Both of these bearing inserts...
Both of these bearing inserts have seen service in a running engine. If you look closely, you'll note that the upper bearing (coated) has a black felt pin "X" mark on its bearing surface. This mark was placed there prior to when the bearing was installed and run. The bearing in the lower image was uncoated before its use.
So we had a particular Grand National engine customer who we'd done three fresh engines and he'd gone to Atlanta for a race. Unbeknownst to me, he failed the first engine during preliminary practice laps, basically warm-ups. On his second qualifying lap, he lost the next engine. I knew we'd run all his engines on the dyno before they left our shop, so something else was wrong. I told him there was likely a problem with his oiling system. In the end, it turned out he'd had his oil filter plumbed backwards.
But here's my point. The first engine that only turned one lap had uncoated bearings. The second engine that got through warm-ups and was on its second qualifying lap had coated bearings. So I began thinking, there's definitely something to this that warranted more testing. The way I chose to do it was I'd put a coated and uncoated bearing on the same journal so that each journal was running a coated and uncoated part, side-by- side, and I set up all the journals like this throughout the engine. Then, when the engine was run through a full cycle, whether it was a specific number of laps or races, teardown showed the coated bearings did look better, in every case. In fact, in most instances, we were able to re-use the bearings. So that pretty well sold me and we've been using coating bearings since then, in the vast majority of cases. In all of our short track, Sportsman, and Late Model engines, we've found coated bearings to be a very beneficial step.
"Beyond this example, we've also found coated bearings to withstand some very severe operating temperatures. For example, we've had numerous cases where an engine was extremely over-heated. One of these got so hot it finally seized the pistons. The crank journals were gun-metal blue, but the bearings weren't hurt."
Do you prefer applying coatings yourself, because some are available at the retail level, or do you like to work with the coating companies?
There are two areas of interest...
There are two areas of interest shown here on this Mahle piston. In this picture you can see that the skirt has a coated wear surface intended to reduction friction (decreasing friction horsepower loss). It's a phosphate coating base with a graphite-based coating applied over the phosphate. Engine builder Keith Dorton says that it has worked remarkably well for him.
Actually, we work with the companies. In particular, we've worked for years with Calico Coatings and we've experimented with different types of coatings, especially engine bearings and the way we do that is like I described before, by staggering them throughout the engine (crankshaft), which I think is a quick way to get a fair and effective comparison between coatings as well as coating versus no coating.
Have you done any experimentation with coating other parts of your engines?
We've evaluated some of the friction-reducing coatings in areas like the crankshaft, connecting rods, oil pans, and those sorts of things that seemed to be popular in the earlier days of coatings. To me, the benefits weren't as cost-effective as I'd liked them to have been, but it seems to be more beneficial today.
We've also experimented a little with some of the thermal barrier coatings, like on headers, and haven't found many reasons to do this other than for corrosion resistance.
Neither have we seen many benefits from coating piston skirts except with the Mahle pistons. They use a phosphate coating and then apply a graphite-based coating over the phosphate. That has worked remarkably well for us. I guess one of the reasons we're continually on the lookout for ways to improve parts durability is because, so far, I haven't found anything I can't tear up, and it's nice to work with companies that are responsive to your needs.
Using ceramics on piston crowns and combustion chambers has been another area we've investigated. I'm sure there are certain types of engines and conditions that would possibly show improvement from coating these surfaces but so far we've not been able to justify the cost compared to the benefits.