The Bench Racers Journal

[Terry Bentley]

Chapter 118

Looking back this last week I did manage to get some things done after school. Not much worth reporting like the progress made Friday and Saturday night, but I did make some headway on our three engines. There was no reason to go completely overboard on little details. Mainly assemble the engines using E-65 pistons and installing the Bradfield rods in all three of them.

Another decision was to go ahead and raise the cylinder wall in the transfer passage area below the intake ports. This makes sure there is a very minimum of restriction in feeding fuel to the ports. Basically cutting it up from the bottom to closely match the notched skirt of an E-65 piston. I believe this is referred to as a slipper cut after reading articles in the magazines.

Yesterday morning had come too early having to do all of that mowing. But the old chainsaw from my grandmother renewed my motivation to get back working on things last night. I had forced myself out of bed this morning to focus on the engines. But since today is Sunday, first I had to attend church. No sooner was it finished, I was on the way home and already trying to get some things worked out in my head before my hands had the chance to over run my brain.

Back in the garage I checked everything over and did some more measuring again. I was considering bolting the internals together after the final trial fit.The Bradfield rod sure looks cool in there. Steve and Chris both have brand new connecting rods in their engines. I am still using the one that originally came in the engine on the Cates kart. There is a bunch of track time on it but shows no signs of wear.

I just kept staring down at the intake and exhaust ports on these engine blocks before final assembly. They sure seemed small to me. There is plenty of room to open them up. While taking some measurements I had an idea. Both sets of ports are 7/16" in diameter. The ribs between them are wide enough to drill these out to 1/2".

But, like there is always a but, I did not like how narrow the ribs would be after drilling them out. Especially if just using the drill press and a 1/2" drill bit to do the work. There was also a risk of possibly chipping or breaking out the cast iron ribs by using a drill bit. So I needed to look at other ways to proceed.

My first thoughts were to go with a smaller drill bit first then follow thru with a finishing reamer. I have that bucket of surplus reamers my grandfather had picked up from an auction where he used to work before retiring. This could get me a safe way of making sure the rib would most likely stay completely intact. As I was contemplating opening up the ports this way, my brain was racking another solution that might pan out a whole lot better.

One of my friends, Jim Scrivner, only lives two streets over. Actually up the dirt road then over one more street. His grandfather is way past retired and likes to fix things in his spare time. Which he now has a lot of.

A while back Jim told me his grandfather had some machines, but a lot fancier than any of mine. So naturally it got my curiosity and I was interested. We grabbed our bikes then took a quick ride over to his grandfathers house one afternoon.

Jim was not that inclined or even interested in building, working or even fixing things. So he never payed any attention or had much of an idea really about the equipment his grandfather even owned in his shop. If only he knew what he didnt know what his grandfathers machines were capable of doing in the right motivated hands.

I had met his grandfather several times. We always had great conversations about working on things. He did mention if I ever needed some help on stuff to give him a holler. He would try to assist any way he could. I just didnt know he had a real vertical milling machine in his garage at the time.

When Jim mentioned his grandfather had a much fancier drilling machine than the one at home, I figured it was just a bigger drill press. A real milling machine was not anything what I had thought in my mind or expected to see. Of course even three years ago I would not have had much idea of what to do with a lathe either.

I was thinking what if my grandfather never offered me that little Craftsman lathe back then? What would I be doing today, if not for the head start I got with him patiently spending his time to teach me to build the lathe? Would I have been so motivated by my self to start making things? Things i would not have a clue about or how to build if not having the opportunity to learn about machinery and what the machines were capable of making.

Steve is a whiz at least in my eyes on working with wood. Of course his dad is a cabinet maker. I have seen his work and amazed how raw wood can be transformed into things so finely built. Steve is really impressive working with wood, but he seems to favor working with metal and engines. I think that is why me and him have become such good friends in the last few years.

So when we headed over to Jims grandfathers house, I found out out first hand what he actually had in the way of equipment. The metal shop at school has two lathes and a whole lot of other good metal working equipment, but no vertical milling machine.

They do have a very small horizontal mill of some type, but I could not figure out how to make that work for anything I needed. Well except for cutting new key slots. That would work great on lawn mower crankshafts that have been machined down to work on horizontal engines.

Today, after the usual greetings, his grandmother invited us in for a late lunch. Jim had called before we left, so they were expecting us. I have learned from past experience, there is nothing quick when having anything to do with the grandparents. That included mine or his grandparents. This is one of the downsides he told me about visiting them. We would likely be stuck there most of the day. But we will be fed and well taken care of the whole time.

After all of the expected casual conversation out of the way, I asked his grandfather if he had any good ideas on how to machine out the ports on the engine blocks I had brought over. All I really wanted to do is open them up from 7/16 to 1/2 inch. But there was a small problem I needed to work around.

At first he suggested the very same thing I had already considered doing. Just to run a slightly smaller drill bit thru each port opening then follow up with a 1/2 inch reamer. That would work, but not the way I was wanting to get them done. I could do this to each center port on both the intake and exhaust, but did not want the ribs to be so thin, if they were to be drilled out that way.

Since I have been called hard headed and probably for a good reason, I wanted to do things the hard way. My thoughts were to move the outer ports over just enough so the rib did not get any thinner like would happen by keeping the holes on the same centerline. I wanted to set up and locate to the center port, then drill it out. After that, I could offset farther past the centerline enough so the rib stays close to the same thickness after drilling the two outer ports.

Jims grandfather scratched his head, then grabbed a pencil and piece of paper. After taking some measurements with his fancy vernier caliper, he figured out how much to offset the two outer ports. Yes Terry, that wont be a problem at all. We can do it that way easily enough. It requires so set up time, but nothing we cant handle. So out to the garage we went.

I was very surprised on my first exploratory visit to find out his grandfather had not only a real milling machine, but also a much bigger lathe than the one I have at home. His lathe is a Southbend and a full size 12 inch model. Wow that would be so cool to have one this big to use all the time. I could make all kinds of things.

The milling machine he has is a Millrite. It is slightly smaller than what I have seen before in a real machine shop. Like an INDEX or Bridgeport. Otherwise it is basically the same in every other way. I have never used one before, but it does not look nearly complicated as the lathe in metal shop does to operate.

It took most of the afternoon as I watched while Jims grandfather explained how to open up the ports like we had talked about. He chose to use what was referred to as a 1/2 inch four fluted endmill. It sort of looked like a short stub of a drill bit that was twisted much tighter and flat on the end. But the cutting edge is very sharp when compared to a regular drill bit.

He explained to me that an end mill would do what I wanted and could cut straight down even when off the centerline from existing port. The endmill would not walk off center or try to follow the old port opening. It will not flex at all like a drill bit always does.

Another thing he did explain, is how a drill bit usually triangulates a hole when drilling. The endmill, if sharp and used properly will leave a near perfectly round hole and almost exactly to size.

To set up for the center port, all we had to do is use a 7/16 inch drill bit shank to hold the cylinder in place while squaring and clamping it to the milling table. Then bore out the center port to 1/2 inch. From there the table was moved over enough for the end mill to just make contact with the rib on each outer port. We did this on all three engine blocks, both intake and exhaust ports. According to his calculations the mill table would be moved 600 thousandths of an inch each way from the center port.

Getting the first block set up and finally drilled out like I was hoping, took most of the time. Mainly Jims grandfather explaining everything to me as he went thru the motions of getting the ports opened like how I wanted them. Since it was set up for the intake ports first, all I had to do was locate back to the center port, clamp the next block down secure, then repeat everything that was done on the first engine block.

After the first ports were drilled out, I was confident enough to do them by myself. While Jims grandfather sat back on his stool he told us all kinds of stories about making things in his shop. He didnt bother so much to watch me working, making sure I wouldnt screw anything up. Just more like enjoying the company of us being there.

The rest of the work did not take nearly as much time. Once I saw how easy it was to operate the milling machine, everything went along with out a hitch. Well I could operate it good enough to drill holes. Past that maybe not so sure how to do much else.

When Jims grandfather was explaining everything to me, I learned how to adjust for backlash in the table screws that move the mill table. For a more accurate way to measure the distance to offset those outer ports, he set up a bracket he made that holds his vernier caliper. It butts up against the table. Before moving the table, you push the vernier caliper up against it. Then make sure it is zeroed, and with enough over travel before tightening up a little thumb screw. After the table screw moves the table to the correct location, you double check the travel on the vernier caliper. If all of the back lash was taken out it is perfectly on target.

Getting this work done did take all day, like Jim had said when we came over here. But I was more than satisfied with the help his grandfather had given me. After we finished up, I made a point to clean the milling machine really well. After oiling everything I wiped it down so there was no chance of rust from making hand contact with the bare metal on the table, ways, and handles. I sure didnt want it to be my fingerprints that were all over the bare metal if it rusted over.

Me and Jim ended up staying there way too long. It was late in the afternoon before we finally left and headed back home. That is fine with me. I am ready to assemble the engines tonight, not matter how late it gets. Except I do have school tomorrow. On the way back I kept thinking about something I was supposed to do or remember today. But what was it?

It had completely slipped my mind that Steve was planning on dropping by today to help out any way he could working on the karts. By the time I got back home he had been there for a while. But I showed him what had been done to the ports in our engines. He seemed more than pleased with the modifications on his engine. So long as it helped to getting us closer running up with those two brothers with the Westbend engines next time out there at the track.


stock and enlarged intake ports

Lookie here Steve, look at those ports. How do you like your engine now? You think this might make some difference over how the engines were running? What do you think?

Hey, dont you want to open up the ports even bigger with the grinder? Dont they usually square them up too? I did look at the pictures in that article on modifying our engines.


Cates kart engine intake ports

Yea that is what I have seen done on a full mod job. Like the way the ports are squared on the Cates engine. But I think we are on the right track doing it this way for now. I still want to clean things up, just not go full out modified yet. I think there is a bunch more to be gained even with keeping the engine mostly stock appearing.

We have been working on gearing and handling with a lot of success. I want to keep going in that direction. A fully modified engine is more or less useless bolted to a kart that is not setup to handle very well. Once we have a good idea of how to set up the karts really well and make changes when needed, then maybe spend some more time on the engines.

With opening up the stock intake manifold to use a Go-Power six petal pyramid reed, I think is going to help a bunch. Then the modified carburetor, well you know how the engine ran with that. I think the engines will be running way better than anything we have put together so far. Using the E-65 piston bumps up the compression enough that it should be noticeable from the tightest turn to running down the longest straight.


test fitting with Bradfield rod

cut piston skirt

It is surprising how well everything is fitting together right now. The Bradfield rod looks so cool installed for a test fit in the block. I am getting so stoked about being this close to having our engines almost ready to be put together. Just about all of the machining has been done and now just deciding on some finish work before actual final assembly of the three engines.

The piston was cut like the intake tract opening. It could only be raised up to just below the piston pin boss. It would have been cool for piston to match. But the amount of material that was removed really opens up the transfer passage more than enough to do some major good.

Another hour after cleaning up the three engine blocks and all of the parts, it was time to finally assemble something. I took extra care to make sure all three of them went together exactly the same way. No compromises that could cause problems later on at the track. If an engine had too much end play, I corrected it. If there was one crankshaft with more resistance rotating it over, I wanted to find out why.

After all this time I had everything ready for a possible final assembly. Steve did put a lot of effort in washing all of the pieces in the parts cleaner. I really hate getting my hands in there more that necessary. Steve had to bail out and get home for dinner. Another one of those times he would either get a decent meal if home in time or possibly be in the doghouse for the rest of the evening if he was even five minutes late.

I had grabbed a ton of new parts already for the engines. There was new points and condensers installed, and I even used a degree wheel to set them correctly. After some input from Mr Grimes and a better explanation from my dad, I even put together a timing light to set it up exactly the same on all three engines.

On my engine, I was thinking about going way overboard on the piston. The stock E-65 pistons have three 1/16 inch thick rings. The original pistons in the A-490 have two 3/32 inch thick rings. So basically the same surface area between them.

Would it be too gutsy to use only use one piston ring? But that was not the issue needing to be addressed. I had to do something with the two empty ring grooves. It has been written in all of the articles these rings can just be left out and no ill effects.

I just could not believe that to be completely true. When the piston is traveling past the port openings, those ring grooves allow the crankcase pressure to escape. As the piston comes down before the intakes are opened up, the two lower ring grooves allow for air/fuel mix to escape thru the exhaust.

Same problem when piston is traveling up. Crankcase pressure is affected before ring grooves are both above the intake ports. So instead of drawing in air/fuel mixture it could pull thru from exhaust ports.

Back earlier this summer right after reading the June karting World magazine, I spent one night swapping out parts to see what did and didnt work. These was conflicting information in the two main articles i read about modifying the engines. This is when I found out about the problem when leaving out one or two of the rings.

After cutting down the skirt shorter on an E-65 style piston so it would fit in the A-490 block, is when I discovered something. I had installed the top ring just to make sure everything worked out. Then completely assembled the engine. After rotating the crank over a few times is when I realized how much crankcase pressure was escaping out the exhaust after the piston ring had closed the intake port.

I may be way over thinking all of this. But if right, then need to come up with a fix. Having only a third of the ring drag using just one of them makes sense. I dont see how it would have less compression, if ring is seated. So trying to work out anything that could cause problems now.

There are two ideas floating around in my head, well three now while I am jotting all of this down thinking about what might work out. The first idea is heating two of the piston rings while in a spare cylinder using a torch. This should cause them to loose tension and not have any drag on the cylinder walls.

One down side I see is the possibility of the ring vibrating or moving around so much that it could break without the tension against the cylinder wall. I didnt think this would be so likely for short term use. But also not wanting to find out I was wrong either.

Another idea is cutting some aluminum rings to replace the stock ones. Cut them to fit tightly on the piston, instead of larger to fit snug in the bore. Again the possibility of breaking without the tension against the cylinder wall came to mind. But this in only me thinking it thru in my noggin. I wont know for sure without trying first.  

If I do machine aluminum rings to fill in the gaps, maybe then use high temp epoxy of some type to make sure these aluminum filler rings stay put. Either Devcon or Marine-Tex could be good choices. The lower ring grooves should run cooler than the top one. Maybe this can work.

While working all of this out in my head, I thought about just filling the ring grooves with high temp epoxy. Then if anything broke out or came loose, might not tear up the cylinder so much. But again without testing any of these ideas is still just speculation on my part.

Should I run all of this by Frank with his store bought education and an engineers degree? At least I can get another opinion. Since he is batting a thousand on being wrong every time, I just do exactly the opposite to what ever he thinks is a good idea.

As I was contemplating about which way to go with the rings, another idea popped into my head. What about building a ring fixture for the lathe? Cut in a stepped recess just big enough around and deep for a ring to sit in there. It would be held in place with a round plate just smaller than the outside ring diameter. Then carefully cut back part of the outer diameter to reduce surface contact.

Maybe leave the top ring alone. Then remove about half the contact surface from the other two rings. Is that too much trouble? Am I putting too much thought into this? I have options now. Maybe try out one or two of the ideas then find out what works well enough for the effort it takes to do the machine work.

My mind still keeps focusing on using some type of filler in the ring grooves. If this does work, I will have the other two rings as extras. By machining the rings, I loose any possibility of having spares if something crashes.