Rod Bearings

[WizardIII]

Hello all, I'm still messing with my 1960 Starflite 75 and if I can find enough parts (specifically mag coil and gaskets) I'm considering re-hab (for the motor). However I can't seem to find the thread on checking for rod bearing wear. I recall reading here something about pushing on the piston on the down stroke. I've done that and feel a 'slight' clunk on each piston. Is any play exceptable? The motor is the original but don't know if it's worth the whole enchilada. Thanks for any info, Steve (1960 Wizard 18)

 

[F_R]

Re: Rod Bearings

Hard to tell what you are feeling. It is not normal for that motor to have any play in the rod bearings. Let me hasten to say that they are not "tight" either. But it should be barely perceptable. Roller type bearings don't wear unless they are beyond hope.

The main use of the "clunk" test is for friction type bearings and wrist pin fit in the pistons. You don't have any friction type bearings, but you do have wrist pins.

 

[WizardIII]

Re: Rod Bearings

Ahhh yes.....the wrist pins. Thanks, that makes sense. OK, my mechanical common sense tells me that zero play would be acceptable. Wrist pins tell me new pistons. If that's the case then I don't think it can happen. I can't even find some of the bearings. Sooo, just what can you get away with in the way of wear and still run on these two strokes before they come apart? This might be just normal wear, I don't know. The only two strokes I've had were chain saws and weed eaters. Thanks for your advice, Steve

 

[F_R]

Re: Rod Bearings

The wrist pin is a slip fit in one side of the piston and press fit on the other side. Obvioulsy, it is a far cry from a press fit if it is clunking. How much can you get away with? I dunno, it's a crap shoot.

Edit: Are you sure you are pushing straight down on the pistons, and not rocking them side to side? The head end of those pistons are a loose-as-a-goose fit in the cylinders. Clearance is measured at the skirt.

 

[WizardIII]

Re: Rod Bearings

Thanks for the helpful info F_R. The pistons do rock a bit but there is a very slight downward clunk. I think the power head would live but I've decided to give up on this one. Some parts are hard to find but mostly a no-confidence vote on the mag/points system. My wallet has me looking at a 1975-80 85hp V4. Seems lika a more dependable ignition System.