I replaced recently replaced my 1989 Bravo 1 top end with an IMCO Extreem SC. I run a 2" shorty lower. I was surprised at the top end speed I appear to have lost. I did some repowering at the same time, 454 to 540, so I don't have accurate comparison numbers but I am guessing I lost 8mph on the top end. When I turn the drive by hand it is very tight. I could spin the Bravo 1 with two fingers. The IMCO takes two hands and some effort.

Are there any adjustments in setting up the IMCO that the mechanic may have overtightened? I was expecting to lose some top end when I upgraded but the drive seems very tight. I have about 30-hrs on the drive at this time.

I am going in for service in a week so I can direct the mechanic check the setup if required.

Thanks

I am lost here, Am I reading this right? you upgraded to a bigger motor and expected to lose performance....why would you lose performance going to a larger motor and a better drive with the same lower? again I am lost. why?

Bryan

If you are comparing an Imco vs Merc upper, there should not be any difference in the feel of the drive. There is something wrong in there. I would bet that the input bearing pre-load is too tight or the bearing is bad. Actually, if the pre-load is too tight, and you ran the drive, the bearing IS now bad.

Thanks Checkmate, I called IMCO and they also mentioned that the resisance I feel when I turn the prop by hand should be about the same. They suggested I bring it by for and they would look at it or I could have a reputable mechanic check the preload.

Thanks

I lost about 100 rpms going with an Imco Extreme upper and the stock bravo lower. I cannot feel any difference when I spin the prop though.

Prop Slip If You Raced The Drive

The drive has to be broken in also for the gears to mesh and take a "set". Imco has the procedure that must be followed. I am still doubting any Bravo style drive. All I hear and read about is headaches and heartache. No matter what parts used , it's like putting a twizzler between the motor and prop. Make the twizzler out of titanium, it still breakes due to design and size limitations. Good luck with your drive. I wish their was a real good option for the Bravo. I'd buy it.

there is a preload could be set wrong or the machining on the upper housing could be off right where the upper meets the lower that would cause what you are talking about

GoodT,
I agree with you about shimming the vertical shaft bearings to get the rolling torque set. Also about the machining.
Since you brought up lowers, you may as well throw in setting the total pre-load for the lower by shimming or using a crush collar behind the bearing carrier for the prop shaft bearings.