MILD THUNDER

iTrader: (3)

Hey Andy! Good point about the straight cut/helical gears.

When I replied earlier, based on his gears he posted, I came up with one drive being a 1.49 Ratio, and the other being a 1.47 ratio?? Is that correct?

Plugging those numbers into a slip calculator with 10% slip, 6000 engine rpm, 28p prop, 97mph, going from 1.47 to 1.49 changed the engine RPM by 50.

I never ran anything fast like you cat guys. A couple seasons ago I ran a set of ssm props, that were both stamped 17x27. MY engine RPM was off by about 200. I brought them in and had them scanned on a prop scan machine. one prop was 27.2'' of pitch, the other 28.0. Other than the rpm difference on the tachs, I noticed nothing ill handling wise. But, that's a 85mph vee, not a fast cat, so its probably moot.

MER Performance

You are correct on that info. I know the 1.33 upper and the 1.125 lower work out to be 1.5:1, what does that work out to be with a 1.31? The math formulas for gear ratios I found need to know the teeth count of the lower gears. I was unable to find the teeth counts in the manual only for upper. Anyone know the final ratio?

yschmidt

I do.

RMPRam

iTrader: (1)

Multiply the 1.31 upper gear set ratio by the 1.125 lower gear set ratio and you get 1.47325 overall ratio for the drive. In terms of overall strength the 1.31 net forged, straight cut upper gear set is far superior to the spiral cut 1.33 original gear that came standard with the #4 drive. Mercury never produced (as far as I know) a 1.31 straight cut, net forged gear for the #4 or #3 drive. When I had the upper gear sets, forged by Mercury's OEM supplier, I had them make a "hybrid" gear with the same forged straight cut gears as were used on the #3A'a and #5 drives and the "shank", as I call it, to fit #3 & #4 drives. I had 10 of these sets polygon'd to use in the #4's. I have, in stock, new forged straight cut, 1.31:1 ratio upper gears for all the SSM drives, #3, #3A, #4 and #5's as well as new LH and RH 1.125:1 lower gear sets and new "big" propshafts to fit all the SSM drives (including the #3 and #4 drives). I hope this adds clarity to the overall ratio and gives a little more background as to what is still available for the SSM drives. My goal in doing all these gears, shafts and parts for the SSM drives is so the owners of these drives do not have to scrap them if they experience any drive issues.

RMPRam

iTrader: (1)

Also, if you are really concerned about the ratio of the drives, you could convert the 1.33 drive, whose upper gear set is NLA from Mercury, to the still available and much stronger 1.31 upper set. Granted I have a vested interest in selling gears, but this seems to be the only way to make them the same ratio.

Gary
612-247-7081

MER Performance

Gary, Hey thank for the help and information. I called you about these gears last year, with concerns on this issue. It was out of my hands on the drive rebuild and I am VERY DISAPPOINTED, in the out come, almost a year for the guy, to resolve getting gears and actually doing it. Why, he wouldn't just have let me get the gears from you and we handed them over for set-up, is way beyond me! I will say; it's non of the top guys we know out here. They would have never taken as long, nor would they follow this procedure of mixing ratios.

RMPRam

iTrader: (1)

Footnote. I just spoke with a friend that has been doing drives for 30+ years for one of the premier offshore shops in Fla. and he informs me that when Mercury switched from the spiral cut upper gears in the SSM drives (#3,#3A, #4 and #5) to the straight cut forged gears, the strength was increased by 50% if not 100%, (his words)

MER Performance

Yes, Thank you everyone for you input on this. Spoke with Gary, today; he informed me 50-75 rpms difference. The bad thing is the person that did the work, charged my client for 2 sets of gears , 2 different ratios. One drive with 1.31 and the other has 1.33 that the parts came from the better of the 2 drives. The other new gear set is on the shelf in his shop, which I informed my client to get. All said and done; he could have had 2 new sets of gears in both drives, so now this is what we are doing.

I have the 1.33 that are used and a new set from Merc. that I will have in my hands by Friday, at that time I will verify the ratio of the new set. If you or anyone is interested in buying the used and new set, let me know. Needless to say; my client is not happy about the drive issue. The guy; told him flat out, they matched in ratios. Pretty sad deal!!!

MILD THUNDER

iTrader: (3)

That sucks.....So is he going with all new straight cut gears? Is he running the 26 spline or 19 spline propshafts? How much power is he putting thru these iv's? Only reason I ask is I too have iv's. I have no idea the history on my drives, as in hours, etc. Been running them for 3 seasons with no issues, but Im starting to worry about them.

MER Performance

26 splines. Right at 780 hp, naturally aspirated.