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PostPosted: Wed May 01, 2019 6:09 pm 
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Supercharged

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Quote:
set on the main bearing saddles


Dat Tru,,
what is important is the relationship of the crank bore to the firing deck,,
and that would be the case on any engine block, not just a slant,,

and I am sure that you were close on the piston check, but an ez way to check piston compression height
is to put a piston pin half way in one piston and the same pin half way in a second piston, set the
two side by side pistons on something really flat, like a piece of glass with the combustion face down.
If there is a difference in the distance from the pin bore to the combustion face (compression height)
for those two pistons you can find it with feeler gauges measuring from the combustion face to the glass plate.


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PostPosted: Fri May 03, 2019 6:27 pm 
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Location: Pauls Valley, OK
Car Model*: 1975 Dodge D100
emsvitil wrote:
So do pistons 2-5 incrementally vary between .099 and .125 ?

Well, it turns out I should've checked this, doing so would've answered some questions.
I took the block with the crank and the two con rod/pistons installed to the machine shop. He was very interested in seeing it after we talked the other day. We measured the deck height on 1 & 6. Using his better instruments he didn't get the same numbers I did, but the difference was still easy to see. I told him about swapping these pistons in the cylinders to eliminate any variation in the pistons or con rods. He asked about 2 - 5 and suggested we put pistons in there to check. We started at 2 & 5, then 3 & 4. These all measured the same as cylinder number 1....
The block is true and square, it's the reman crank that is off on number 6.
Using his tools we measured 1 - 5 at 0.112" down the hole, number 6 is 0.94".

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PostPosted: Fri May 03, 2019 8:27 pm 
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Supercharged

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So , #6 is .008 deeper than 1-5, that certainly will not kill a nice street build.
Having that information may help you to understand why, down the road when
you service the spark plugs why #6 may look a little different.

Have you looked closely at the crank, I would get a micrometer and get good checks
on all the main and pin diameters and roundness. Especially #6. That .008 has to be somewhere, if not
in the pin diameter, it is in how #6 pin is indexed. Meaning that when #1 is at TDC, #6
is x degrees BTDC or ATDC.


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PostPosted: Mon May 06, 2019 9:47 am 
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TBI Slant 6
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Location: Pauls Valley, OK
Car Model*: 1975 Dodge D100
DadTruck, I respectfully ask that you please check your math. I come up with #6 being 0.018" deeper. Is that going to still not kill a nice street build?
I do not have a micrometer for the mains and pins. I'm looking into getting my hands on one.
Concerning the indexing, I made a simple, adjustable depth piston stop and found TDC on cylinders one and six. They both hit the same TDC measured on the balancer.
After that, I measured the deck height at BDC; #1 is 4.245", #6 is 4.282" (0.037" difference)
It looks to me like the one cylinder is indexed properly, but has a longer stroke.

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PostPosted: Mon May 06, 2019 6:26 pm 
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Turbo Slant 6

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I didn't review all the posts here, but if the problem is that the deck is not parallel to the crankshaft centerline, I experienced that same thing once. When I determined it had been cut at a slight angle I sent it to Mike Jeffrey who brought it to his machine shop. They put it on their decking machine and said it was okay. I assured Mike that it wasn't. The machine shop looked at it again and they found that it wasn't registering properly in their machine which must have worked the same as the one where it was decked originally. I never did exactly understand the problem, but they figured out how to get it in the machine properly, and cut a new deck that was parallel. Maybe the same thing happened to your block. You can tell if you take a 12" caliper and measure the distance from the top of the main bearing bore to the deck on the front and back of the block.

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PostPosted: Mon May 06, 2019 7:12 pm 
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Supercharged

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Quote:
check your math


I never did get the hang of that 'new math' but I agree with your finding.
and that is enough to work to resolve.

(check your post from May 3rd, you have a mis placed decimal point
Quote:
number 6 is 0.94"
)

so you are saying
there is a .018 difference in stroke with 1 & 6 pistons at TDC
and
There is a .037 difference in stroke with 1 & 6 pistons at BDC

seems to me that if a crank throw was .018 short at TDC
the resultant stroke being 4.12 - .018 = 4.102

the same crank stroke would be the same .018 short at BDC


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PostPosted: Mon May 06, 2019 7:55 pm 
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Location: Pauls Valley, OK
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The stroke would be longer, wouldn’t it? A longer stroke travels higher in the cylinder then moves farther away at the bottom, doubling the difference, right?

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PostPosted: Tue May 07, 2019 8:16 am 
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Supercharged

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Quote:
A longer stroke travels higher in the cylinder


I was considering the shorter one, but regardless if it is long or short.

the rod journal on the crank travels in a round circle around the main bearing journals.
the radius of the circle will be equal at all points.

if the rod journal was welded up then reground to the correct diameter but in a different position to change the stroke,
the rod journal would still travel in a round circle around the mains.

If it is .018 tall on the TDC it will be .018 deep at BDC, for a total stroke increase of .036, so maybe we are thinking the same
just saying it differently.

Exner mentioned measuring the distance from the center of the main to the top deck on the ends of the block,
that would be a good thing to do. Your machine shop may have a caliper that large.


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PostPosted: Tue May 07, 2019 11:53 am 
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TBI Slant 6
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Thanks again for the replies, fellas. I really appreciate the help on this.
DadTruck, great minds think alike. Some communicate their thoughts better than others, I guess. :wink:
I'll check with my machinist and see if he's got a caliper for making the measurement that you suggested, Exner. I considered that measurement with the stuff I have on hand but I can't think of a way to get accurate results. I'll let you know what we come up with.

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PostPosted: Tue May 07, 2019 1:51 pm 
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Is it more likely that your stroke is the same and you just got one odd piston when they rebuilt it? One with a different pin to head distance.

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PostPosted: Tue May 07, 2019 3:57 pm 
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TBI Slant 6
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Location: Pauls Valley, OK
Car Model*: 1975 Dodge D100
I don't think so Rick. The tall deck height stayed in the same cylinder using a piston/rod from another cylinder. Likewise, the short deck height didn't change when measured with the piston/rod from the "tall" deck cylinder.

Today I call the reman shop, Crankshaft Supply, asking about the condition of the crank. The man I spoke with said the crank was likely that way when the factory first installed it in the engine. I asked if he knew if there was an OEM tolerance range for stroke offset or if it was common to find the factory cranks this way, he didn't have an answer. I asked if they check for this during the reman process, he said they didn't concern themselves with the stoke, they just cleanup the journals and make sure they aren't bent. I asked if they could have "accidentally" increased the stoke if a particular journal needed a lot of work to get right, he said no, they don't offset grind cranks.
There sounded like a lot going on at the place when I called and he seemed to be getting annoyed by all the questions so I ended the call at this point. I could tell I wasn't getting anywhere with these guys.

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PostPosted: Tue May 07, 2019 5:16 pm 
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My local machine shop does offset grinding and I'm sure would index such a crank. Terry Walters Machine in Roanoke, VA. They are not very fast, but do quality work for sensible prices.

Lou

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PostPosted: Tue May 07, 2019 5:23 pm 
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Supercharged

Joined: Thu May 12, 2005 11:50 pm
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Car Model*: 64 Plymouth Valiant
3.400 bore
4.125 stroke

37.5 cuin 613.72cc

3.4
4.161

37.8 cuin 619.08cc

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64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

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PostPosted: Tue May 07, 2019 8:02 pm 
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TBI Slant 6
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Location: Pauls Valley, OK
Car Model*: 1975 Dodge D100
Lou, a friend recommended a shop in Norman (40 miles north) that will be able to grind the crank. I plan to call them tomorrow. I have the day off Friday and can get it in as soon as that if all works out. Fingers crossed!
Ed, the added stroke doesnt amount to much there. I plugged those numbers into UEM's compression calculator. Comparing the two different stokes and associated deck heights (all other things equal), the DCR goes from 8.184 to 8.513. :shock:

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PostPosted: Wed May 08, 2019 12:13 am 
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Glad to hear it! Hope the Norman shop is tip top.

Lou

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