran a 455 with the 3.25 crank in a dirt track stock car at a pretty constant 6000rpm. Nothing compared to a 500 mile nascar race! It takes more main bearing clearence compared to a 3. When the spacer was available in the mid 2000s it was more because there were steel cranks available for 3 inch mains and not 3.25. That quickly changed and the spacers became obsolete.
Jay
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Douglas Willinger
Sitting Bull

USA
140 Posts

Posted - 08 Aug 2018 :  7:51:19 PM  Show Profile  Reply with Quote
quote:
Originally posted by Steve C.

"The thrust on the crank would need to be welded."

Been there, done that. Many years ago in conjunction with putting a 455 crank into my numbers matching 400 block. This years ago before these aftermarket cranks were available. Who ever is doing the work had better know what they are doing ! At the 600+ HP level after some use my set up resulted in a cracked crank and block damage. My original numbers matching block ended up being toast.


.




*My original numbers matching block ended up being toast.*

Damn! Am saddened to read that. How bad is the damage? Photos?

Have you looked into the feasibility of a repair? I know that Central Virginia Machining offered block repair services.

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Douglas Willinger
Sitting Bull

USA
140 Posts

Posted - 08 Aug 2018 :  7:55:29 PM  Show Profile  Reply with Quote
quote:
Originally posted by Corncob2061

I think in addition to Nunzi, Program engineering made a spacer for a while to put the 3 inch crank in a 3.25 engines.

I can not see it being worth doing either, at least not for less friction. 3.25 was ok for the SD421 nascar engines, we ran a 455 with the 3.25 crank in a dirt track stock car at a pretty constant 6000rpm. Nothing compared to a 500 mile nascar race! It takes more main bearing clearence compared to a 3. When the spacer was available in the mid 2000s it was more because there were steel cranks available for 3 inch mains and not 3.25. That quickly changed and the spacers became obsolete.
Jay




Reading between the lines, I suppose it is possible but has machine shop issues, basically regarding the treatment for the thrust bearing, and thus not worth any such added costs, with at least a cost of a few hundred dollars (assuming that the work was done correctly).

Was asking because I plan on a future 1972 Trans Am 455 HO build, and interested in the reduced friction.

Edited by - Douglas Willinger on 09 Aug 2018 12:05:12 AM
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Corncob2061
Cochise

USA
268 Posts

Posted - 08 Aug 2018 :  10:58:29 PM  Show Profile  Reply with Quote
Light weight internal parts, and gas port type rings would be the great places for less friction. Jay
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Douglas Willinger
Sitting Bull

USA
140 Posts

Posted - 09 Aug 2018 :  12:28:08 AM  Show Profile  Reply with Quote
quote:
Originally posted by Corncob2061

Light weight internal parts, and gas port type rings would be the great places for less friction. Jay



My 434 (400 block, 3" journal, 4" stroke) build's 6.7" MOLNAR PWR ADR rods are 797 grams each- slightly lighter than the more commonly used Eagle and SCAT rods at about 804-805 grams each.

Don't yet know the weight of the pistons that shall be ordered.

Gas port type rings? I shall research that.

What about smaller rod bearings? Say 2.1" SBC size? Or even 1.88" Honda size? My guess is that these would require custom rods and hence be more expensive, but how much more so? (my MOLNAR 6.7 BBC were $654). Smaller rod journals though are going to reduce if not eliminate the crank's overlap of its rod and main journal areas. Indeed, for that reason, any 3.25" main journal block would thus be better off using a crank wit the 3.25" journals.

And of course what about the lifters, with rollers combined with relatively light weight and,, as I have already raised, the variableness of the Rhoads style, particularity the adjustable VMAX?


Edited by - Douglas Willinger on 09 Aug 2018 12:29:58 AM
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Steve C.
Chief PONTIAC

1884 Posts

Posted - 09 Aug 2018 :  06:58:24 AM  Show Profile  Reply with Quote
The art of creating problems that weren't even there.
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Corncob2061
Cochise

USA
268 Posts

Posted - 09 Aug 2018 :  1:22:44 PM  Show Profile  Reply with Quote
LOL, it is. I admire the thought of dreaming up stuff like this though.

This build comes to mind: http://www.mondello.com/page8.html
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Steve C.
Chief PONTIAC

1884 Posts

Posted - 09 Aug 2018 :  2:17:47 PM  Show Profile  Reply with Quote
Dream "Pontiac"

https://www.youtube.com/watch?v=n41m27SzhCg

https://www.youtube.com/watch?v=vP2fdX-QZEU

And there are other similar builds. That said, some might not feel these are real Pontiac engines. For them parts NOT Allowed might include but limited to...

Bug killer ignition
Electric fan
Electric water pump
Roller cam
290-325 cfm aftermarket aluminum heads
NOS
Line Lock
Holley carb
Flowmaster mufflers
Single plane intakes
3400-3600+ RPM converter
3.73, 4.10 gears

Etc, etc.

.

Edited by - Steve C. on 09 Aug 2018 2:22:28 PM
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tjs44
Crazy Horse

USA
533 Posts

Posted - 09 Aug 2018 :  8:50:13 PM  Show Profile  Reply with Quote
All that small bearing stuff is nice on a max effort build.A couple wise engine builders,one winning the first EMC told me to forget it.HP starts with the heads,everything in the top end follows it,virtually no real HP gains in the bottom end.I have built 2 366 RA V engines,one with a short deck,2 1/2 mains,alu rods,the other a std deck,steel rods and 3in mains.HP was within a few HP of each engines.One was stupid expensive to build,the other not so much.Spend away!FWIW,Tom
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Douglas Willinger
Sitting Bull

USA
140 Posts

Posted - 10 Aug 2018 :  12:30:39 AM  Show Profile  Reply with Quote
quote:
Originally posted by tjs44

All that small bearing stuff is nice on a max effort build.A couple wise engine builders,one winning the first EMC told me to forget it.HP starts with the heads,everything in the top end follows it,virtually no real HP gains in the bottom end.I have built 2 366 RA V engines,one with a short deck,2 1/2 mains,alu rods,the other a std deck,steel rods and 3in mains.HP was within a few HP of each engines.One was stupid expensive to build,the other not so much.Spend away!FWIW,Tom



That is what I was already thinking- diminishing returns. Sure the reduced friction is nice and perhaps even physically practical. Yet because of the added need for custom parts, one will spend hundreds of dollars extra for minor power increases.
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tjs44
Crazy Horse

USA
533 Posts

Posted - 10 Aug 2018 :  10:47:17 AM  Show Profile  Reply with Quote
THOUSANDS in most cases!Tom
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