Bruce Macbeth Engine, European Version

[fumopuc]

The shock loadings from the camshaft can be quite large. Is there a possibility that the crownwheel and pinion driving the camshaft could be jumping teeth?

Hi Roger, no idea.
To understand it completely it needs a partly disassembly that I can push the crown wheel beside.
That means to solve all 4 intake lobes and pull the shaft a bit to the left, than the crown wheel will be pushed to the right with this action an the surface of the relevant spot under the CW will be visible.
At the end it will be the necessary job to do.

[Dan Williams]

Hi Achim,
 Again, I appreciate your response to my PM regarding cam lobe adjustment on this engine. At this point in my build, I got some consistent firing with a 3mm carb and that was at part throttle. I have yet to get it to run consistently and continuously on it's own. When it tries to run, it just eats up the fuel prime right now.

I don't think you have a carb size issue at this point. I suspect your cam and ignition timing slippages are your main issue. I've had multiple issues with cam lobe slippage, crown gear slippage and pinion gear slippage. I resorted to machining flats where all the gears fit their shafts, but now my only way of adjusting cam timing is with the lobes. These small setscrews make it difficult to get a good, firm grip on the shaft.
My biggest issue with the overall design of the engine is in the cam drivetrain. Disassembly to correct any sort of issue means total re-timing of the camshaft.

Good luck sorting it all out. 

Dan

[fumopuc]

Hi Daniel,
I have to say you have been right.
It is possible to run the BME with a 3 mm carb.
After some maintenance and a new adjustment of all timing another attempt to get it running at its own.
Et voila.
<a href="https://www.youtube.com/watch?v=8qUb62jXW6s" target="_blank">http://www.youtube.com/watch?v=8qUb62jXW6s</a>
My engine will just idle with this small 3 mm carb, to give more throttle impossible, it is fully open already.
But now there will be first some other things on the to do list.
Sealing the wooden floor will by #1 to do.
Followed by the assembly of the whole cooling system again.
If all this is done I will try it with another carb again.

[Kim]

Excellent!
Congratulations on getting it running, Achim!   

Kim

[Dave Otto]

Congratulations Achim!
That has got to a great feeling of accomplishment for you have it running.
Sounds good too!

Dave

[Roger B]

That sounds rather better      Did you find where the timing had slipped?

[Admiral_dk]

That must have a relief to you - congratulations, you got a very nice runner (even if only in idle) 

Per

[crueby]

Excellent!! 

[Don1966]

 


Don

[Dan Williams]

Outstanding! Glad you have it running more consistently now. They certainly do take some adjusting, that's for sure. I may make a new camshaft with flats 90 degrees offset for both intake and exhaust, making sure of the correct angle difference between intake and exhaust, to keep the cam lobes from working loose. Those tiny setscrews sure don't hold all that well.

After running mine for a bit, I decided that I'd better get the cooling system finished. It got rather warm!

Dan

[fumopuc]

Thanks you very much to all of you how have watched and written the friendly word.
I do appreciate it very much to get any feedback.


Daniel, here a picture of my solution with the connection lobes to shaft.
This has increased the possible length of the grub screws at bit.


Under the crown wheel are to flats for the two grub screws.

[fumopuc]

That sounds rather better  Did you find where the timing had slipped?

Roger thanks.


The position of the crown wheel at the shaft has slipped.
I could recognize when I toke the distributor cap off.
Crank shaft and CW has been in the right relationship to each other.
Easy to check, because I have made a marker at TDC #1 at the CW.
But the finger has had a position of half way to #1 ignition wire now.
Original adjusted in December was pointing exactly to the little piece of tape, what indicates cylinder #1.
 
   

[Rustkolector]

Achim,
The 3mm carb is more than adequate to run your B-M at a considerable load factor, but it is a crudely made carb designed for alcohol fuel and high reviving engines. As such it takes a little bit of work to improve operation on gasoline and even more to run propane. Once done it makes a pretty good little self compensating carb. The threaded sleeve on the needle shaft often leaks air through the needle threads giving an erratic fuel mixture at the lower intake manifold pressure and slower speed of a 4 stroke engine. Use a short stack of 1x3 mm O-rings to seal at the bottom of the needle sleeve. Make sure you use the O-ring to seal the carb to the intake manifold. The barrel opening at 600 RPM idle should be almost closed when using propane. I have never tried liquid fuel on this engine. Your need to run at wide open throttle is not normal for this carb.

I have not had the trouble you seem to be having with the cam gear and cam lobe set screws loosening. As you initially adjust these parts numerous times the cup head set screws very quickly become worn and no longer grip as they should. In doing your timing adjustments do not repeatedly reuse the same set screws. There should be two set screws on each gear hub and cam lobe at 90 degrees apart. Once you find the right timing install new set screws one at a time. On small set screws put the short end of the wrench in the set screw and using the long end, tighten until the long end deflects about 30 degrees. This is as tight as they need to be and DO NOT use a thread locking compound. Regrind your  wrench tips frequently. 

The B-M is meant to be a slow constant speed engine and as such uses no crankshaft counter weights. It does not need stiff valve springs. Make sure you used the same spring wire diameter and spring dimensions as listed on the plans. The listed springs are good for well over 3000 RPM. 

What cam timing are you using? I noticed a spark plug shorting to ground.
Jeff

[fumopuc]

Hi Jeff thanks a lot for visiting and all the helpful comments.
Good idea to replace the grub screws.
I have tried it all the time to handle them very smooth and carefully.
I will attack it to build a carb by my own.
A CAD model is available already.
The original design is from Malcolm Stride, publishes with his Lynx engine plans.
I have modified the venturi, decreased to 4 mm.
At the pictures how it should look like.


My timing is adjusted as recommended in Doug´s description.
The exhaust does start to open at 40° before BDC.
The intake at 10° after TDC.
Ignition is 5° before TDC.


The assembly with the cooling will start shortly, than I will do some more experiments.

 

[Roger B]

Hi Achim,

There is a little design trick in these simple carbs, the bore on the air intake side is larger that the bore on the outlet side that gives a measure of mixture compensation. For a given engine the sizes are found by experimentation. Fine adjustment can be made with an air bleed screw.