Monday, May 14, 2007

Flat Track and Old Iron

Last fall a long time local flat track racer by the name of Billy Hofmeister approached me about doing some work on his iron XL heads and cylinders. Since I have recently seen a resurgence in interest in porting work on these heads, and have done a few sets in the last year, I agreed to take a look at his heads.

His bike is an original factory XLR which is now outfitted with a 1969 XLCH 900 which he runs in local races in the open class. Last time out he had a cylinder break at the base, possibly because it had been shortened in an effort to raise the compression. Another used set of cylinders was in order, as well as some headwork.

The heads he had been running had been ported previously, but without benefit of a flowbench. They flowed about as good as can be expected with no way to check the work. Over the winter, as time allowed, I installed 2" intakes and 1 3/4" exhaust valves and a full porting job. Along with the head work, I found a set of 11.0:1 compression pistons.

Nothing too exciting here, you might be thinking; and I would agree, but what may be more interesting is the coatings we will be using. Cast iron does a great job of holding heat. Just what you don't really need in an air cooled engine. It tends to lead to all kinds of annoying little things like seized pistons and valves and such. One way of combating this heat build up is by the use of thermal coatings on the engine parts. While this technology is not new (I recall that the fuel class bikes were using them 15+ years ago) I have not seen or heard much about it in regards to antique motors.

Seems like a natural, but truth be told, I may not have thought of it except for Joe, one of my customers for whom I recently finished a big twin Flathead stroker build. He had done research on coatings and had many of his engine components done. The whole idea behind ceramic coating is to put a heat barrier on the part to prevent combustion heat from "soaking" into the part. On his Flathead, we had the combustion chambers in the heads, the combustion chambers in the cylinders, the combustion chamber side of all 4 valves, the "back" side of the exhaust valves, and the exhaust ports ceramic coated. In other words, everything that is exposed to combustion temperatures. We also had the a teflon treatment done to the piston skirts.

Unfortunately, due to some issues with the company that did the coatings on his motor, (horrible packaging for the return trip leading to broken fins along with coating the wrong ports) I was not about to entrust any parts to them. Luckily there was a local alternative. I have been having piston skirts teflon coated by a local business for a number of years. When I asked him about ceramic coatings, he said he had done some a few years ago, and would order some fresh materials if I was interested. I was.

So with the start of the racing season only a week away for Billy, I needed to get his motor wrapped up. Last Saturday I had Billy drop off the bike so I could do a "mock up" with clay to make sure there were no valve to valve or valve to piston issues. Just a very small amount needed to be removed from the intake pockets to give a little more radial clearance for the larger valves. Thursday morning I dropped off the pistons, heads and valves for teflon on the skirts and ceramic in the combustion chambers, exhaust ports and valves. Friday morning I picked up the finished pieces and started assembly. New high performance valve springs from Kibblewhite were in order, since with the porting work, the engine should want to rev higher.

So as of this writing the bike sets on a lift in my shop with just the carb left to install. I, for one, am pretty anxious to see how much the performance is improved with the increased airflow, higher compression, and a cooler running engine!

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