Crank Damage

Things were good. I was doing a Keigwins at the Track day at Buttonwillow on June 29th, running slicks on the 748 for the first time, and things were going well. In the afternoon, I decided to swap wheels over to a brand new set of Dunlop D207RRs, just to see how they fared at the track.

It was bloody hot, but I set out for one of the last "A" group sessions of the day. After a couple of turns, I got the flickering oil light that always seems to come up when riding the bike hard in really hot weather for extended periods. Not such a big deal - it's happened before, but I'll keep an eye on it. Couple turns later, the bike revs but the engine spins down in a big hurry off the throttle, like there's lots of friction. The oil light goes solid shortly thereafter, and I pull right back in - my day is done.

On Tuesday the bike is back at Nichols Manufacturing. I explain the situation to Jim, and he immediately says, "rod bearings." Turns out they just had another bike (curiously also around 25k miles) that had the same problem. That one was due to a water leak into the oil, apparently. Jon had the same thing happen in his bike, but that was due to a very badly balanced crank, which flattened the bearings in short order, leading to loss of oil pressure.

Jim dumps the oil while I'm there, and as predicted, little bits of copper pour out, are sitting in the bottom of the case, and are caught in the mesh filter. Joy. Hopefully the crank is okay, though, which would only require a bearing replacement.

Fast forward to today (July 12th), and I find myself at the shop with Jon, looking things over. The crank is definitely scored. The bearings are wiped out of course. So, the crank needs to be sent off to be turned, and undersized bearings fit. :-/

This all begs the question, though - what exactly went wrong? I was banking on the oil plug in the crank backing out, but turns out that wasn't the problem. My plug wasn't very tight, and definitely wasn't Locktite'd, but it didn't back out either. BTW, this plug was steel, whereas earlier models had an aluminum plug.

Next on the list: oil pump. Some pumps have loose tolerances, which leads to iffy oil pressure. Hmmm...now we're getting somewhere. Jon took the pump apart, and found the play at the end of the gears to be on the high side - about 0.004in, while max spec is 0.0027in. Jon points out that since the pump body is aluminum (i.e., expands) and the gears are steel (i.e., more thermally stable), the high heat will increase that tolerance even more, leading to oil pressure problems. Jim's 748 has also exhibited this flickering under similar conditions, and after tearing it down and blueprinting it, the problem has gone away. Hmmmm...

Jon notices some odd wear on the rod bearings, so bolts the endcap back on with bearings in place (the set that wasn't obliterated), and checks for circularity. It should be mentioned at this point that Nichols has some of the coolest equipment at the shop for taking measurements! I don't even know what the doohickey was called that he used to touch various points along the inside of the bearing surface, taking samples, to get the runout (all hooked up to a computer) - very, very cool though! Anyway, upshot is there's a fair bit of runout. Next step - new rod bearings in the same rod, and measure again. Still too much runout. Uh oh.

We've now been poking around for about an hour and a half, and I let Jon go because I know he needs to get down to the races at Laguna. I don't think he was even supposed to be at the shop this morning, but made sure he met with me so I could see the crank damage first hand before he sent it off, and see what the overall damage was. He's going to check into things further to see if the rod itself is out of whack; I should know more on Tuesday next week.

Again, I have to thank Jon and Jim for both going waaaay out of the way to make sure I knew what was going on, how, and why. They're both insanely meticulous, which is why they're the only ones that touch my Ducati. It doesn't hurt that they're two of the nicest folks around, either...

I took some pictures while I was down there of course, which you can see below. As usual, click the image for a larger version...

Two other quick notes:

I got a new flywheel! I was worried for a second when Jon told me, but he just wanted it for proof positive that the flywheels last. This particular unit has seen some 20,000 miles of hard use, and looks like new. Apparently some folks are complaining that the splines wear out, due to the aluminum material. Jon showed me a sample of this. What was painfully obvious, however, was that the flywheel hadn't be torqued down properly, and had come loose, resulting in lots of slop, which eventually wore out the splines. No matter how trick the part, poor installation will still cornhole the whole shebang.

Since the engine is torn down, cases split, etc., now seems like a fine time to go through it (main bearings and such) and drop in an 853 kit. I knew there was a silver lining in there somewhere... :-)

 Closeup of the crank, showing the torn up rod journal on the left.

Slightly different angle, which shows the scoring better...

Full-frame shot of the crank.

The large threaded hole on the side of the crank is where the infamous non-Locktite'd plug backs out. Earlier models used an aluminum plug, which would gradually shave itself to bits, fall out, and result in an instant loss of all oil pressure.

Backside shot of the damage.

Closeup of the backside damage...

Ah, the bearings. Units on left have seen better days... :-) They're quite thrashed, worn, scored, and flattened. Bearing to the right didn't see nearly the damage.

Closer shot of the two toasted bearings. You can better see the flattening in this shot.

And finally one of the roasted ones along with one of the more normal looking ones...

Jon lightened the rear disc for me because he thinks my bike is cursed. :-) It's really quite nice looking! You can also see in this shot that I didn't even get a full lap on my brand-spanking-new tires. >:-( Oh well...another trackday is always around the corner.
Last modified: Saturday, 13-Jul-2002 01:07:02 PDT
Questions/Comments/Problems: Paul H. Yoshimune