"Topsy" 0.375c.c. compression ignition engine

[roadrage17]

This is my first build it is a engine called "Topsy" 0.375cc compression ignition engine by G Hugh.
Should be an interesting first build , got the plans , going to start it next week .
It should look like this hopefully...

Pictures to come ...

Thanks Roadrage.

 

[Maryak]

RR,

Good luck with your build. IMHO these are fascinating little engines.

Plenty of piccys please

Best Regards
Bob

 

[GailInNM]

Roadrage,
Small compression ignition engines are fun.
I am just finishing up a work in progress thread on a series of three that are about 1.6 times the displacement of yours. If you have not seen it, it is at:

http://www.homemodelenginemachinist.com/index.php?topic=4422.0

There are a few tips in it that work for me. Of course everyone has their own way of doing things.

Please keep us posted as it progresses, and of course photos are always appreciated.

Gail in NM,USA

 

[itowbig]

ya i got to keep tabs on this build . ;D

 

[roadrage17]

heey guys

thanks GailInNM ive had a quick look and some of the processes you did wer interesting.
hopfully get some build time tomoz so some pics then.

thxs roadrage

 

[roadrage17]

oki here we go first day

Thought i wud make a start on the crankcase .
its made out of dural. have plenty left over for muck ups lol.

Then here we go think i went overboard on the amont of pictures
Also my camera died so theres no pics of me on the divideing head.

Show you how small it is.

well thxs for looking , its starting to look like something lol

Roadrage

 

[90LX_Notch]

Very cool roadrage17! Thm: Did you purchase the plans or are they a download?

 

[roadrage17]

90LX_Notch they are purchased from http://www.myhobbystore.com there are loads of other plans aswell

thxs for your comment

Roadrage

 

[90LX_Notch]

Thanks roadrage17 for the prompt answer.

 

[roadrage17]

had few hours build time so heres some pics of what i a have done...

My set up.

Putting the rads on the underside of the crankcase..

What i ended up with after my lunch break hehe...

thats all for now

thanks roadrage

 

[Maryak]

RR17,

Very nice. :bow: Gee it looks to be very small, can you put a rule against it in some future shot please. ???

Edit:

Just looked at it in your hand - "IT IS SMALL"

Best Regards
Bob

 

[roadrage17]

hey guys

i have a question when i get to lapping the cylinder and piston , im not really going to have a clue.
the piston going to be made out of cast iron and cylinder out of EN25 or 24 cant remember similar to toolsteel i think .
the way im thinking about is to turn up a piece of material to the size i want to cylinder bore to be and just run it up and down on the lathe with some lapping paste.

questions..
1. Is what ive just said correct?
2. What material should i use to lap?
3. How much should i be under sized on piston or cylinder?
4. should i mate cylinder and piston.

 

[roadrage17]

haha :big: thxs bob , yes it is small i didnt realize that it would be that small lol.
And more still got to come of it yet. Not going to be much bigger and 1" .

RR17

 

[Maryak]

RR17,

Bob's version of lapping.

1. If your lap is made to the bore size then the bore will be oversize when its lapped. I try to machine the bore to 0.001" undersize and the last thou is removed by the lapping process. The lap must be small enough to accommodate this plus some lapping compound plus working room - say 1/64". The lap to cyl length ratio should be a minimum 3:1, i.e. the lap should be 3 times longer than the cylinder.

2. Ideally the lap should be of a softer material than the object being lapped - definitely NOT harder.

3. cyl 0.001" under piston 0.001" over.

4. Most definitely - I do this by mating them with tallow after the piston has entered the bore about 80% of the way by a hand push.

It is very important that ALL traces of lapping compund are removed before attempting to mate the parts.

Hope this helps. ??? ???

Best Regards
Bob

 

[roadrage17]

Thanks bob all helpful and i saw your video on it and thats the way im going to do it .

One question though say that the piston had to me 1" , so i would turn it down to 1.001 like you were saying, but with the lapping material did you mean the 1/64 is how much it should be undersize to the piston so 0.984 is what i should turn the lap to . Am i just confusing myself. sorry if im not making sense :big:.

thxs

RR17

 

[Maryak]

RR17,

Yep, it's easy to get confused.

For a piston and bore of 1" nom.

cylinder length 2" - Lap length min 6" lap diameter 0.985"

Piston length 3/4" - Lap length max 1/4" lap diameter 1.015"

The 1/64" clearance applies irrespective of the aimed for diameters, (within reason).

Hope this helps.

Best Regards
Bob

 

[roadrage17]

Got you bob thxs for your help, Im sure you will come in handy when i get stuck ;D
any reccommend lapping paste to be used?

Best regards RR17

 

[Maryak]

RR17,

I use automotive valve grinding paste fine, followed by dremel polishing paste, and lastly tallow for the mating.

Best Regards
Bob

 

[ozzie46]

RR17,

I use automotive valve grinding paste fine, followed by dremel polishing paste, and lastly tallow for the mating.

Best Regards
Bob

Bob, What does the tallow do? I never heard of this before. I have heard of lapping and such but not mating and tallow. I thought the lapping took care of the fine fit.

Ron

 

[Maryak]

Ron,

The tallow acts as a wetting agent and allows movement between 2 parts which would not be possible using lubricating oil. In the case of a model CI engine the compression ratio is from about 16:1 to 20:1 and relies on the fit of the piston and contra piston in the cylinder to achieve this. The wetting action of the tallow allows the final face to face mating to a very fine tolerance. The mating is complete when the tallowed power piston will pass all the way through the cylinder with a reasonably tight hand push.

Hope that explains it. ???

Best Regards
Bob