Pinion Bearing MC-1/R versus MR

[76SeaRay]

So, I am test fitting parts to get ready for assembly of my lower unit. The new lower housing I bought came with a lower roller pinion bearing pre-installed. When I tried to insert the vertical driveshaft, it would not go into the bearing. Looking closer, the rollers in the bearing are larger than the ones in the old housing and old pinion bearing. If I check part numbers, the pinion bearing for the MC-1/R is part number 31-92366A1 and the pinion bearing for the MR is part number 31-42647A1. Is the lower gear case housing the same for MC-1/R and the MR? If so, can I remove the larger bearing that appears to be a MC-1/R bearing and install the MR bearing? Did the driveshaft size change from the MC-1/R to the MR? Trying to decide if I need to return the housing...

 

[Bt Doctur]

housings have different numbers and you cant install a driveshaft with a preload pin into a case to replace a shaft with no preload pin.

 

[76SeaRay]

Thanks, after much research I finally got to the bottom of it. Although the housing was sold as a brand new 1623-8951A37 which is used on an MR drive, it is really a 1623-5356A4 housing which is used on an R drive. Yup, they are not interchangeable. I am returning the housing for a refund and again searching for a correct 1623-8951A37 housing.

 

[Bt Doctur]

Without the correct tools and shimming tools its mush easier to just replace with a SEI lower

 

[76SeaRay]

I have all the Mercruiser tools including the shimming tools... The only issue is how many shims to start with for the forward bearing... If it is not right, then you have to pull the race to add or subtract.. That appears to be the most difficult part.. Since you suggest and SEI lower unit, I assume the lower housing they sell is of good quality...