Saturday, July 19, 2014

An expensive lesson

European (and especially Italian) motorcycles are much like a high-maintenance girlfriend, they don't tolerate neglect and if you're foolhardy enough to neglect her needs she WILL make you pay.
In all seriousness, European motorcycles are very expensive to own and maintain, with Ducati and BMW heading the list.  Many prospective and first-time Ducati owners are shocked to realize that they will be facing maintenance costs of 600-1200 dollars (depending upon exactly what is needed and who does the work) EVERY 6500-7500 miles. This maintenance simply can not be deferred as these bikes will not suffer neglect the way that some other bikes can.  It is simply the cost of owning an exotic vehicle and something to keep in mind if you're contemplating the purchase of a bike like this.

Here we have a 2003 Ducati 999 Monoposto, looking very seductive in her bright yellow dress and carbon fibre jewelry.  Hot, yes?  It has 13,000 miles and is due for its second major service.  Apparently the starter clutch started playing up and rather than getting it taken care of immediately, the owner put it off until the sprag failed completely.  The extent of the damage is detailed below.

Here is the alternator cover ready to be removed.

Once the flywheel was removed, here is what was found.

After cleaning everything, the full extent of the damage becomes apparent as the gear and the outer race are also destroyed.

Here is the new starter gear, compare to the failed gear in the second photo.  Yes, much of the metal that used to be that gear ended up in the oil.

Here is the new sprag and flange ready to be assembled to the flywheel.

Here I will show just how easy it is to screw things up if you aren't careful during assembly of the flywheel/sprag/gear assembly.  In these photos only the bearing and spacer are shown for clarity.
There is a thrust washer that goes between the crankshaft timing gear and the starter gear.  The inner bearing collar MUST pass THROUGH the thrust washer when assembled, as shown in this photo.

When it is correctly assembled on the crankshaft, it will look like this.

If the thrust washer slips off during assembly, this is what will happen.  Note that the washer is off-center and is trapped between the bearing collar and the crank gear.  If the flywheel nut is tightened with this condition present the thrust washer WILL FRACTURE and also relieve the torque on the flywheel nut, causing much damage.

The correct way to reassemble the assembly is this, use some grease to hold the thrust washer in place and rotate the starter idler gear while sliding the assembly onto the crankshaft splines.

Speaking of splines, you can't just slap the flywheel onto the crank any old way.  The oil hole in the flywheel must be aligned with the large groove in the crank.

The last step before closing up is to reinstall the alternator rotor.  Contrary to what the manual says, the rotor bolts must be replaced.  The updated bolts are class 10.9 whereas the old-style bolts are class 8.8.  There is a considerable difference in strength.  They also should be thoroughly degreased and Loctited and torqued to proper spec.  I assemble the rotor to the flywheel with the flywheel installed because it's easier than doing it on the bench.  The stock flywheel nut is only temporarily holding the flywheel.  The final assembly is with Nichols double nuts, Loctited and torqued to 140 lb. ft.

 I will not go into replacing the belts, etc in this post as that procedure has been detailed elsewhere in this blog.

One final note: 
There is a lot of talk on forums about shortening the sprag spring or replacing it with the spring from some seal or other, in order to prolong the life of the sprag.  This is nothing less than butchery.  If you can't afford the parts, maybe you shouldn't own a Ducati.  If you take the bike down this far and don't do the job right, maybe you shouldn't own tools.

Monday, May 5, 2014

The moment of truth....

Today was dyno-run day.

Here are the results.
Almost 52 pound-feet, at 3500 RPM with 22 degrees total ignition advance (via restricted advance weight movement) and the cylinder head temp simply would not rise past 200 degrees Farenheit on the dyno.  This is with small valves, small carbs, stock everything except the combustion chamber mods.  The bike feels very similar to my K100RS 2V in the way it responds to throttle and is completely ping-free.  Oh yeah, everything between the head gaskets has 117,000 miles on it.

I think that the combustion chamber modification has been a successful experiment.  I will post fuel economy numbers once I get tired of playing and actually ride it responsibly.

Sunday, April 13, 2014

Airhead update

Well, it's back together and running.  I am waiting on an appointment for some dyno time to get some hard and fast numbers and more precisely dial-in the ignition timing for MBT.  In the meantime here is a short video clip.  The bike is rolling at 3000RPM and the throttle is simply opened quickly, no bouncing, tugging or any other "help".  It's completely stock from head gasket to head gasket, with stock intake and exhaust systems.

The bike has much-improved bottom-end and midrange and is utterly ping-free.  I fully expect to also see a major improvement in fuel economy.

Wednesday, March 19, 2014

At the flowbench

The chambers, seats and finally the ports are finished.  What follows are some photos and video that may be interesting to some of you but there will be no photos posted of the finished ports (for obvious reasons).
Here is a head set up to measure airflow through the intake port.

 For my purposes there is no need to have the entire intake tract set up with the head, but we do need to make sure that the air enters the intake port in a smooth stream that is repeatable from head to head.  Some guys will use a clay bellmouth on the intake stub but I doubt that I could sculpt a perfectly matching bellmouth on two heads so I simply machined one from nylon.  It snaps right on and I put a dab of clay on either side to make sure that it stays put.

Here are some photos of airflow visualization using smoke.  The way the bellmouth turns the airflow can be plainly seen.

I have been experimenting with wet flow visualization, in the following videos you can see that at valve lifts of .100", .200" and .300" the new combustion chamber contours act as very effective half-diffusers and keep the airflow attached to the head around the entire periphery of the valve head while also enhancing intake flow swirl.  As we know, a properly designed diffuser converts the flow's velocity back into pressure with minimal flow loss.  The flow in the original configuration was mostly straight across the top side of the valve in two very strong streams that tended to travel straight across the chamber with no swirl.  I am much more concerned with flow velocity at the lifts between closed and full-open than I am about flow numbers at full-lift.  Think about this, with a cam that has a symmetrical profile, the valve will see every stage of lift twice (once on opening and once on closing) while it sees full-lift at one point and then only for an instant.  This is why it is not well to get hung up on obtaining maximum flow numbers at full-lift.  Remember, the flowbench is an abstraction, as no piston-engine sees prolonged steady-state airflow at full-lift.  The flowbench is best employed as a comparative tool.   The fluid that is used for visualization is much heavier than gasoline and so tends puddle a bit but the airflow visualization is accurate and there is no explosion hazard (life is stressful enough).

There is one other item to take care of before reassembly and dyno-tuning, that is the crankcase breather system.  The engine's crankcase volume is fairly small and that, combined with the fact that it fluctuates by an amount equal to the engine's displacement twice every revolution, tends to push a considerable amount of oil out of the crankcase breather.  While it is common knowledge that subjecting the crankcase to a vacuum is beneficial, the way BMW chose causes more grief than it's worth.  Venting the crankcase to the airbox and using intake vacuum to evacuate the crankcase results in the engine ingesting a not insignificant amount of oil.  As we all know, ANY oil ingestion is highly detrimental as it dilutes the incoming fuel-air mixture, helps set the stage for detonation and is the primary cause of combustion chamber coking that airheads are famous for.  Pull the intake elbows from any large-bore airhead and you will find this.
That is engine oil dripping from the crankcase breather pipe (which itself is quite an obstruction to airflow).  I am not an advocate of removing the airbox (since the intake length is beneficial to this engine), but this crankcase breather system (along with the pulse-air exhaust injection system) is going to go.  I will use a catch-tank plumbed in series with an electric vacuum pump.  This should keep a negative pressure(vacuum) in the crankcase regardless of the piston position, give the oil control rings an easier life and maybe free up some power, but most of all, NO MORE OIL IN THE COMBUSTION CHAMBERS.

Wednesday, March 5, 2014

Volume check

The last part of the combustion chamber modification is to measure and equalize the volumes.  The target volume was 80cc which will yield a compression ratio of 10.0:1.  The right cylinder head measured at 79.9cc while the left head came in at 78cc and so needed some adjustment to be equal to the right head.

That's it for the combustion chamber modifications.  Next will be the port work, which I will detail here.  Here are the finished chambers.

Friday, February 28, 2014

KTM 950 Starter Clutch (sprag) Failure

 When all you get from the starter is a whizzing sound, this is why.  All of the metal that used to be part of the gear is now circulating throughout the engine in sizes ranging from dust to "Oh No".
 If your 950 starter starts acting up, don't put off getting it repaired or it WILL get much more expensive.

New guides and someplace to sit

Installing the valve guides:
Here is the shop-made driver that drives on the top shoulder of the guide, it is piloted and counterbored so as to miss the sharp-edged, tapered portion at the top of the guide.

The guides were reamed and honed to proper size and then the valve seat counterbores were machined.

The seats were machined from C63000 bronze.  This material is a superb heat conductor, has a similar expansion rate to the aluminum heads and is hard enough for unleaded use.  They are machined to a .007" interference fit in the heads and radiused (.062") so as not to broach any material when installed.

The heads are heated to 400 degrees F and the seats are frozen before being driven into place.
Here is a photo of the shop-made driver, note the o-ring to hold the seat in place on the driver.

Once the seats are installed they are contoured to match the combustion chamber shape.

Then the actual seating surfaces are cut (as well as a 60 degree back-cut and 30 degree top-cut) and zero seat runout is verified using a shop-made runout gauge.

Here are a couple photos of the runout gauge and a pilot.

Next step is to match the combustion chambers for volume (cc'ing) and then many fun-filled hours at the flowbench working on the intake and exhaust ports.