miniature 2 stroke gasoline engine

[Zephyrin]

Hi,
I’m planning to build a small gas engine, a 2-stroke engine this time, 1/2" bore and 1/2" stroke, 1.6 cm3, (0.097c.i.), with spark ignition. therefore a tiny engine, with a pleasant vintage style...
the plan comes from an old and unknown magazine that I’ve found here :
http://www.plans-for-everything.com/hen_ic_engine_plans.html

It is the “Parohl” engine whose link for the PDF is at the bottom of the page.

I don't know from which magazine this copy comes from, and the date, but it looks pretty old and the engine very appealing !
The author of the article says it is a (modified) plan by Henry Parohl.
 
A point that worries me is the transfer through a port in the skirt of the piston...as in the attached figure below.
   Although this arrangement is often present on 2 strokes, I have never seen it on model glow or compression-ignition engines.
I fear that the gas flow during the transfer will be hindered around the connecting rod small end  just in front of the piston port owing to the very small size of this engine.
   What do you think of this plan and are there other model makers who have already made this engine?
Before cutting metal, I made new drawings with a few dimensions in metric units according to my tooling, and the corresponding angular diagram, and nothing unexpected in it.

I will start by casting a few parts in aluminium from patterns in boxwood I'm doing.

PS: I have just found that this copy comes from the magazine "Mechanics and Handicrafts", may 1937...

[Admiral_dk]

Hi Zephyrin

I would be very surpriced if it runs poorly, but with that said - it will not be a performance engine either.

Oh and just to clarify - No modern high performance two-stroke, from 50cc to 500cc, has any "windows" in the piston (from the factory - aftermarked is a differen't story) - but I have seen a number off Car model racing engines still have them. I'm pretty sure that the reason the aftermarked still sell them with has everything to do with old dogs wanting what was "Top of the Pops" in their youth + haven't got a clue that two-strokes has evolved quite a bit since. If nothing else - that still applies to the Veteran Moped crowd here in Europe ....

[lohring]

That's a very old design.  I am writing a series on modern, high power glow ignition engines.  The first articles in the series are:
namba.com/content/library/propwash/2018/october/14/ --History
namba.com/content/library/propwash/2019/april/24/ --Piston & Cylinder Fit
namba.com/content/library/propwash/2019/october/4/ --Head Design

Lohring Miller

[Admiral_dk]

Thank you for the history lesson Lohring 

You did not post those as links, so I will try here :
http://namba.com/content/library/propwash/2018/october/14/
namba.com/content/library/propwash/2019/april/24/
namba.com/content/library/propwash/2019/october/4/

[Zephyrin]

lots of exciting things in these pages, thanks Lohring...
I understand all that technics, flat piston top and Schnurle scavenging, multiported transfer etc.
But I'm not equipped to build competition engines, with brass chromed cylinder liner etc., therefore the old fashioned engine I'm doing has a deflector on the piston !
I rank myself rather in the category of veterans or old dogs mentioned above !

first metal parts yesterday, a few usable aluminium castings
I like to watch after casting the pieces out of the sand.

[Alyn Foundry]

Hi Zephyrin.

It's great to see the " Art " isn't quite dead! Some nice looking castings.

If I may suggest? Your castings would have come out even better had you placed them in the " Drag " bottom box rather than the " Cope " top box.

You have the advantage of extra " head " pressure from the " Sprue " and any shrinkage will form in areas that won't be seen. 

Castings rule!!

Cheers Graham.

[Zephyrin]

Thanks for advices, Graham, being a beginner any suggestion is welcome !

If I understand correctly, I did the pour as in A in the figure, and I should have done it as in B ?

[Alyn Foundry]

Good morning Zephyrin.

Yes your patterns should be placed as in " B " but there's no need to run them from below.

The " pit " of the sprue in the drag is a good thing as it allows for hotter and cleaner metal to enter the mould cavity.

When moulding " loose " patterns, like you have, the " in gates/runners " can be cut from the sprue to the cavity either in the cope or the drag. The choice is determined by.... Needing to " fettle " the side of the casting if from the drag. Or not if the runner enters from above the cavity ( cope ) box.

Cheers Graham.

[Zephyrin]

Hi,
Thanks again Graham ! great forum with so much of shared expertise !

Crankshaft machining today, 2 crankshafts in fact as the first one was out of alignment, oh no! sh..

I did first as in the paper, entirely between centres: crankpin first, then the main journal, with a spacer between the webs of course, but it is difficult to estimate the flexibility between looseness and over tight centres.

I did the second with my usual way to do for small crankshaft, first the main journal between centre, both side to the finished size, then I machine the crankshaft blank in the three jaws, held in a specially made eccentric collet that holds the shaft off centre and the crankpin centered, thus, I eliminate the problem of the flexibility with so small diameters. One has to do a precise jig, but the result is flawless…as far as I can measure between such small web.
the shaft also should not be permitted to slip or turn in the jig...with a positive indexing as a pin or a milling for the web.

as I have the jig already made, I also did the crankshaft for the single bearing version, as it has the same throw, one never knows…

[lohring]

Actually, I think a flat topped piston style engine is easier to build than a deflector piston design.  You just need to get the transfer ports approximately right for moderate performance.  A lapped cast iron piston in a steel sleeve also works well.  Around 60 years ago I built an engine in high school shop.  It was a state of the art deflector style engine for the time.

Lohring Miller

[Old School]

Lohring

I have just read the article you have written on head design very interesting I will try some wider squish bands in one of my engines over the winter testing and development for my tether car engines

[lohring]

This is a link to a really good book on model two stroke design.

Lohring Miller

http://controlline.org.uk/phpBB2/viewtopic.php?t=11848

[Old School]

Thanks

I have a copy interesting read, I have seen some of his work its very nice Gordon is currently working on 1.5cc diesel engine with a cnc machined crankcase that he is producing himself.
My interest is high speed glow engines (Nitro) but no nitro just 80% methanol and 20% castor oil, my 2.5cc tether car engine runs around the 40,000 rpm range.

[Zephyrin]

Hi
Machining the aluminium casting is done, whew; not first class metal, which get soldered on tool and raises edges, making precision a chore!
I fear when I will have to tap hole in that junk...
The 2 half of the crankcase are not identical, one have a male and a female part.
I have removed a surprisingly large amount of swarf from so little castings, and the result is very very light.

[lohring]

Thanks

I have a copy interesting read, I have seen some of his work its very nice Gordon is currently working on 1.5cc diesel engine with a cnc machined crankcase that he is producing himself.
My interest is high speed glow engines (Nitro) but no nitro just 80% methanol and 20% castor oil, my 2.5cc tether car engine runs around the 40,000 rpm range.

That's not a particularly high piston speed for a 2.5 cc engine.  The connecting rod big end bearing starts to be the main issue as speeds go up.  Jim Allen has done a lot of work on this in 15 cc engines turning in the 40,000 rpm area.  My take on this is Big End Blues.  (http://namba.com/content/library/propwash/2012/April/#/11/ ) I'm not sure that needle bearings have been tried in really small engines, but it would be interesting.  Another issue is the rigidity of the crankcase and crankshaft bearings.  I plan to address these mechanical issues in a future article.

Lohring Miller