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I'm trying to find what would cause this in the cylinder walls. The dimples are at the top and bottom of the cylinders and on both sides. Recommended wall-to-piston clearance for the pistons is .0035" but actually measure .00065" and .0009" in the dimples.
The piston skirts are scuffed on the bottom of one side and higher on the other side.
The engine is 4.185" bore x 4.125" stroke, 13:1, 7800 rpm. 3500 street miles and ~100 1/4 mile passes.
The blueprint sheet says the PTW was set to .0043"-.0045 which is more than what is recommended by Wiseco (.0035"). Now, after 3500 mi, PTW is .0065" and .009" in the dimples.
My local engine builder says the cylinder walls look like they have 100k miles on them.
Thats a good amount of stroke, could you post what length rods you have, and what pistons you have, and is that a dry sleeved 5.3 block? Have you measured how long your sleeves are? Almost looks like the piston is being pulled out of the bottom of the bore a little too much and getting a little rocking action going on.
Prolly my old eyes, but that sure looks like about a 1/2" vertical crack in that top pic...
I saw that when I got home but haven't been back to the shop to look closer. That isn't my question though. The block is junk now anyway...at least the sleeves are.
Thats a good amount of stroke, could you post what length rods you have, and what pistons you have, and is that a dry sleeved 5.3 block? Have you measured how long your sleeves are?
6.125" Ultra H beam, don't have piston info in front of me right now, yes, (ERL) dry sleeve 5.3 block, sleeves are 5.8".
I saw that when I got home but haven't been back to the shop to look closer. That isn't my question though. The block is junk now anyway...at least the sleeves are.
That's usually what the "dimples" are; cracks in the sleeves/cylinders. At least in my experience it has been. You really see it when you try to hone them and you get shadows where the hone shoes don't touch.
Not an expert here, my .02 both Spanks13, & Slogo are correct.
Long Stroke,Short Rod = High Side Loading +Thin Wall due to max Bore, now add perhaps
Excessive Piston to wall clearance, 7800 RPM Magnifies all of the above.
The Domino effect of stacking intolerances.
Piston speed is just astronomical in a 4.125" stroke application at 7800 rpms and adding to that a not so rpm friendly rod/stroke ratio plus extra PTW clearance
I'd actually say you got your money's worth outta that combo being that far off
Piston speed is just astronomical in a 4.125" stroke application at 7800 rpms and adding to that a not so rpm friendly rod/stroke ratio plus extra PTW clearance
I'd actually say you got your money's worth outta that combo being that far off
You're probably right. I have a buddy that thinks a 4" stroke would help a lot (1.48-1.53) but I'm sticking with 4.125x4.185 and proper PTW clearance and loosen up the wrist pins and try again. Maybe bring the rpm down. It has never been on a dyno so that would help to see where the power is.
Piston speed is just astronomical in a 4.125" stroke application at 7800 rpms and adding to that a not so rpm friendly rod/stroke ratio plus extra PTW clearance
I'd actually say you got your money's worth outta that combo being that far off
Oh, since you mention piston speed, I had a couple mechanical over-revs this year due to miss-shifts and rpm hit 8400.
Not an expert here, my .02 both Spanks13, & Slogo are correct.
Long Stroke,Short Rod = High Side Loading +Thin Wall due to max Bore, now add perhaps
Excessive Piston to wall clearance, 7800 RPM Magnifies all of the above.
The Domino effect of stacking intolerances.
Oh, since you mention piston speed, I had a couple mechanical over-revs this year due to miss-shifts and rpm hit 8400.
SIXTY % of an engine's rotational friction is the piston rings.
your pistons/rings are traveling 715 linear feet PER SECOND..
A 4 inch stroke reduces that figure to 693 feet 4 inches
for reference an NHRA Pro Stock engine sees 758 feet 4 inches with a 2:1 rod to stroke ratio
I've read quite a bit and never heard of a cylinder bore cracking because of RPM, nor Excessive Piston to wall clearance. The wall clearance being to much is the worst thing I see listed. Thin Walls or a bad set of sleeves sounds like the problem. Also if you have dimples sounds like debris as anything dealing with pistons and bores generally leaves scars.
I'm sticking with 4.125x4.185 and proper PTW clearance and loosen up the wrist pins and try again.
Sounds like a winner! There are a few guys running that combination and revving it. Correct pistons Fix most known problems, so if the pistons weren't hurt then what? Bad set of sleeves added with to much play with the pistons & walls. Maybe, but bad sleeves is what I guess.
Call up ole uncle Steve @ RED he's post here also. To actually get some Factual based knowledge from experience. Hope you get it corrected, it sounds like your already at it! http://www.raceenginedevelopment.com/contact-us/
SIXTY % of an engine's rotational friction is the piston rings.
your pistons/rings are traveling 715 linear feet PER SECOND..
A 4 inch stroke reduces that figure to 693 feet 4 inches
for reference an NHRA Pro Stock engine sees 758 feet 4 inches with a 2:1 rod to stroke ratio
06-29-2017, 11:19 AM
Dimpled Cylinder Walls 
