ShedBoys' First Engine

[vcutajar]

Brock

I have been following your build with interest and learning new things.

Not to pour water on a fire, but just a comment from an inexperienced model engine builder.

If you leave the lettering on the side of the flywheel aren't you increasing the chances of having an unbalanced flywheel? Or isn't this a problem at the relatively slow RPMs that we operate model engines?

Just a thought.

Vince

 

[JorgensenSteam]

He could actually use the imbalance to offset the weight of the rod/piston, etc. and thus use the imbalance to his advantage.

 

[ShedBoy]

Good point Vince. I will put it between some centres and see how bad it is.

Unicastings that made no sense to me and probably perfect sense to alot of people.

Looks like I need to look up some balance ideas. Should I mount the crank, flywheel, piston and rod between some centres and look for definate heavy spots and go from there? Does anyone have any idea how to balance this thing or should I just spin it in the lathe and see if it vibrates? Now I am confusing myself. Someone must have pics of balancing in progress.

Brock

 

[ShedBoy]

Started making some rings today from some spun cast iron. I am using the method Bob described in his hit & miss thread

Thre rings cut and ready to split and finish to size. Got side tracked mid morning by a new tool.

Brock

 

[Ken I]

Coming along nicely Brock.

I wouldn't worry too much about ballance for now - just keep it in mind for later.

Ken

 

[ShedBoy]

Well me and piston rings don't get along. I think the material I have is not spun cast iron. I think a viton ring is looking good at the moment.

All three broke like that. I need to do some more research into ring making. I am going to make a crank pin and conrod instead before I go back to work tomorrow.
Brock

 

[Blogwitch]

Brock,

Don't let things like this get you down, you are doing just great.

You have to learn to walk first, and when you have a little more time, you can spend it on making piston rings.

I have forgotten the number of rings I have broken over the years, and I used to make quite a few at one time.

Go with the Viton ring, get the engine running, and come back later if you feel the urge to fit a cast iron piston ring.

It is only yourself that is kicking you in the butt, everyone else is hanging on your every word because you are doing so well.


John

 

[vcutajar]

hear hear.

We have a saying here which loosely translated says, "If you can't get through the door, then go through the window".

As John said the get it running and then if you want you can always come back and try again the rings. Personally if its running I wouldn't touch it again.

Vince

 

[ShedBoy]

The pain continues with unidetified metals. But first a conrod

Piston on the rod with o-ring

This is the cylinder where it now lives and belongs. This was the spline end on a CAT scraper drive shaft it turns not to bad, a bit hard on tooling. When it come to drilling holes in it and then tapping it you have another whole set of issues. One broken drill and a blunt one later (one of the bits that snapped off lodged in the back of my finger at speed) the thing ended up in the bin. At this point I thought maybe they don't harden the part of the shaft which is not splined. I tried to cut it away from the splines on the left over shaft but after 30 seconds in the bandsaw I had removed the rust only. It is going to the scrap man. At this point the assembly of parts was put in a box and stored until a later date. The later date turned out to be the next day.

Cylinder #3, no complicate turning, easy fabrication coming.

Making the stand

Welding on the stand and squaring up. Back at the same stage.

First tool off the new grinder for cutting the valve seats

First valve seat cut beautiful, the second suffered act of zig when I should have zagged with the handwheels, one valve seat is alot widerr than the other but it should still work, if not I can fave the thing and make a valve cutter and recut the seats.

Machining the top of the head.

Brock

 

[ShedBoy]

Head sitting on the cylinder, needs a plug hole.

Successfully eyeballed the plug into the right spot. Ignore the huge valve seat, I do.

This is where I finished last night, one machined valve guide. Now I am off to find some info on turning valves successfully. I have left the rest at the angle I turned the seats at. If anyone has a link or site they can point me to it would be good. Thanks for looking in.

Brock

 

[Blogwitch]

Brock,

A simple way to cut valve seats is to use a 90 degree countersink tool in your tailstock, which is the angle that is required.

Take it steady to avoid chatter and they make a perfectly shaped valve seat. The rest is taken care of by grinding in.

John

 

[ShedBoy]

I often thought about using one of them but was worried about getting it straight. The head is fine, it is the valves which I need to do now. If I need to take a skim off the head to narrow the valve seat I will give it a go. Turns out my con rod is too long also, I may just cut and weld it.
Brock

 

[ShedBoy]

Well I have cut and welded the conrod to get the correct compression ratio I think (about 5.5 to 1) but now my piston comes out the bottom of the cylinder a bit to much for my liking :-\ I may just bore it out and put a cast iron sleeve in it with an extended skirt. The head now has ports drilled and is waiting on some valves. I have been a bit lazy on the photo front. I also made another crank gear as the first one did not get finished due to work hardening and wrecked involute cutter. I made one out of some stainless steel which cut like butter so I am assuming it is one of the nice grades, maybe 303.

Just need to drilled for a set screw and part it off. Back to work tomorrow :'(. Gives me time to relax and have a think. I think I am going to build from plans for the next engine as this measure and make system I am using with this engine is not the most effective way to use your time. I don't have meny parts left to go though. Thanks for checking in on the madness.
Brock

 

[Ken I]

Just keep digging - the welded conrod gives me the heebies - I would make a new one once all the bugs are ironed out.

I design very thouroughly before making anything - the do it as you go or back of a fag packet approach invariably leads to trouble.

Its a lot easier to fix on paper (computer RAM - whatever) than in metal - and even then I've made some monumental errors (like a drive shaft going through another moving part of a machine and even gears that needed to go in opposite directions to each other.

As SWMBO says I'm just a man and can only juggle one thing in my mind at a time - two's a push.

Plan ahead.

Ken

PS Confucius says "Never look up at mountain - just keep digging !"

 

[ShedBoy]

I had some thoughts on the welded conrod also and knew it would put some people off but I reckon 25mm of good weld will be stronger than two 4mm big end bolts under the same forces. I am sure someone good with numbers will chime in with some calculations. The rod is 10mm thick and was prepped with 4mm bevels all round then welded with a red hot Mig welder, I am confident it will be strong enough, but I will stand on the other side when I run it. I have nearly made every other part twice so it will probably get done. If I can get this thing to run on its own for a couple of minutes and maybe start a second time I am going to shelf it and move on. I really need to learn how to use some CAD software one of these days, it would make life alot easier. I know I am diggin myself into a hole but my work as an underground miner has prepared me for that, you can always go sideways and come out somewhere else and if you can't dig anymore blow something up :big:.

Brock

 

[Ken I]

Can't fault your logic on the strength issue - But

(theres always a "but")

The root of a weld is always considered to be a crack (metalurgically speaking) and under cyclic loads cracks propogate.

Hence my comment about the heebies.

My concern would be related to long term use - its a small concern only FYI.

Ken

 

[ShedBoy]

Back from work so back to the man cave. I have been dreading making valves again after my previous attempt. I have finished the gear for the crank just need to get some grub screws to lock it in.

Mesh is good for my first go at gears.

Inlet valve with 1 little booboo. I learnt from my mistake and aced the second. I am going to call it lightening, you'l see it

Should have faced the head off last on the first one. Live and learn Brock

Woohoo looks like valves and seal good so far, still need lapping in.

My lightening hole. I am telling myself it will be less weight for the vacuum to move :big: :big:

The dreaded head is nearly done. Now I have duties to perform which are not in the shed, DROLL. Will be back to it later today, I am told I will get early parole today.

Brock

 

[tvoght]

I'm watching this Brock. Moving at a good steady pace!

 

[metalmad]

Hi Brock
looking good Mate
But If it was me, I'd be a little worried that valve has been badly weakend and if its the exhaust I'd definitely make a new one.
I normally make the exhaust a little thicker then the intake as its gunna take more punishment, especially if it runs as well as your last one did.
Pete

 

[ShedBoy]

Gday Pete
It is the inlet valve and I have decided if it fires up I will make one to replace it, really getting sick of polishing this turd, I am just going to roll it in glitter. Worst part today was I went to get some grubs screws but they were shut for a stocktake well back to the action.

Simple rocker stand

The rocker takes shape

I noticed some of these rockers in my scarp metal bucket, nice hardened pad on it. I had an idea form. Grinder time

I thought a hardened tip couldn't hurt

Silver solder away. Pad stayed hard, couldn't scratch it with a hacksaw.

Final shape and alignment, I am happy.

It all works as it should, ended up with 1.25 ratio rocker for about 2.3mm of lift. Should work okay. With no O ring on the piston there is a suction at the inlet port when you spin it with the drill but I need a stronger exhaust spring. Thanx for looking in.

Brock