Side Port IC Engine Design

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jackdaw
Posts: 165
Joined: 16 Feb 2018, 20:30
Location: Wet and Windy North Wales

Side Port IC Engine Design

Post by jackdaw »

THIS IS A SIMILAR POST OF MINE ASKING THIS QUESTION ON ANOTHER FORUM HOPING FOR AN EXPLAINATION.

A question to those who are knowledgeable on design aspects of side port IC model engines, like the venerable Mills 1.3 etc. It's new not SH or a bitsa. Currently on sale. Modern version based on a 70 year old design. To the best of my knowledge and experience(I have numerous examples of each type of engine: Irvine Mills 1.3 & 0.75, Indian Mills 1.3 & 0.75, MP Jet 040 & 1.8, CS Deezil, ED Comp special, etc) the induction is controlled by the piston skirt uncovering the induction inlet hole/s in the liner rear side wall. All my engines bar one, recently acquired (no names no pack drill), do not uncover the liner holes by the piston crown when at BDC. To me this is a serious design/manufacturing flaw as any residual combustion pressure could/would vent into the inlet against the flow of any fresh incoming charge in the inlet tube thus adversely affecting the breathing of the engine.

There are two other failings, to my mind, with this engine, one fixable the other like the above not really fixable. 1/ the front piston skirt obstructs the gas flow into the transfer ports from the crankcase as the piston nears BDC; fixed by cutting away part of the front piston skirt. 2/ the piston crown goes way lower than the bottom edge of the exhaust ports leaving a significant volume that will not be scavenged of exhaust gas; only fix I can see would be is by lowering the cylinder in the crankcase casting, this would also address the inlet port issue.
These issues have been determined by visual examination of the engine in question and comparing it with others I have that employ side port induction. With these other engines the piston crown goes no lower than the bottom edge of the exhaust port; the liner inlet holes are only uncovered by the piston(skirt) on its way up to TDC and then blocked on it's way down to BDC, the holes are never uncovered when the piston is at BDC allowing partial opening at the top edge of the liner inlet holes because the piston crown is too low; some of the other engines have cut away front piston skirt as and when needed by the design.

It's almost as if the wrong liner for the stroke of the engine has been used.

Any comments from those who are knowledgeable on engine design welcomed.
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Shaun
Posts: 1049
Joined: 15 Feb 2018, 21:49
Location: West Yorkshire

Re: Side Port IC Engine Design

Post by Shaun »

I'm no engine wizz, I just flick them and hope they start but do they run well as currently designed:
If so does it matter that different designs have been used for different versions or does that affect something else?

Shaun.
jackdaw
Posts: 165
Joined: 16 Feb 2018, 20:30
Location: Wet and Windy North Wales

Re: Side Port IC Engine Design

Post by jackdaw »

Information I have indicates no more than 2/3 the power of the 70 year old original design. Not good considering original was plain bearing crank and new is twin ball race.
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Shaun
Posts: 1049
Joined: 15 Feb 2018, 21:49
Location: West Yorkshire

Re: Side Port IC Engine Design

Post by Shaun »

I would try to have a word with John Goodhall at Barton Model Products. www.bamopro.co.uk

He would be the man with all the answers for you.

Shaun.
bluejets
Posts: 316
Joined: 19 Jun 2019, 04:09

Re: Side Port IC Engine Design

Post by bluejets »

Without any detailed drawings of your verbal explanation , it is difficult to see what exactly you are referring to, allbeit normally a matter of timing requirements.
As previously stated, who cares, flick and go, all done.
Must remember, engines are built with ease of starting, adjusting etc. not necessarily for top possible performance.
In my experience, engines modified with the latter tend to be a right PIA, finger biting snarly little devils.
Used to do quite a bit with engines modded for sport pylon.
Pchristy
Posts: 413
Joined: 16 Feb 2018, 13:57
Location: South Devon, UK

Re: Side Port IC Engine Design

Post by Pchristy »

Not sure if this will help or not, but many decades ago I used to race karts. Not the silly fixed gear ones you get at kart tracks, but full on gearbox equipped ones. The class I ran in (Class 4 standard) restricted you to the use of a 200cc Villiers 9E4 engine - which was a side-port motor.

The standard procedure for fitting a new piston was to;

1) Clamp the piston in a vice and file the cheeks down! (This was because a Villiers always seized on the cheeks!)

2) File diagonal grooves in the piston skirt. (This was to trap oil and carry it up the cylinder walls)

3) Cut half an inch off the skirt on the inlet side and one inch off the skirt on the exhaust side. This was to change the induction and exhaust timing. (I may have got those the wrong way around - this was back in the late 60's, early 70's!)

4) Fill all available empty spaces in the crankcase with "stuffers" - usually balsa wood, as these wouldn't do much damage if they came loose! This was to increase compression in the crankcase.

5) Turn the flywheel down to almost nothing, and replace the magneto with battery ignition. Reducing the flywheel mass improved throttle response, but it wouldn't tick-over. Like a WW1 rotary engine, you had to constantly blip the throttle to keep it running on the grid!

The end result was a motor that would propel you to over 100 MPH down the straight at Dunkeswell, and was actually capable of taking on the Bultaco and Montessa powered "International" class karts! The only downside was the notoriously unreliable 4 speed gearbox, which was full of false neutrals!

Transfer timing wasn't changed - there was already a cut in the piston skirt (on the sides) to control this. And remember that these were ringed pistons! Don't try this on an ABC or plain piston!

Most of these motors were rescued from the old blue "invalid carriages" or Bond 3-wheelers (both peculiarly British concepts!) which they propelled at a very sedate pace! Until I got involved in karting, I'd always regarded side-port engines like the Mills and ED Cadet as seriously under-powered, albeit generally easy to start. Doing a ton (+) with my backside only an inch off the concrete entirely changed my perception of them! :shock:

Of course, these racing engines were essentially single speed devices - flat out or nothing! But it did demonstrate that you can get remarkable amounts of power out of a rather staid engine with only minor modifications!

I should add that all this experience was gleaned through the Technical College Kart Club. We had four karts - 3 Villiers powered, and one 100cc fixed gear, which the girls drove! (I didn't make the rules! ;) ) We had one engine professionally tuned, and when we got it back, we tore it apart, and used the excellent college workshops to replicate what the tuners had done. Most of the important work (the piston) however only required a big vice, big file and a hacksaw! There were three or four of us to each kart, and most of the members were either professional or trainee mechanics - I was the odd one out!

So yes, you can make a side-port engine go like stink, but as with everything else, where you gain in one place, you lose in another. Also most old side-port model engines are long-stroke types (under-square) which do not lend themselves to high RPM.

No idea if this answers your queries or not, but it does indicate what is possible!

:D

--
Pete
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