Yamaha F100 Bearings Selection

[bamafan]

I am rebuilding a Yamaha F100 and have a factory manual as well as a clymer manual on the engine. Both say to measure the connecting rod clearance using yellow color code bearings with plastigauge and then select the appropriate bearing combination from a chart. I did all of that and ordered the appropriate bearings from a dealer. When I received them I decided to recheck the oil clearance with the new bearings (green color code)and the clearances are the same as they were with yellow color codes. When I inspected them closely they appear to be the same bearings - markings are the same and both are marked (STD). Has anyone ever had a problem with bearings being mis-marked? Is their something I'm doing wrong ? It took 7 weeks to get the green bearings and they appear to be identical to the yellow color code bearings. Both yellow and green color code bearings measure about .038 mm clearance when the manual says range is from .024 - .035mm.<br /><br />Help

 

[bamafan]

Re: Yamaha F100 Bearings Selection

Forgot to identify the bearings in question. It's the connecting rod bearings (big end). The crankshaft is brand new out of box and the connecting rods and pistons are new out of box.

 

[rodbolt]

Re: Yamaha F100 Bearings Selection

hello<br /> the plastigauge method is a reccomendation but if your not used to reading it the readings can be so small that a .0005" change is not really readable by eye. I use the old math method. I measure the rod big end ID. then measure the bearing thickness. double the bearing thickness and subtract it from the rod ID. now measure the crankpin diameter. subtract pin diameter from the bigend-breaingthickness and that is clearence. you can use plasitigage to verify it. remember there are several different thicknesses of plastigage avalible as well so make sure your using the correct one.<br /> it gets confusing and the clearences are small so take your time and it will work. no worries.<br /> math is your friend. what you are trying to do is set the bearing clearence for an oil film between the bearing ID and the crankpin and the bearings are a select fit due to production tolerences.<br /><br />good luck and keep posting

 

[bamafan]

Re: Yamaha F100 Bearings Selection

Rodbolt - I want to thank you for the insight on the bearing selection process that you use. When I did it my measurement rather than plastigauge the tolerances became apparent and fell right within specs. I ran the thing for 2+ hours today. Everything appears ok. Smooth as silk.<br /><br />Thanks once again.

 

[rodbolt]

Re: Yamaha F100 Bearings Selection

hello<br /> glad I could assist a bit. if your not used to plastigauge its tough to read. I use the math then use the plastigauge to back me up but my micrometers are better than my eyes anymore.<br /> good luck and keep posting