The Bench Racers Journal

[Terry Bentley]

Chapter 43

I was having a very difficult time trying to explain the advantage of this flywheel being cut down to Steve. Just not finding the right words to make myself clear. I can see it clearly in my head, but just not explaining it well enough to even convenience myself.

Hey Steve, can you point the fan over this way a little more? There is a decrepit box fan that had seen better days, years, a millennia, sitting behind both of us. It is on its last leg literally. Or that is what I am hoping at this very moment right now.

Dont bother getting up off the stool, just kick it around with your foot. Steve stretched his leg out far enough to give a good swift kick to it just below half way up on one side. The fan nearly falls apart and crashes down then lays back flat on the floor. That was real slick. You knew that would happen, Terry.

Steve gets off the stool and tries to set the fan back upright. You are sure being a jerk tonight. As Steve bends over to pick the fan up, he realizes how much faster the motor is spinning now. Hey whats up with this? The motor is hauling butt when laying down flat like this. What gives?

Yes, I could not find the words to clearly explain what I wanted to, but knew the fan would fall when he kicked it. That is what I was trying to explain to you just now Steve. What does this old fan have to do with butchering up a flywheel?

Steve, the airflow has been blocked so there is no drag on the blades there. Without the air being pushed thru, it takes less power to spin. So now the rpm has increased. Same as on the flywheel. You cut off the fins, then it doesnt have as much drag pushing air thru now.

Ok, that makes some sense, but then you have a motor that wont stay cool. Big deal. That doesnt sound smart. Steve think for a minute. Didnt I run the kart for a long time at the track that night? Was the motor overheating then? Well, I guess not. But why would they make it that way if it didnt need all those fins?

Steve that engine was never designed for karts or racing. There wasnt anything at all like real racing karts when these motors were first built. The vertical shaft models for lawn mowers and the horizontal ones for edgers, rotary mowers, and stationery pumps. They can run for hours just sitting there without any problems.

I bet if you could keep the gas tank full might run for months like that. Now someone looking for a cheap engine adapts it to use on a racing kart. Things are very different. Similar to a lot of motorcycles that dont even have air shrouds. They can run all day without problems. But they are usually moving at some speed where the air is still passing thru the fins to pull the heat away.

This motor on a kart doesnt really need all that air to cool. Plus the kart is zooming around the track with even more air movement. What do you think the top speed was last time out? I bet it was close to 40 miles an hour. Well it at least felt that fast. I sure dont see anyone pushing a lawn mower any where near that speed, do you?

This is a lot of air movement to add with the forced air from cooling fins on flywheel. One other thing to think about. Using this motor on a kart we are running much higher rpm's too. That means even more air is pushing across. Are you getting the picture yet Steve?

OK I am with you now. Makes more sense, after picking up the fan. It slowed down a bunch as the air movement increased. So it takes horsepower to overcome the drag from air flow. We dont need that much air to keep the engine cool enough for racing. We also want as much power as possible to make it run faster on the track. Cut the drag, then increase speed. Do I have that right?

Sounds close enough. That is what I was trying to explain, but thought if the fan fell over, like it does all the time, might make it easier to understand if you see what the point is I am trying to get across.

So you saying all that work done is really worth the little bit of gain? I dont see how it can make that big of a difference. Steve, every little bit adds up. Several small things may knock a ton off the lap times. Another thing is how heavy the flywheel is. That one is cast iron. Heavy as crap. There is supposed to be an aluminum one that also fits this model Clinton too. But for lower horsepower, sometimes a heavier flywheel actually helps more than it hurts.

Remember that oddball lawnmower we found a while back? We never could keep it running at first. After putting the engine back together, we decided to leave the blade off, just in case, for safety reasons. But the motor would only pop. It would not start up and keep running. We tried over and over, nothing.

After tearing it apart a few more times we gave up for the day. After giving up we went ahead and bolted everything back complete, just so not to misplace any parts. The next day, it fired up just fine. We finally figured it out when the blade came loose. I didnt tighten it up so much, since there was no plan to put any more time to it right then. So it came loose fairly quick by accident.

The engine would just lay over and die with just a very light load. Then would not start back up. Tighten the blade, that motor would stay running just fine. You thought the key must have sheared and removed the flywheel to make sure. Remember how light weight that one was?

The flywheel had a magnet, and its counterweight. But nothing else really. It was open on the other sides. The fins on top were very thin and short. The weight of cutting blade is what was used for the flywheel effect on that particular lawn mower engine.

It got late in the night when we finished hashing out everything that had been discovered with the little Clinton. There was still tons more we were completely clueless on, but ready to learn what or how on all of it. Saturday late morning came early for us. Steve had decided to skip out on rest of the weekend. His parents had acted so strange, that he wanted to go check up on them. So the rest of my weekend was less involved on the kart.

For some reason, mom had convenienced me I needed to learn how to type. She shook her head every time I tried to peck out a report for school. Summer school had a two week course. It was only an hour each day. Even early enough so I wouldnt really miss out on anything for rest of the day. I caved on it and come Monday morning it was back to school. Summer schooll. Yuk!

There was a positive side to going back to school for a couple of weeks. Actual summer classes were taking place for those who chose not to do their work during the regular school year. I had some ideas of my own that might pay off in a big way. But first needed to find out who was teaching health science.

Mrs Hailey was our regular science teacher. But for the summer flunkies, it was Mr Pennington. He was one of the football coaches and a regular math teacher. Not really the physical type coach. More of an organizer. Now he is a science teacher too. Who would have known? How talented. I dropped in after the typing class was finished. He had a class going on. But the students were reading silently and he was sitting at his desk.

I walked in and said my hello. He informed me I was not on his summer class roster. I told him his loss, and he just gave me a smirk. So what can I do for you young master Bentley? I wonder if he ever calls anyone by their first name? My question to him was about possibly using some equipment if it didnt disrupt the class.

There was a nice tri-beam scale sitting up on the little laboratory table in the corner of the room. I wanted to weigh some things, that is, if he had no objections. There was none from him. I asked if tomorrow would be alright, and he agreed. Under one condition tho. He was curious about what I was doing and wanted to be kept in the loop of information. I said that was fine and would see him tomorrow about the same time. Also to thank him.

Tuesday came around soon enough. I had a heavy box with me. My typing class couldnt get over fast enough. This mind was elsewhere the whole hour for some reason. These fingers were doing the walking. But kept finding a box sitting on the floor instead of the right key to punch on the Underwood in front of me at my desk. Finally class over, I am out of here.

Looking thru the glass window with wire mesh thru door I see Mr. Pennington passing out some papers. He motions me inside. Keep quiet and do what you need. I nodded at him and headed back to the corner. Open the box and pull out two cast iron flywheels. One has been cut down a bunch, the other is completely stock.

After figuring how this tri-beam scale works, I first check weight of the cut down flywheel that was on the engine from Cates kart. After a few attempts and finally getting enough weights on to ba1ance, this cut down flywheel weighed in at 2215 grams. The flywheel felt heavy enough. Now I know how many grams of weight that is. Hmm. Why cant this be in ounces? I dont have anything to gauge the gram thing with. Will have to do some conversion math later.

Now for the big surprise. Swapped over to the stock heavy cast iron flywheel that came out of the box of parts. I was real curious how much heavier it was comparing to this chopped up one. OK something is a bust here. The scale is tipped the wrong way. Am I using this thing correctly? Check over everything again and again. Yes that has to be right. But no way. This makes no sense. How can the stock cast iron flywheel weigh less that that chopped down lightened one from the kart engine?????

After checking over again, the scale clearly showed this stock flywheel to weigh in at 2177 grams. I am just shaking my head. How can this be? Mr Pennington is done with passing out papers and comes over to investigate what I am working on.

After explaining what I knew, he double checked everything himself and confirmed the weights were indeed correct. He looked over both flywheels closely and then used his thumb and index finger like a micrometer to gauge the thickness of different parts on each flywheel.

Here might be your problem. The castings are much different, even tho they look nearly identical. The thickness varies a lot comparing the two. I am surprised with this much material cut off, that it is still heavier than the stock flywheel. Are these the exact same part number? Could this lighter one be a newer replacement?

I really didnt know what to tell him. Just more things to figure out. I thanked him again for the help. He said anytime. Be sure to let him know what I find out on these flywheels. Sure thing, Mr Pennington. Then I headed out and back home.

It was shortly after lunch time when I pulled up at home on my bike. Hunger pains were working me over hard, but the grey matter was working harder. Back to the garage with these two flywheels. I did as Mr Pennington was doing with his thumb and finger. There is some difference in thickness in several places. But how could it be so much different in weight between the two. And just opposite what anybody would think by looking both over very closely.

Both of the flywheels were close enough to the same weight to not be sure which one was lighter just holding one in each hand. I have these numbers to confirm which one is lighter. Just not the one I would visually pick.

Ok, this has got me thinking. If the lighter stock flywheel is cut down the same way, then how much more weight could be removed from it? Hmm. I wonder if the little Craftsman lathe can handle a flywheel? Only one way to find out. If I can get this one to fit, it is getting the full treatment.

First tho lunch is screaming at me. My stomach is not liking the lack of attention it has been getting. I need some nourishment. A quick roast beef sandwich with provolone and the one Mountain Dew I have stashed out in the garage fridge. This should keep me from passing out for a few more hours.

The little 6 inch lathe might have trouble chucking up a 6 1/8 inch diameter flywheel. I remember dad mentioning the lathe can swing up six inches with no problem. I was hoping there was enough clearance to maybe swing just a little bit more. But as usual when I start working on something new for the first time nothing seems to pan pan out like I would hope for. Just like it is at the moment. Time to think this out.

Dad had gone over different ways to do things on the lathe. This one problem is way outside of everything he had covered. At least the things I understood and retained in my head. After a few false not so promising starts, then a couple of complete failures, one way came to mind. It took some effort to rig up. But might work.

I had to machine an extended dead center that fit into the headstock. It was soft material. I think it is even a homemade center from the looks of the finish. The part sticking out is extended and already machined down to 1/2 diameter then to a point. I didnt need the point, but did need a taper that matched the flywheel taper.

I cut a new taper so the flywheel fit. It only fits inside the taper most of the way, but not completely thru. Then use a live center in tailstock with a small flat plate to hold flywheel tight in the tapered shaft. Rigged up a short bolt to work as a dog so the flywheel would keep rotating with headstock. Everything looked to be running true, so time to make chips.

This thought to be little job turned in to lots of chips. Tons of them all over the place. It took me all afternoon and well into the evening to cut most of the dead weight off this stock flywheel. Close to midnight, it actually resembled the existing lightweight flywheel a lot. Well that is until I put them both side by side.

Now I can see how much different the castings actually are. Just visually you can see the cooling fins were really big and thick on the kart flywheel. It must be an earlier model for sure. What is so amazing is how out of round this stock flywheel was. There was nearly 1/8 inch I had to remove before it was making a complete cut. Originally just rough cast on the outside, now a smooth flat concentric finish.

For no particular reason I  decided to cut the outside diameter down to exactly 6 inches. Just like the other flywheel. Those fins were machined down to nearly flush with the reinforcing ribs. I swung the top slide on lathe around to a 45 degree angle. Might as well angle the outer part of these fins in much as I can. Cut more off the the very short fins. Just keep chopping it down and get as much weight off as possible. The same on back side of flywheel too. Basically I tried to copy the already chopped down flywheel close as possible.



Finally they both looked very similar. This time there was a noticeable difference. I could tell which was lighter just by holding one in each hand too. But how much difference in actual weight did I remove? Geez, tomorrow cant get here soon enough. Oh crap! Tomorrow has already been here for a while.

Time for a quick shower and off to bed for the night. Fortunately typing class doesnt get rolling until 10am. It wont be a total loss tonight. I was out not much longer after laying my wet haired head down. Sleep came quick and easy. No brainstorms going on to keep me awake tonight.