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Member postings for John Olsen

Here is a list of all the postings John Olsen has made in our forums. Click on a thread name to jump to the thread.

Thread: Honda SL125 timing - SANITY CHECK.
12/04/2021 14:57:37
Posted by Ady1 on 12/04/2021 13:04:02:

Electronic timing running two sparks?

No, it is not that sophisticated. The two marks for the high speed are I think intended as a tolerance range for where the spark should occur when running fast. My experience was that there was a lot of jitter in the spark timing at speed, which given the mechanical advance retard is probably reasonable.

Apparently there were later versions of the CB125 with CDI, I dunno if that ever made it into the SL version


12/04/2021 12:29:34

As you say, the unannotated marks are correct for when the engine is revving. It is more important for the ignition timing to be correct at high revs than at idle. If the advance retard unit is a bit worn it may be giving more advance than needed, you can tweak the stops in a little with brute force if this is required.

It might not be all that sophisticated compared to modern stuff, but over 100 bhp per litre is not too bad. You can also get well over 100 miles per gallon if you try. From what we could tell back in the day, the 100 cc version produced just as much power as the 125, maybe because the valves and the carb were the same size. Although my 100 ended up with a 125 barrel, a hot cam, and a 24mm carby instead of the 22mm. It went really well like that.


Thread: Substitute Stuart taps?
10/04/2021 22:35:28

When I purchased my Unimat 3 nearly 40 years ago, it came with a set of Stuart 10 castings without screws and fasteners, and with a booklet giving all fasteners and dimensions as metric sizes. It all worked fine. So it is certainly feasible to change any or all of the threads to different systems, within reason.


Thread: Honda 125 electrics
30/03/2021 01:12:27

These alternators don't have any earth connection on either of the coils, since they use a full wave bridge rectifier. If you disconnect the alternator from the rectifier you can check for resistance to the frame, it should be open circuit. The Lucas one on my Blazer SS went short to ground, so I had to rewind it. The ones on bikes with a magneto combined with the lighting coil often do have the coils earthed at one end, but the type on the CB/CL/SL 100/125 range don't.

It is actually possible to use the existing Honda coils to charge a 12 volt battery. This will raise the engine rpm at which charging starts, approximately doubling it. If you spend a lot of time at low RPM this might not give adequate charging. I actually rewound mine at the time, with just one winding with a few more turns, and fitted a home made shunt regulator and a 12 Volt battery. That meant that I was able to fit a 55Watt H4 Hella quartz halogen light, which was much better than the original and was good for night riding. It was actually better than the light the 750 four came with at the time. So a bike capable of maybe 125 mph came with a headlight that was barely adequate for 60 or so.

A shunt regulator is a pretty simple circuit, the main thing to remember if you build one yourself or find someone to do it is that this is a high vibration environment. My first attempt worked fine for a short time, until most of the components fell off their leads. The second attempt was potted in epoxy and lasted until I sold the bike, which by then had been taken out to 125, fitted with a hot cam, and a larger carb. It was capable of 80mph and might have done more if I could have arranged higher gearing. Oh, it also had the front end out of a Suzuki 175, mainly so I got the 8 inch twin leading shoe brake, which wouldn't fit into the Honda forks.


29/03/2021 11:03:17

At that time the Hondas up to about the 350 twin all had permanent magnet alternators. Some, including the 200 twin, had a regulator. The fours came out with proper excited field alternators, which gave decent regulation and a lot more available power, which didn't stop Honda providing a totally inadequate headlight on the 750 four. Earlier British bikes either had a dynamo with a regulator, which would have been fine apart from the inadequacies of the maker, or else a permanent magnet alternator, improved about 1970 by the addition of the zener regulator. My Triumph Blazer SS 250 had one of those, and also a large electrolytic capacitor so you could in theory take the battery out to save weight. That implied that you could get the engine turning over fast enough to generate enough power for the battery and coil ignition to work...I never tried that.

They didn't change the excitation, the alternator had two windings, one always connected, and the other switched in when the headlight was turned on. The alternator had six coils, one winding was two of them and the other was four. If you need to pull the alternator, take the screw out, remove the back axle from the back wheel and screw it into the large female thread on the alternator magnet casing. Do it up firmly, give the end a tap with a lead hammer, and repeat until the magnet housing comes off. This worked on every Honda of the sixties and early seventies that I ever had the chance to try it on. Saves buying a special puller.

I would check if the rectifier is selenium or silicon, if not silicon I would change it. A shunt regulator would also be a good idea, it needs to be rated for about 60 Watts. Otherwise you can cook a battery quite quickly if you are running with lights on in the daytime and the headlight bulb blows.


Thread: 1.1 kw brushed motor Torque
29/03/2021 10:44:07

Usually when we talk about swing, it is the diameter of the largest item, so for instance a centre height ot 3.5 inches like my Myford is a swing of 7 inches. It used to be that Americans went by swing and Brits by centre height, presumably so that they could fail to communicate more effectively!

But anyway, while I don't have any experience of either of these machines, my feeling is that these variable speed drives are fine for slowing the machine down for light work, but not so good for serious machining of big items. This is because the maximum torque at low speed is no more than it was at high speed, when for turning large diameter items you really want more torque at the low speed. This is especially true for turning a cast iron flywheel, where you may need a decent cut to get under the hard skin that castings often have. So although my own Myford has a VFD, the pulley steps and the back gear still get a fair bit of use when larger items come up, since you can step the speed down and then take a decent cut. It takes long enough at slow speeds, without having to reduce the cut to a mere skim. Also, if you are having to take light skims, you will probably want to use HSS tooling rather than carbide, the carbides tend to work better if you are removing a decent amount.

It does all depend though...if you are only doing a very few large jobs, you can probably put up with them taking a long time. You can also do things like taking off the hard layer with a grinder before putting it in the lathe, so long as you don't overdo it.


Thread: Honda 125 electrics
28/03/2021 22:44:35

The SL125 has the same setup as my 1971 CB100 had. The permanent magnet alternator has two windings, one which is always connected to the rectifier and one which is switched in when the headlight is turned on. This type of alternator has no regulator, and depends on the alternator acting like a constant current source at higher RPM. For that to work, the load current must be approximately equal to the design current, for each switch setting. Any excess current will overcharge the battery, while if there is a shortfall the battery will go flat. So it is important for the bulbs to be the specified wattage, no use trying to put in a more powerful headlight for instance. You can put in a better one of the same wattage. Things that are only on intermittently, like the flashers and brake light, will use stored capacity from the battery and the charge will (hopefully!) be made up during normal running. This means that there is likely to be a bit of excess charge, which is not good for the long term prospects of the battery. A shunt regulator like the Triumphs of the era used would be a good addition, not that Lucas electrics were generally any good!

But since your current problem is with the engine not running, I would be looking for high resistances in the circuit. The problem could be in the ground path, which is through the frame, or in the live connections or switches. If you have painted the frame and then screwed on the ground connection for the battery, that could be one cause for instance.

I think I still have my CB100 workshop manual somewhere, I wonder if I can find it.


Thread: Bolt circle without DRO
20/03/2021 20:39:30

You can get a very reasonable accuracy by drawing it full size in CAD, printing the diagram, and then using that as a pattern to centre pop the location of the holes. I've also done quite a few with a simple direct dividing attachment. With that you just have to get the first hole at the correct radius, then step around.


Thread: Stepper Motor Protection
07/03/2021 03:21:51

Usually there would be protection diodes to protect the electronics against back emf. Sometimes these are inherent in the MOSFET drivers, but effectively still there. If not there, they should be added. The wasp in the jampot is that such diodes, when the motor is driven by external torque, will power up the circuit, possibly leading to undesirable results, especially if the motor is driven fast enough to generate a higher voltage than the circuit is designed for. So ideally the motor should be either electrically or mechanically disconnected when the shaft is being driven by the handwheels. Might not cause any problems in many cases. but no guarantees!

Makes me wonder what might happen if you tow an electric car that has permanent magnet motors. Has the designer thought of that case?


Thread: Dipping a toe into VFD stuff
06/03/2021 02:18:34

First, you won't get your money back if you put in a three phase motor and VFD. It's like an old car, you might put in a new engine but you will still only get an old car price. Sales people don't normally have consciences, they find them an unnecessary burden!

Second, marketing BS is not necessarily rationally explicable. Peak power is pretty meaningless. Power is the rate of doing work, if you store energy in a flywheel and then dump it into a load, you get a very high peak power but the average is still low. The advantage of the vfd is that the torque of the three phase motor will be smoother and higher than that of a single phase, if your wife wanted to keep it and use it the VFD would be a good idea.


Thread: Design of boilers
05/03/2021 23:32:34

If it is efficiency you are after then we need to increase the temperature difference between the hot end and the cold end. Usually this also involves raising the pressure, but I suppose under club rules you can't go past 100 psi. So lots of superheat I guess. Actually with a flash steam generator you should be able to go to any pressure you like, since there is no pressure vessel. The exhaust end needs a condenser, which needs to be as cold as possible, I guess we could carry ice, or get even more ambitious and carry dry ice, or liquid nitrogen. Although it would be awkward if the condenser iced up, i guess that would have to be prevented in the design somehow. The engine part would need to be a compound, reciprocating engines are limited in the temperature and pressure they can usefully cope with in one stage.

One thing is sure, the whole thing would be bulky, and it would not look much like any conventional steam locomotive.

It is easy to get hung up on efficiency, what really matters is a whole lot more subjective, eg how effective is this device at doing what I want at a price that I can afford.


Thread: Inherited ML7 in need of some love - where to start?
05/03/2021 02:24:53

I would start by giving everything a good cleanup with the minimum of dismantling and then see how it goes. No point in stripping down ready for a bed regrind if it doesn't actually need one. Many parts can be cleaned and reconditioned (if needed) separately without taking the whole lot down at once.

It does look like a great start. I've cleaned up an 18 inch shaper that looked much worse than that.


Thread: A Marine Condensing Engine
04/03/2021 21:40:03

Just thinking some more about drain cocks, in a lot of full size practice things like this discharge into a copper funnel, which then has a pipe to who knows where. The point seems to be that you can see the discharge so that you know it is working. This is of course especially important with things like gauge glass test cocks, where you want to know if it is discharging steam or water. With the drain cocks, when you are warming the engine it is good to be able to see when it is hot enough inside that it is discharging steam rather than a mixture of steam and water.



Thread: water level sensor
04/03/2021 20:33:57

Is this for a plant in a small boat? I wonder if in fact it would be simpler to arrange a variable stroke pump and then adjust the setting over a number of trials until the sweet spot is found where the boiler level is maintained correctly without needing continuous attention. You might think that would not be possible with the speed of the engine possibly varying, but in my not so small steam launch, I have found that (purely by chance) one of the two pumps will maintain the level correctly in the boiler for long periods without having to either turn the pump off or turn the second pump on. When I say long periods, last Monday a group of us made a trip in Whanganui that took about five hours, and the pump settings were not changed for most of that time...I had the two on briefly at the start to get the level up to a good point, then left them alone for most of the trip.

Another approach that has been used in small but man carrying launches is to have a float in the hot well controlling the pump bypass. The requirement here is that no water should be being lost anywhere else in the system, through glands or excessive whistle blowing etc. So there is a fixed amount of water in the system, and if it is in the hotwell then it is not in the boiler and vice versa. This wouldn't work for me at present, since water is escaping somehow into the bilges slowly, so every couple of hours a bucket or so from the makeup needs to go into the hotwell. I think it is escaping from the pump glands slowly.

There is a much more sophisticated system used in full size practice where you have a closed end tube connected to a column at the desired controlled water level. The tube slopes upwards from the connection point. When the water level in the boiler is at the height of the connection point, the steam above it will condense due to heat loss from the tube. Water is not a good conductor, so the top end of the tube will cool down. When the water level is below the connection point, any water in the tube will drain out, it will be full of steam, and will be hot, since any condensate can run out and be replaced with steam. So a temperature sensor here can detect the change and be used to control the pump. This works very well in full size practice, but might be harder in a small size, especially if it is in a boat that bounces around a bit.


Thread: Newcomen Plans or kits - looking for.
03/03/2021 04:56:37

How big do you want it? The Auckland (NZ) Steam engine society has what is probably the only full size working Newcomen engine in the world at present, a semi replica built by club members, it stands about twenty feet tall. I don't think there were ever any detailed drawings made.

There was also a model one being sold a few years back, stood maybe a foot tall. I think they were from the UK.


Thread: Why do plumbing fittings have cast nuts?
03/03/2021 04:51:35

Are they cast or are they hot pressed? Some years ago our club visited a place that was making brass fittings for LPG gas service. They were done in large power presses by heating up a suitable length of brass bar and then stamping it in the press. This gave quite complex shapes with good detailing including quite fine lettering. I think Stuart used to do some of their brass parts this way.


Thread: A Marine Condensing Engine
26/02/2021 09:07:50

Some engines actually have some volume between the HP exhaust and the LP inlet, most don't, so receiver is just a fancy or maybe short way of saying "the piece of pipe between the Hp exhaust and the LP inlet". Of course sometimes this is actually built into the castings so there is no external pipe at all. My simpling valve just takes steam from the main steam pipe to a tapping on the said pipe. It would probably be nicer to take the steam from after the throttle valve.

My drain cocks just vent to atmosphere. Probably not ideal, it would be nice to save the water. Into the hot well would be my choice, you don't want the vacuum plumbing too complex as leaks in it are hard to trace.

Unless you are modelling a specific full size prototype, you don't have to worry too much about being strictly correct to full size practice as most possible variations will have been tried somewhere. So as long as it is reasonable and works it is ok


26/02/2021 05:03:58

Clockwise or antiCW will depend on which end of the shaft you choose to look at. CW looking from astern seems to be normal for single screw vessels, twin screw ideally should have a handed pair.

90 degrees is good since it means that your simpling valve will actually work to help start the engine. It doesn't matter which ones leads since they are usually double acting. So either the top or bottom LP inlet will open when either the top or bottom of the HP is about half way through its stroke.

There is a convention on locomotives for which side leads. If anyone tells them your model is wrong tell them they are looking too close.

There are at least two different types of simpling valve. The most common is probably the shot of steam type, which just feeds a bit of inlet steam direct to the receiver, putting back pressure on the HP. A more sophisticated type uses more valves and reconnects things so that both cylinders take boiler pressure steam in and exhaust to the LP exhaust side. This gives more starting torque, at the expense of heavy steam consumption, and is more likely to be found on a locomotive than a marine plant. Some old timers called the simpling valve the "God Almighty".

My own plant will reverse most of the time just by throwing the lever over, but has the shot of steam type of valve for that one time when the wharf is rushing up, you throw over the lever, and nothing happens. Actually it is more likely to fail to reverse in that sort of situation, since you are probably already throttled back to very low inlet pressure to go slow, whereas if you are cruising along at a good speed and throw it into reverse, there is plenty of pressure and the water forces on the prop are likely to move it off dead centre too. So the usual practice is to throw the links over and give it a little shot as well, before you even know if it has decided to reverse. It has an American locomotive style Johnson Bar rather than a more typical marine style screw reverser, since a small boat is more likely to need to reverse frequently than large boats do.


Thread: Condenser Cooling water flow
26/02/2021 04:21:31

On this question of whether or not the air/condensate pump creates the vacuum or not..

My experience is that you won't see any vacuum until the pump is working. At the beginning of the process, the condenser will be full of air, which is rather hard to condense, so until that has been pumped out you won't see any vacuum. Actually of course steam from the warm up might well have displaced a lot of the air, but if the cooling tubes are full of cold water that steam will condense and the condenser is liable to be flooded with condensate.

However, the point that someone no doubt was trying to make way back in history, is that the whole process would not work if steam/water did not have the lovely property that the volume of the water is about 1600 times less than the volume of the corresponding steam. So to maintain the vacuum it is only necessary to pump out a relatively small volume of water, plus of course any unwanted air that has made its way in.

The same thing is also an advantage on the feed pump side. Compare the relative size of the feedpumps to the main engine, then compare the size of the compressor on a jet engine to the turbine. Sadly for steam we also need a relatively large boiler to heat the working fluid, much bigger than the combustion cans on a gas turbine. Perhaps a better comparison is the much larger size a typical hot air engine needs to generate a similar power to a steam engine

Practically, on my own plant on "Dancer", it is necessary to open the vacuum breaker for a bit on starting out. This allows starting out without pressurising the condenser and allows the circulating pump(driven by the main engine) to start the flow of cooling water. After a short time, the cloud of steam over the side from the vacuum breaker diminishes greatly and condensate starts to be returned to the hot well. At that point, the vacuum breaker can be closed and the air/water pump starts pulling down the vacuum. When all is well it takes maybe 10 to 20 seconds for the vacuum gauge to climb around the scale.

Running on salt water was relatively common in the early days of marine steam, even into the 1850's.. It is very wasteful since the boiler tends to get loaded up with solids so has to be blown down frequently or even continuously, and the salt content raises the temperature required to boil the water. A boiler full of salt water is also very prone to priming.

All this is of course pretty irrelevant to a model, where efficiency is not a great concern, but it is kind of satisfying to do things properly even if it doesn't matter. Condensing the exhaust, even if you don't care about the vacuum, will reduce the cloud of steam that would otherwise result, which might make it nicer to run on steam for a public display.

My own favourite reference would be "The Efficient Use of Steam" by Lyle Watson.


24/02/2021 08:26:33

The contra flow is definitely the ideal.

On the subject of trying to keep the condensate as hot as possible, if you want a good vacuum this is a mistake. Where you have water (condensate) and steam in contact, the lowest pressure that you can attain is determined by the temperature of the water. If you try to lower the pressure further, the water will just boil off, and you can happily boil water off at room temperature with a good vacuum pump. So what you do is use the coldest cooling water you can find, and the biggest condenser you can manage, and draw off the condensate as close as possible to the cooling water temperature. then you pump the condensate, now at atmospheric pressure or higher, through an exhaust steam feedwater heater to bring it back up to near boiling to go into the hot well. The hot water will absorb less air than colder water, as your goldfish would like you to know. I haven't made an exhaust steam feedwater heater yet, so my hot well is running colder than is ideal but when all is well I can get a good vacuum.

You will see discussions in steam boat circles with guys claiming that they can get really hot condensate out of a condenser while also getting a good vacuum. This is not possible and if you consult a set of steam tables you can see what vacuum is actually attainable for any nominated condensate temperature. At 100 degrees C the best you can expect is 14.7 psi absolute, or 0 inches of mercury

Then of course you only need a pinhole leak somewhere in your system, as I seem to have with "Dancer" at the moment, and all that wonderful vacuum will get out.


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