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Discussion Starter #1
I measured the deck height of this used shortblock I picked up last night. I first found TDC using a dial indicator & base.

Once I determined that I found TDC in the center of the piston, I zero'd the dial indicator (made sure to have some preload first), then I placed the dial indicator on the deck, right next to the bore. I got .034". I tried this a few times and got the same result.

To verify my results, I also layed a straight edge across the bore and used a dial caliper to measure the distance from the top of the straight edge down to the center of the piston. I then zero'd the dial caliper and then measured the thickness of the straight edge and again got .345".

I proved to myself that there is a lot of variance from the .025" rule of thumb for 350 deck height.



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The way I read this you just checked one hole. That's fine but if you used a reconned rod it will be short. Lots of variables. Do the 4 corners and some blocks will freak you out. That's why we deck them before we bore them with a boring bar. It fixes the deck heights to the crank as well as the deck angle so you can true the bore to the deck with the boring bar. RM
 

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Discussion Starter #3
Real McCoy said:
The way I read this you just checked one hole. That's fine but if you used a reconned rod it will be short. Lots of variables. Do the 4 corners and some blocks will freak you out. That's why we deck them before we bore them with a boring bar. It fixes the deck heights to the crank as well as the deck angle so you can true the bore to the deck with the boring bar. RM
Yes, just checked one cylinder. I'll go check another cylinder now and reply with my findings.



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Yeah, you may find a lot of variation. This is what gets people in trouble when they try for min. squish. The 9.025" number is a nominal dimension but in real life it varies and can vary front to back and bank to bank. As mentioned variations in crank throws, rod lengths and pistons all can conspire against "nominal" dimensions. Blueprinting is all about closing in tolerances.

Equalizing minimum squish is can difficult if the rods aren't the same length.
This is why you have to mock everything up, juggle parts around and make several trips to the machine shop when trying to get the squish right.


....Just sitting around waiting to go to work. Last night we drove up to Port Huron over to Lansing, then Grand Rapids down to Kalamazoo west almost to Benton Harbor and back to Allen Park. About 490 miles.
Maybe we'll drive to the Mackinac bridge and back tonight. I'll be glad when this test phase is over.
 

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I just measured my 468 deck height a week ago during mock up. Mine is using new SRP pistons with twice reconditioned stock rods. Had my block decked @ 9.780, and the pistons vary .013 to .000 in the hole. Mine isnt a max effort engine, so I have been told these numbers arent bad.

I also was told that until you get into the $125.00 each rods, you will be searching, and swapping alot of parts during mock up to get them all the same.

I am interested in what others thoughts are here...

Dale
 

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You can correct and equal all the rod lenghts when you bore the small end to bush them if they had pressed pins. We use to do that. Decent rods are cheap now and unless you have rules on the motor they are cheaper than messing with stock rods. Cheaper piston have wrist pin hole tolerances so you can match the rods to the pistons and get them pretty darn close usually. JMHO, RM
 

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Paul Wright said:
Maybe we'll drive to the Mackinac bridge and back tonight.
Thats a nice area...been over that bridge about three times.......Northern Mich is quite pretty....:)
 

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Real McCoy said:
You can correct and equal all the rod lenghts when you bore the small end to bush them if they had pressed pins. We use to do that. Decent rods are cheap now and unless you have rules on the motor they are cheaper than messing with stock rods. Cheaper piston have wrist pin hole tolerances so you can match the rods to the pistons and get them pretty darn close usually. JMHO, RM
Experience is no doubt the best teacher. Wish my machine shop would have offered some of these ideas. I didn't know any better, and it probably is my responsibility as the assembler/builder, and owner.

I am sure the desire for more power is in the future, so I will be doing this again. :)


Dale
 

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DriveWFO said:
Ok, I measured on the centerline, front and back of each piston.

#1: .032"
#2: .033"
#3: .027"
#4: .029"
#5: .029"
#6: .029"
#7: .029"
#8: .027"
Now you can see the problem. If you only measured #1 and cut it .032" to get zero deck you'd be five thou too much on #8 and #3.
If you assumed .025" clearance you'd be short 8 thou on #2.

Is this the super secret squirrel blue bag engine?
 

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Paul Wright said:
Now you can see the problem. If you only measured #1 and cut it .032" to get zero deck you'd be five thou too much on #8 and #3.
If you assumed .025" clearance you'd be short 8 thou on #2.

Is this the super secret squirrel blue bag engine?

Paul, so would the first thing you do now is mix and match your parts in an effort to make the deck clearance measurment more uniform? And once you get it the closest you can you would then deck the block, if you were going for zero deck, to match the piston with the least deck clearance? (not sure if I explained that clearly)

for example in his numbers above, if this was as close as he could get his parts to match, would he then deck the block to match cylinders #3 & #7 (deck the block .027")?:)
 

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Discussion Starter #12 (Edited)
Paul Wright said:
Now you can see the problem. If you only measured #1 and cut it .032" to get zero deck you'd be five thou too much on #8 and #3.
If you assumed .025" clearance you'd be short 8 thou on #2.

Is this the super secret squirrel blue bag engine?
Yes, this is the budget blue light special engine in the bag.

I do see the problem now having measured instead of assuming. The variations could be caused by the pistons, rods, crank, deck or all of the above. Now I see why it is imperative to try different combinations of rods & pistons at an attempt to equalize the variations.

Is it coincidental that the deck height of the front two cylinders (#1,#2) are greater than the rest??? If I new for sure that the variations were due to the rod/pistons, I would remove them and reassemble. Is there an accurate method for me to measure this without having a machine shop do it?



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DriveWFO said:
Is it coincidental that the deck height of the front two cylinders (#1,#2) are greater than the rest???
I suspect this is partially caused by the throw itself.......


DriveWFO said:
If I new for sure that the variations were due to the rod/pistons, I would remove them and reassemble. Is there an accurate method for me to measure this without having a machine shop do it?
hey go floaters and you can swap the parts around at home yourself;)
 

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Discussion Starter #14

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DriveWFO said:
The pistons have pressed pins. I'm wondering if it would be worth swapping rods/pistons around to see if I can even out the deck heights at all???
I would as all it would cost ya is some time....you might be able to get them closer then the .006" spread you have now:)
Plus with the rods out you could check out the rings to see if they are box fit, file fit or???? There could be a pony or two waiting to be released if the current rings are box fit (normally they have a wide gap) and you install some file fit or gapless rings in their place


DriveWFO said:
Also, the piston compressed height is 1.560". Is this a pretty typical compressed height for a 5.7" rod?

I believe it is the typical pin height for a 5.7" rod with a 3.48" stroke crank:)
 

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NEVER FINISHED64 said:
Is that advisable swapping things around once the rings are seated? They would probabbly hit a new height or bottom in another cylinder where the ridge has allready formed?
thats a good point....I guess it would come down to how used that used short block is...I wasn't thinking about that when I mentioned swaping parts out...hmmmm
 

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Discussion Starter #18 (Edited)
69NovaSS said:
thats a good point....I guess it would come down to how used that used short block is...I wasn't thinking about that when I mentioned swaping parts out...hmmmm
It's never been run...just assembled.

Rings:
Top Ring Included: Yes
Top Ring Thickness: 5/64 in.
Second Ring Included: Yes
Second Ring Thickness: 5/64 in.
Oil Ring Included: Yes
Oil Ring Thickness: 3/16 in.
Oil Ring Tension: Standard
File Fit: No
Gapless: No
Top Ring Material: Iron
Top Ring Facing Material: Moly
Second Ring Material: Iron
Second Ring Facing Material: Cast iron
Oil Ring Material: Stainless steel



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DriveWFO said:
It's never been run...just assembled.
well then hop to it and get to swaping around the parts....you got a drag racer to build:D ;) :)
 

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Discussion Starter #20
DriveWFO said:
Ok, I measured on the centerline, front and back of each piston.

#1: .032"
#2: .033"
#3: .027"
#4: .029"
#5: .029"
#6: .029"
#7: .029"
#8: .027"
I suppose I could try swapping #1,#2 with #3,#8. How do you check for clearance between the rods and between the rods and crank? Feeler gauge? I need a ring compressor too.



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