Transmission Replacement

[Bill Shreeves]

I'm wondering what engine you have.  The top speed that I've seen published by the MFG for any M25 is 3,000. 

[Noah]

Might confirm your speed instrumentation calibration, too. Take this from a man who once reported he was motoring at 7:5 knots!

[Breakin Away]

Good points. If he's using a paddlewheel for STW, then growth on the paddlewheel could have an even greater effect on the observed speed than growth on the hull and prop.

As stated before, I don't know what prop specs apply for his particular engine/boat combination. But if a 15x10 is recommended, I still wonder why he had 15x9 before, and what issues caused him to increase pitch. Those issues could say more about the true root cause. Obviously, prop pitch is usually adjusted because of too high/low engine RPMs at full throttle, and miscalibrated tach could lead to an incorrect prop selection.

[Bill Shreeves]

BTW, I know the hard way that the engine is capable of running faster.  I made a minor cable adjustment to get my RPM up from 2,900 to 3,000 @ full throttle.  The following weekend, after getting a photo tach, I checked it and learned my cockpit tach was off.  At full throttle the engine was actually running slightly over 3,100.   So, I "fixed" my cable adjustment.  Yeah, I know, a smarter person would've checked first...  Fortunately, I've almost never run near full throttle and was only testing after knowing the engine was a full operating temp. Now I know I need to calibrate my cockpit tach.

[Noah]

Lots written here to read and learn about 9 vs 10 pitch with lots of differing opinions and experiences. Campell vs Michigan, 2-blade vs 3 blade, fixed vs folding--there is no "correct" answer.

[Bobg]

I am in lake superior and there is no growth on the boat, not even stain, I use the hand held laser to check engine rpm and shaft rpm while my friend drives the boat.  I have the m25xp engine, Original equipment was the 15/9 prop, but as many others have done with this engine I repitched it to 15/10 to get a little more speed,
"The boat is pretty much empty,  2 people on board, someone once said maybe its the fuel lines, supply and return, I have changed the fuel filters, and cleaned the fuel pump screen, I have used my handheld gps, phones, boats traveling alongside to check speed, the knot meter is right on with these.  frustrating, dirty injectors?  I do get close to 3200 rpm with the hand held laser wide open and can achieve 6 knots, but don't like to run the engine over 80% of full rpm.  used to be at 2500 rpm I could hit 5.6 knots before I pitched the prop, Then I got 6 knots at 2500 rpm till it started to slow down, now I get around 4.6 knots at 2500 rpm, maybe it isn't even the prop or tranny, I don't know, but I got all winter to ponder it.
  Thank you all, didn't mean to hijack this post but when I saw transmission posted, thought I would ask,  I do believe my manuel says it is a2:1 reduction, Hurth 50, maybe it has nothing to do with the repitch, might have been starting to slip anyway, like I said, it reads a little less than half rpm at all points of throttle,  2000 engine, 950 shaft, 2600 engine, 1230 shaft, could that much less rpm on the shaft mean that much slower boat speed?   Does anyone know any Hurth transmission people to call?  Thanks again  Bob
I

[KWKloeber]

Bob

See hurth auth service contact earlier in this thread

Ken

[Ed Shankle]

My thought as well, Stu. My boat is always faster under power earlier in the season.
Bob, I see you said the bottom was clean, were you power washed when you hauled out for the winter? Wondering if you had growth but didn't get to see it before the power wash.

Regards,
Ed

[Bill Shreeves]

Bob - I'd like to think you could identify whether or not the tranny is slipping while under load with your hand-held tach by knowing the gear ratio.  I haven't done this but, I can't imagine why this wouldn't be accurate.

On the Hurth / ZF transmissions the gear ratio is shown on a label attached to the top of the tranny near the shift lever.  If its a hurth HBW50 or ZF 5 its probably labeled as 2.05.  According to the manual I have, the "A Ratio" is either 2.045 or 2.722 on a ZF 5 M.  If the label shows "A=2.05" on your tranny, multiply the shaft RPM by 2.045 while in forward under load. This should be the rpm of the engine assuming the connection between the tranny and shaft is good.  If so, the tranny isn't slipping and your problem is not the engine or tranny.

After that, the following guesses come to mind.  Is anything causing the prop to be less efficient than it was when you first re-mounted it after the prop pitch change?  Did it become bent, is there slop in the cutlass bearing or strut, is the key in the prop doing its job or does the prop slip while under load?

[Bobg]

Thank you Bill, I am not at the boat right now but will certainly do that check this summer, and where I sail in Lake Superior, the water is so clean that it leaves no growth on the boat at all, and yes I was there when we pulled the boat, I power washed it anyway, interesting bit about the key in the shaft, I think I will remove the prop and check that out as well as long as the boat is out of the water.  I have a number of shaft and engine speeds written down at the boat, I will look at those figures and do the multiplication using the gear ratio off the tranny, and see what i come up with..Thanks again guys  Bob

[Bill Shreeves]

Along with a new gearbox, I want to add a gearbox cooler.  Since I don't have one on my ZF 5 and new to this, I'm not sure how the raw water lines are run.  I'm pretty sure it's added as a loop before the heat exchanger however, not sure if its in-line or added with "T's" etc.  My concern is that if in-line might it restrict the flow to the HX?   Maybe a pic or two or a diagram that has a tranny cooler installed on a ZF10 / Hurth HBW100?

Thanks

[Bill Shreeves]

The previous ZF 5M was painted with the Universal silver/gray paint.  I have a new ZF10M that is unpainted.  Should I clean and paint it taking care not to paint output shaft seal and the dip stick vent?  The gearbox is aluminum and i've read some just keep a light film of WD40 on them to protect.

[Stu Jackson]

No need to paint it, Bill. Paint traps heat, right?   But throw away the WD40.  I think of it as silicone (only place to use it is on the Beckson ports).  Get Boeshield T9 for that use, and PB Blaster to remove stubborn nuts & bolts.

[KWKloeber]

Be very very (and very) careful to not get any blaster near the seal or you'll be replacing that. 

Same for anyone trying to get a shaft coupler freed up.

[Breakin Away]

No need to paint it, Bill. Paint traps heat, right?   But throw away the WD40.  I think of it as silicone (only place to use it is on the Beckson ports).  Get Boeshield T9 for that use, and PB Blaster to remove stubborn nuts & bolts.

Just to keep this fact-based, what offending ingredient does WD-40 contain, and what are its objectionable effects?