Super Hawaii 40

The Boat (Super Hawaii 40) was built in 1991. I purchased it (prior to last winter) with two 502's (Carbs) They had been rebuilt several times. The past owner said that he was unable to get his starboard motor to reach the same RPM as the port. I replaced the following last winter:
1. Two New 502 EFI MPI's (Checked alignment)
2. New Throttles from Gaffrig (Checked linkage so both open wide)
3. New tachs from Gaffrig
The starboard still would not run like the Port (4800RPM vs 5100RPM) The mechanis said it must be in the drives. We found that the two drives were not brother & sister. (different castings Starboard - 1589-8867c, and the Port - S 1589-8867. He did not remember what the "S" stamp ment but both are oilers. He determined the gears must be different in the drives so the quick fix to get out on the water was to change the props pitch (from 21 to 18) on that drive until I had the time & money to take it apart & replace the gears. The three inches did the trick for last summer.We went after the gear switch this past winter but found that the gears were the same except that one did look like it was newer. The following was fould on the gears:
1. The drive that was newer is the one with the trouble, not the old.
2. Pinion tooth count on both was 27
3. Gear tooth count was 29, that should give me a 1.36:1 but when We turn the input shaft i complete turn we got the prop to spin 3/4 a turn. (1.5:1??)
4. Took apart the pinion assembly and got the part numbers off the back of the gears and found the newer had # 43-815661 and the other 815661 with a smallar number away from that 3733 (cast number?). The lower gears were both the same with tooth counts of 15/19.
NEED HELP - CAN ANYBODY SHED SOME LIGHT ON WHERE WE ARE IN ERROR?

Mbam

When checking your ratiio, turn the prop shaft 10 times, then divide, input 13.6 /prop 10 = 1.36. Much easier to count full turns.

As far as thr RPM did you try switching the props?

Reckless32

Mbam, I think that's what he has done already. Starboard drive's prop pitch was reduced from 21" to 18" to balance out with the port drive/engine which runs strong at 5000 with a 21" prop.

Starboard only wants to get 4800 with 21" installed. Apparently the formwer owner had the same problem with the older carb'd 502's. He's trying to figure out what his next step should be after having discovered the above minor differences...

Rick

Mbam

Rick, I understand, but the idea is to verify the props first. Who knows if that 21 is really a 21, or the 18 for that matter? The math is all wrong, an 18 should turn 600 rpm more than a 21 (assuming they are the same type of prop). Also 300 rpm could be the tachs, unlikely but possible even though they are both new. We use either a Shimpo photo tach or a pair of 4 digit Aetna (or Gaffrig) digital tachs when testing even though with a little practice you can at least tell if they are synced by ear. Both of these tachs are accurate to 1 rpm and eliminate any chance of tach error.

It is so easy to perform the prop test with a Bravo it is silly not to.

When I first started in this business, I cannot tell you how much time I spent chasing phantoms when the problem was something simple !

cigarette1

Could the gimbal bearing be binding and causing an extra load on the motor???

G

MnFastBoat

on my 1999 Advantage with502 mpi's I have the EXACT same thing!
I was told it is because the drive is turning backwards since it is NOT a counterrotating drive. Not sure but several people have told me this.
I have seen it in a few boats

Mbam

FastBoat, I don't think that is true in regard to the Bravo. The drag in the drive is the same in either direction.

formula31

Check the preload on the upper timken bearing. Its the nut on the end of the u-joint shaft after you remove the assembly from the drive housing. Its supposed to be around 12 inch/ounces I think. I found one once that was torqued to 12 ft lbs and it ran hot and slow. I was surprised the horsepower loss didnt blow it up. Just something to look at. Did you try and swap drives to see if the low rpm went with the drive?

blue thunder

Formula31, I think the preload is 12 in-lbs, not inch-ounces. That would equal 1 ft-lb. 12 ft-lbs of preload would be a disaster for sure! I agree with Mbam. eliminate all easy stuff first. I think I would switch the drives and see if the problem follows. That'll narrow it down some.

BT

formula31

Ooppss typo I meant inch/lbs. And I think it was 6-10 inch/lbs. Did find one from the factory that was way over torqued. Thats for the correction.