Crankcase questions on .6ci engine...

[mikeschn]

Hey Guys,

Gotta question here that I'm hoping you can help me with...

I downloaded the plans for Peter Cook's .6ci engine. I am trying to model it in CAD but there's a bunch of dimensions missing.

Right now I am working on the crankcase, and the holes are breaking thru everywhere. Can anyone point me in the right direction...

For those of you who can read step files, here's what I have so far...
http://www.mikenchell.com/images2/crankcase.stp

Here's a quick pic of what I am trying to model

And here's the areas where it is breaking thru

Thanks,

Mike...

P.S. Here's the download that I got from this forum...
http://www.homemodelenginemachinist.com/index.php?action=tpmod;dl=item224

 

[ksouers]

Mike,
Just guessing, but are those really supposed to be through-holes? My guess is they should be blind.

I didn't see these details in the plans you linked to, just going off the drawing you posted.

 

[mikeschn]

Mike,
Just guessing, but are those really supposed to be through-holes? My guess is they should be blind.

I didn't see these details in the plans you linked to, just going off the drawing you posted.

Kevin,

I agree. I think they should be blind holes. But I have no experience in these engines. If it's a blind threaded hole, what size would that be, and how deep should they go? 10-24 unc-2b x 3/8" deep???

Mike...

 

[kf2qd]

Actually i had the students drill the holes 1" deep. made it easy to clean the chips out. By the time you run a SHCS in them and tighten everything down there in not going to be any leakage. This design was created for a college class in machine tool practice for Engineering and Technology majors. Through holes are easier on taps for those who don't have much experience with a tap.


All 12 screws are 10-32 because i have had problems with 10-24 loosening up on me. 10-32 doesn't require and lock washers and still stays tight.

Pete Cook


Hey - Anybody else have a keyboard that insists on spelling the teh?

 

[ksouers]

Hey - Anybody else have a keyboard that insists on spelling the teh?

Yeah, mine does all teh time ;D

 

[cobra428]

Is that the only problem....My keyboard goes dyslexic all the time wthi a lto fo wodrs... see.. :big:

Tony

 

[mikeschn]

This design was created for a college class in machine tool practice for Engineering and Technology majors. Through holes are easier on taps for those who don't have much experience with a tap.

Pete Cook

Hey thanks Pete.

Would you by any chance have a couple pictures of the parts that I can look at? And a movie of the assembly running?

Mike...

 

[kf2qd]

The 3d version you have is dead on. Any particular detail you want, I can dissassemble it and take a few pictures, though my camera has its limitations...

The only detail that might not be totally clear is the top of the block. The 1.063 diameter in the top has to fit the cylinder liner before you machine out the material for the transfer ports. That is what provides the alignment between the cylinder and the block.

 

[mikeschn]

Hi Pete,

What kind of a fit do you like between the cylinder sleeve and the crankcase? How about the fit between the cylinder sleeve and the cylinder?
Any way you like to tell me is fine, I'll look it up in the machinery handbook.

Tell me about the piston. You use a piston ring, right? What size?

Can you tell me about the fit between the cylinder head and the cylinder sleeve? the ø.9375 part...

While you are at it, can you tell me about the connecting rod? The fit between the connecting rod and the crankshaft. And I don't see a pin for the ø.25 side. Can you tell me about that too?

Sorry I have so many questions, but I am a newbie!

Mike...

P.S. Opps, almost forgot the most important fit, between the crankshaft and the front bearing?

p.p.s. Is the cylinder sleeve supposed to cover those holes like that?

 

[kf2qd]

The sleeve should have a slip fit to the crankcase and the cylinder. A nice close fit that will let you disassemble it if you wish. The top of the sleeve should not overlap the holes for holding on hte head. Fits are the kind a student who has never seen a machine shop before would make. The little bit of oil in the model airplane fuel does grreat for sealing thing up.

Don't try to overthink this engine. I tried to kep it as simple as I could.

The ring was made out of the same cast iron I made the sleeve out of. It is "L" shaped and no special heat treat was done to make it work. I used a carbide scribe to scratch around it in one place and then carefully broke it. Then I put it on the piston. Because of the shape it will seal on compression , even though it may have almost no compression it you turn it over slowly. The ring is the same OD as the piston, just a nice sliding fit. (loose will work, its very forgiving.)

When I made mine I used a smear of Permatex #2 on the surfaces and nothing between the head and the sleeve. Ran great.

 

[mikeschn]

Okay, I'll try to keep it simple too...

One last question then... Since yours obviously ran your just fine, can you tell me why I am showing an interference here... see arrow...

Mike...

 

[kf2qd]

Those notches in the top of the crankcase serve 2 purposes - 1 is to connect with the transfer ports, the other purpose is to provide clearance for the conrod. the 2 on the side need to go all the way down, the 1 at teh back only goes down 3/8 because teh back of teh crankcare helps keep teh rod on the crankshaft.

The chamfer on the inside bottom of the sleeve - 1 makes it easier to slide the piston in the sleeve, 2 the other is for clearance of the conrod.

As you might be able to see - I screwed up and bored the crankcase through at 1.500 and had to plug it.

Here's a few pictures of mine -

 

[mikeschn]

Thanks Pete,

Okay I made the side notches 1" deep, and I changed the chamfer from .0625" to .09375". That fixed everything.

See for yourself! ;D

http://www.mikenchell.com/images2/point_six_motor.mov

Mike...