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.

Sunday, February 2, 2014

Hemi no more

Both chambers are roughly mirror images of each other.  Once I've machined new seats they will be installed along with new valve guides.  The chambers will be exactly matched for contour and volume after the valves are installed.  The intake valves will remain at their stock size of 42mm but the exhaust valves will go from the stock size of 40mm down to 38mm (more on this later).