Hey folks, I have a -618 block in my Z/28 (NOM) and it runs fat, always. It has 6000 miles on it. I put new pistons in it back then, .060" over. All machined up/honed correctly some years back and recently I have noticed a bit of oil smoke at idle. Under power it runs clean, but always fat. I plan on digging into this "fatness", and have been only semi-successful, but over time, the smoky idle is a concern. It's not heavy, but it is noticeable. My dangerous assumption is that the rich mixtures have washed down the bores, and the rings no longer have a good seal at low power. I surmise that under power, cylinder pressure keeps the rings against the bores, but when idling, not so much, hence the smoke. I may crack this open this winter but if I can do it, would a new set of rings and a LIGHT hone help? The pistons are Hypereutectic 11:0-1's. I don't want to cheap out, but my question may be obvious....either give it a try...or STOP, this will not work. Any similar experiences? One more point...compression tests have been done several times, and all cylinders are 185-192psi. ( I blame the Crane repo Z cam.) I gotta blame something...I replaced the original Holley with a new 650, and the fatness persisted. To hone or not to hone...that is the question.
Can I hone this a bit?
ChuckD
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1969 Z/28 Restomod, 350, Stealth Sniper, TKO-600, 17" Cragars, Concealed Vintage Air System
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1,906 Posts
I have a new engine that smokes too. It only starts smoking as the temps come up. I too was thinking the rings never seated. But then I read about the intake sealing issue as copo9560 mentioned. I am going to try looking at that first as maybe you should. Easier than a total disassembly.
That said, I have always broke in my engines at the typical 2,000 RPM for 30-45 minutes. I recently read that a better approach would be to run it for only 15 minutes to break in the cam and then drive it under a load to seat the rings. Just running it with no load for up to an hour just glazes the cylinder walls. However, I don't ever remember having a ring seal issue with my method.
But, if you do decide to do a hone, better described as deglazing, a 400 grit ball hone will do the trick, assuming you are using moly rings. Just a few passes are needed to remove the glaze and to get the correct pattern. I have also read that some do a plateau pass with a courser grit, (I think), with a straight stone hone to flatten the peaks of the finish.
All of this info is just my opinion with my relatively limited experience in building engines.
That said, I have always broke in my engines at the typical 2,000 RPM for 30-45 minutes. I recently read that a better approach would be to run it for only 15 minutes to break in the cam and then drive it under a load to seat the rings. Just running it with no load for up to an hour just glazes the cylinder walls. However, I don't ever remember having a ring seal issue with my method.
But, if you do decide to do a hone, better described as deglazing, a 400 grit ball hone will do the trick, assuming you are using moly rings. Just a few passes are needed to remove the glaze and to get the correct pattern. I have also read that some do a plateau pass with a courser grit, (I think), with a straight stone hone to flatten the peaks of the finish.
All of this info is just my opinion with my relatively limited experience in building engines.
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