Cylinder wall condition, should I be worried?

[gezed]

I recently tore apart my motor cause of some oil leaks, it was built with supertech forged pistons and all the machine work was done at a reputable machine shop

there seems to be scoring marks near the lower half of the cylinder wall, some are not very noticeable but 2 cylinders the marks can be felt by running my fingernails across it

Not sure if I should be worried, but I've read that sometimes the piston skirts can make marks on the cylinder walls

before teardown compression test was done and results were around 160 across so doesn't seem too bad, never burned oil; considering that results are on forged pistons with wider clearances, its not bad at all






UPDATEL: Found the problem....
Thrust bearing thats been shaved off by about .4mm all copper material on flywheel side is gone, just been one problem after another...

[gtrkrauss]

if you can feel them with your finger nails then yes you should be concerned.

[gezed]

what could cause this?

everything was clearanced properly

[NismoS-tune]

I had my engine built at Ztune and after 1200kms, mine looked the same way. Went in the garbage as it was also cracked. Who built it? I'd check out what their blueprints were showing for numbers.

[Dragon Humper]

It's most likely the same old, same old. There was some crap that wasn't cleaned properly in the bottom end and some grit got caught up between the skirts and the wall. Happens more than you think.

Double check the clearances and if everything checks out just run a 3 stone hone through there untill you can't feel any sharp edges anymore and screw her back together. You need to do two passes, one with the course stones (180 iirc) just enough to make most of the glazing disappear and then finish with the fine stones (220 iirc) untill you get a nice even crosshatch. In your case I would spin the stones in both directions to knock the edges off both sides of the scratches. Don't worry about the pistons. If your bores were done right and no core shift has happened, that shouldn't take very long. A Lisle set from Crappy Tire, KMS Tools, etc is all I have ever used.

I have freshened motors up to 3 times using a basic set of stones, works just as good as a machine shop set if the bores are not all twisted up. Re-use the rings after a good wash in the solvent tank (leave them on the pistons) and put the slugs back in the hole they came from. You will still have those grooves in the walls but they will be less apparent, you won't get rid of them without a full bore job and new pistons. Make sure everything is squeaky clean going back together. Break in the deglazed bores with the more aggressive method of motor break-in and you should be fine.




Jon.

[gtrkrauss]

Jon does the typing so I dont have too. haha. Good information. Time to take apart that bottom end and start honing.

[nimblestix]

If you had the work done by who you told me you were thinking about at the time, then you need to talk to those that assembled it.
As we've talked before about their credibility and skills I can imagine they are where the problem lays.

Have it assessed by rob from Alecs and then talk to "you know who" about what your options are.

As nismo s-tune said about the ztune guys, specifically one builder in particular, (not mentioning any names) both his and my engine failed in the exact same way and time frame and with the exact same scoring. My bet is your bearings might be toast too as were ours.

Rip it apart. At the absolute least your going to need a good hone, and new gaskets now that you've opened it up.
be for warned that my engine showed the same signs of wear which lead to a full bore, new pistons, crank grind, etc etc.
1 word to sum it up. Expensive.

Forgive me for carrying on, but this is the sort of crap that really grinds my gears.
I'm tired of seeing people pour their bank accounts into these things only to need a rebuild shortly after.
If the hacks out there that are claiming to be mechanics can't get a simple overhaul done correctly, they should give up their trade and stop playing car doctor.

At the least go back to school and learn how to do it right before taking anyone else's money. Were not talking hundreds here, more like thousands.

I'm out.
Text me if your looking for some help man, I've got a pretty good understanding now of everything after having gone through this already.

Brent.

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[gezed]

thanks for the input guys, i still haven't had time to drop the oil pan yet but i will have a look from below and have a peak at the lower half of the skirts and bearings

Jon, in regards to what you said, is it okay to reuse rings with DIY rehone? you mentioned that you've done this 3 times with you motor, did you actually use the same rings for all 3 refreshes?

[Dragon Humper]

It was a different motor and reused the rings once then a fresh set the 3rd time around. After that the bores were too big an a new set of pistons were needed. A Big Block Chevy on spray. Now that I've heard more history on the builder (no names) you really must do a full teardown and check her all out. If the builder made everything a little tight a hone job will correct that and the score marks. You could get off lucky and only need a hone.



Jon.

[Rush_in]

man, its storys like this that scare the piss out of me when trying to find a shop that will care about my motors well being as much as me!

[Dragon Humper]

That's why I get the shop to do all the machining and do the assembly myself. I have caught some serious booboos over the years, would the shop correct that before they put together? Maybe, maybe not.

The score marks could be a result of a bunch of sharp dags and shrapnel at the bottom of the bores. That happens after a bore job (sometimes). These should be removed but the sharp edge should be left as an oil scraper for oil control. It's a fine balance.


Another thing to realy pay attention to is the ring gap, too loose is not a big deal, to tight is death. Same with the brg clearences to a lesser extent.



Jon.

[curtisgoodman]

Yeah I went to Alec's for my engine rebuild... quality work there... Ask for Rob he does it right the first time

[gezed]

funny you shud say that...thats where i got all my work done

[cortexx]

That I can almost guarentee is the result of the ring gap being too tight , when the rings heat up the gap disappears and the rings bind on the bores , you are seeing the wear on the thrust side of the cylinderwall where a binding ring will exert most of its force.

Remove the rings from the pistons , put them in the bores and measure the gap . Also do this at the top middle and bottom of the bore .

A good hone will fix the walls and a new set of rings should be mandatory . They might look ok but overheated rings become brittle and break soon after . Check the piston skirts for signs of early wear too .

If the builder cant get the ring gaps correct i'd at least plastiguage the bottom end , be prepared for a new set of bearings and resizing the rods as i doubt this was done correctly.

On a related thought did he install the oil squirters when he built it ? some shops pull them out and blank them off especially with aftermarket pistons (mahle ones come to mind) .

The engine going in my car soon was built slightly loose as i plan to track it and rev it - the ring gaps are larger than spec , the mains and rods are also a generous tolerance but this is compensated for by a tomei oil pump that can make up the loss in oil pressure with a higher volume of flow to keep everything very well lubed .

[nimblestix]

funny you shud say that...thats where i got all my work done

Did rob or anyone at Alec's do the assembling after machining? Or was it only machined there then assembled elsewhere?

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