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401 Advice/Machining
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Keller View Drop Down
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    Posted: Jun/12/2022 at 1:23pm
Hi all, and thanks for the add. I've been following this site for some time and have learned a ton of info along the way. Much appreciated! I am new to the AMC world and was fortunate enough to acquire an AMC 401 from a 1976/J20 last summer. The intended use is for street/weekend driver and I was hoping to bring it back to life and restore the hp back to that of the 401's of the early 70's. I have turned it over to a local machine shop and expressed those goals but am losing confidence in the shop. I'm not feeling good about their knowledge about the AMC, turnover has lead to passing the motor around and ultimately creating mass confusion about the goals. My initial goals shared with the shop were to bring the compression back up to the early 70's range of 9:5.1 and hp 300-400 range. They cleaned it up and determined that it would need to be bored to .20/.30 over. I went with .30 due to availability and ordered the Wiseco Pro Tru R/Dome -27cc, Lunati Voodoo Cam (268/276) along with lifters/springs and timing gear set, with hopes of using stock rods, correct sized head gasket, and RPM Air Gap to reach the original goals.

I love to hear your thought's on this build or any advice that you my have to help. 

Back to my shop concerns, so I originally had plans to have them build the motor and and break it in based on our initial talks. However, the more I talk to them the less confidence I have and had decided to have them just assemble the short block. After speaking to them last week I am now thinking just finish the machining and I'll do it all myself. I've not built an AMC before but I know enough not to treat it like a SBC which I'm feeling more and more like they are every time we speak. Speaking with them Friday they explained to me that they honed out the stock rods small end (original press fit 1.007) to accommodate the Wiseco floating wrist pin (1.000) making it full floating. Again, I'm new but this math doesn't seem to add up for a proper fit. My question is this acceptable or is there a better way of handling this issue. Thanks in advance and any advice would be greatly appreciated.

Harold
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WesternRed View Drop Down
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Points: 5808 		Post Options Post Options   Thanks (1) Thanks(1)   Quote WesternRed Quote  Post ReplyReply Direct Link To This Post Posted: Jun/12/2022 at 5:46pm
I'll let others who know more chime in, but to my knowledge usually you bush (bronze bush) the small end of the rod if you are going to run floating pins.

If there is an extra zero in there with the clearance it would be more likely, i.e. 0.0007", typical numbers I'm seeing quoted are 0.0006-0.0013".
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6PakBee View Drop Down
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Points: 5458 		Post Options Post Options   Thanks (1) Thanks(1)   Quote 6PakBee Quote  Post ReplyReply Direct Link To This Post Posted: Jun/12/2022 at 6:10pm
Originally posted by WesternRed WesternRed wrote:

I'll let others who know more chime in, but to my knowledge usually you bush (bronze bush) the small end of the rod if you are going to run floating pins.

If there is an extra zero in there with the clearance it would be more likely, i.e. 0.0007", typical numbers I'm seeing quoted are 0.0006-0.0013".


Bronze bushing is the traditional approach for full floating pins.  That having been said I know of more than one B/RB Mopar that is running floating wrist pins in forged rods with no bushings.  But if it were me, I'd still bush the rods.
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PROSTOCKTOM View Drop Down
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Points: 2458 		Post Options Post Options   Thanks (2) Thanks(2)   Quote PROSTOCKTOM Quote  Post ReplyReply Direct Link To This Post Posted: Jun/12/2022 at 6:14pm
Floating steel rods it not any concern I would have. 390 Fords were floated from the factory without bronze bushings.

Tom
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Rebel Machine View Drop Down
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Points: 5121 		Post Options Post Options   Thanks (1) Thanks(1)   Quote Rebel Machine Quote  Post ReplyReply Direct Link To This Post Posted: Jun/12/2022 at 7:17pm
If they have assembled the short block I'd want to know what the main and rod bearing clearances are. I had trouble with that some years ago. You can't clearance them the same as the small block Chevy, you'll have low oil pressure and tear up cam bearings (like I did).

Since you're not confident with this shop I'd find out before assembling the rest of the engine.

-Steve-
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hacksaw1971 View Drop Down
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Points: 1404 		Post Options Post Options   Thanks (1) Thanks(1)   Quote hacksaw1971 Quote  Post ReplyReply Direct Link To This Post Posted: Jun/12/2022 at 7:55pm
full floating in a cast rod????
its the little things that make the biggest difference
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WesternRed View Drop Down
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Points: 5808 		Post Options Post Options   Thanks (1) Thanks(1)   Quote WesternRed Quote  Post ReplyReply Direct Link To This Post Posted: Jun/12/2022 at 8:00pm
Originally posted by hacksaw1971 hacksaw1971 wrote:

full floating in a cast rod????

401 rods are forged.
I've finally given up drinking for good...........now I only drink for evil.
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hacksaw1971 View Drop Down
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Points: 1404 		Post Options Post Options   Thanks (1) Thanks(1)   Quote hacksaw1971 Quote  Post ReplyReply Direct Link To This Post Posted: Jun/12/2022 at 8:24pm
i know that.... but i think the pins are full floating on the 360 at the shop and thay are cast rods.
its the little things that make the biggest difference
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Keller View Drop Down
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Points: 59 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Keller Quote  Post ReplyReply Direct Link To This Post Posted: Jun/12/2022 at 9:11pm
WesternRed, thank you for the input. You're correct that I left out a "0". The specs for the stock wrist pin are 1.0007-1.0008. I have read much of the same that a brass bush should be installed as well as oiling holes. This was my concern along with the potential of a pin walking out and destroying the bore. I have much to learn but I would rather not learn the hard way. Thanks again.  
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Keller View Drop Down
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Points: 59 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Keller Quote  Post ReplyReply Direct Link To This Post Posted: Jun/12/2022 at 9:15pm
Originally posted by 6PakBee 6PakBee wrote:

Originally posted by WesternRed WesternRed wrote:

I'll let others who know more chime in, but to my knowledge usually you bush (bronze bush) the small end of the rod if you are going to run floating pins.

If there is an extra zero in there with the clearance it would be more likely, i.e. 0.0007", typical numbers I'm seeing quoted are 0.0006-0.0013".


Bronze bushing is the traditional approach for full floating pins.  That having been said I know of more than one B/RB Mopar that is running floating wrist pins in forged rods with no bushings.  But if it were me, I'd still bush the rods.

6Pakbee, thank you for your thoughts. I feel the same in that I'd prefer to error on the side of caution considering it is a 401. If it were a more common engine I may gamble.  
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