Author Topic: Bruce Macbeth Engine, European Version  (Read 58849 times)

Offline fumopuc

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Re: Bruce Macbeth Engine, European Version
« Reply #660 on: February 02, 2022, 09:21:52 AM »
Achim,
You need to verify valve opening and closing degrees to determine the correct valve duration. When things don't work as expected, it is a logical place to start looking for the problem. Nominal durations: I - 200, E - 220 with no overlap at TDC.
Jeff


Hi Jeff,
it toke some time but now I have been able to check my timing against your figures.
Thanks to Mike/Vixen for showing the way to show it easily with one picture in his post about the Bristol Hercules engine.
I have tried to do it here in a similar way.
First picture below does show the combined Information about Dougs recommendation to set up the timing from the HSM plans.
exhaust should start to open at 40° BBDC
intake should start to open at 10° ATDC
and the duration is from your above post.
The second picture is showing what I have just measured.
The duration of the exhaust is much longer than the above mentioned 220°, it is around 270°.
Intake is close to your mentioned  200°.
So first thing I have done to understand the difference, was a check of Doug´s exhaust cam drawing.
Below a screenshot of my sketch of this in Fusion.
In my understanding it it impossible to get a shorter duration of opening, because of this shape.
By earlier starting of exhaust opening it should be possible to decrease the overlap at TDC, but no idea if it does make any sense.
In my understanding new cams has to be made to archive the duration of 220° exhaust opening.
Is it really necessary ?
And why are there other values at the original plans ?   
May be someone of the more experienced IC engine builder will teach me, please.
« Last Edit: February 02, 2022, 01:22:25 PM by fumopuc »
Kind Regards
Achim

Offline Roger B

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Re: Bruce Macbeth Engine, European Version
« Reply #661 on: February 02, 2022, 11:16:01 AM »
Your new carbs Looks very successful  :)  :)  :ThumbsUp:  :ThumbsUp:

Depending on the shape of the cam the opening and closing points of the valve can be significantly affected by the valve clearance. Can you easily increase the clearance of a pair of valves and measure the timing again?
Best regards

Roger

Offline fumopuc

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Re: Bruce Macbeth Engine, European Version
« Reply #662 on: February 02, 2022, 12:46:27 PM »
Your new carbs Looks very successful  :) :) :ThumbsUp: :ThumbsUp:

Depending on the shape of the cam the opening and closing points of the valve can be significantly affected by the valve clearance. Can you easily increase the clearance of a pair of valves and measure the timing again?


Hi Roger,
yes I am very happy about the result.
Not expected in this way.
Hopefully the good performance can be transferred to the little brother carb.
The housing with both covers, the barrel and the lever are already finished.
Just waiting for the new tap and die set M3x0.35 for the new spray bar and needle.
That should arrive tomorrow, if I believe in the tracking data from DHL.


Concerning the valve clearance, first adjustment was between 0,15 and 0,2 mm, we are currently more close to 0,1 mm due to the setting of the valves.
I have something about 70 Minutes of run time in the records. I have scheduled a check and readjustment after 100 Minutes of run time.
The test with more clearance I have done already unintended some time ago during the first regular set ups.
The deviation was not so dramatic.


May be Jeff will read my post later and perhaps he will have more information about this timing story.
His engine is running with propane only and Doug is using fuel only.
So may be there is already a reason for a different timing.
Currently my engine is running not so bad with the timing it has right now.
We will see what a finer needle adjustment will generate.
« Last Edit: February 02, 2022, 12:49:51 PM by fumopuc »
Kind Regards
Achim

Offline Rustkolector

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Re: Bruce Macbeth Engine, European Version
« Reply #663 on: February 02, 2022, 06:19:57 PM »
Achim,
I built my B-M a long time ago. As it sits I have no idea of my B-M valve timing but it was built to the plans. It runs well under very slight 6-12 watt electrical load but does misfire at no load when engine is warmed up. I very recently had running problems with another of my engines which I believe I have resolved. It now runs smoothly with or without load at 550-600 RPM. Keep in mind this engine varies in two ways with your engine. Mine runs on propane and it has a 5:1 compression ratio unlike the B-M 4:1 C/R. I made two changes. First I increased the spark gap to .023”. The spark is now stronger looking and sounding.  And second, I changed valve timing to  I -200⁰ and E - 220⁰ crankshaft duration as I suggested to you. Unfortunately I did not make these changes independently. That’s a bad habit of mine.

Engine experts say that the closing of the intake valve is the most critical valve event in the 4 cycle engine. The B-M engine design is for slow speed operation (~450-600 RPM) and in my opinion I do not believe any valve overlap will increase volumetric efficiency in slow speed model gas engine operation. In high speed model engines it may be different. I just don’t subscribe to the belief that in a tiny slow speed model gas engine that intake air has any inertia effect adding to cylinder fill on the intake stroke. Inadequate cylinder fill on a slow speed engine is often evidenced by 8 cycling which is a very rhythmic exhaust sound of the engine firing every 2 or 3 power strokes. Try using a light hand applied load to your running engine flywheel (and...don’t scratch the paint!). If you can smooth out the engine running with a little load and a carb adjustment the problem is very likely inadequate cylinder fill and the intake cam timing should be extended. I do believe on a tiny model gas engine that additional cylinder fill can be obtained with a non overlapping and longer duration intake stroke as I suspect there is still negative intake pressure at BDC due to (no-load) throttle restriction. Intake valve closing at 20⁰-30⁰ degrees ABDC should help. Exhaust should close at, or just after TDC. Note: when I mention valve timing I use seat to seat timing measured at the valve spring retainer. No valve lash is included.

Jeff

Offline fumopuc

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Re: Bruce Macbeth Engine, European Version
« Reply #664 on: February 03, 2022, 07:18:26 AM »
Hi Jeff,
thank you very much for your answer an all the useful explanation.
Your input and also the engine timing collection of Mike/Vixen in his Bristol Hercules post has given me a lot of clearance and better understanding of model engine timing.
It is very much appreciated.
At the end it could be useful to build a very simple one cylinder engine, with easy to change cam lobes and already know behavior by a specific bore/stroke and carb.
May be this will be a future project for the R&D department, it could be really fun to do some own experiments there.

Kind Regards
Achim

Offline fumopuc

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Re: Bruce Macbeth Engine, European Version
« Reply #665 on: February 06, 2022, 10:52:45 AM »
There is a decision done how to proceed.
The measured and above shown timing of my Bruce Macbeth engine is definitive not suitable for a low reving model engine with no load.
By all what I have seen, is the opening duration of the exhaust cam much to long.
Compared with the information to Mikes collection of model engine timing and also the values at petertha collection showing something different.
I will do some experiments with other adjustment, but at the end I will need new exhaust cam lobes.
« Last Edit: February 06, 2022, 11:50:08 AM by fumopuc »
Kind Regards
Achim

Offline fumopuc

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Re: Bruce Macbeth Engine, European Version
« Reply #666 on: February 07, 2022, 03:23:26 PM »
Hi everybody, the R&D department does report some success.
I have tried to get ride of the massive overlapping by adjustment only.
The timing as recommended by the plan and set up instructions at the first picture below.
There visible the long overlap, a bit more than 40° crank shaft, 20° cam shaft.
Now, after the new adjustment, the exhaust cam does start opening at 60° crank shaft before BDC already, 20° earlier.
The overall situation shown in the second diagram below.
I have measured the duration at all 4 cams several times to be sure, but the result was always the same, 260° crank shaft.


With this new configuration it seems to be another engine.
Running much smoother, carb nearly closed and I have measured less than 800 revs.
The engine does react nicely to the throttle if it will be moved slowly.
 :pinkelephant:
Kind Regards
Achim

Offline Craig DeShong

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Re: Bruce Macbeth Engine, European Version
« Reply #667 on: February 07, 2022, 03:31:43 PM »
Great news Achim;  Looks like not only I have been watching Mike's valve event drawings.
Craig
The destination motivates us toward excellence, the journey entertains us, and along the way we meet so many interesting people.

Offline fumopuc

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Re: Bruce Macbeth Engine, European Version
« Reply #668 on: February 07, 2022, 04:08:05 PM »
Great news Achim;  Looks like not only I have been watching Mike's valve event drawings.


Hi Craig, thanks.
I do like Mike´s way to show timing very much.


Here is a small video of the engine running slow.

Kind Regards
Achim

Offline kuhncw

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Re: Bruce Macbeth Engine, European Version
« Reply #669 on: February 07, 2022, 04:40:50 PM »
Achim,

Congratulations on a nice running Bruce Macbeth.  It sounds very nice

Chuck

Online Kim

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Re: Bruce Macbeth Engine, European Version
« Reply #670 on: February 07, 2022, 06:04:27 PM »
Just beautiful, Achim!  your persistence has paid off!  :cartwheel:

Kim

Offline Admiral_dk

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Re: Bruce Macbeth Engine, European Version
« Reply #671 on: February 07, 2022, 10:16:58 PM »
Really worth the effort you put into the adjustments  :praise2:

I like the sound too  :cheers:

Per

Offline derekwarner

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Re: Bruce Macbeth Engine, European Version
« Reply #672 on: February 08, 2022, 12:42:58 AM »
I think we all understand where work is done, the energy consumed will result in heat  :Mad:, so it is most realistic to see steam exiting the water Cooling Tower [and tank] in a model combustion engine plant.....

We also saw this in the January the 22nd clip, I just didn't mention it  :Doh:

Do you mean that 95 degrees is the intended max operating temperature of the engine, or that is the limit of the cooling water system?

[it appears that the probe of the thermometer is at the lower level in the water tank?]

:facepalm: .... just beautiful Achim

Derek
« Last Edit: February 08, 2022, 08:07:15 AM by derekwarner »
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Offline fumopuc

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Re: Bruce Macbeth Engine, European Version
« Reply #673 on: February 08, 2022, 08:09:59 AM »
Chuck, Kim, Per
thanks for watching and the friendly words.
Kind Regards
Achim

Offline fumopuc

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Re: Bruce Macbeth Engine, European Version
« Reply #674 on: February 08, 2022, 08:17:29 AM »
I think we all understand where work is done, the energy consumed will result in heat  :Mad: , so it is most realistic to see steam exiting the water Cooling Tower [and tank] in a model combustion engine plant.....

We also saw this in the January the 22nd clip, I just didn't mention it  :Doh:

Do you mean that 95 degrees is the intended max operating temperature of the engine, or that is the limit of the cooling water system?

[it appears that the probe of the thermometer is at the lower level in the water tank?]

 :facepalm: .... just beautiful Achim

Derek


Derek, thanks.
I have no real idea, what could be the max running temperature for a long run.
95°C in the water tank, measured direct in/at the water out to the pump, means around 100°C to 110° C measured at each cylinder head with the Laser/IR thermometer.
In my feeling that should be max.
A bit hotter and the coolant coming out of the radiator is cooking with bubbles.
That was the basic for setting my limit.
Kind Regards
Achim