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2 bolt main convert to 4 bolt main. |
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BrunoBZH 
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Joined: Mar/19/2012 Location: Pontivy FRANCE Status: Offline Points: 23 |
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 Posted: Nov/26/2012 at 12:32pm |
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Thanks Steve and Kirk.
I found this on Summit:
http://www.summitracing.com/parts/mil-81187/applications - http://www.summitracing.com/parts/mil-81187/applications
But I can't see the 68' 390... but others (360 , 401...).
Is it an omission from Summit?
I can find on Jegs:
http://www.jegs.com/webapp/wcs/stores/servlet/KeywordSearchCmd?storeId=10001&catalogId=10002&langId=-1&Ntk=all&Jnar=0&Ne=1%2B2%2B3%2B13%2B1147708&searchTerm=milodon&search=MkMdlYrSearch&redirect=false&N=1521734&mkYEAR=1521676&mkMAKE=1521716&mkMODEL=1521734&mmySubSearch=on - http://www.jegs.com/webapp/wcs/stores/servlet/KeywordSearchCmd?storeId=10001&catalogId=10002&langId=-1&Ntk=all&Jnar=0&Ne=1%2B2%2B3%2B13%2B1147708&searchTerm=milodon&searchType=MkMdlYrSearch&redirect=false&N=1521734&mkYEAR=1521676&mkMAKE=1521716&mkMODEL=1521734&mmySubSearch=on
(hope the link works).
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White70JavelinSST
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Joined: Aug/08/2012 Location: Minnesota Status: Offline Points: 4866 |
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Posted: Nov/26/2012 at 4:49pm |
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back to the photo in the earlier posts, the one placed by crossramrambler, of what appears to be four bolt main caps on a 390 block, and I'm just saying this for conversations sake.
Would it be possible to machine a flat surface on that part of the main web that is outside the normal two bolt cap's mating surface and place a very accurate "shim" under the four bolt cap, or machine a special four bolt cap to fit onto that flat machine surface? It would sort of be like a "step down" splayed four bolt cap. Is that area of the block beefy enough to do this?
And for more conversation, if the four bolt caps were torqued in place, without any special machining other than the additional drilled/tapped hole, wouldn't the cap be distorted at the time the line boring/honing was done, and would that be repeatable when retorqued? just sayin...
What say you guys,
Armand Edited by White70JavelinSST - Nov/26/2012 at 4:52pm |
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70 Javelin SST, second owner, purchased 1972
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SKeown
AMC Addicted 
Joined: Jul/30/2009 Location: Texas Status: Offline Points: 3085 |
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Posted: Nov/26/2012 at 5:19pm |
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many thangs that are possible aren't practical. If you must have four bolt mains, get yourself a 401 block and sell the 390 block. I never experienced main bearing problems until I had four bolt caps installed. Faerman Racing Engines performed the line boring and somehow the #4 cap was tighter than the others. Consequently trash from that bearing fed to the #6 rod bearing causing the need to start over with a re-do on the line bore and crank grind.
Don't outsmart yourself, unless you're attempting to make real serious power, just use good studs and keep an eye on the contents of the oil filter.
SKeown
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brownspirit
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Joined: Mar/07/2009 Location: Georgetown, MA Status: Offline Points: 1020 |
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Posted: Nov/26/2012 at 6:24pm |
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Just to be clear, if you have a 70 390 block I believe it will accept the 4 bolt caps the same as a 401... I think. Andy
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69' BBB AMX 390/4-speed
69' s/crambler project 69’ International F210d Cummins/5+4 |
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JonnyB
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Joined: Nov/26/2012 Location: Indianapolis Status: Offline Points: 51 |
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Posted: Nov/26/2012 at 6:25pm |
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I install Pro-Gram caps frequently...You will have $350 in labor where I work plus the $350 for the caps and $80 for the studs, but don't forget you will have to have outer bolts too...
There is more than just bolting them on, drilling, line bore, and line honing...You actually have to fit the cap to the register then set the air-gap under the stepped/splayed portion of the cap... They do have flat bottom caps for other aplications, but I don't really see that style working out all that well on the 390 because once you machine it flat there wouldn't be enough depth in that area for the cap to 'snap' into the register... You could machine that area flat and make a spacer, ect...but you're prolly just looking for problems if you go that route...Not to mention you're prolly lookin at $1000 total just to make it splayed 4 bolt...Money better spent elsewhere... |
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435853
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Joined: Nov/21/2009 Location: Brookfield,CT Status: Offline Points: 25 |
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Posted: Nov/26/2012 at 6:30pm |
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435853
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Joined: Nov/21/2009 Location: Brookfield,CT Status: Offline Points: 25 |
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Posted: Nov/26/2012 at 6:33pm |
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With all the information I have recieved I am going to leave this 390 block a 2 bolt main.
Thanks for all the help. |
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whitelumpy401
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Joined: Aug/31/2009 Location: bentonville Status: Offline Points: 247 |
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Posted: Nov/26/2012 at 6:38pm |
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Forget the main studs on a 2 bolt main use bbc arp main bolts just use a botton tap on block and make sure the bolt screws all the way in with out the washer . If you look at a stock bolt they have a shoulder under the head that is the same as the hole in the cap to help hold it in place the stud is the same size top to bottom . and when changing bolts or studs have the line hone checked
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whitelumpy401
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crossramrambler
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Joined: Dec/13/2008 Location: Reno,Nv Status: Offline Points: 494 |
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Posted: Nov/26/2012 at 8:39pm |
No, the picture that I posted is a 70 block. If I had known I would of used a 401 block.........Jim
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bulletbuilders
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Joined: Nov/14/2012 Location: Southern Orygun Status: Offline Points: 53 |
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Posted: Nov/26/2012 at 10:05pm |
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From my experience as an engine builder for 25+ years, the reason you use studs instead of bolts is for increased clamp load on the part in question.(in this case, main caps). Fine threads (studs) always clamp more uniformly than coarse threads (bolts). When it comes to main caps and heads, I always insist the client purchase studs when the horsepower target is over 350 and/or when he is using a power adder
On AMC's, I use my main cap girdle to prevent 'cap walk'. It also spreads the load to adjacent caps. Larry |
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brownspirit wrote: