Wednesday, October 13, 2021

Racing Into the Past, Part 4

 

Time flies when you’re having fun, as they say.  I certainly did not anticipate taking so long to get back to relating the saga of prepping the replica of the 1987 version of The Beast for last 4th of July’s Humboldt race.  When I left off (with a race report intervening) I had filled in some of the details on the frame and crankcase modifications.  At that point there was no more time to write as all my time was taken up with finishing the bike in time. So, back to the build …

Due to my inherent streak of being a cheapskate, I did not order the flywheels from Truett and Osborn when I should have.  Yes, sticker shock.  It turns out that the 5-1/4” stroke I wanted, made them a special order adding to the cost of the quite reasonable price of their normal 5" wheels.  Now, I could have just gone ahead and built the motor with 5-inch wheels as a 114 inch, like the original, but my drag racing philosophy has always boiled down to building as big a motor as practical and put it in as light a chassis as practical.  Besides, my preliminary calculations with rod length, cylinder length, and the compression height of the pistons that I had on hand showed that the 5-1/4 wheels would put me where I wanted to be for piston deck height. Once I finally decided to bite the bullet and place the order, it was nearly too late given the normal delays that happen in manufacturing.  But T&O came through and I had the flywheels in my hands with about 30 days left to finish the motor.

 

They really were in the mail!




 
 
Just what the doctor ordered

 

Did I say, “finish the motor”?  Sounds easy, doesn’t it?  Truth is there are a lot of items on the motor build that depend on the flywheels.  For instance, I needed an initial mock up to see how much the flywheel diameter would need to be reduced in order to clear everything.  As it turned out, the wrist pin ends of the stock length Evo rods that I intended to use would not clear the wheels at bottom dead center, which was not a surprise. That required reducing the flywheel diameter by .420”, which in turn, required building up the flywheel scraper in the crankcase to compensate. With that done I could finally add an oil shedding coating to the flywheel and gearcase compartments.  But with those details attended to, there was still much to do.  Once the crank could be mocked up to rotate in the crankcases, there was still the matter of insuring that the pistons would work with the heads before they could be weighed in order to balance the flywheels.  That turned out to be just as difficult as I had foreseen.  The domed pistons that I had on hand were a used set from a previous drag motor, probably from the latter half of the 1980’s.   

I had two sets of heads to choose from.  One set was actually from the original 1987 version of the Beast and the other from my last attempt at a serious drag bike which was nicknamed the White Knuckle Express (can you guess what color the bike was?) which I often abbreviate as WKE. It didn’t take me long to make the choice.  The Beast heads were missing the valves and guides, and had quite small ports to boot.  The WKE heads on the other hand were complete just as I had run them last in the mid 1990’s, not to mention they had generously sized ports to go along with their 2.100 inch intake valves (compared to the 1.94’s on the original) and highly reworked exhaust ports. However, the more highly modified heads did provide one unique challenge.  The WKE employed a centrifugal supercharger, so I had welded in the sides of the combustion chamber a bit to get some squish from its flat topped pistons.  Being unwilling to start grinding out the welds, thus undoing my many hours of labor from 30 odd years ago, I set about modifying the pistons to match the combustion chamber shape.

 

30 year old chamber mods

 

I began by making a cardboard template of the chamber perimeter and “tracing” it on to the pistons as closely as possible, followed by some careful carving on my antique mill.  Then it was it was matter of mocking the engine up more times than I can count as I crept up on removing the minimum amount possible from the sides of the domes while still attaining enough clearance to avoid contact when running.  So, with the mocked-up engine finally able to be rotated, I should have been ready to balance the flywheels, right?  Well, I admit that with time running short I did consider calling the pistons good and settling for whatever compression ratio was left.  But my desire to make the motor as fast as I reasonably could won out.  I set up one of the pistons in a cylinder and used my trusty 100cc burette to measure the dome volume.  Just what I had feared, the dome volume and the resultant compression ratio was significantly lower than what I had hoped for (under 10:1, if memory serves).

Once again, I found myself welding up the tops of piston domes.  Its not a practice that I would normally recommend, but what’s a guy suppose to do when money is short and time is even shorter? So, trusting in the ceramic coating that I would add to the domes when finished to compensate somewhat for the metallurgical mistreatment of my welding, I set about adding aluminum until the domes came to a peak.  I like to keep an old wrist pin in the piston while welding in the hope of keeping distortion to a minimum.  It assume it helps, but I can’t be sure since I haven’t tried it without. When finished the pistons seem fine, though I will add that you want to remove the wrist pins before the pistons cool completely or they are liable to stick in the pin bore.  Incidentally, this particular set of pistons had received a “Teflon” type skirt coating back in my serious racing days by a friend who does industrial coatings. That same coating not only survived whatever torture test I put them through in the 1980’s, it came through the welding on the domes with flying colors as well.

 

Modified piston domes with ceramic

 

After a bit of shaping to the fresh welds, the dome volume revealed an acceptable 13.75:1 compression ratio (and no easy place to find any more).  After a bit of lightening on the inside of the pistons under the dome, an oil shedding thermal dispersing coating was added there, and the balance weights could finally be computed.  No surprise that all of the extra weight on the crankpin half of the flywheels had to go. Finally, the flywheels were balanced, assembled and trued! Even with time running out to make the July 4th deadline, the rest should be relatively simple though, right?

Not quite. 

With the finished lower end firmly bolted into the frame, the first mock up of the heads revealed even more last-minute work to do in the short time left.  I knew the pipes would require some fairly major revamping due to the chosen heads having had the exhaust ports radically re-positioned, not to mention being rectangular in shape.  Pressed as I was for time, my backup plan was to install the short “zoomy” style pipes from the White Knuckle Express that still hung on the shop wall.  The were too short and probably too large of diameter, but at least they would bolt onto the heads.  That was not to be, however, despite how much time they might have saved.  The difference between the three rail Truett frame of the White Knuckle Express and the position of the front down tubes on the stock FX frame meant that those pipes were nowhere close to fitting The Beast.  So, I went back to the original plan of installing a set of vintage 2” FUBAR exhaust pipes that I had saved for just such a possible project. They were a dead ringer for the pipes used on the 1987 Beast, but due to the new port location about the first 12 inches of the pipes had to be cut off with new bends and flanges fabricated in order to miss the frame rails. Apparently the Lord was not trying to tell me to abandon my quest to finish in time for the Iowa race, because I managed to scrounge just enough mandrel bends from a box of miscellaneous tubing I had stashed under a workbench.

 

Rear Exhaust Port

 

Front pipe modified and installed

  

The intake side of the heads did not prove to be any easier that the exhaust, though it did catch me completely by surprise.  A month earlier I had ordered a couple chunks of aluminum from which I planned to fabricate adapters to transition the 44 Mikuni carbs to the oval ports on the heads (the width of the oval being taller than the height).  What I had not foreseen was that the angle at which the ports entered the heads would have put a good portion of each carb in a space that would be need to be occupied by the other.  That had not been an issue on the WKE since it had employed electronic fuel injection with the throttle body before the blower and the injectors (4 of them) just before the plenum style manifold that attached to the heads. 

 

Rear head as run on White Knuckle Express

 

Back to the drawing board.  I would need to fabricate curved adapters so that the carbs could nestle side by side as God intended and the laws of logic demanded.  The same box of odds and ends that supplied the pipe to finish the exhaust came through with a couple short sections of curved steel tubing that matched the inner diameter of the carbs well enough.  I was able to shape the inboard end of the adapters into an oval so that the height matched the heads, but that still left the ports in the heads wider than that of the adapters by more than I could tolerate, so I broke out the porting epoxy to fill in the sides of the ports in the heads. With time running out to have the bike ready for the 4th, I resisted the natural urge to put the heads back on the flow bench to see exactly how the impromptu port shaping had affected things.

Curved carb adapter in place

 

With less than a day to go, I was finally ready to bolt the heads on – or was I?  The final squish distance of .037”, piston to head, was based on no base gaskets (a light coat of sealer) and no head gaskets. The now vintage Axtell cylinders sported a groove so I just knew that all I needed to do was install a copper wire into the groove, add a little “Copper Coat” as insurance, and torque them down as I had done many times in the distant past.  Oops.  Turned out that these cylinders, being the last that I purchased (nearly 30 years ago) had what was then the latest technology, meaning the groove was the correct dimension for a Viton o-ring rather than copper wire. Needless to say, it had been decades since the last time I had a set of these o-rings in stock.  But with time fleeting, I took a few measurements and found that early inner primary to crankcase o-rings were the correct thickness, though I had no idea if they are of a suitable material.  Since the heads had previously been lapped to the cylinders, I didn’t waste any time second guessing myself and went ahead and installed primary o-rings shortened with a diagonal splice.

On Thursday afternoon we were able to do the initial fire up on The Beast, with time left over in the evening to load everything and still get a bit of sleep before the trip to Humboldt and time trials on the next day.  So I guess that overall, you might say that getting the replica Beast finished up in time was just another routine build for the average drag racer.   

 

Or, how we got from this ...

 

... to this

 

4 comments:

B.C. said...

Interesting read Lee, to a humble home garage hack such as myself, I'm always fascinated by the science that goes into a build like
this. Achieving great speed quickly ain't no easy feat. God bless.
B.C.

Unknown said...

Thanks B.C., but in my case, its probably part science and part insanity.

47str8leg said...

Just great stuff as usual Lee.
I thought you’d finally gave up on your blog which was bumming me out. Glad to see you’re still posting.
Tim

Unknown said...

Thanks Tim, I'd like to write more, but paying the bills just seems to take too much of my time
Lee