[swisstyphoon]

Need your advice, what to do now...

Last year, when I received my car here in Switzerland, I noticed a rough idle, random miss firing when cold, and the car also showed bad fuel trims. Turned out the shop, that did the pulley, tune and plugs, gapped the spark plugs way to close.
While I was changing the plugs, I looked inside the cylinders with my endoscope. I noticed a big ol scratch on cylinder wall nb. 2
I did a leak down test, result was good.
The car run fine after I changed, and gapped the plugs correctly.
Been driving 5000mls since then, the car doesn't burn oil, or anyting.

Now I'm in the process of doing heads, cam, Magi 2650 etc. over winter, so I pulled the heads yesterday. I had a closer look at the scratch on the cylinder wall. It is not deep, you won't hook with your finger nail. But you can still feel the scratch. Not sure what caused it, maybe a burr or something from the factory... ?
The car would probably run many miles more without a problem leaving the scratch. But still not comfortable leaving it like that at this point. I already have everything apart, and hopefully it can be fixed by just honing.
I would have to find a machine shop over here, that is trustworthy to work on a LT4, and probably buy a torque plate on my own. Or I have to send the block to the US to have it fixed there..

What dou you guys think caused the scratch?
What would you do next in my position?

[gtfoxy]

If it were me, I’d yank that slug just to check the rings & give it a good cleaning. It may not be bad now, but there may be an issue & it could get progressively worse.

You don’t need a torque plate for a quick hone job like that.

[Stephen12ZL1]

in my opinion, I have seen quite a few scratches like that which don't affect anything except esthetics. If the leak down/compression is testing OK in the cylinder, then everything is OK. If oil consumption is OK and no problems with oil control rings, then proceed as usual IMHO.

Obviously, we all strive for perfection but in this case I don't feel this scratch is detrimental in any way if testing has determined standard parameters to be within normal limits. I see a lot of work ahead for zero gain except to contain worry. That scratch is likely from the edge of one of the compression rings (they can be really sharp) in the fresh bore upon installation and initial start-up.

[gtfoxy]

Originally Posted by Stephen12ZL1

in my opinion, I have seen quite a few scratches like that which don't affect anything except esthetics. If the leak down/compression is testing OK in the cylinder, then everything is OK. If oil consumption is OK and no problems with oil control rings, then proceed as usual IMHO.

Obviously, we all strive for perfection but in this case I don't feel this scratch is detrimental in any way if testing has determined standard parameters to be within normal limits. I see a lot of work ahead for zero gain except to contain worry. That scratch is likely from the edge of one of the compression rings (they can be really sharp) in the fresh bore upon installation and initial start-up.

That’s one scenario.

The other is a tad tight ring gap or an issue with the oil control ring.

Looking at the point the scratch ends & the wear point of the top ring on the cylinder it puts it at right about where the oil rings would be. If you pulled the piston it would be more evident the scenario if the scratch continued past the lowest point of either top rings.

[Yves ZL1]

Originally Posted by swisstyphoon

Need your advice, what to do now...

Last year, when I received my car here in Switzerland, I noticed a rough idle, random miss firing when cold, and the car also showed bad fuel trims. Turned out the shop, that did the pulley, tune and plugs, gapped the spark plugs way to close.
While I was changing the plugs, I looked inside the cylinders with my endoscope. I noticed a big ol scratch on cylinder wall nb. 2
I did a leak down test, result was good.
The car run fine after I changed, and gapped the plugs correctly.
Been driving 5000mls since then, the car doesn't burn oil, or anyting.

Now I'm in the process of doing heads, cam, Magi 2650 etc. over winter, so I pulled the heads yesterday. I had a closer look at the scratch on the cylinder wall. It is not deep, you won't hook with your finger nail. But you can still feel the scratch. Not sure what caused it, maybe a burr or something from the factory... ?
The car would probably run many miles more without a problem leaving the scratch. But still not comfortable leaving it like that at this point. I already have everything apart, and hopefully it can be fixed by just honing.
I would have to find a machine shop over here, that is trustworthy to work on a LT4, and probably buy a torque plate on my own. Or I have to send the block to the US to have it fixed there..

What dou you guys think caused the scratch?
What would you do next in my position?

Hello geographic european neighbour 🙂🙂

If I understand well you are going to unsettle all thé engine ??🤔
Do you make it by yourself ?

[Bangkok_ZL1]

Good luck.....

[swisstyphoon]

Originally Posted by gtfoxy

That’s one scenario.

The other is a tad tight ring gap or an issue with the oil control ring.

Looking at the point the scratch ends & the wear point of the top ring on the cylinder it puts it at right about where the oil rings would be. If you pulled the piston it would be more evident the scenario if the scratch continued past the lowest point of either top rings.

Thanks for the input guys.
I think I will remove that piston and have a closer look, since I'm pulling the block anyways to upgrade to the new Katech oil pump.
Like Stephen said, probably nothing to worry, but then my ocd is kicking in.. lol

[swisstyphoon]

Originally Posted by Yves ZL1

Hello geographic european neighbour 🙂🙂

If I understand well you are going to unsettle all thé engine ??🤔
Do you make it by yourself ?

Hello French neighbor
Yes I take the engine apart myself, I'm a mechanic.

[Yves ZL1]

Originally Posted by swisstyphoon

Hello French neighbor
Yes I take the engine apart myself, I'm a mechanic.

Ohhh give me your adress... I’ll come and see you this summer....🙂🙂🙂
I often have hollyday in Switzerland.... or near annecy like this previous summer.

You could do the maintenance of mine 🙂🙂🙂🙂

[gtfoxy]

Originally Posted by swisstyphoon

Thanks for the input guys.
I think I will remove that piston and have a closer look, since I'm pulling the block anyways to upgrade to the new Katech oil pump.
Like Stephen said, probably nothing to worry, but then my ocd is kicking in.. lol

If you’re yanking the motor & pulling the pan it’s a no-brainer. Besides, the piston would need to be out for a good hone.

I’d even consider getting fresh cross hatching on all 8 along with new rings. Then you can check the rod bearings also.

[swisstyphoon]

Originally Posted by gtfoxy

If you’re yanking the motor & pulling the pan it’s a no-brainer. Besides, the piston would need to be out for a good hone.

I’d even consider getting fresh cross hatching on all 8 along with new rings. Then you can check the rod bearings also.

Yeah of course no honing with the piston in it...
Freshen up all 8 while I'm in there was crossing my mind also.

[gtfoxy]

Originally Posted by swisstyphoon

Yeah of course no honing with the piston in it...
Freshen up all 8 while I'm in there was crossing my mind also.

You’d think, but you’d be surprised what I’ve heard people admit to doing.