Alignment specifications

[chris07732]

I repowered with a new Yanmar 4JH4-TE 75hp in 2010, put boat in water late that summer, only ran engine for 7 hrs. Didn't notice vibrations. Summer of 2011, had the cutlass bearing replaced, prop resized/pitched to increase WOT rpms, but ultimately, never got the boat in the water. This year, after delays due to painting hull, finally got boat in water in Sept. In doing speed runs to check out effects of prop resizing, I'm feeling vibrations at 2400 rpm and above.

Looking at the prop shaft while underway, I think I see that it is "blurred", that the shaft is vibrating or running out.

I measured shaft runout with dial indicator to be .008" -.010". What would be allowable runout specifications?

Do I need to be concerned that the engine was originally installed with a marginally sloppy cutlass bearing, and now that the bearing is brand new and a tight fit, that the engine should have been realigned, on general principle? Someone also said that the alignment should be checked anyway just by the passage of time since a new engine install. Agree? Despite only having 10hrs on the new engine install?

Thanks for any help

[sailorchic34]

Yes you need to check the engine alinement after a new cutlass bearing install. Should be set so you have less then 0.001" play between the flanges per inch diameter of flange at the engine end of the shaft. Checked with feeler gauge at 4 sides of the flange with the flanges loose but against each other.

So for example for my 4"diameter flange I should be at or under 0.004" max on any of the four sides /quadrants (top, bottom, left and right).

[NoTies]

Don't forget the radial runout. it sounds like this is the problem here rather than axial runout.
Sailorchic, you probably get plenty of marriage proposals but have you ever had an online job offer on a forum?? Vanuatu is a real nice place to work you know.

[delmarrey]

Originally Posted by chris07732

I repowered with a new Yanmar 4JH4-TE 75hp in 2010, put boat in water late that summer, only ran engine for 7 hrs. Didn't notice vibrations. Summer of 2011, had the cutlass bearing replaced, prop resized/pitched to increase WOT rpms, but ultimately, never got the boat in the water. This year, after delays due to painting hull, finally got boat in water in Sept. In doing speed runs to check out effects of prop resizing, I'm feeling vibrations at 2400 rpm and above.

Looking at the prop shaft while underway, I think I see that it is "blurred", that the shaft is vibrating or running out.

I measured shaft runout with dial indicator to be .008" -.010". What would be allowable runout specifications?

Do I need to be concerned that the engine was originally installed with a marginally sloppy cutlass bearing, and now that the bearing is brand new and a tight fit, that the engine should have been realigned, on general principle? Someone also said that the alignment should be checked anyway just by the passage of time since a new engine install. Agree? Despite only having 10hrs on the new engine install?

Thanks for any help

What size is your prop shaft? Does it vibrate in reverse?

When I re-powered with a new yanmar I found that the shaft (1") couldn't take the high torque of the new motor. I ended up after several alignments, balancing the prop and change to a Pythondrive that the shaft just couldn't take the push while getting up to hull speed (2200 RPM's). I installed a 1-1/8" shaft and all is well.

This may or may not be your problem but it's worth mentioning.

[sailorchic34]

Could be radial, but I'm betting the loose play in the old cutlass bearing was partly due to a miss aligned engine. With the new cutlass bearing the prop end is now fixed so the other end is vibrating the engine mounts. Least wise till the new cutlass bearing wears in (or out) more.

This as he just had the new cutlass bearing installed and picked up a new vibration. If he had a new prop shaft installed then radial might need to be checked too. Probably should have pulled the old shaft to check when the cutlass was done.

The good news is even if it was done in the yard (on the hard) it still needs to be redone again, once the boats back in the water. This as the hull will shift a tad (we're talking thousands of an inch).

Of course if he has an auto prop, then it could be a setting off on the pitch too.

If I'm lucky I might swing by Vanuatu sometime. Though need to head south first...

[bobconnie]

Im with sailorchic on this one ! ck the alinement very carefuly, I even go so far as to use a dial Indicator for my final ck between the 2 flanges on the out side, and attempt to keep the runout under .001 if possible! but then Im sorta nit picker! but my stuff runs smooth!

[cosmic pete]

idealy there should be between zero and four thou runout and needs to be realigned every time the boat comes out of the waterdoes no matter if it is a one cyl motor or a v 16 it is the same measurement, a worn cutless will give false readings as will soft engine mounts , have fun