Chevy 4-bolt main conversion under $300

[SmokinLowriderSS]

A co-worker loaned me a Chevy High Performance magazine due to an article in it on a conversion process to convert the stock Chevrolet 2-bolt main block/caps to a 4-bolt configuration.
chevyhiperformance.com The article is titled "Rat Motor Upgrade" Four-Bolt Mains Under $300 by Steve Magnante, April 2006 issue
I can't put the pix on here and the article is not YET available online (I looked) but the text & instructions are as follows. Hope it may be of use to somebody.
4-Bolt Mains under $300
26 April 2006 Chevy High Performance Magazine
chevyhiperformance.com
Most owners of '65-'90 Mk-IV 396-454 Rat motors with 2-bolt mains don't
know that a simple machining operation is all that stands between them and
the added strength and reliability of 4-bolt main caps. But, It's true. Virtually
every Mk-IV block was cast with enough bearing bulkhead material to accept
either 2-bolt or 4-bolt main caps on the assembly line.
Armed with this knowledge, the people at Johnson Machine Service (JMS)
devised a novel method of literally tapping into this unused potential, but with a budget minded twist that retains the stock 2-bolt caps. That's right, instead of spending upwards of $800 for billet 4-bolt main caps, the stock JMS reconfigures 2-bolt caps to accept a second row of 7/16" fasteners.
Though the add-on 7/16" outboard fasteners are smaller than the
factory-specified 1/2" bolts used on OE 4-bolt blocks, there's no denying the
extra fasteners are better even if they are a bit smaller. Proving the point, the JMS crew has several customers with converted Chevys putting out as
much as 840HP without problems. Follow3 along as Don Johnson shows
how to transform a 2-bolt bottom end to super-sexy 4-bolt status for dimes
on the dollar.
Unfortunately, I have no way to put the pictures on here.
Step 1, a 4-bolt Chevy rear main cap is required to set up the Bridgeport mill for the 3.060" distance for the outboard row from the crankshaft centerline. It also is required to properly locate the x/y axis locations for the staggered outboard bolt locations for the 2-bolt rear main cap modification. Install the block properly leveled & squared on the Bridgeport.
Step 2, Install and tighten down the 2-bolt caps so they cannot move. Install the 4-bolt #5 main cap with the 2 stock bolts.
Step 3, use 3/4" end-mill to spot face caps 1-4 3.060" outboard from
crankshaft centerline. Due to variances in the caps designs, the depth of cut
will vary. The finished spot does not need to be perfectly circular. To do that
that could unnecessarily reduce the cap thickness on certain low-mass caps.
It is only necessary to remove enough material to leave a nearly circular pad
capable of fully supporting the bottom of the 0.650" diameter Allen-bolt head.
Step 4 Drilling depth is set to make 1.0" holes into the block.
Step 5 To insure perfect alignment, pilot drill the caps & block in 1 operation. A U-drill bit was used to make the pilot holes .012" smaller than the 7/16" holes needed for the bolts. This extra material is the root diameter for the threads after tapping.
Step 6 Use care in taking the cap holes out to 7/16" final size so as to not remove any block material
Step 7 The block tapping begins by using a 3/8" drive ratchet and a #5 tap socket. The 7/16" holes in the caps perfectly center the standard tap as it cuts threads in the block. Follow the standard tap with a bottoming tap to insure full thread depth & engagement. Use compressed air to remove chips between tapping operations.
Step 8 Install the Grade 8, 1 1/4" X 7/16" NS Allen bolts that'll help prevent cap-walk and extend bearing life. Don says reduced-head hex head bolts can also be used but he prefers Allen bolts because they are easier to install and just as strong.
Step 9 Torque specs fro the outer row of fasteners, 65 foot-pounds on 30wt motor oil on threads and under the heads to prevent galling & false readings.
Step 10 Unlike the rest of the caps, #5 has staggered bolt holes offset 0.343"
Failure to match this will cause you to drill through the back of the block and into the crankcase resulting in a persistent oil leak between engine &
transmission. This is why it is critical to use the stock 4-bolt cap or an
identical aftermarket cap during set up to use as a centering fixture and
show you where to put the holes.
Step 11 Spot face & drill the #5 cap the same procedure used on #1-4 but take care to not enter the block just yet.
Step 12 With the cap removed, the same x/y co-ordinates to drill the cap are duplicated on the mills digital readout. Then, drill with the u-drill exactly 1" deep into the block. Breaking through the block will not destroy the block but is guaranteed to foster customer complaints about excessive oil leakage. Don as not lost one yet.
Step 13, Reinstall the cap centered atop 2 3/16" spacers and drill the final 7/16" holes in the cap only for the new bolts.
Step 14 Reinstall the cap fully and tap the holes using the same procedure as the #1-4 holes were.
Step 15 The upgraded bottom end looks impressive. Don says that if this procedure is done on a good-running engine, there is no need to align-hone the main caps after the 4-bolt conversion. Still, JMS usually align-hones the blocks just to be certain. JMS charges $250 for the conversion process
(including fasteners) and $150 if align-honing is done.

[holorinhal]

SmokinlowriderSS,I was startin My 454stroker489 build and was building for a pleasure performance boatbefore I got struck with the need for speed bug.
At any rate I changed the focus of my performance and HP goals,but was tsuck with a two bolt block.I had allredy sunk too much money into my block ,what with purchase of the motor and all machening expenses,to justify switching to a 4 bolt block.
I was'nt happy with the HP numbers that I was told the 2 bolt block would be limmited to.My machinest told me that He had been toying with the Idea of converting a two bolt to a 4bolt and if I wanted to be the ginne pig ,He would try it.Itold Him that I would think about it,and lo and behold A bout a month later,that article came out.
I about fell out when I saw it ,here was a sep by step istruction guide to what I was thinking of doing.
I imediately purchased the Mag and went staight to the machine shop.
After dennis read the article He said He didnt see any problem with performing the upgrade,and it should be good to atleast 850 HP.He told Me He would do the work for what the article said it costs, as a test.
To make a long story short,I had that upgrade done,and now my HP goal is limmited only by My finances!
Before I thought i would be lucky to get to 550 Hp,now I can build To atleast 850HP.It will be a slow build,as I can only buy parts as I can afford them,But thats My goal.May be too much motor for My Kona But we will see.
The upgrade turned out great,and for only 300 bucks! Now I just have to get My Mag back from My Machineist....Hal

[UBFJ #454]

Your conversion similar to this one?
http://www.dvorakmachine.com/4boltconversion.shtml

[Moneypitt]

This is exactly what Art Anderson, (gofastracer), was saying a week or so ago. He has been running one for awhile w/o any problems. I have a question about required machine, (mill) size. Will a standard shop size Bridgeport type mill do this job? Does a 36-40" table have enough travel in X? And are the valley ends square enough, or are shims required to square it up? Hold downs T'd to bottom of cylinders for anchoring down?........I seriously intend to try this and have a busted block to practice on if I have access to a big enough mill..........MP

[Fiat48]

I want to enter this food for thought.
What do 4 bolts do for the main cap? Do they keep the main cap from walking? No. Maybe they help if splayed but they dont help with straight.
Using main studs does not stop the main caps from walking either.
Since I never saw a bbc main cap actually break....I have to wonder what converting to 4 bolt caps really does for me? Is it possible this is more cosmetic than structural?
I understand the resale value of a 2 bolt engine vs a 4 bolt. And for that reason alone would not consider sinking a bunch of money in a 2 bolt motor.
But if the main caps are walking around....transferring metal from one surface to another and changing the dimensions of my critical line hone....I have to ask myself what am I solving (except for etticut) by going to 4 bolt caps?
Would it not be better to dowel pin the caps? How about a girdle?
These are questions in my mind and have been for many many years. What I have seen is the more hp....the more the caps walk regardless. Perhaps shortly I will have a little more data. My current engine runs high rpm and is splayed cap (but it is a Dart). Now that it has run 3 seasons it will come apart
and be inspected.
Also a 427 was fitted with a girdle and it has been run hard all season and it will come apart also for inspection. Maybe some data there.

[GofastRacer]

This is exactly what Art Anderson, (gofastracer), was saying a week or so ago. He has been running one for awhile w/o any problems. I have a question about required machine, (mill) size. Will a standard shop size Bridgeport type mill do this job? Does a 36-40" table have enough travel in X? And are the valley ends square enough, or are shims required to square it up? Hold downs T'd to bottom of cylinders for anchoring down?........I seriously intend to try this and have a busted block to practice on if I have access to a big enough mill..........MP
Yes it will do the job but you will need a spacer to raise the head!..

[Moneypitt]

Yes it will do the job but you will need a spacer to raise the head!..
Is this an accessory for the mill, or a homemade deal? Pics?.........Ray

[GofastRacer]

Is this an accessory for the mill, or a homemade deal? Pics?.........Ray
It is an accessory and pricey, I don't have a pic because I don't have one on mine, used to do it on a friend's mill now I have to get it done!..

[Blueoval]

Hey Gofastracer!!
I was looking over your photo's on your web page?? (Parker ski race) I noticed you have a few pictures of a Ford engine Twin turbo>>>
Do you have any info on the engine, builder, owner??
Thanks!!!

[Kurtis500]

How about a girdle?
Thats exactly what I intend to do with the 496 now.