Cogsy Builds Rupnow Engine

[Cogsy]

After many recent trials and tribulations, I've finally managed to make a proper start on my build of Brian's fantastic Rupnow I.C. Engine with Governor. While I'm hoping I will progress quickly, realistically I expect this build might take me quite a while.

Due to a current lack of available funds (one more tribulation ), I haven't been able to get hold of any aluminium plate of the proper size yet, so I'm going to be jumping all over the plans and making whatever I've got the material for first.

First up then, I had these bits of 1020 bright steel to turn into flywheels. As you'll see, I had some difficulty machining it.

Here they are, warts, chatter, witness marks and all... I just can't seem to get along with steel. I'll paint them up all pretty later though, so I'm not overly worried about their appearance yet (and they do look a little better in the flesh than in the photo). The shafts are only in place for work-holding - they're not what I'll be using.

Next up will be the crankshaft between the flywheels, but this log is being done in real time, so I'm not sure when the next installment will be.

 

[Brian Rupnow]

Cogsy--First, let me say "Welcome Aboard"!!! Secondly, you are very brave to follow a build on an as yet unproven engine, but I am working on that. Lack of funds--Lack of time.--We've all been there at one time or another. It sucks, but---it passes. Get some 180 grit and some 220 grit emery paper--That will remove 95% of your chatter marks, and don't feel bad. Every builder on this forum gets chatter marks at one time or another, and every one of them is well acquainted with the magic of emery paper. I wish you the greatest of success, and thank you for pursuing this build.---Brian Rupnow

 

[Cogsy]

Got a little bit more time today, and managed to make the crankshaft from a bit of mystery metal I had laying around.

I wouldn't say it was all that difficult to machine, but there are lots of places to make mistakes and it took quite a while for me to get it right. It fits where it's supposed to, all the holes line up and the bolts pick up their threads so I'm very happy with it.

Not sure what part I'll move onto next, maybe the valves and cages or possibly even the gears. Hoping to get at least a handful of parts done over the weekend.

In case you're wondering, the bit of plate in the background will be the base of the ball turning tool I need to make so I can make the governer balls. At last I have an excuse to make a ball turner!

 

[Brian Rupnow]

Parts is parts Cogsy. They all add up to an engine, eventually. Its a bit like eating an elephant---One bite at a time. Good work.----Brian

 

[rcfreak177]

Looking good Cogsy,

Watching with interest, keep up the good work mate.

What sort of bike does that front wheel in the first post belong to?

Baz.

 

[Cogsy]

Thanks Baz. That's my wife's front wheel on her 2004 YZ85 big wheel. I've got a couple of little Chinese quads tucked away for the kids as well, and a 140cc pit bike for my eldest daughter. Mine is 2007 KX250 2 stroke. Just wish I had the time to get them all dirty...

 

[Path]

Great start and looking nice.

Will following your build with great interest.

Thanks for sharing.

Pat H.

 

[Cogsy]

My collection of parts is slowly increasing, although not quite at the rate it should be.

I now have the cam and crank gears made, and one of the 2 crank spacers (the other one will only take a few minutes, I just forgot about it).

I picked up a nice chunk of cast iron bar, so I thought I'd whip up the cylinder. Seems easy enough looking at the plans, but I soon realised I didn't have the proper tooling to bore 2.7 inches deep :wall:. With crossed fingers I decided to give it a go anyway, and it was a painful experience.

I drilled a 1/2" hole to the required depth and then used a less than rigid boring bar stuck way too far out of the toolpost, to take very slow 5 thou cuts up to the 0.875" bore size, with MANY spring cuts every 40 thou, and many more approaching the final size. I'd guess I may have made as many as 150 slow passes before I was done. The good news is that I do now have a useable cylinder, once I've honed and lapped it.

Here's a pic of all the parts so far. It's winter here in Australia, and I noticed just a little surface rust creeping onto the flywheels. Imagine my surprise when I came inside tonight and downloaded this photo off my camera I swear the rust is barely visible to the naked eye.

I should have a few hours tomorrow to get some more done, including getting rid of that rust, so hopefully I'll have another update tomorrow night.

 

[Brian Rupnow]

Al---My digital camera does that too.---Picks up all kind of horrible stuff that you don't even notice with the naked eye. I find it helps to give anything steel a wipe with an oily rag if its not being installed right away. What you found when boring your cylinder is exactly why I wait until after the cylinder is bored to make my piston. That way if you do wander a few thou over on the bore diameter to get it cleaned up properly, you simply machine the piston a few thou over to match it. I'm not sure whether you posted your intentions or not--are you going with the water cooled engine or the air cooled.---Brian

 

[Cogsy]

Brian - I never make the piston first for the same reason. I'm not sure what's going to happen when I attempt a multi-cylinder and have to make multiple bores identical, I imagine I'll end up with lots of scrap pieces...

I'm going to be building the water cooled version, I just like the look of a water hopper better for some reason. I haven't machined the bolt reliefs on the cylinder yet - I want to wait until I make the head first, but I still haven't got material for it. Tomorrow I may get a piston and cast iron rings made, and finish off the last 25% of the conrod that I started but put aside to get the cylinder done. I don't know why I dislike making conrods, but I have to be in the mood to get them done.

Good luck with your electronic ignition. I'll be interested to see your design for mounting it. I have a rough idea in my head of how I was going to mount mine, but its a ways off yet. The el-cheapo Chinese one I have on my Upshur works well, but for some reason altering the timing by as much as plus or minus 20 degrees has very little effect on engine performance, although I am still trying to fine tune all sorts of things on that engine so it may become more responsive as other gremlins are sorted.

 

[Brian Rupnow]

Okay Al--That was what prompted my question----I didn't see the relief scallops for bolt clearance cut out of your cylinder. Initially I didn't think I would need them, but I just couldn't "squeak" the bolts past the major diameter of the cylinder and get them started to thread into the water jacket without those relief scallops.---Brian

 

[Cogsy]

Now I'm really glad I haven't added them yet. I didn't want to own up to it but I bought the wrong size cast iron and I had to take the flange down to 1.4" to clean it up. I figure I'll just have to match the water hopper to the new diameter. Possibly with the slight reduction I may not need the scallops at all.

 

[Path]

Al,

Nice to to see that you are making progress.
I have yet to start mine ... but I'm making progress getting to starting line and should be there soon.

Pat H.

 

[Cogsy]

Thanks Pat. I have no doubt you'll catch up and pass me pretty quick.

It is a fun engine to build so far, and very different from anything I've done before. I'm having to learn all new machining techniques which makes it an even more rewarding experience.

I'll be watching your build thread with interest.

 

[Swifty]

Hi Cogsy, great to see some more progress. Regarding boring bars, I've made quite a few in the past from round stock with a hole towards one end to take a broken 1/4" HSS cutter, held in by a grub screw. Just choose some round stock to suit the hole size, allowing for cutter stick out.

Paul.

 

[Cogsy]

Thanks Paul. I hadn't even thought about making one but it sounds like a great idea. My to-do list just got a little bigger

 

[Cogsy]

Just a quick update today and no photos. Sorry, I'll include them with my next progress report.

I got the cylinder nicely honed and it's ready to go. I used my little 2 stone brake cylinder hone - worked a treat and didn't take long at all.

Then I made the crank spacer I forgot yesterday, twice. Why twice you ask? I trusted my memory rather than taking the two steps to look at the drawing and cut it too short :wall: Of course I was making it from an offcut and there wasn't enough meat left on it for a second one, so I had to start from scratch. Lucky it's an easy part to make.

After that fiasco I managed to carve out a pretty decent piston from a horribly 'gummy' piece of Ali bar that I've got about 6 feet of. I almost had to continually flood it in WD40 just to part it off. I'm slightly deviating from the plans here and running 2 cast iron rings, so I used my best judgment on groove placement.

Finally I cranked out half a dozen cast iron rings, as it takes no more time to make extras. I've only split and heat treated the two I need at this stage until I make sure I've got the right amount of ring tension on them. If these two work then I'll split and treat the rest as spares.

And that was all I got done today, even though I spent most of the day in the shed and it felt like I was working pretty quick, but somehow the day just disappeared on me. Fingers crossed I'll get some more time during the week.

 

[Brian Rupnow]

Cogsy--I generally use 6061 heat treated aluminum for all the material on my engines, mainly because that is what my supplier stocks. It machines very clean with no gumminess. I know there are many other grades of aluminum out there, some gummy and some not. As long as you were able to get the piston carved to size, probably it will be fine,---its just outside my experience. It will be interesting to see what happens to the aluminum when you go to lap it into the cylinder.---Brian

 

[Cogsy]

Brian - I'm not exactly sure what you mean by lapping the piston into the cylinder (I'm pretty new to all this machining stuff remember). I just went off what I learned from my Upshur build and made the piston around 0.001" smaller than the bore (for expansion maybe?) and figure I'll let the rings do the sealing. Nevertheless, with no rings on the piston it slides nice and smoothly through the bore and sealing off the end with the palm of my hand produces reasonable compression/vacuum. Please let me know if I've got my thinking wrong and I'll remake the piston if necessary. Thanks.

 

[Brian Rupnow]

Cogsy--You may be alright without lapping. I think I covered it in my thread on the Rupnow engine, but I will go over it again and give you the condensed version.--After I have machined and honed my cylinder, much the same as you have done, the inside of the cylinder will still be full of microscopic grooves from the honing process. If you are going to run cast iron rings, this is good, because those microscopic grooves will hold a small amount of oil to lubricate the rings, and will also act somewhat like fine sandpaper, to "wear the rings in" so they end up being a very precise fit to the bore of the cylinder. However, those same microscopic grooves left from honing are really bad news for a Viton o-ring, because they wear it away very quickly. That is why I lap the bore of the cylinder. I generally make a solid round lap about 3" longer and .001 to .002" smaller in diameter than the bore of the cylinder, and coat it with 600 grit carborundum paste. The lap is then worked back and forth thru the bore of the cylinder in a twisting manner from end to end to polish away the small ridges left by honing, and give an almost mirror like finish to the inside of the cylinder bore. Then I turn the piston to be about .001 to .002" smaller than the cylinder bore and repeat the process to polish the o.d. of the piston as well, and remove any "tight spots" that the piston may have in the bore. That is also the process used on steam engines which use a softer ring material than cast iron. It is also the process used on engines which don't use any rings at all. Since you are going to use cast iron rings, you may well be able to skip the lapping process completely with no ill effects.---Brian