Cylinder misalignment question

[Igor_toko]

Hello,

I am building my first engine (4 stroke spark ignition) and one of the questions I have is regarding how much error is accepted in the position between the crankshaft and the cylinder. Theoretically they should be perpendicular, but does anyone know if a slight angle deviation will cause the engine to not run? It is a stationary model engine that won't be very loaded.

Also, when it comes to connecting rods, how tightly should they fit to the piston and to the crankshaft? Will a slight looseness help with correcting any misalignments or will it make matters worse?

 

[Jasonb]

Angle is not good but doe swepend somewhat on which way the angle is. If radial to the crankshaft eg it leans to one side it won't cause too much of an issue. However if it leans inline with teh crankshaft eg front to back that wil cause probelms with the bearings binding and tightness of the engine.

Sideways float is OK on the conrods but not lean.

 

[Jasonb]

here is an example of how you don't want things to lean, This engine wa sbought part made. You can see how low the lefthand side is by the gap to the height gauge as well as how the cylinder mounting flange gets thinner towards the left. Engine would not turned over

 

[krypto]

Ouch!

That's just sad...

 

[jquevedo]

Crankshaft can be offset from the pistons center line, side offset, check one of the Westbuy designs which does have I think 1/8 inch offset to deal with some odd measures in connecting rods and making room for camshaft tapetts.

 

[jquevedo]

sorry forgot to mention the engine which is the seal minor, 30CC o seal Major 50 cc

 

[lee webster]

I don't know if this will help. People who race Austin Seven powered cars often "bell" the big end bearings to allow for the whip in an A7 crankshaft, which only has main bearings at each end. At high revs the crank can develop quite a whip. Because the two middle pistons will then be thrown up a bit further than the outer pistons, the tops of the middle ones are reduced in height. A7 oil pressure is about 3 PSI when hot.

 

[johwen]

Why not set up the crankcase and re-machine the cylinder mounting face square and the piston looks to have sufficient metal in the crown to reduce same by a similar amount. John

 

[Jasonb]

Why not set up the crankcase and re-machine the cylinder mounting face square and the piston looks to have sufficient metal in the crown to reduce same by a similar amount. John

That is not the OP's picture, I did remachine the casting true.