fivetenguy Posted March 22 Report Share Posted March 22 Back story: Years ago I had some guy freshen up a KA motor I had. I bought a rebuild kit and gave it to him to do the work. After about 2 weeks he told me the motor was ready so I picked it up and put it aside since the motor was for a future project car. Fast forward to the present. After looking at the motor for a while, I had my doubts about the head. I had the suspicion that the head was never worked on. I pulled the front cover to take off the head and found this. After pulling the head I turned the crank to look at the cylinders and found scoring on the #4 cylinder. Why the heck would you not stop there and reach out to me and tell me that the block has damage?? Now I will have to get the cylinders bored and buy over size pistons. I was looking for suggestions and opinions from you guys. Should I just get the cheap off the shelf aftermarket pistons or should I put in some $700 (the cheapest forged pistons I found) pistons in it? Are there other Nissan pistons that I could interchange? The engine will remain stock and go into a 510 wagon that will see spirited driving. I don't want to have to open this engine up ever again after its been installed. Thanks in advance. Quote Link to comment
fiveoneO Posted March 22 Report Share Posted March 22 I've never rebuilt a KA before, so I don't really have an answer to your piston question. But years ago I rebuilt a Toyota 4AGE using a cheap set of pistons and that engine had some real noisy piston slap. Something to think about. 1 Quote Link to comment
Stoffregen Motorsports Posted March 22 Report Share Posted March 22 The scoring in the bores may be superficial. If it's not measureable, then I'd run it. It's certainly not ideal, but a new ring may wipe away some of that shadow of rust left behind from a blown head gakset. At this point, why not try it before you tear into it? Can you feel it with your finger or finger nail? Do you have a dial bore gauge? Buy a cheap one and see if it shows up on the gauge. https://www.amazon.com/Oudtinx-Diameter-Indicator-Measuring-Cylinder/dp/B0B422QSG6/ 1 Quote Link to comment
datzenmike Posted March 22 Report Share Posted March 22 I had this in my Z24. Ran just fine. You can't feel it. More like a pencil mark. 2 Quote Link to comment
iceman510 Posted March 22 Report Share Posted March 22 1 hour ago, Stoffregen Motorsports said: Can you feel it with your finger or finger nail? I second this. Those marks and the orientation seem somewhat odd to be typical damage. Some darkening or discoloring where the rings sat? Maybe clean up with a ball hone? 1 Quote Link to comment
datzenmike Posted March 22 Report Share Posted March 22 The dark band is probably a sitting rusty ring. It's also a long way down the bore. 2 Quote Link to comment
fivetenguy Posted March 22 Author Report Share Posted March 22 Thanks for your replies. 2 hours ago, fiveoneO said: I've never rebuilt a KA before, so I don't really have an answer to your piston question. But years ago I rebuilt a Toyota 4AGE using a cheap set of pistons and that engine had some real noisy piston slap. Something to think about. That's something I'm afraid of. I don't want to have any issues with this motor after it's installed. 2 hours ago, Stoffregen Motorsports said: The scoring in the bores may be superficial. If it's not measureable, then I'd run it. It's certainly not ideal, but a new ring may wipe away some of that shadow of rust left behind from a blown head gakset. At this point, why not try it before you tear into it? Can you feel it with your finger or finger nail? Do you have a dial bore gauge? Buy a cheap one and see if it shows up on the gauge. https://www.amazon.com/Oudtinx-Diameter-Indicator-Measuring-Cylinder/dp/B0B422QSG6/ I can definitely feel the grove and it seems pretty deep per say for a cylinder wall. 50 minutes ago, datzenmike said: I had this in my Z24. Ran just fine. You can't feel it. More like a pencil mark. I've seen other cylinders like the ones you pointed out and like you, I never had any issues. 26 minutes ago, iceman510 said: I second this. Those marks and the orientation seem somewhat odd to be typical damage. Some darkening or discoloring where the rings sat? Maybe clean up with a ball hone? I can try and see if I could hone it out since I already gutted the block. Quote Link to comment
Stoffregen Motorsports Posted March 22 Report Share Posted March 22 The only way you will be able to hone it out is with a power hone, which also increases the bore size. A ball hone will scuff it up, and that may be enough for a good motor. If you're racing or drifting or adding boost or nitrous, it would be best to have it bored or honed to the next piston size. Again, I'd just run it. What's the worst that could happen? 1 Quote Link to comment
Stoffregen Motorsports Posted March 22 Report Share Posted March 22 1 hour ago, iceman510 said: I second this. Those marks and the orientation seem somewhat odd to be typical damage. Some darkening or discoloring where the rings sat? Maybe clean up with a ball hone? Rust from moisture sitting in the bore causing the ring to rust to the cylinder. 2 Quote Link to comment
fivetenguy Posted March 23 Author Report Share Posted March 23 I see what you guys are saying. Makes perfect sense. That groove I'm feeling should clean up after the piston rubs off. Thanks for taking the time. 1 Quote Link to comment
datzenmike Posted March 23 Report Share Posted March 23 Looks like it was already honed so don't add to it. I assume new rings? Let them break in and do their job. 2 Quote Link to comment
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