Checking piston to wall clearance on a my Wiseco 6394F3 pistons. I'm getting the following:
#1 - .0056
#2 - .0055
#3 - .0053
#4 - .0048
#5 - .0053
#6 - .0052
#7 - .0055
#8 - .0054

I'm not sure what the spec is for these (I've read about .004), but I'm wondering if this is too much to run NA. The variation is the other thing that's bothering me. Measuring the bores, I come up with about a .0005 difference from the top to the bottom, except for one bore, where the difference is about .0009. Other than that, the block seems fine. Machine work was done by a shop in Jersey. I'm about tempted to scrap this block and move on to something else.

 

If you aren't measuring with a torque plate attached, it may explain the variation. Wiseco pistons usually have .0035-.004" clearance, so whoa you're seeing is a little loose, but it would run just fine.

 

Thanks, I guess I needed a sanity check because I AM NOT wanting to invest in another set of pistons lol.

 

Rather than scrapping the block you could look at piston coatings to make up a little distance.
Here is one I looked up, There are several companies that can do it for you. I'm not sure of the cost though.

PC-9™ is commonly used to salvage a motor that has excessive piston to wall clearance. Vintage motors and other applications with hard to find pistons can have up to .004” of PC-9™ added to the diameter of a piston to tighten piston to wall clearance.

http://swaintech.com/race-coatings/r...piston-skirts/

 

Yea, I've thought about it. I hadn't done much research into it though. I'm just frustrated with this thing right now.

 

Another option is to remove the pistons from the rods, tape off the ring lands, and have a local shop media blast the skirts. Similar to old school knurling this will reduce the clearance by .0018"-.0022" depending on the sharpness of the media used.

 

Call me stupid, but how does media blasting reduce the clearance? I would think if anything that would increase it.

 

Best simple explanation I can give you is to take a piece of flat stock metal and wack a starter punch with a hammer. Like as if you were trying to create a starting point to center a drill bit for a hole.
Now when you run your finger over that spot you feel the ridges from the metal deformation. media blasting does this thousands of times to the soft surface of a piston skirt which by puffing the surface up, this in turn reduces the wall clearance.

 

those clearances and variations look great, I'd run it.

Which parts of the bore are you measuring? do you have a torque plate or head bolted on for measuring? Even if the block was finish honed with a torque plate, when you bolt the head on the bores will not be round anymore.

 

For the two of you that said those clearances are fine, so you're saying .005+ clearances on forged pistons will not in anyway make considerable noise at cold startup and/or excessively wearout the rings?

 

That is the average from the 5 measurements I took in each bore. From top to bottom, about an inch difference between measurements.

I don't have a head bolted on for measuring. Btw, this is an iron block. I know these don't expand nearly as much as the Al blocks.

 

I highly doubt it will wear out the rings, but it may make noise at cold start up and then again, it may not. I've seen stroker engines with almost that much clearance not really make much more noise than the valvetrain.

 

Will probably run great, loose pistons=fast. One of the fastest SBC engines I ever raced had loose out of spec pistons in it. It used some oil but wow that engine made power.

 

Did you measure at 12:00 and 6:00, or 3:00 and 9:00, or both? Also, do you have the long head bolts or the short head bolts?

 

yes. My 12k mile stroker motor has loose ptw clearances with Wiseco 2618 pistons and zero noise and great compression.

 

Those measurements were at 12:00 and 6:00. I'll go back and measure at 3:00 and 9:00 and see where they are at.

I have long head bolts I think (2004+ block).

 

2004+ would be the short head bolts. My theory is that the short head bolts are better because they limit bore distortion when the head is bolted on. I have not tested this theory yet, but I'm getting there.

 

Remeasured everything at 12-6 and 3-9, 4 different points. These are the Averages I got. I used the piston size of 4.0262 as thats what most of them measured. Looking at my measurements, the bores definitely look out of round. How much would be problematic? I don't have my book handy for factory specs.

12-6
#1 - .005625
#2 - .005125
#3 - .005100
#4 - .004675
#5 - .005425
#6 - .005125
#7 - .005800
#8 - .005300

3-9
#1 - .004550
#2 - .004625
#3 - .004975
#4 - .004875
#5 - .004875
#6 - .005175
#7 - .005375
#8 - .004625

 

No thoughts? Beuller? Beuller?

 

4032 alloy should be around .0025"-.003"
2618 alloy should be around .0045"-.005"
Will it run ??? YES
Is it right ??? That's your judgement call !!!
Plenty of folks would beat that ****** and spray the **** out of it; others might want it factory quiet with no oil consumption issues.
Keep in mind that as the rings seat/wear in, those numbers will increase.