MOPED ARMY

Next is the cylinder. There's a couple other writeups on this kit so I won't get too in depth. I added material to the hobbit cases and bored it out to fit the cylinder skirt. It's not necessary to add material to the transfer ports. However, I thought it would be a good idea down the road if I get a bigger kit, I've already got the work done.

I took a sanding drum to the exhaust port to smooth out the cast aluminum. I also case matched the cylinder to the case. I really opened up the boost port on the base so it'll match the case well. The piston got a window. I wasn't sure how big I wanted to go. I think I'll make it more square on the bottom with large fillets like the top. The bridge on the cylinder will be removed.

I also powdercoated the cases after I was finished with the dremel work. I found its easier to keep them clean and they look sharp. the varnish look on the machined surfaces is just residue from the tape I haven't cleaned off.

Nicely done!....keep the pics coming...love watching the process.

Looks great!

What if you got rid of the tube in the middle of your frame?

What size tubes?

I'm planning on using 1" diameter 1010-1026 type steel tubing. Either .060" or 0.083" wall thickness. I'm leaning more towards the 0.083", most of the mopeds run that thickness and I should have some safety margin over weight savings. Definately gussets at the headtube and the shock mount area. This is a poor and nonproportioned rendering of what the frame would look like at an angle.

JBOT: Fear is the Mind Killer Wrote:

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Yup

Yea jbot is back. !!!!!

Looking good Joe! Quality craftsmanship as usual!

I purchased some .75mm gasket material and made a 1.5mm aluminum spacer. I played around with the different thicknesses. I'm not sure what I was seeing yesterday, but I don't think I need all that base thickness. If I used the original 3mm base spacer, the exhaust duration would be 185 degrees and transfers at 138 degrees. Using only the aluminum spacer(1.5mm) the piston sits at or just under the transfers and sticks about .25mm above the bottom of the exhaust port. The port timing at this height drops the durations to 177 for the exhaust and 126 for the transfers. Those numbers to me seem like a winner. The small amount of piston in the exhaust port is negligible and can be dealt with with some sanding. What I didn't want was the piston to drop below the port and have a lip the gasses would ram into.

The piston pin needs some spacers on either side of the conrod to keep the bearing centered. I drilled out some 5/16 thru-hard washers out to 10mm so they don't wobble about when running. At 1/16" thick, two of them gives me 0.5mm of side play. I do like the big oiling hole in the conrod.

A question regarding the base spacer. Should I run the aluminum spacer with goop or use one of my earlier made 1.5mm thick gaskets with goop? I'm leaning towards the aluminum, both for removal in the future and keeping the piston height and squish consistent.

I don't know why I didn't even think about cutting the bridge on the skirt port, I knife edged it like a dummy.

The powder looks nice! Did you preheat the cases before applying?

Good advice on annealing the aluminum. My toaster oven/powdercoat oven goes up to 500 degrees so that'll work. I did not preheat the cases. Just a good connection between the cases and the powder gun.

I took 0.75mm off the head and 1.25mm off the top of the cylinder. With the 0.5mm head gasket, It'll give me 1.14mm of squish. I didn't measure the head volume before I decked it. The volume with the material removed is 7.4cc. I haven't measured the squish band area percentage but would like to keep it around 40-45%. This one seems a bit thick and I like to keep the msv on the low side to avoid preignition at high rpm.

If I can offer my $0.02 on the frame construction... the design looks great, but I think you're overkill on the tubing spec. I would be going with something like 3/4" x .049" 4130, much higher strength to weight ratio, but not insanely expensive either. It's more expensive than mild steel, but if you're going to put all that TIG time into it anyways, I feel like it's worth the extra dollars. Wick's Aircraft Supply (a web store) will do small orders and has pretty good pricing.

I've got a custom frame built from (mostly) 3/4" x .035" 4130 that isn't anywhere near as rigidly trussed as your drawing, and it's, uh, quite stiff.

see here

Obviously there are design differences but I'm just offering a reference point from my personal experiences.

Also, we have a Hossfeld bender with 3/4" and 7/8" dies at my shop if you need someone to bend some frame components for you. (I'm looking at the sideview with the parts that mate to the front motor mounts)

Either way, looking good.

I briefly though about using chromoly early on, but was worried about cost and welding/machining. I'll need about 20 feet of tubing to complete the frame. If I use mild steel, it'll be about $40. Chromoly in your size is about $85 for the 0.49" wall thickness. However, I save about 9lbs on the frame. I did some reading on the steel and I don't think I'll have any issues with cutting or welding it. Chromoly it is. I modified the frame to the new 3/4" tubing and extended the lower tubing up to the top of the head tube. I've seen many frames with it like this. Once the plans are finalized, I'll start ordering materials.