Piston to Cylinder Clearance
Thread Starter
TECH Fanatic
Joined: Jun 2011
Posts: 1,343
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From: Katy, TX
Piston to Cylinder Clearance Looking for feedback on my methodology for measuring pistons, cylinder walls, and selecting the piston to fit the cylinder.
The engine is an iron block 383.
K1 4" crank
Wiseco -3cc pistons
Eagle H rods
No boost or nitrous
Longevity is my goal
The instrumentation used is a Mitutoyo .001mm Dial Bore Gauge and .0001" micrometer.
The piston paperwork recommended 0.0035" clearance.
I measured the piston largest skirt OD's (at the bottom) with the mic, and here are the values.
3.9000
3.8995
3.9000
3.9000
3.8990
3.9008
3.9005
3.8993
Is it normal for Wiseco pistons to have a +/- .001" tolerance?? That seems high to me.
After I had those measurements, I set the dial bore gauge to 3.9000, and recorded the cylinder bore diameters from 0.5"-5" deep. The cylinders are ~5.5" long overall. The measurements were taken at the point where the piston skirt will ride. Here are the results:
This is conditional formatting in MS Excel. Yellow is low, Green is middle, and Red is high.
Is it normal for the cylinder bores to all have a wider diameter at 4" deep?
Now that I have the piston diameters and the bore diameters, I set out to select the piston to most closely fit the .0035" recommended clearance. Here is what I got for each cylinder, by depth (2"-5"):
This has the same MS Excel conditional formatting. Yellow is low, Green is middle, and Red is high.
Note: I omitted the results for 0.5" and 1.0" deep, as the piston skirt will never be that high in the cylinder.
How do these piston to cylinder clearances look? Is it ok to have some at .0045"?
Thanks for any help.
The engine is an iron block 383.
K1 4" crank
Wiseco -3cc pistons
Eagle H rods
No boost or nitrous
Longevity is my goal
The instrumentation used is a Mitutoyo .001mm Dial Bore Gauge and .0001" micrometer.
The piston paperwork recommended 0.0035" clearance.
I measured the piston largest skirt OD's (at the bottom) with the mic, and here are the values.
3.9000
3.8995
3.9000
3.9000
3.8990
3.9008
3.9005
3.8993
Is it normal for Wiseco pistons to have a +/- .001" tolerance?? That seems high to me.
After I had those measurements, I set the dial bore gauge to 3.9000, and recorded the cylinder bore diameters from 0.5"-5" deep. The cylinders are ~5.5" long overall. The measurements were taken at the point where the piston skirt will ride. Here are the results:
This is conditional formatting in MS Excel. Yellow is low, Green is middle, and Red is high.
Is it normal for the cylinder bores to all have a wider diameter at 4" deep?
Now that I have the piston diameters and the bore diameters, I set out to select the piston to most closely fit the .0035" recommended clearance. Here is what I got for each cylinder, by depth (2"-5"):
This has the same MS Excel conditional formatting. Yellow is low, Green is middle, and Red is high.
Note: I omitted the results for 0.5" and 1.0" deep, as the piston skirt will never be that high in the cylinder.
How do these piston to cylinder clearances look? Is it ok to have some at .0045"?
Thanks for any help.
Stock cast hypereutectic piston to bore is right at .002" in the gen3's ,,,,,the gen4's are I believe .0007 piston to bore . You're Wisecos must be forged as forged pistons expand more than cast pistons like the factory 1's . All I can tell You is set it up to as close as You can to what Wiseco recommends . To answer the 1 question yes in an engine with some miles on it the bore will usually be larger 2" to 3" down the bore .
Your going about this *** backwards. The bores should be fit to the piston, not the other way around.
That being said, the bores shouldn't have taper in them. It looks like they are barrel shaped, which should have been taken out in the final hone.
Personally, I would opt for a set of 3.905 pistons and take the block back to the machine shop and have the bore honed better to the pistons.
That being said, the bores shouldn't have taper in them. It looks like they are barrel shaped, which should have been taken out in the final hone.
Personally, I would opt for a set of 3.905 pistons and take the block back to the machine shop and have the bore honed better to the pistons.
Thread Starter
TECH Fanatic
Joined: Jun 2011
Posts: 1,343
Likes: 8
From: Katy, TX
Your going about this *** backwards. The bores should be fit to the piston, not the other way around.
That being said, the bores shouldn't have taper in them. It looks like they are barrel shaped, which should have been taken out in the final hone.
Personally, I would opt for a set of 3.905 pistons and take the block back to the machine shop and have the bore honed better to the pistons.
That being said, the bores shouldn't have taper in them. It looks like they are barrel shaped, which should have been taken out in the final hone.
Personally, I would opt for a set of 3.905 pistons and take the block back to the machine shop and have the bore honed better to the pistons.
If they did the machine work with the pistons you are measuring, I wouldn't worry about it. They know what they are doing.
And not to be a dick, but chances are they have better measuring equipment than you do.
And not to be a dick, but chances are they have better measuring equipment than you do.
And also, I see you measured at the bottom of the skirt. Try measuring 90 degrees from the wrist pin on the same level as the wrist pin. That's the largest area of the piston as they are cam ground. Meaning they are slightly egg shaped to account for expansion...so when it heats up is is totally round.
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Thread Starter
TECH Fanatic
Joined: Jun 2011
Posts: 1,343
Likes: 8
From: Katy, TX
they don't
And also, I see you measured at the bottom of the skirt. Try measuring 90 degrees from the wrist pin on the same level as the wrist pin. That's the largest area of the piston as they are cam ground. Meaning they are slightly egg shaped to account for expansion...so when it heats up is is totally round.
Thanks for the help guys!
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Thread Starter
TECH Fanatic
Joined: Jun 2011
Posts: 1,343
Likes: 8
From: Katy, TX
Depends on what you need. If you're running a power adder or larger shots of nitrous a 2618 alloy forging is going to be better. It's more brittle however. You'd also want to run a chrome stainless top ring. Wiseco sells such rings with their 2618 forged pistons.
For the street, the 4032 alloy is probably better as is a plasma moly ring. Both would work better NA in a street car. Mahle sells this setup.
For the street, the 4032 alloy is probably better as is a plasma moly ring. Both would work better NA in a street car. Mahle sells this setup.
