Single cylinder design

[John Rudd]

I'm embarking on a single cylider engine designed to run off petrol...
So far my specs are:
Bore 1 inch
Stroke 1 inch
Piston length 1 inch

Compression ratio Yet to be determined, around 5:1 or as advised by the group.

Cylinder length ermm I think it needs to be around 2 inch Could someone verify this for me please?

Length of conrod...ermm again tbd..I'm guessing its a function of stroke..Could someone offer guidance on this too please?

So far, I have my piston blank machined to diameter, going with 2 ci rings, cast iron liner with an aluminium barrel/cylinder and aluminium cyl head.

Crank maybe overhung or I may go for a fully supported unit and a bolted big end cap.

Need to figure out lubrication too.. :-\

Any comments or offerings appreciated

 

[b.lindsey]

Hi John,
Just for comparison the little Briggs project was also a 1" bore x 1" stroke. Keep in mind I was scaling from an original engine but the piston length was 1.060", cast iron sleeve length was 2.050" and center distance of con rod from wrist pin center to crank center was 1.813". Ther will be some miniumum value here lest the piston run into the crank webs at BDC, but the length will be more determined by the design of the design of the crankcase and sleeve position relative to the crank. Compression ratio will depend largely on the volume in the cylinder head. Overall your numbers look reasonable. Can't comment on lubrication as that would depend on whether the crank is overhung or fully enclosed.

Bill

 

[John Rudd]

Bill,

Thanks for the info so far...

I've almost finished the liner, bore is currently at 1.000 inch same as the piston..
What amount of clearance do I need to shoot for in relation to piston skirt and bore?

I guess I ought to reduce the piston diameter rather than bore?

I think if I go for a reduction in piston diameter it will be easier to achieve and if I make a mistake, the piston is easier to replicate....

 

[b.lindsey]

John, the piston diameter is .998" and is aluminum also. Once I shrunk fit the cylinder liner into the aluminum crankcase I knew it wasn't coming out again so I agree its easier and best to adjust the piston. You can always remake the rings too if needed since they are the actual contact/wear surface against the cylinder liner.

Bill

 

[John Rudd]

So far,
The cylinder liner is machined up...(I'd post up snaps but 'Er indoors has buggered off with my camera ) and is a tad over 50mm...(shouldnt mix units I know... ;D )

Basically it needs honing now to smarten up the bore, I'll do that once it is in the alloy cylinder where it will reside...

Piston blank is turned and is a snug fit into the bottom of the liner...I've left a spigot on it so I can return it to its collet and machine the ring grooves and finish the rest of it on the mill.( gudgeon pin holes and con rod clearances...)