Top main bearing clearance?

[vissertrades]

Anyone know what is typical for clearance between the top main bearing and crank journal? Motor is a '95 50Hp 2-cyl Johnson. Looking at the service manual the top journal has the most tolerance of the three, 0.005". I keep going back to the fact that I can "feel" radial play when pushing the flywheel fore-aft and less/none side-to-side. I recently re-torqued the upper main bearing bolts and that significantly reduced the "play" but there's still a hint of it left! Maybe due to cool weather as it was 35 degrees out last time I monkey'd with it. Also, hint of play would go away and return based on crank rotation. If I had to guess I'd say play was around 0.02-0.03" before re-torque and 0.005-0.01" after. Flywheel turns freely and motor has NOT been run after re-torque.<br /><br />Thanks!

 

[R.Johnson]

Re: Top main bearing clearance?

The tolerance you are talking about is the amount of allowable tolerance on the journal diameter. The tolerance is .0005, or 1/2 of one thousance. They don't state what the clearance between roller bearings, and journal's should be. You can mearsure the crank with a good micrometer. I don't know how you would measure a roller bearing outside of an inspection lab. Most times if you see damage on a crank, or rod journal, you are past that .0005 tolerance. I don't know how you could remove side play by retorqueing the main bolts. The only way I can think of to resolve this question would to tear down the power head, and look. If you could hook a dial indicator to the flywheel, and bolt a dead-stop to the block, you could measure this side play. Unless there is something very wrong, I'll bet it is not as much as you think. As for hooking up an indicator, that would depend on what you have on hand, and how curious you are.

 

[vissertrades]

Re: Top main bearing clearance?

Thanks for the reply. Yes, journal diameter tolerance is 0.0005", I missed a zero! Top main bolts were not at 20 ftlbs and I think that was allowing some bearing movement fore-aft but none side-side. here's some background (previous post)if your interested:<br /><br /> http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=28;t=018155 <br /><br />I just may put a dial indicater on the block to quantify the movement. It's winter and I'm bored!

 

[R.Johnson]

Re: Top main bearing clearance?

I looked at your previous post! If you had 1/32 in. fore, and aft play, you would be spitting fuel, and compression out of the case halves. I am not aware of the service bulletin you refer to. Maybe Rodbolt, Seahorse, Dhadley, or Kenny can help.

 

[rodbolt]

Re: Top main bearing clearance?

hello<br /> there really should be no noticeable lateral motion of the crank. if it concerns you,a tear down before a catastrophic failure is a minor procedure. most crank bearing failures start with the lower main ball bearing. this bearing takes both an axial load and the vertical thrust loads the other 2 main bearings just go round and round.I have seen some rebuilders use loc-tite bearing and stud mount to fill minor variations between the block and the bearing shell. I dont have access to any tech bullitins from that year here. check what the AP bearing kit for that motor is. I think all the bearings will be less than 250. <br />good luck and keep posting.