Steve,
Can you elaborate? I am also about to "garage refresh" a 80k engine. Pumps/bearings/rings/pistons are on the list.
I have also heard of filing the oil rings a bit wide so they are a bit looser at high temps during racing?
Trying to send specs to the shop so they dont just use whatever is in there.
Thanks.
-Z
I am reluctant. It is important to note that I am not an expert. It is also important to note that recognized experts won’t necessarily agree on these issues. It’s not as bad as economists mind you, but there is a lot of “I’ve always done X and never had problems†or the like. When pressed you will probably find that they have certain built-in assumptions which are relevant but different than those of someone else. I’ve used multiple machine shops going back to my street cars in the ‘70s and done my own assembly the vast majority of the time, so I’ve had this discussion a few times. For that very reason I am comfortable saying don’t take any simple answer as gospel.
However, as I see it, assuming stock rings and round straight bores, one of the biggest factors is your break in procedure. As I once posted years ago in more detail on the old site, like making a good first impression you get only one shot at it. If the rings don’t seat correctly from the start they never will. With a typical “street†engine build that requires a seemingly brutal process with minimal no-load running just to confirm no leaks or bad noises, then a series of progessive accel-decel runs with increasing throttle position and RPM. (decel always in gear, engine braking only). FWIW, when I described the process on the old site, Tim from Mazdaspeed endorsed it.
Unfortunately most of us would find it difficult to perform such a process without getting arrested. We have used an out of the way industrial park on weekends and even gotten permission to use the parking lot at the race track. I’m pretty sure none of the popular engine builders are attempting such a process for each engine even if they offer to break it in for a fee, and I’ve not heard of any recommending it.
So what’s the deal? If Jim was serious about using an 80 grit hone then you pretty much have your answer. That’s
really coarse. Your local machine shop will probably think you are nuts but I can tell you he is not alone among top builders to do that. My assumption is that they want to ensure the rings seat during a gentle break in process. We aren’t trying to get 100k miles from a set of rings so some extra wear at break in is acceptable, and possibly beneficial. Think back a dozen years to when Race Engineering was intentionally using narrower low-tension rings in an effort to get that last bit of power. Over done and poorly executed IMO, but the concept is an old one. Point is, it should be possible to use a relatively course hone to achieve better seating if you can’t follow an ideal break in process, and at the same time wear the rings in to their optimal state more quickly.
Similarly, if you can’t achieve an optimal ring gap with the “correct†ring set for the pistons then you can go up one size and trim the ends. Of course even after adjusting the gap that results in a tighter than normal fit, so whether or not you do a tough love break in an extra coarse hone can be used to cut them down somewhat from the start.
But don’t take my word for any of it. Talk to a few speed shops and press them on the details which may make your situation different than what they normally assume. And since there are multiple builders who frequent the site I welcome any conflicting or supplemental information they are willing to provide. Like I said, I’m not an expert but “I’ve always done it this way and not had a problem.â€
Indeed, our engines have always retained exceptional leak down numbers and looked particularly clean on tear-down.
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