Cylinder wall pitting, is it bad enough?

[CyFi6]

Well with my new build I am doing, I went with Wiseco .5mm oversize pistons. This block was rusted out pretty good, but when I measured it I was sure it would clean up. The entire block cleaned up except for this one part. The machine shop gave it back to me like this, but the more I look at it the more uncomfortable I am with it. There is already a lot of work into this block, so really my only other option would be to sell the .5mm pistons and go to a 1mm oversize, but is it worth all that extra time/money/effort or am I making a big deal out of nothing? I measured the spot with a bore gauge and found it was almost .003" larger in the deepest part of the pitting compared to the cylinder size, which is worrysome. Any advice?

 

[Zumtizzle]

Is only the one cylinder like this? Maybe have it sleeved?

 

[hvyman]

What's up with the cross hatch right there?

Who and when did you get the pistons ? Maybe possible to return them for 1mm oversize and just bore the pits out. That's what I would do.

 

[IJ.]

How far down is it?

 

[CyFi6]

Is only the one cylinder like this? Maybe have it sleeved?

Just that one cylinder and that one spot. Not sure if sleeving is something they can do with a 7m block?

What's up with the cross hatch right there?

Who and when did you get the pistons ? Maybe possible to return them for 1mm oversize and just bore the pits out. That's what I would do.

Crosshatch is fine, probably just looks different because I have been wiping the oil away from that spot. Bought the pistons from SupraStore but returning is out as the packets inside have been opened.

How far down is it?

Looks about halfway down, definitely within the ring travel, but not in the upper area where all the pressure is.

 

[IJ.]

Take some measurements, as it's down in the low pressure part of the stroke you might just have a little extra blowby, which cylinder is it?

 

[CyFi6]

I did take a measurement with my bore gauge it is about .003" larger in the deepest part of it. Its on cyl. 5. I most worried about burning oil.

 

[IJ.]

I meant for how far down the bore it is compared to the ring stack at the bottom of the stroke.

 

[CyFi6]

Ah gotcha. Just measured it and its approx 2.9" from both the top and the bottom of the cylinder. I have no idea where the bottom of the ring travel is because I don't have my crank or anything in the motor right now, but comp height on these pistons is 1.299, if that helps anything.

 

[IJ.]

Piston will be 20 thou out of the hole at TDC, measure to the top ring then subtract that from 91mm, measure this distance down the hole is where the top ring stops.

2.9" is about 73.6mm.

 

[CyFi6]

Top of piston to top of top ring : 8.3mm
Distance of lowest part of pitting from deck surface: 71.8mm
Material removed from deck: .2mm
Top of piston to bottom of oil groove: 21.2mm

91mm-8.3mm= 82.7mm



So in this case the top ring will go about 11mm past the pitting? Lmk if I am getting this.

 

[IJ.]

That looks "right", personally I wouldn't use it as is

Might get away with it as a GE but not a performance GTE..

Way back I nipped up a ring and trashed a bore on a set of 2000 Km old Ross pistons in a brand new block, pistons survived no probs but I had to go to the next OS bore...

 

[CyFi6]

Yeah I don't want to chance anything. Considering how much money goes into a build, I would hate to have to do it all over again for something stupid like this that is deep inside the motor. Still sucks though as I am going to lose a bit of money on machine work and the pistons. Shop might work with me a little bit, considering they really should have told me about this before doing the rest of the work on the block. Thanks for the advice. I think if I let it be it would be one of those things that would always be at the back of my mind...

Is sleeving an option on the 7m, or am I stuck with boring them all over.

 

[IJ.]

"might" get away with 1 sleeve but I wouldn't for a performance build due to the 7M's siamese cylinders adding so much strength to the 7M's wet noodle block (would have been so much worse with conventional bores)

 

[CyFi6]

I am only aiming for about 400HP and under with this build. The forged pistons aren't a necessity but extra assurance. I will have a talk with the shop and see what they think. If I were to get the block sleeved I imagine they would need to resurface the block again.

 

[IJ.]

I am only aiming for about 400HP and under with this build. The forged pistons aren't a necessity but extra assurance. I will have a talk with the shop and see what they think. If I were to get the block sleeved I imagine they would need to resurface the block again.

100%, if they're going to sleeve it make sure it's the thinnest sleeve they can get.

If your pistons are good I'd look at selling them to offset another set and bore it but that's just me, the 7M is enough of a gamble even when everything is "right"

 

[Nick M]

Take some measurements, as it's down in the low pressure part of the stroke you might just have a little extra blowby, which cylinder is it?

I think he will burn a little extra oil also.

 

[CyFi6]

Well I took it down to the shop today and he was apologetic and offered to bore it out free of charge to the next larger size. They are going to take that bore out a few more thousandths to make sure it cleans up before I purchase the pistons.

 

[AJ'S 88NA]

Find another shop, they shoundn't touch the bores until they have the pistons.

 

[Nick M]

Sure you can. You just can't hone without them.