Prop shaft runout

[Nattylightmike]

Well I got the boat in the water finally. I noticed that the shaft log seal was flinging grease all over. Looking at it a little closer it looked like is was vibrating while in gear. It just didn't look right like something was out of balance. I pulled the prop shaft and put it on a couple of v blocks got the dial indicator set up and turned the propshaft by hand. Depending on where the blocks and dial indicator were I had between .007 and .020 runout. I am guessing the shaft is slightly bent. What is an exceptable figure for runout?

[Florida Inboards]

On a tournament boat ( Ski Nautique) the runout tolerance is .003. Not sure what is acceptable on the mondo high HP flatty's. My old flatty I hold to .003 however it is getting another re-do over the winter and new a shaft will be in order, along with SS underwater gear....

[Nattylightmike]

What is the correct way to measure it?

[Florida Inboards]

I have a fixture that was manufactured just for checking shafts. There are four dial indicators set up on it at common stress points. I rarely use it except when I set up underwater gear with unknown parts (E-Bay or Swap meet parts). Most of the inboards that come thru my shop are obvious if the shaft is bent. Their are a lot of stumps here in north Florida.

You can also chuck it up in a self centering lathe and set your dial indicator up at numerous points on the shaft to check run out. Near the prop taper a couple of areas in the middle and at the coupler end. Any machine shop can do it for you.

[Nattylightmike]

That's what I was thinking I was going to do. I am going to take it to the machine shop before I spend $400 for a new one. Thanks

[Florida Inboards]

If it turns out that it is bent, Do not let someone tell you it can be straightend!! They are only good for two things after they are bent: Prybars and they make great horse shoe posts!!!

[RiverRacer]

How much slop in the strut bushings????:confused:

[Florida Inboards]

Yes those pesky strut bushings! Do any of you guy's have any kind of cool tool to drive them out while still on the boat? the ski boats tend to have the brass/rubber type and they can be a bugger to drive out while still on the boat. The fiber ones do not seem to be as difficult.

[gfinishline]

Burbank Steel Treating did my straightening and normalizing of prop shafts. They offered down to .003" (over 72") as "straightened". Their machine (big lathe) had about .001" in it. Ran boats up to around 168MPH with their "straightened shafts". Had no problems with their work.

[RiverRacer]

Yes those pesky strut bushings! Do any of you guy's have any kind of cool tool to drive them out while still on the boat? the ski boats tend to have the brass/rubber type and they can be a bugger to drive out while still on the boat. The fiber ones do not seem to be as difficult.

Never heard of a tool to drive them out, I made one to install them, I just use a hacksaw blade to split them then they fall out!..

[wagspe208]

I know the fuel guys bend them pretty regular like. I was told by a prominent fuel boat owner here in the midwest, they just put them in a holder that normally holds their vise. They just bend them back. Now, this is at the races, between rounds. I was astonished. I would not recommend that, either.
Now, what do you think that shaft does when you whack the throttle from an idle. I will guarantee you it looks like a pretzel. We generally worry about bend at the taperr end or the v-drive end. The middle will change soon enough. LOL I have no idea if that is right or not, though.
Picky people will want it perfect, general racers don't give a damn.
Wags

[RiverRacer]

I thought them fuel guys replace them after every round??..:confused: