AQ260/290 Shimming lower unit to intermediate Units

Hello Ricardo,
I was told you are the expert on these older Aquamatic drives. I recently bought a 1986 SunRunner with twin AQ260/290 units in it. The engines were rebuilt last year and run fine. The is only 210 hours on the meters. I am replacing the intermediate and lower units with two good used fresh water intermediate and lower units because mine have suffered years of neglect and saltwater abuse that much of the aluminum is so badly pitted and overpainted, this just made sense. BTW, the boat is going into freshwater on the Ohio River.

My question is regarding the shimming of the lower unit to the intermediate unit. I have read and measured multiple times and still dont know what to do. I do not have the bearing race tool to hold down the bearing race on the lower unit. Should I get one or make one? Also, I did not rotate the vertical shaft or tap on it.
My readings are as follows. My B reading is 7.70mm and my A reading is 8.13mm. Doing the math, B-A= -.043mm. This puts it into a preload condition over the limit of 0.02mm. and it is similar on the other unit as well.
What am I doing wrong? I dont think I should disassemble the lower units at this point to check the gear pattern or anything in there, should I? These seem to be in excellent condition.
Any suggestions on how to get this tolerance in range?

Thank you in advance for your help.

Regards,

Kevin

Based on my conversation with Rick, I was able to measure the intermediate location where the Bearing race sits, better known as "B", and the top of the Bearing race on the lower unit, also known as "A".
I did purchase a depth gauge and now get a "B" reading of .312" and an "A" reading of .275", so doing the math B-A=.037". Based on the tolerance of +0.001 to -.0015, I am going to use a .035" shim in the intermediate housing.
Rick, would you agree or should I go tighter?

Thanks Rick,

Regards,

Kevin

Kevin, this shim value (above the race) controls the vertical shaft uplift as well as a portion of the gear back-lash.
If the back-lash is OK when the vertical shaft is held down firmly by the bearing race, then your math would appear to be correct.

But keep in mind that the two cases (where the measurements were taken) never come fully together when tightened up.


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RicardoMarine said:

Kevin, this shim value (above the race) controls the vertical shaft uplift as well as a portion of the gear back-lash.
If the back-lash is OK when the vertical shaft is held down firmly by the bearing race, then your math would appear to be correct.

But keep in mind that the two cases (where the measurements were taken) never come fully together when tightened up.


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Would you suggest shimming it and bolting it together and then checking the backlash to see if it is correct?
That would tell me if my uplift on the vertical shaft was correct, yes?

Kev