The Bench Racers Journal

[Terry Bentley]

Chapter 48

Now it is dark in the garage. Not outside. It is still very bright with the west sun late in the afternoon. I fish around for pliers. Hopefully ones with insulated handles. The plug end pulled loose from the outlet without issue. I feel my way around to the back of garage to the breaker panel. It has only two breakers, so one has to be tripped. I turn off and reset that one Federal Pacific breaker on the left. The lights come back on and nothing seems amiss. All is good now.

With all these dead engines just sitting here, my motivation was strong and kept focused on the Clintons. So decided to tear at least one of the chainsaws apart. Much as I have a new interest in my very first McCulloch, just cant tear it down to a box full of pieces. No, not just yet. I know these are very expensive chainsaws. Sure dont want to screw something up from being too impatient or plain stupid.

The model D2 Clinton looked to be much older than either of the D35 saws. It had the remnants of some type of gear reduction. Or at least looked like might have been a belt drive to the bar. This saw was partially torn down anyway, so didnt see any reason not to check what the insides have to offer.

A few minutes later most of the engine was in pieces on the work bench. I was surprised to see the rod was aluminum and had a cast in bushing. Sure dont want to skimp on oil with this chainsaw. It might just weld itself up good and tight. At least that is what I think might happen. This saw would have to smoke up a storm when cutting down a tree. Guess one good way to run off mosquitoes.

It was really disappointing to see this D2 saw had a smaller piston that the Panther series kart engines.  Several things about this engine were noticeably different, but most of the parts looked interchangeable with the Clinton on Cates kart.

There was a big difference in the transfer passage between this D-2 and the Cates Clinton side covers. The Cates A-490 has a directional transfer passage. Not really uniform either. From my understanding both right and left hand A-490 engines share this same directional side cover. I remember reading somewhere the left hand engine is faster right out of the box, and maybe because of the design of this passage. The D-2 chainsaw engine is right hand drive.




I also read the A-490 is lower on horsepower than the A-400. But no one has explained about it that I have found out so far. It is recommended to start with the A-490 because of the pto ball bearing for racing purposes. For modifying the engine it is an all out definite. Maybe we can add the pto bearing to the A-400 crankcases. Looks like it should be possible.

On this D-2 side cover the crankshaft was supported by both a needle bearing and bushing with thrust face on flywheel side. But only a long bushing on the pto. I would have bet the farm there would be a ball bearing there instead. Oh well, if it works, it works. The crank was stepped down to 1/2 inch and extremely worn where the clutch rode. Doesnt look like it is worth using for anything.

This smaller piston bore measures 1 7/8 inches. I checked the stroke and found it to be the same as the kart engine. So time to try out some equation using this formula I had found in the geometry section of a machine shop book. It supposed to give me the volume of a cylindrical shape. It is pi x radius squared x length.

That equates to 3.1416 times half the piston diameter of 1 7/8 squared times 1 5/8 stroke. If this math gets more complicated I will be the one with a stroke. Ok need to decimal everything. I hate fractional math. It sure doesnt jive when trying to use the lathe either.

Dad had worked with me for a long time about using the lathe and learning how to read a micrometer and vernier caliper. With a little understanding, decimal math makes sense to me. Fractions are too much work to add, subtract multiply or divide. Common denominator and all that stuff.

Dad also kept harping about the importance of math when trying to build anything at all. Without it you cant really do much. But if you apply math to something tangible, it makes a lot more sense. But to me fractions are just that, fractions. I know that a whole cake can be sliced into fractions, but I am not that hungry right now.

So the equation goes, 3.1416 x (.9375 x .9375) x 1.625. I think that is correct. A little pencil pushing and what do I get? Why does the pencil tip always need to be sharpened? Man this takes forever. Geez, this saw is only 4.48 cubic inches. That is gutless. Why would anyone buy a smaller displacement engine if the weight and size is no different than the larger one?

Looking in the handbook, there is an alternate equation too. (3.1416 ÷ 4) x dia x stroke. OK So if I math out the first part, that gives me .7854. Now I can simplify it to be .7854 x dia x stroke. This might be easier to work with out here in the garage. I scribbled this on the wall above the work bench right in front of me. It is simplified and applied.

One more tear down since I am in the mood. Then should be time for dinner. There was that one parts crankcase that had a chunk missing in the side. But looking in thru the hole there I see the rod is still intact. It is also a steel connecting rod with needle bearings. Good.



This engine doesnt have any length of crankshaft sticking out on the pto. Only a stub. But there is an internal spline. It also has the exhaust ports opened up in a large chamber. Huh, this might be from an outboard motor. The exhaust ports look huge comparing to the others. I pull off the funky shaped intake manifold and notice a rod bolt is missing.

Guess I know what put a hole in the crankcase now. Wow, it does not look like there are any any other problems. The rod is still tight and piston skirt appears undamaged. Looking closer I see the head of rod bolt is just broken off.  Otherwise everything is nice and clean inside.

Maybe if that broken bolt can be removed, then swap some of these parts to another block, I can get away from the bushing rod on the kart engine. For our weekend racing, I dont think they check or really care. There is no engine tech after the races, so why not make it more likely to last most of a season.

Another hour had passed and now several of these engines are torn apart all over the garage. I knew this would happen. I just knew it! Eventually anyway. Didnt really expect it to be so soon tho. Taking a loose inventory, I realize me and Steve could possibly build up two identical Clintons that would be just like the kart style A-490 engines.

I was also thinking about using the needle bearing cranks and rods. Go ahead and cut the cast iron flywheels down and shorten the air shrouds . This is the easiest way I know to get rid of that extra weight and drag. It should be worth all this effort.

Maybe discuss this with Steve and see if we can agree on something. It would be cool to build another kart and have two that would be nearly identical to race with. More like a team thing now. That sounds neat. Our first race together we can battle for last place. Now that is funny! But likely might just be the way it happens.



My intentions are to leave the D35 chainsaws untouched. At least for now. And for a good reason. I learned a little bit about these after digging thru a repair manual last winter. That is when I tried to figure out what was causing the McCulloch mower to keep self destructing. If I am right about these two saw engines, they are nearly identical to the E-65 model kart engine. This would be fantastic.

The E-65 engines are not that fast or as competitive so much. But were very popular only a couple of years ago. These are supposed to produce about 4 1/2 horsepower. If doing some of the same modifications to them and maybe get close to what a stock Mac runs like. Might be way past wishful thinking already. Just thinking out loud here. Who am I talking to right now? This is weird.  

These engines sort of, well are likely way out of the league for the faster junior class. But might work out good for me and Steve until we can step up to real kart engines. I dont even know what engines are allowed for the other junior class. Still one more thing to find out.