1988 Chaparral 2850 SX twin 350 Magnum with B code drives

[23SX]

Greetings,

I have a 1988 Chaparral 2850 SX with twin 350 mags with Alpha drives and 21p Mirage props. I had a shaft seal leak on my starboard (standard rotation) drive last year without knowing and it destroyed the uppers without any warning until they stripped out. I went to order a new drive knowing it should have 1.5 ratio drives and found both drives to have B code serial numbers which I show to be 4 cylinder drives (1.98 ratio). I didnt have my tools so I am going to go back and count the teeth in the upper on the counter rotation drive which is still good.

My questions are i see the gears should be 20/22 for the 1.5 ratio but not sure if that is 20 teeth on the input gear/horizontal input shaft or veritcal shaft gear going to lower?? I have never had twins before and not sure if 21 pitch sounds right for this boat, both engines only pull about 4200 rpm and would like to switch to 19p props if the gear ratio ends up being 1.5 to get back solid in the WOT range. If its not would there be an issue with putting another B code drive on the starboard side??

Thanks!

 

[Bondo]

and found both drives to have B code serial numbers

Ayuh,.... What's the "B code",..??

The ratio for a 4 cylinder is 1.98:1, yer 350s oughta be 1.5:1s,....

 

[23SX]

No Title

Port Drive serial number is 0B927364
Starboard Drive serial number is 0B928240

I thought the "B" designated it was a 4 cylinder drive

 

[Scott06]

Per the document the letter is on the splined yoke not your serial number, is there a drive ratio stamped next to the serial number number ?

 

[nola mike]

I can't imagine a 350 spinning at 4100 with a 21p on a 1.98...but the drive gear is at the end of the input shaft, the driven gear is on the vertical driveshaft. 20/22 for the 1.5.

 

[23SX]

It's a little hard to count the teeth with the drive still on due to the swim platform so I might just pull it off. No ratio was seen stamped on either one but will double check. I thought if it was a 1.5 ratio the serial number would start with 0F________

 

[Bondo]

I thought if it was a 1.5 ratio the serial number would start with 0F

The prefix of the serial number changes with the date/ time/ sequence of manufacture,....

OA's came before OB's, etc,.....

 

[23SX]

Thanks for the replies everyone. I knew about the sequence on the serial number for the engine but never really had any drive issues and thought the B designated the ratio. I will check the yoke and/or count the teeth.

 

[nola mike]

You can also just turn the engine and see how many shaft revolutions/prop revolutions