Hey guys I wanted to get your guys opinion if you think this is normal wear on the cylinder with supertech (low expansion) pistons?

Cylinder 3 intake side

Cylinder 3 exhaust side


cylinder 3 piston, pic's of both sides.



I had asked the machine shop for piston to wall clearance of .0028"
But when I measured it, because my gauge only reads .0005 increments I found it between .0025-.003"

This is after only 60miles of hard breakin. Didn't sound weird or do anything weird and when I did a compression test to check if the rings seated it was really high, 250psi.

Pistons are the supertech pistons rated for 12:1cr in b18c with a PR3 head.

It seems like a lot of wear on the cylinder walls. I don't usually pull the motor apart this soon to check, just this time I had the opportunity to do so, so I saw this and wanted to see what others thought. Not sure if that's just how it is with forged pistons or the machine shop got the tolerance too tight.

Thanks

 

That doesn't look bad IMO. How many miles?

 

The piston crown is contacting the cylinder wall. See how your anti-detonation grooves (the area directly above the 1st ring land) look beat.

 

The skirts look ok but like rocket said the piston crown looks damaged and worn. Almost like the engine ingested something.

 

From CP pistons

Anti Detonation Grooves (Contact Reduction Grooves) are grooves that protect the top ring by disrupting detonation waves. Also know as contact reduction grooves, these grooves limit the piston/cylinder contact during high temperature and RPM

 

ive seen this when pulling pistons...

wiseco,arias even cp...

even with proper p2w

then i find out the owner has been driving and racing around with a velocity stack and no filter just a screen...

could possibly be some dirt/sand but def check the tops and chambers.. detonation is likely the case

how come there isnt a picture of the dome?

 

must be some good heat thrown into that motor. shouldnt the piston be tapered with the skirt being the biggest part. this mean the top would have to heat up a lot and expand to be hitting the bore.

what cams are you using and what is your afr and egt if you have a gauge

 

pay close attention to the crown... some "things" are imbedded in it piston looks intact so it cant be "pieces" from the piston

 

The piston is tapered at the top. I'd say its the tune OR not enough wall clearance up top. Most machine shops have trouble getting the bore straight from top to bottom, so make sure you run your bore gauge top to bottom and check to see how round it is.

Those need replaced by the way...and you might as well go up a size. That won't hone out.

 

WOW, You guys are really good for spoting that on the top of the piston.

I didn't mention that it dropped a valve in cylinder1 (was embarrassed to say) , sucked in pieces of the valve/piston into the intake manifold and redistributed out to the other cylinders. That's what the damage on the piston crown is from I bet. We are going to a 82mm piston now.

Yes, the tops of the piston have small chunks of piston/valve enbeded into them I've ordered the new piston and stripped down the block already.

Reason i'm concerned about the wear on the cylinder wall is, should I still use that same machine shop? did they do the proper piston to wall clearance the first time.
4piston, your right I should measure the bore from the bottom, middle and top of the cylinder.

Rocket, thanks for your insight, I didn't know those were called anti-detonation grooves that's pretty neat. Good to know and i'll check out the rest of them to see.

 

93egSLEEPER: 60miles only

blackeg: skunk2 pro1 cams, a/f is 12-12.5:1 at full throttle, 13.5-14.5 at partial throttle, no egt

 

ah crap I just realized what you guys are all telling me? it's the metal debri that got caught on the piston/anti detonation grooves(thrust angle) that's causing all those marks.

So it's really hard to tell if it's from the debri or the machine shop didn't get the piston to wall clearance bored properly.

 

Damn I didn't even notice the top of the piston. And I was hoping you were going to say thousands of miles, not 60. Those must be deeper ridges than they apear to be on the computer.

 

With you having the motor let go, its kind of hard to diagnose. I'd start fresh and just do it again. Probably nothing the machine shop did.

 

definitely the crown damage that caused that to happen to the cyls, not anything the machine shop did.

 

i had a feeling there was a reason why the pictures

specifically avoided the "dome" shots hehehe


IMO dropping a valve would throw debri into the intake runners, up the plenum and have number 3 or other pistons suck it in , from piston 1(chamber)


i agree i dont think it could be debri from the machineshop ,

OS pistons should do the job well.. and afte boring and honing make sure u clean the block well. use papertowels to wipe the bore and see if its clean or dirty still

 

...use brake cleaner when doing this

 

Wash cylinders with hot water and laundry detergent. Brad told me they like Tide (those Nascar guys love to rep their sponsors).

Wipe down with ATF or Marvel Mystery Oil with Brawny paper towels afterwards to pick up any remaining honing debris. And then relax by smoking some Marlboros.

 

That sounds about right, especially if your gage only reads to .0005". In reality that measurement is probably only accurate to within a .001" on your gage. Hopefully the machine shop would have a .0001" reading gage, but they also have tolerances as well.

The damage is alsmost certainly from the dropped valves obviosuly.

 

Start looking at your valve problem first. Make sure you have the correct keepers, the correct retainers, check for coil bind of the spring with your cam, and also check for valve to valve. Show us the top of the piston and a chamber.

 

footnote :

first post/pic u can see the scoring go beyond where the piston stops at tdc

there is damage at the lip/top of the bore where the deck is..

so there is also a high probabiity th scoring was amplified with debri when dropping a valve a cyl1

 

thanks again for all the input guys. Every ones comments have been very helpful.

 

what valves and springs where you using ? what rpm did it drop