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PostPosted: Mon Mar 25, 2019 9:52 am 
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If the bores are all between 3.403-3.406" at the top and 3.401-3.402" at the bottom, it sounds like you're still within spec for taper. Did you take measurements at 90° to each other to check for egging? I don't have my FSM on hand, but I think the allowable range is 0.010" taper and 0.005" egg. Not sure if 3.406" is outside the overall range, but I think I could live with it

If you're still within spec for egg and don't have much of a cylinder ridge, I'd be tempted to ball hone and slap it back together with new rings. Use standard (cast iron) rings if you're not having the bores machined and specifically honed for chrome-moly (which shouldn't be necessary for this level of build anyway).

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PostPosted: Mon Mar 25, 2019 4:23 pm 
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Frank, you're spot on with the specs in my Haynes book; 0.010" taper and 0.005" egg.
After I got home I went straight to the garage and measured again for the egg. The range on the 90 degree measurement was 3.404" to 3.408". The biggest out of round measurement was 0.003", found on two cylinders.

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PostPosted: Wed Apr 03, 2019 1:19 pm 
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Good day everybody.
I finally got the block dropped off at the machine shop. The plan includes milling the deck .060" and cleaning up the bores. After getting his hands on the block my machinist says more than a hone is required. He even doubts the bores will clean up at .020". He'll let me know where we wind up so I can order the correct size pistons for final fit.

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PostPosted: Wed Apr 03, 2019 1:52 pm 
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Go all the way to .060! :twisted: :mrgreen:

~THOR~

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PostPosted: Thu Apr 04, 2019 8:56 pm 
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THOR wrote:
Go all the way to .060! :twisted: :mrgreen:

~THOR~

Might as well, right? I've been looking at pistons, most have been priced the same regardless of oversize. I'll talk to my machinist tomorrow and see where we're at.
Speaking of pistons... the dished pistons, like Silv-O-Lite 1294, what is the advantage with using these? Specs I have seen show the compression height is +.020" over the flat top pistons. The specs also show 13.5cc for the dish. I used these numbers in the UEM's compression ratio calculator and with no other changes, they lowered the DCR by 8/10 of one point, from 8.03 to 7.21. Does this allow for more milling of the deck and head?

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PostPosted: Sun Apr 07, 2019 10:55 pm 
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Just a point of clarification, they don't lower your DCR; they lower your SCR.

Would it allow more milling of the head/block? Not necessarily; but they would require more cutting of the head and block and achieve the same increase in compression.

~THOR~

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PostPosted: Mon Apr 08, 2019 3:08 am 
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Question: Why are you looking at a dished piston, instead of a flat top. The dish will lower your CR, even thought the compression height of the dished piston is .020 more then the flat top.

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PostPosted: Mon Apr 08, 2019 11:15 am 
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EFI Slant 6
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Car Model*: 1975 Dodge D100
Thanks for the replies, fellas.
I stopped by the machine shop and told him we want to go with the .060" overbore.

THOR, thanks for the clarification. I was basically thinking the same thing but struggled to type my thoughts clearly.

Charlie, I was asking about the dished pistons just to satisfy my own curiosity about their application, I wasn't considering a purchase. No need make things harder on myself, this being my first build and all. :oops:
Thanks again for your interest in my project.

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PostPosted: Wed Apr 10, 2019 7:30 pm 
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EFI Slant 6
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Car Model*: 1975 Dodge D100
Pistons arrived today!
Attachment:
IMG_9858.jpg
IMG_9858.jpg [ 64.32 KiB | Viewed 3482 times ]

One of the first things I noticed on the box is the weight tolerance is +/- 2 Grams, so I weighed them. Box is stamped 655.
Attachment:
IMG_9859.jpg
IMG_9859.jpg [ 49.84 KiB | Viewed 3482 times ]

On my electronic scale one weighed 655, two 658 and three are 656. With a range of 655-658, his set is outside the +/- 2 Grams with these weights, right?
Should I attempt to bring the two 658 pistons down to within 2 grams? What would you guys do?

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PostPosted: Wed Apr 10, 2019 9:56 pm 
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Concerning the piston/pin weight,,,
You could remove a bit of weight from the heavy pistons, or
Consider, on an inline six motor, pistons 1 and six move together as do pistons 2 and 5 and pistons 3 and 4.
So install a heavy and light piston on 1 and six.
A heavy and light piston on 2 and 5
And on 3 and 4.
The reciprocating weight will balance out.
To be absolutely correct you should also consider the
the weight on the top half of the rod that is also reciprocating,
but you will be fine.
There are other items much more critical than the piston weights.
Are you going to assemble the motor or is the machine shop?
A few of the really critical items are:
Bearing clearances at the crank and rod ends,
Torque on rods, mains , head bolts, cam gear bolt
Piston ring end gaps
Rear main seal install
Oil pump gear drive depth to cam gear drive
Perhaps cam timing
And most definitely,
Cleanliness,, case, head, crank, inside of oil lines

For the cleanliness, even though the parts look clean on the outside, there is no guarantee they are free of debris on the inside. Prior to assembly, get a selection of bottle brushes and go through every oil line. You can use brake cleaner or other slovent as a flush. Remember to also do the oil lines in the crank.


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PostPosted: Thu Apr 11, 2019 2:33 am 
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I am not sure myself what is acceptable for balance tolerances on different parts and have been wondering this recently. What RPM will be your max? If not above 5500, then I would probably not touch them. Yes, you could grind a little off the heavy ones on the underside and away from thin/critical areas. Stock pistons (and rods) had substantially more variation than this.

Also, those are completely within spec. If you take the average of all 6 and then take a window +2 and -2 g around it, then your pistons will all fall inside that. The absolute number 655 means nothing since you don't need to balance bobwt on an inline 6.

Lou

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PostPosted: Thu Apr 11, 2019 8:39 am 
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Balance on a reciprocating engine is another greatly misunderstood topic.

I first always like to admit I don't know much about it. That puts me way ahead of the average hot rodder/professional engine 'builder' who thinks he does. I do know that when I peeked under the hood of my Lexus LS460L - one of the smoothest vehicles you can buy - I'd see some very fancy hi-tech motor mounts. Why would Lexus do that when they have a staff of very smart engineers, a killer R&D lab, and the ability to manufacture just about anything they want?

They do it because they understand you're never gonna 'perfectly balance' a reciprocating anything.

As for piston weight....if you have a digital scale that weighs in grams, the first thing is to find out what its margin of accuracy is. On a 655 gram piston, you might learn that the scale itself is only accurate within a few grams.

Then, you'll find that if you weigh the same piston a bunch of times on the same scale, you'll get a bunch of different readings. Which do you believe? If I were assembling an engine that was gonna spin 10,000RPM with 1-1/2 lbs. pistons, I'd use a statistical approach by weighing each piston 20 times, throwing out the 2 high and 2 low readings, and averaging the rest to come up with a value.

The bottom line? Use the pistons 'as is' and never think about it again. Especially on a 4500RPM Slant Six that has a 75lbs crank...


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PostPosted: Thu Apr 11, 2019 10:08 am 
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EFI Slant 6
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Location: Pauls Valley, OK
Car Model*: 1975 Dodge D100
Thanks, everybody for the replies and reassurances.
GregCon, your take on the question puts in perspective, thank you.
I hadn't considered the range of weights being within spec of the average, I was only looking at the overall range. Since I don't plan on spinning it close 5,000 rpm, I will leave them as they are and match them up as you describe, John.
I plan to do the assembly myself using Doug's book, this message board and related articles as my primary source for information and advice. In anticipation of getting the block home soon, I do have an assortment of brushes, cleaners and spray paint ready to go for the initial assembly stage.

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PostPosted: Thu Apr 11, 2019 12:03 pm 
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Sounds like a plan!

Lou

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PostPosted: Thu Apr 11, 2019 6:09 pm 
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Weigh the piston pins.

Then match a light pin with heavy piston.

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