We started out the weekend with desperately poor clutching. The engine was revving out to almost 10K, so we did the only thing we could do that didn't require parts: pulled the driven clutch and dropped the helix spring preload from #2 to #4. Paddock testing revealed no change.
In our "application" The drive clutch is accessible from the side, but not the end, so we could easily get to the weights, but not the spring without pulling the engine. Then there's that whole blowing your face off thing. So a weight change it had to be. Minimal research had revealed that we wanted about four more grams on the weights, so that's what we sent Fish to the nearest Polaris dealer for. Unfortunately, the nearest Polaris dealer was in Citrus Heights. So no testing for us on Friday.
Upon Fish's return we busted out the clutch weight removal and installation tool (a four-foot 2X4) and pried the drive clutch closed enough to R&R the weights. Surprisingly quick and easy. It would have been impossible without the SAE hex-key set lent to us by the good people at Eyesore Racing. You might not have heard of them, but they are stand-up folks. I think they have a website or something.
Anyway, Poo is an American company, but Fuji makes their engines, so working on a Polaris is like working on a mid-eighties GM car. It turns out that a 1/8" allen wrench is the critical tool for Mazdolaris clutch tuning. We used one both to remove the fly-weight pivot bolts and to lock down the clutch-end jackshaft bearing when the intermediate bearing (our previous axial constraint) decided it no longer wanted any part of the whole rotating thing.
Anyway, anyway, we got the new weights installed, but as before, paddock testing revealed no change. Poop. The strange thing was that we should have seen SOME change in operating RPM but didn't. I think now that we were actually running up against an engine rev limiter, and that the things really wanted the engine at 12K or something. Of course there is no reference to a rev limiter in Polaris' documentation. At this point I was reasonably irritated and it was dark, so we decided to drink beer.
Later investigation revealed that our drive clutch spring is not stock like I thought it was. Rather than bright blue like god and Polaris intended, it is bright blue with an intermittent red trace. It's an aftermarket spring with an extra twenty pounds on both ends of travel. We really needed an extra TEN grams on the weights. So at 10:00am on Sunday while cars are filtering out on track, there we are making phone calls trying to locate the appropriate parts while Wayne, one of our drivers and all-around mensch, was already most of the way to Sacramento hoping for some direction as to where he was headed. Wayne actually picked the appropriate parts up from the shop in Citrus Heights before we got through to the parts department, and he was on his way back before we got on track just in time for the green flag.
The early part of Sunday was, shall we say, characterized by full-course cautions. We didn't have functioning wipers due to a certain dearth of amperage, the engine was still trying to rev itself to death, we couldn't get enough heat in the motor to get the temp gauge (which was only getting enough juice to work at full revs) off the pin, the radios had failed, and I was concerned about burning up the belt if I had to stop on the hills going into turns 2 and 6. Things were going far better than I had expected. The car was actually running and driving and passing other cars.
Trying to keep a vehicle with a CVT from revving up isn't easy. Who knew? I couldn't do anything about the visibility, or the engine temperature, or the radios, so I mostly just concentrated on the belt. Oh, and not spinning. A couple of you guys got to see my monster tank-slapper exiting turn 6 through the puddle. One of you threw me a thumbs-up, which I appreciate. Between getting up on the clutch and getting up on the pipe, power delivery is somewhat non-linear.
My solution to the potential belt-burning issue was to lay back on the straights during yellow flag situations so that I could maintain a bit of speed up the hill. My apologies to the cars behind me when I was doing this. I wasn't trying to mess with your race, I just didn't want to add another caution to the mess by having to take a strap. I did get stopped on the hill into 2 a couple of times and learned that just booting the throttle works pretty well. Nice little crab-walks result.
Eventually the spark plug in our low-compression cylinder fouled out to the accompaniment of rather disturbing crackles and explosions out the tail (side?) pipe and our triple turned into a twin. I hit the pits at just about the same time that Wayne arrived with the new clutch weights, so we stuck those in and I went back out. Success! Throttle mashing took the engine to 9100 RPM, then it dropped back to 8600. A bit low, but conservative and completely acceptable.
The rise-then-drop is indicative of the drive clutch sticking somewhere internally. Reversing the preload changes we made to the driven would possibly have put us a little closer to our 9000 RPM goal, but you might have noticed that it was damp Saturday night, and I didn't feel much like crawling under the car to pull the jackshaft.
The big problem we were having was that pesky temperature. It took all day to figure out that our inability to get up on the clutch and rev past 7000 RPM exiting, like, turn 6 wasn't plug fouling: it was over-cooling. We were running so cold that it wasn't making any power. Exiting 11 the engine was a touch hotter because of the hard pull through 9a and 10 followed by slow speeds through the corner. It would rev properly off the line, the fall back off the clutch and drop to a pokey 7000 RPM near the end of the front straight. Sitting in traffic would help for a while. Things were peachy for a lap or two following a pit stop, then 7K again. We have a 140deg thermostat, and it seems to be working, but the big ol' brass radiator sitting out front was just cooling too well.
The stock cooling solution is to circulate the hot water through two or three heat exchangers mounted along the underside and rear end of the tunnel. The exchangers are little more than finned tubes, and are cooled by snow kicked up by the track. These engines also seem to run really cool. I would have theorized that a lot of heat comes out the exhaust with the oil and smoke, but even that seems pretty cool. The triple pipes have a lot of surface area, and we've got the big-ass pipe running inside the front fender and passenger side door skin, so maybe that cools the exhaust down. Dunno.
For Sunday we bent up a couple of slices of drip tray and zip tied them in front of the radiator and the thing ran at 125 - 150 all day. We left provisions for "tuning" the temperature, but turned out not to need them. Problem solved. I think we'll investigate a less-manual solution, though.
Sunday's warmer temperatures also had us running a bit rich. The plugs said that we were tuned perfectly on Saturday, but Sunday they were more black than brown. The combo of rich plus clutched too low plus dumping horsepower into our recalcitrant intermediate bearing (the jackshaft was blue by the time the bearing balls made their escape)* was limiting our acceleration somewhat and our top speed more. When I got out of the car at 3:30ish top revs were down to 7800. John reports that he was back up to 8600 after our emergency bearingectomy. I'm looking forward to driving the car once we get it sorted out a bit.
* That parenthetical was originally phrased somewhat differently. Use your imaginations.