Mercruiser upper gear replacement

[solocam]

I'm replacing the upper gears in my alpha one gen 2 and when I put get the drive gear in the housing and torque down the retaining ring the gears seem to have some play. My question is does anyone know how tight the drive gear and driven gear should fit up?

Thanks in advance.

 

[Bt Doctur]

Hard to describe but you should feel/hear a soft click gently trying to turn the inputshaft back and forth.

 

[achris]

Are you using the correct shimming tools? If so, then the shim tool to gear clearance (for both gears and tools) is 0.025". If you have that, then the backlash between the gears will be correct. If you are not using the correct shim tools, there is no way to get it right. You could get the backlash right, just by feel, but you have no idea if the driven gear height and the drive gear depth is correct. Either of which will cause the gears to howl.

Chris.......

 

[solocam]

Are you using the correct shimming tools? If so, then the shim tool to gear clearance (for both gears and tools) is 0.025". If you have that, then the backlash between the gears will be correct. If you are not using the correct shim tools, there is no way to get it right. You could get the backlash right, just by feel, but you have no idea if the driven gear height and the drive gear depth is correct. Either of which will cause the gears to howl.

Chris.......

I have the original shims in correctly (I believe) for the drive gear, but there were no shims on the driven gear that I am aware of. Is the driven gear normally shimmed?

 

[Bt Doctur]

If you mean the vertical shaft the shims are under the bottom bearing cup and under the top cover bearing cup
Using the correct tool the vert shaft distance is set first,(bottom race) then the preload for the shaft is set next.(top race )
Then the depth of the horiz gear is measured and set with the shims.
With just the upper unit:

Correctly assembled the inputshaft will spin with very little to no resistance and you will feel/hear a slight click from the backlash
Read about installing a ring and ping gear,basically the same thing .What your looking for is a "heel and toe" wear pattern.

 

[Bt Doctur]

http://www.boatfix.com/merc/Servmanl/6/6A3R3.PDF

 

[Rick Stephens]

solocam, Bt Doc and achris do this for a living and are gracious enough to share their expertise. Note the number of special tools and shim packs required to swap out the gears in the upper case. You can't shortcut this and expect the drive to last. Replacing the gears means we start the assembly from scratch and do shimming and rolling torque tests until it is within spec. You can't do this without a number of special tools, including an inch pound torque gauge sensitive enough to work in the single digit range. It doesn't take much to be off and have the drive fail, usually fairly spectacularly.

I would also note that it isn't that hard, technically, to do this assembly correctly. It just takes following the steps and having the right tools and shims on hand to get it right..

 

[solocam]

Thanks for the replies, you all are very helpful. The lower shims were a surprise to me because there were none present when I disassembled the upper. Are they always present? If so I could have just lost them.

 

[achris]

Never seen a drive without shims in all 3 locations. If you're replacing gears or bearings, you must do the shimming with the tools and set the preloads. The clearances won't be the same as the old ones.

Chris.

 

[Bt Doctur]

you need to pull the race under the bearing to see them but they are there

 

[solocam]

you need to pull the race under the bearing to see them but they are there

Are you saying the shims are under the race inside the housing? If so, what is the procedure for pulling this race? I was confused by the parts diagram apparently. Thank you.

 

[Bt Doctur]

A small 1 or 2 jaw slide puller but untill you measure what you got first you wont know if or how much or what direction to go.
Instead of guessing get some Machinist Blue Dye and check the heel and toe pattern
https://www.ringpinion.com/Content/Book/Reading-and-Adjusting-Ring-and-Pinion-Tooth-Patterns.pdf

 

[Bt Doctur]

http://www.alloyusa.com/gear-patterns

http://www.freeasestudyguides.com/ring-pinion-tooth-contact-patterns.html

 

[solocam]

A small 1 or 2 jaw slide puller but untill you measure what you got first you wont know if or how much or what direction to go.
Instead of guessing get some Machinist Blue Dye and check the heel and toe pattern
https://www.ringpinion.com/Content/Book/Reading-and-Adjusting-Ring-and-Pinion-Tooth-Patterns.pdf

I'll get the dye tomorrow, but I'm pretty sure the driven gear needs to move upward.

 

[solocam]

I put the dye on and ran the gears. Total depth of gear measures 0.1735 and the die shows opposite gear depth into the gear at 0.1465. pattern is centered horizontally spreading across about 3/4 of the gear length. I feel like this is a good pattern. Does anyone have suggestions?