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M_Dragan

To bore or not to bore

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Hi guys, I was disassembling my engine when I noticed this. I can just barely catch my fingernail on it, and its tiny. I've had very mixed answers or suggestions on what to do. Some say that I should just leave it if "I just want it to run" and others seem to think it'll be okay. Also, there is one of equal size or smaller on the apposing side of the cylinder. Should I bother boring it? Whats the worst that will happen if I clean it up and leave it? its pretty far up on the cylinder, almost at the top. (I can't catch my fingernail on anything else but those two scratches and all other cylinders are fine)

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22 minutes ago, M_Dragan said:

Hi guys, I was disassembling my engine when I noticed this. I can just barely catch my fingernail on it, and its tiny. I've had very mixed answers or suggestions on what to do. Some say that I should just leave it if "I just want it to run" and others seem to think it'll be okay. Also, there is one of equal size or smaller on the apposing side of the cylinder. Should I bother boring it? Whats the worst that will happen if I clean it up and leave it? its pretty far up on the cylinder, almost at the top. (I can't catch my fingernail on anything else but those two scratches and all other cylinders are fine)

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Those marks don't happen naturally. What does the corresponding piston/piston ring look like?

 

Bottom line is if it is a scratch it will affect engine life. Kind of a cost/benefit type situation. I've seen people ignore things because they can't afford it, end up having to replace or rebuild it later and not finish the project because of a lack of funds, I've seen people overbuild spend all of their budget making sure things are 10/10 and never getting around to finishing. 

 

I don't think you will be able to get all of it out with a hone tool. Hone tool is really just there to kind of restore the finish not to bore out scratches. You can try and see, for $20-40 it isn't a bad way to see if you can get it good enough. I will say I don't know many places that loan dingle ball hones, the three stone hones are a bit harder to get a nice pattern with so buying the right size dingle ball hone might be a better idea. Build a booth and wear a shirt you don't care about it will make a mess. Remember never to stop in the cylinder and maintain a rapid up and down motion continuing to spin as you pull it out or you will leave vertical scratches.

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Thanks for the tips, I made my attempt and I think it turned out pretty well! The dark spot and vertical line aren't able to be felt with my fingernail. The main problem area us just below the vertical line. What do you guys think of the crosshatching?

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15 hours ago, M_Dragan said:

Thanks for the tips, I made my attempt and I think it turned out pretty well! The dark spot and vertical line aren't able to be felt with my fingernail. The main problem area us just below the vertical line. What do you guys think of the crosshatching?

When you re-ring it, use regular Cast Iron rings... not Moly. Cast Iron rings with bed in nicely on a hand hone. Moly rings require  a very fine and  precise finish that cannot be duplicated with a hand honing tool. 

 

My L28 was hand honed and assemble with Cast Iron rings and it has virtually zero oil consumption.  

 

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I think I would like to see more spacing as in a faster up and down movement more helixy less springy, but honestly for a hand hone you shouldn't expect perfection.

 

Yea....that piston is done. That doesn't bode well for the rest of the engine I imagine. 

 

The problem as chickenman says is going to be re-ringing it. Make sure you get a sufficient size ring. I can't imagine you actually bored out a size, but best to check. If you plan on running 500hp like you say, make sure you have an appropriate ring gap. Now would also be the time to maybe look at GTE internals if your engine was a VVTI GE.

 

The bummer is with the piston in that condition, you really are going to want to have the block, head, and crank flushed realistically. Bits of metal can really screw with oil pressure and lubrication. In addition the crank apparently can store quite a bit of crud even after being cleaned, so right now I imagine it is quite guncked. I believe real street has a very good video on how to clean out the crank AFTER it has been professionally cleaned, and how to install it correctly to prevent crank walk so keep that in mind.

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Got it, I'll be looking more into that crank walk issue and those iron piston rings. I do have non vvti internals that I was co aoderig putting in the engine. 

 

 

What are your honest opinions though, will the motor just consume a little oil or will there be an even bigger problem?

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I'm not a professional engine builder, but as long as the bore is not oblong, and you gap the rings appropriately I don't think that little scratch will be catastrophic.

 

The concern wouldn't be that it would burn and consume a little oil (with the ring gap you probably want it most likely will a little bit anyway) it would be that the rings wear prematurely or maybe get filed down to a weak spot and breaks. 

 

GE VVTI internals won't be able to handle the goals you are aiming for from anecdotal evidence, so swapping to at least non vvti internals would be a good idea, swapping to GTE internals would be even better if they can be found and I think they would lower the compression a bit without having to resort to a thick head gasket.

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Without any way of knowing how deep that scratch was it'll be hard to give you a solid direction. If it was barely worn, then knocking off the glaze on the cylinder walls and run a new set of moly rings is a good way to go. But if that scratch was more than .005" down, you'll likely be running a pretty loose piston to wall clearance. 

 

When it comes to the bottom end though, that's the foundation of the motor, and like building a house, you don't want to cut corners and start with a crappy foundation. 

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At the end of the day do you really want to cheap out on something that could potentially cause premature failure, breaking down on the side of the road and possibly hundreds/thousands in fixing it again?.....


Spend the $40 a cylinder and get it taken care of by the shop ... Just my personal experience and opinion.

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I appreciate all the comments guys! After reading all this i noticed that the rod for the messed up cylinder was bent in a direction that the piston/crank do not move. So, I was going to go .020 over or more on the cylinders but I came across a block on the Facebook marketplace for $20. Took a gamble and bought it, and all the cylinders are okay aside for some glazing. I'm a happy guy right about now, I have a stock block for my current build and a block that I can bore in the future.

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