Opposed 4 cylinder 4 stroke

[petertha]

I just realized this engine was posted Aug-2011. Hope I have not missed the maximum allowable time period for dumb, newbie questions!

Can you elaborate on the crankshaft. I'm drawing up something similar right now & your parts are very intriguing. Appears the socket cap screw tightens the pin into position, but the slit goes inboard in the counterweight direction. Maybe this was because it would more throw radius than what could be accomodated in the crankcase if the slit & bolt feature were on the outboard side?

- how did you make that slit extending from the crankpin hole?
- are the crankpins keyed to the counterweight parts in that slot, or just clamped?
- can you elaborate on jig or method you got the assembly aligned beforehand?

 

[JaamieG]

The low rev humming is lovely.
Neat and high quality work.
Thanks for sharing all the awesome pictures and videos.
Cheers,
Giacomo

 

[Tin Falcon]

Nice how did I miss this one . good work.
Tin

 

[wildun]

That's a really great effort, I must say!

 

[Art K]

Geoff,

Your engine is quite impressive! At 120cc what is your bore and stroke? Out of curiosity having both cylinders on the same rod journal do you got much vibration? I'm working on my own design for a flat four that is 117cc. 1.375 x 1.212.

Art

 

[geoff_h]

Thanks everyone for remarks. Sorry for the late replys, have not been on the forum in a while.

Can you elaborate on the crankshaft. I'm drawing up something similar right now & your parts are very intriguing. Appears the socket cap screw tightens the pin into position, but the slit goes inboard in the counterweight direction. Maybe this was because it would more throw radius than what could be accomodated in the crankcase if the slit & bolt feature were on the outboard side?

- how did you make that slit extending from the crankpin hole?
- are the crankpins keyed to the counterweight parts in that slot, or just clamped?
- can you elaborate on jig or method you got the assembly aligned beforehand?

You are correct, the bolt is located between the pin hole and counter weightfor clearance. There is very little room inside the crank case. I had to drawthe entire motor in solid works in order to check and make clearance for the differentcranks and rods I tried.

The slit into the crankpin hole was made by locking the crank into the lathechuck, custom grinding a parting blade and putting the blade horizontal in thetool post and parallel with the ways then with the carriage wheel going backand forth like a shaper, taking a small amount off and turning in the crossscrew. It took a while to do all the parts but once the blade was oriented togive a good cutting and relief angle was simple.

The pins are not keyed just a very close reamed fit. I must have tested 40 differentcombinations of drills, feeding rates, speeds, lubricants and reamers in orderto get one that would consistently give a good fit. The pins are made from bitsof a hardened rod I ground to length.

The crank parts where made individually with lots of effort to locate thecrank pin hole accurately in each half. I then loosely assembled the cranktogether in the crank case halfs with the bearing carrier’s tightened down.Then the bearings align the crank and small adjustments where made by hand toget it to turn as free/true as possible then tightened the bolts to clamp thepins.

 

[geoff_h]

Geoff,

Your engine is quite impressive! At 120cc what is your bore and stroke? Out of curiosity having both cylinders on the same rod journal do you got much vibration? I'm working on my own design for a flat four that is 117cc. 1.375 x 1.212.

Art

It was very smooth at all rpms. I built a single cylinder .27ci flat head 4 stroke turning a 9" prop that vibrates that same test bench much more.

Stroke is 31mm, bore 35mm

 

[flyingtractors1]

Not a professional machinist? I'd say a very expert one. Beautiful work. Ralph

 

[///]

Very nice work Geoff. Like Tin, I'm not sure how I missed this. :shrug:
I love the sound of a boxer, so much so I drive a Scooby daily ;D
Would one day like to model an EJ205 engine.

 

[Niels Abildgaard]

Hello Geoff

Enjoy pictures of full size Hirth 504 crankshaft parts.105 mm boreand 115 stroke
How on earth did You make Yours and why did You change the construction as it was not the Hirth coupling that gave in?

Kind regards

Niels

 

[///]

Neils, I was about to ask you how the hell all that worked.
I was trying to figure how to screw those items together tightly without a gap in the 'teeth'.
Then I saw the spline for a tool inside the 'bolt'* and had an 'ahhhhh' moment which was very quickly followed by a 'huh?' moment as I realised screwing the bolt thru would mate the parts but wouldn't actually tighten them.
But that moment was then soon followed by an 'Ahaaaa!!!' moment when I inspected the 'bolt' more closely.
That system is pure genius!

*(please forgive my lack of correct terminology for items I've never seen before)

 

[Niels Abildgaard]

Hello Simon

It gets worse.

The later versions had an undivided crankcase so assembly was one part after the other from one end ; six hardened main bearings,eigth side pieces,four conrod bearings and four conrods.
Crankshaft was first assembled without conrods and given final grinding.The relative positions was marked on the parts; everything taken apart and then put together with conrods inside crankcase.
Common consent in danish airforce ,that opperated both,was that it was a better engine than the british hanging fourcylinders used for training aircrafts.

Kind regards

Niels

 

[geoff_h]

Not a professional machinist? I'd say a very expert one. Beautiful work. Ralph

Thank you, honestly I was 27 when I built this motor and had owned a lathe for 2 - 1/2 years. I had never used or touched any type of lathe or mill before I bought one. Never had any formal training, just had lots of questions and do alot of reading in places like this forum. Then spent even more time experimenting and making lots of scrap parts.

Hello Geoff

Enjoy pictures of full size Hirth 504 crankshaft parts.105 mm boreand 115 stroke
How on earth did You make Yours and why did You change the construction as it was not the Hirth coupling that gave in?

Kind regards

Niels

I did not use it on the other cranks that had 1 piece rod journal and throws because there was not enough space between the throws to installand tighten a bolt. It also would have been difficult to index the coupler on each half so the rod journals where perfectly aligned.

I made it by putting the part in a lathe chuck on a rotary table set horizontaly and at a slight angle to the table with a wedge. The crank is vertical. the table needs to be at an angle so the teeth being cut would have full contact from the od to the id. Without the angle as the adjacent teeth merged towards the center of the crank the height of the tooth gets smaller and the teeth form a concave shape if looking across the entire diameter. Used a drill point endmill to do the cutting.

http://www.shars.com/products/view/19206/316__SE_Solid_Carbide_Drill_Mill_4_Flute_90_Degree_Point_


When I cut the teeth in each half I had not drilled the hole for the rod journal or cut the counter weight as I did not want to try and index the coupler to align the rod journal. Figured it would be easier to make the coupling then with both half’s fastened together drill the rod journal and cut the counter weight. I supported the bottom half of the crank drilled the hole and cut the counterweight then without moving the setup bolted the other half of the crank to the coupling and did the same to the top half.

It took a lot of time and thinking to figure out how to make it but once I had it figured out was rather simple to make.

 

[barnesrickw]

Making cams intimidates me without a CNC.