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thriller
05-10-2004, 10:24 AM
After setting up the rear prop blade to be at the 6 oclock position and the inside prop to the 12 oclock position, I was unable to get optimum performance. After receiving my BH manual I decided to put the props in proper alignment only to be disapointed in the new set up.I wish I had of marked/scribed the previous setting..:( My rpms increased but wot was only 4100 rpm and a dismal top end speed of only 62 mph. Rooster tail was absent and the noise was like a buzz saw..Obviously I need to change back to original un timed setup? Props are like new 31P and no visual damage? Can any BH owners shed some lite on this kind of reaction?

Cheers MM

Woodsy
05-10-2004, 12:05 PM
Mike...

Sounds to me like you are one or two splines out of time... How did your WOT rpms go up if your only spinning to 4100RPM. This combo should be spinning anywhere from 4700RPM to 4900RPM...

If the props are properly timed, they should be opposite of each other... forming the 6 points of a hexagon at the prop tips.... make sure you grease the shaft well, and check the condition of your thrust bearings...


Woodsy Von Outboard

thriller
05-10-2004, 01:49 PM
It makes that much difference? I did exactly as the book says but I will check alignment after I getr home tonight.I will move it over a couple notches. I will look for rpm increase as suggested. The previous set up was ok but I wasn't getting enough rpm..When I looked at the old set up compared to what the manual said it was obviously wwaaayyy out. But now it is reasonably close to the hex set up and the performance is brutal..weird...I thankyou for your reply
MM:smash:

Woodsy
05-10-2004, 02:06 PM
Mike...

That pic
doesn't look right to me.... align the front prop with one blade straight down in line with the skeg... so it looks like a "Y", align the rear prop with the top blade in line with the bottom blade like an "upside down Y".

This is a 502MAG boat? The props you took off were 31 Pitch? What was your RPM prior to messing with it? Have you had the engine aligned? Whats the condion of the gimble bearing.

The timing of these props is EXTREMELY important. You are lucky the imbalance didn't tear the drive to pieces...

Call me if you have any ??? 978-502-5465

Woodsy Von Outboard

thriller
05-10-2004, 04:36 PM
Woodsy
I tried calling..no answer...Hey this prop thing...can't be way out.... as I have always had it in the hex position just as you have stated.It's just when I got the manual to explain/detail the prop timing that I noticed the set-up was wrong..Now to correct my tweaking I will do just as you and the manual have told me to do..If I am still not getting 4800-5100 rpm WOT what else can I look to adjust..Throttle throw? Engine alignment has never been touched as far as I know.. The boat only has 28hrs on her.When reinstalling the leg that I took off to repair a sticky shifter/throttle issue, the leg went right back in with nio binding issues. Bearings were well greased etc. Lubed the u joint/gimble etc. Ran great after the re and re but really poor performance once I messed with the prop set up. I have never been able to see 4800-5100 since I bought it and I have had it pinned a few times..:mad:

boldts
05-11-2004, 01:34 PM
Just guessing and I have absolutly NO experience with the BlackHawk, but I'm assuming it isn't possible to mount the outer prop on the inside and vice versa?

thriller
05-12-2004, 09:01 AM
The props are actually different blade size and the front one is actually larger inside bore...:)

mattyboy
05-12-2004, 10:29 AM
I would imagine merc would make it so you can't put the lh rotation prop on the rh rotation hub, That would make docking a bh a real handful :eek: fake left go right

hey Swanson over there I wanna go over there!!!


Matty

Greg Maier
05-12-2004, 07:01 PM
Thriller,

Are you sure that you took Woodsy's advice and checked the thrust bearing, i.e. that is is there? I would say that the buzzsaw sound is the prop hub grinding into your BH case because of the lack of a thrust bearing. That would also explain the loss of speed.

As for the prop timing, IMO, a spline or two off, won't cause a big drop in speed. I have had my props in all sorts of different timing configurations, and, to be honest, I didn't notice a discernable difference.

For what it is worth, I would call Dave Bostic at Hoss Propelers in Oklahoma. He worked on the early BH prototype props. He told me that the way Merc tells you to time them is actually wrong. By the way, he can also make you a set of BH props for a large fee. He said that he can easily squeze a few more MPH's out of a BH by playing with pitch and diameter.

blackhawk
05-12-2004, 10:12 PM
I think Greg hit the nail on the head! Sounds like one of your thrust washers is missing. Maybe it fell out when you were re-timing your props.

The timing of the props is not that critical that you would lose that kind of performance. I doubt you would ever notice a spline or two out.

Greg, if you don't mind me asking how did Dave tell you to time the props?

Thriller, I never see 5000 rpm on my tach.

gero1
05-14-2004, 09:57 PM
got my b/h home and saw the picture in the book, both props were straight up, timed them like the book shows and have had no problem

Lenny
05-15-2004, 01:28 AM
How come I hear "straight up, and together, AND, inverted "Y" s..Which is right?, and I hope it got better for you Mr. Miller... certainly confused now...

Greg Maier
05-15-2004, 07:07 AM
Scott,

Dave Bostic told me that the proper timing is slightly off from what the merc manual specs. He really didn't get into the exact details of it. He also told me that the back prop is supposed to have 2 inches more pitch then the front prop, i.e. the 31 inch props are actually 30 on the front and 32 on the rear. I had my props reworked last year to both be 31 pitch (I didn't know they were supposed to be different), and I could definitely tell the loss of performance.

Lenny: Here is what the merc manual says about timing the BH Props:

Merc Manual (http://www.donzi.net/forums/attachment.php?attachmentid=1304)