|Hall 3HP Engine Timing Problems
Post Number: 93
|Posted on Wednesday, November 14, 2007 - 01:48 am: ||
Cheerfully looking for suggestions/advice.
I have an Australian Hall 3HP single cylinder 2 stroke engine. This has recently been done up with new rings, piston, bearings. machine work etc. It has great compression.
So far all is good, however I've hit a bit of a stumbling block, major really. We can't time the engine properly!
Firstly a bit of background on the timing mechanics for this engine. It uses a magneto Lucas RS-1). The engine is built very much like a model airplane engine. That is it has a long single sided crankshaft with 2 bearings on one side. The shaft, then the crankweb and then a long crankpin. The conrod slips over this pin. There is no second crankweb nor shaft.
So the crankshaft slips into the crankcase from one end. A dished plate then closes the crankcase. As is said exactly like many model airplane engines.
On the inside of the dished plate is a piece of square rod that is very nearly as long as the internal crankcase circumfrence. This rod is driven by the end of the crankpin and drives a shaft through the plate. This shaft drives the magneto.
The idea behind this is that the engine can be started in either direction without changing any settings. The crankpin will capture the end of this rod in one direction. Reversing the engine direction will allow the the crankshaft to rotate 180 degrees (less the angle formed between the the rod and centre of the crankpin) before contacting the rod again and hence driving the magneto.
I trust this makes sense, if not I will take some pictures when it stops raining here.
To me this all seemed pretty simple to time. The approach taken was to find TDC and the advance should be the same on each side of TDC for each direction.
However this is where I'm now at after 8 hours. The engine runs fine in notional reverse, in fact it runs great- idles well, revs well and is nice and crisp. But in notional forward it barely runs, throttle is unresponsive and just chugs along.
Changed plugs and leads still the same. I suspect the magneto. However this where the plot thickens. In the reverse direction the spark is poor, orangey and very short. In forward its good silvery blue 3/8" or more.
So now I'm perplexed. The next step is to put a timing light on and confirm the timing is Ok although I'm sure it is.
Has anybody timed a Hall engine? If so do you have any pointers?
One thing we have noticed is that this engine is very sensitive to timing. An eigth to a quarter of an inch on the flywheel is very noticeable.
You may ask why not just run it in reverse. Well I have an orginal Hall Boat which this engine is going into and I really need the forward and reverse functionality.
Thanks in advance,
Post Number: 29
|Posted on Wednesday, November 14, 2007 - 03:02 am: ||
Lovley little motors. I have 3 Halls, a 1948, 1956, and a 1962 Ball race Crank and alloy crankcase.
If it is running ok in reverse then the timing is out by 180 degrees. I had the same problem when I overhauled my first engine. Take the rear plate off and turn the shaft 180 deg so that the crankpin drives the other side of the bar.
They are not meant to run in reverse although like most 2 strokes they will.
The reason in spark quality is that the RS1 is set up to run in one main direction only, in other words the armature is timed to produce the hottest spark in one direction only.
I have been running the 62 model Hall in a 12 foot Carvell putter and gets along quite well.
Have had quite a few conversations with Frank Hall (Son of the founder) and got quite a lot of the history of the motors.
If I can help you more just email me direct. I am located just South of Newcastle on Lake Macquarie.
PS I will be in Narooma this weekend for a regatta but taking my new boat with the Stuart P55.
Post Number: 94
|Posted on Wednesday, November 14, 2007 - 05:21 am: ||
I'll rotate the bar 180 degrees and let you know how I go.
The mag field strength I understand, what had me confused is that the engine runs very well in reverse with a terrible spark.
The engine in the boat is an iron plain bearing model, there is some history attached to it which I can talk to you about. I also have an alloy crankcase model out of a lighting plant.
Both engines are pretty good as they have never seen salt although the alloy model has a "frost crack" in the cylinder.
The boat is "glass" 13 foot and obviously moulded from a wooden clinker boat (not symetrical). I understand that Specialty Engineers produced it later on. The rear of the hull is a tunnel!
So we will see how this outfit goes: )
There are some pictures attached.
Post Number: 30
|Posted on Wednesday, November 14, 2007 - 07:30 am: ||
Just had a long reply ready to send and had a computer lock-up and lost it all.
Just to let you know, I will be away from Tomorrow 15th until Next Wednesday the 21st so will catch up with you then.
You might let me know where you are located, I may be passing one day!
Hear from you soon,
Post Number: 96
|Posted on Thursday, November 29, 2007 - 06:57 pm: ||
I trust you had a good time in Narooma?
The good news is that the engine is now running fine.
As suspected the magneto was the culprit.
It would seem it was breaking down under pressure. Changing coils resolved the problem, although both coils measured the same on the multi-meter. Hence the assumption that the original was breaking down under pressure.
I'm not too far from you at Woy Woy. Again thanks for your help.