Gallery, Projects and General > Project Logs
Fixing the how NOT to make an engine
bogstandard:
I am trying to blast on with this engine to get it finished, so I spent a little time in the shop this evening, getting a little stress relief.
Last time I mentioned cleaning up the bores a little.
I grabbed a bit of PVC rod and turned it down to about 1 thou under bore size. Then using a couple of different grades of valve grinding paste, then finishing off with a chrome cleaning liquid, I got the bores nicely cleaned up. I am not after micro finishes and sizes on these bores, as long as they are smooth and within a thou or so they will be fine. Don't go chasing your tail trying for perfection. As stated before, for an IC, flame licker or Stirling, yes, then try for the best you can. With these small engines, near enough is usually good enough.
Nice semi matt bores, and both measure the same.
I am making new pistons, and here they are in rough size. They still need to be turned down to length and diameter (0.002" or 0.05mm smaller than the bore).
I have now marked each piece as part of an assembly, with either one or two tiny pop marks on each part. This will ensure that when I have finished, I will have two perfectly fitting assemblies, with all parts matched to each other.
I found in my little stash, two perfect matched o-rings to the crappy ones that were in there. So I did a quick check on the plans for groove dimensions. If I had made the grooves to the plans, the o-rings would have been sitting lower than the piston edges, and so performing nothing to sealing the pistons, just there for decoration. The great ST strikes again.
So armed with a bit of paper and a pencil, the CORRECT dimensions were worked out.
Pistons now to size, o-ring grooves and widths correct.
Now V-E-R-Y happy with the piston and ring fit. They should work perfectly.
So a bit of flange drilling, and the assemblies will be ready for fitting.
Next bit will be making new big ends.
Bogs
bogstandard:
Just to tidy things up on the cylinders, I knocked up a couple of end caps out of brass.
So now onto the big ends. I like the very hard wearing properties of ali bronze, so instead of phos bronze, I wacked some hex ali bronze down to the required size.
It was soon into the lathe for a bit of shaping, drilling and tapping.
The pair were then slipped onto the mill and cut and drilled to shape. Great I thought, everything had gone smooth as silk and I had the new big ends within 5/10ths of drawing, so basically, spot on.
Before I cleaned them up, I wanted to see how they fitted. Then the problem reared it's ugly head, they didn't, fit that was.
As you can see, they wouldn't fit onto the crankpin.
Then I thought, how come a great company like Stuart Turner could make something that was wrong, I must be me at fault, as they are so great, they would never make a mistake or ten.
So I double checked the parts to drawing, yes, I had made them correctly. So why didn't they fit?
Oh! Dear, someone in the world famous ST empire must have had a slip of the pen and marked up the plans incorrectly, Oh! and someone must have forgotten to proof read and test the drawings, FOR OVER 10 YEARS!!!.
I just wonder how many pairs of these big ends have been made over the years, and how many have had to be remade, just like I will have to do, and how many people must have complained about it, and how long would it have to be before ST put the plans right. Plus maybe reimburse the poor newbie for the wasted man hours and materials, not.
So if anyone wants a duff pair of big ends to not fit a Stuart Turner V-Twin engine, the send me the cost of postage, and you can have them.
It is my own fault, I know how bad Stuart Turner casting sets and plans can be, I should have checked and quadruple checked beforehand.
Bogs.
NickG:
That's terrible for a company like them. I thought they'd be perfect but I won't be buying any of their castings!
I hate the design of that offset big end too.
Well done John, it's going to run superbly well when it's fettled.
Nick
bogstandard:
Don't get me wrong Nick, Stuart Turner used to have a great reputation, and their collection of unique casting kits is second to none, but ever since going thru a few changes of hands, things have gone thru a few changes, in my mind for the worst. Quality of the castings have got worse and prices have jumped up beyond what they should have done. To me now, they are being made down to a price, and being sold for above market rate.
Maybe not too bad for the larger and more expensive in the range, purely because they will most probably be using old stockpiles of castings, but any of their usual high throughput stuff, I personally would worry about what I was buying.
I have had numerous people talk to me about rescuing ST castings, mainly because the castings were actually too small for the dimensions given on the plans. This suggests to me that rather than using proper oversized patterns that allow for the shrinkage of metals after being cast, they are using original castings as the patterns, so that when cast, the molten metal then shrinks away from the correct sized casting mould and they then come out say between 3% to 6% undersized, depending what metal is being used.
This doesn't usually cause a major problem to someone who has worked or is working from castings and has a lot of experience, as they can usually see what is needed and swap a few figures about and get things to fit. Stuart Turner expect everyone that makes their engines to do just that. Make it fit.
But it is a totally different thing when a newbie gets a set of undersized castings. He doesn't understand that the castings have to be measured up first, before doing anything else, and then cross referenced to the drawing dimensions (and as I have shown, the drawings aren't all that good either) just to double check that the part can be made out of the casting. Usually, after taking the initial cut, the engine is doomed to failure.
Stuart turner are not the only ones on the money making roundabout. Reeves, who have most probably the largest casting collection in the world, have started to go downhill on quality, to such an extent, I personally would only recommend some of their castings being used as high priced fishing weights.
You pays your money, you takes the chance.
Bogs
bogstandard:
I have managed to get rid of my overseas visitor (at last), and have got back into the shop again for a while, at hours to suit myself.
I got a new pair of big ends made, with the holes in the correct place this time. By the time I had finished working them, the ali bronze had gone rock hard, and I had trouble dressing the burrs off them. Just what is needed.
The next job to do was to get the tensioners made and sorted for the other side of the engine. New spring holders and knurled nuts were made up, these just need a set of acorn nuts making to lock everything up when the tensions have been correctly set.
This shows the throttle valve area.
No instructions for making the stop or setting it up came on the plans, so using my experience on what is required, I fitted a stop pin, and dressed the throttle stops. This is so that when in the fully one way position against the stops, the horse shoe cutouts in the valve face align perfectly with the port holes drilled in the main block, so depending which way the valve is swung, either fully fwds or reverse is obtained, and variable throttle and stop is obtained between the two.
Now that I had the port faces being pulled against each other, and putting the big ends in their running positions, I could dress the the face of the crank disc to give a little running clearance. I gave it 0.020" (0.5mm), which should be more than enough if ever the cylinders get blown off their faces at an angle because of excess steam pressure.
Now that I had all the bits set up for correct clearances etc, it now warranted setting up the RT to do a little offset drilling. Waiting until now meant I only had to set up the RT just the once and get all the bits done at the same time.
This is now the time to show that accidents do happen to the best of us, and this was because I broke one of my golden rules, NEVER RUSH TO GET THE JOB FINISHED.
The wife had stuck her head out of the door and shouted 'lunch in ten minutes'.
I was just making the knurled nuts that are shown above, and being a smart a**e, I thought I could get them finished in time.
So instead of taking the small drill out of the tailstock and putting it back in it's box, by rushing, I forgot to do it.
Swung away with the toolholder to change for the next one, and this fleshy and tender part of my anatomy dragged against the razor sharp edge of the drill still in the tailstock chuck. Ending up as a rather deep cut, any deeper and the sewing machine would have had to come out.
The dog learned a few new choice words, the cat did a runner because it knows what happens to my boot when I am in a bad mood, lunch was delayed, as the wife patched me up and patted me on the head as though I was a little kid, and I lost the rest of the day in the shop, while I waited for it to stop bleeding and heal up.
All because I acted stupidly in a dangerous environment.
Anyway, enough of my stupid antics, back to the job in hand.
The RT was centred up, offset in the Y axis for the drilling for the pin in the crank disc. Notice that it is sticking up from the chuck jaws a bit, this saves drilling into the chuck jaws as you break thru.
Next offset was for drilling the holes in the bottom cylinder bearings. Because I didn't want to drill into the chuck jaws, I put a couple of washers underneath as the jaws were tightened up, just to raise it away from the jaws slightly, so as the drill broke thru, no damage would be caused to the jaws. The washers are removed before starting to drill.
The same offset was used for the top caps, but thinner washers this time. I didn't have as much to hold onto with the chuck jaws. I was just a little more careful as the drill broke thru.
All bits drilled, and the washers lived to be used another day.
Now these bits have been finished, it allows me to progress a little further and get other parts that have been made previously, fitted onto other assemblies.
Not much to finish with this time, only, as and when I get some more done, I will post it up.
Bogs
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