Re: RE Pistons?

[Don Dulmage <big-d@xxxxxxxxxxxx>]

Boring as a machinist
In general terms if the many ufacurer makes a poston for it in a size it is 
a pretty god bet that it is ttally safe to bore it that size. Back before 
sonic testers .010 .020 .030, .040. .060. There is not any .050 oversize 
normallly made. How do i know tat it is safe? Because a major manufacturer 
like silvolite would not invest the time to make a pistn that might leave 
them vunerable to lawsuits for failed bore jobs. Think about it. Niether 
would you. Gary mentione .040 and I think that would be always safe without 
question however, a 413 is a bit of a different animal having been cast back 
when men were men and women were glad of it. Previous to about 1970 when we 
bored an engine the piston was the oversize and we added clearance to fit it 
right. Now  since then we went to what sis often called Nominal bore size 
where the block is just bored the .030" and the clearance required is built 
into the piston. One of the reasons they did this is because some machinists 
from the dark ages seemed to think that tighter is always better. This 
elimnated that. for performance and marine use we still add a bit of 
clearance. If we were using Forged Racing pistons clearances were huge. For 
instance TRW 426 hemi pistons called for a MINIMUM for .008". In the old 
days that would have been with a .060" over piston like an old Jahns forged 
for instance , 4,250" bore plus the .060" oversize , plus the .008 clearance 
which would have been 4.318" or just.002 short of a 440 bore. This was never 
a problem and failures were rare if not noexistant. Now do you really think 
that if we snuck the bore out .002"more to the 440 size the wall would fail 
if it was ok at 4.318? remember now that is only .001 per side or .001" of 
the wall thickness.
Can you do that? I have never done it on a 426 hemi but i have done it 
several times on a 426wedge. Far as I know all those mtors are still runnng 
and i know of two others as well. The reason being that there was not a good 
selection of standard style pistons for the 426 marine engines which all 
these were originally but 440 pistons were a dime a dozen. Same hold true 
for the 413 . We know beyond a shadow of a doubt that it will take an .060" 
overbore without a whimper. it we were living back in the day it would get 
the extra clearance too which like the previous example will bring it up to 
just a whisker below a 426 bore size and the block will go the extra with 
ease. In fact the great Dan Dvorak told me he prefers a 413 block.  I would 
do it in a heartbeat thats all I can say.  Now will a cast piston survive 
6000 RPM. i am going out on a limb. I defy any of you to hurt a stock type 
Mopar piston. I have built many experimental motors and often used cast as 
we call them pistons because these are experimental and we didnt want to 
spend a huge amount on an experiment but we have yet to bust any and many 
have seen 7000rpm +
In fact they are not cast BTW that is a misnomer maybe diecast would be 
closer to the truth. Years ago the piston companies like Jahns did make cast 
pistons and they were cast but they are not in the same leaque as the 
pistons that we would find in say a 340 or 440 mopar.Don't believe me. Take 
an old 440 piston and your best hammer and beat on it. It will be in al 
likely hood a long long time before you bust  of any piece. They are touff. 
Someone asked my oceabout this before and I said other than a dropped valve 
or foriegn matter droped into a carb i have never seen a broken 440 piston. 
Having said that I do often have forged custom pistons madefor special 
projects . They are relatively cheap as even the most expensive would only 
be just over $600 made to my specs. Sometimes people get a manufadturer to 
do a sort run as did Maz---i for the 426 wedges a few years ago. That saved 
about $70.
Sometimes we whimp out too and I being a cheapskate myself have done this in 
the past for myself. In reality worrying about spending 350 or 600 for a set 
of pistons for you favourite car is about as sensible as trying to buy a 
used diamond ring for you future bride. If I need a ci ustom piston for a 
finished experiment I have no trouble spending the gold. It might mean I 
have to wait a month or so while the piggy bank fills up but time is the 
alternative to riches.
Still if you have a project that is not going to be a fulll blown racecarand 
thereis a stock style piston available in the cmpression ratio you need run 
it you wont bust it. If you need something special then have the custom 
forged made since there is no good alternative.
Don
I know most of the current crop of machinists are to young to remeber those 
old days but it was so. It changed while i was apprenticing.
----- Original Message ----- 
From: "Herb" <zephyr9900@xxxxxxxxxxx>
To: <1962to1965mopars@xxxxxxxxxx>
Sent: Monday, February 02, 2009 4:50 PM
Subject: Re: RE Pistons?




Just something to read!!

http://www.440source.com/blockinfo.htm

Herb


-------Original Message-------

From: Gary H.
Date: 2/2/2009 3:33:15 PM
To: 1962to1965mopars@xxxxxxxxxx
Subject: Re: RE Pistons?

Seems I read that boring to 0.020" is good, but not to exceed a 0.040" bore;
413 to 440 would exceed that bore model, yup.

Gary H.

-----Original Message-----

 >I can't
> bore a 413 to a 440 piston.  I can go to 426, but cylinder walls would be
> thinner than I would be comfortable with.

[Non-text portions of this message have been removed]


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Please address private mail -- mail of interest to only one person -- directly to that person.  I.e., send parts/car transactions and negotiations as well as other personal messages only to the intended recipient, not to the Clubhouse public address. This practice will protect your privacy, reduce the total volume of mail and fine tune the content signal to Mopar topic.  Thanks!

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