Prop shaft run out spec?

[WaveyDave]

1999 Johnson 130, 20' leg (J130PLEED)

While changing the prop I noticed a very slight amount of run out on the prop shaft - I haven't put a dial gauge on it yet but, I will. So, if I try to move the prop shaft side-to-side or up/down I can feel it hit the limit of its run out but not see it. Given that the prop shaft is supported by two roller/needle bearings about 8" apart I suspect there has to be a little movement due to manufacturing tolerances but, how much is too much? Obviously, if it moves too much the seals will not be too happy. The last oil change yielded milky oil - normally it comes out just looking just like new. So, maybe I have a failing seal which I'll verify with a pressure and vacuum test.

I have the OMC service manual for this engine, but it makes no mention of run out specs. Maybe it's 0?

 

[Scott Danforth]

first, welcome aboard

with any milky oil, you need to pressure test to see if you have a bad seal

there should be minimal slop in the bearings. you could also have a bent shaft.

 

[dingbat]

My prop shaft has the typical in and out movement but no discernible side to side play or run out.

No such thing as a tolerance of zero. Guessing 0.003 to 0.005" max.

 

[ct1762@gmail.com]

tip it upside down and leave it there for an hour. anything comes out, you know what to replace. the driveshaft seal and shift shaft seal and gasket are most prone to failure, both very easy to replace.

 

[jakedaawg]

I am confused maybe. You say runout. When I straighten shafts I shoot for 0.002". If you are talking just side to side or top to bottom play then I agree with dingbat.

 

[WaveyDave]

Yeah, I should have just said side-to-side play. My suspicions are:

1) my SST prop (older heavy OMC painted Stainless) which has a slight wobble at the hub is likely out of balance and toasted the rear needle bearing. Basically the front the prop hub wobbles opposite to the rear of the hub. though *** would sort itself out under load but maybe not.

2) I messed up the shift shaft seal while putting the lower unit back on after swapping the water pump.

I did a pressure test at 16psi for 35 minutes with no pressure drop - it was a static test though, I didn't rotate/shift anything. I'll do a vacuum test next.

 

[WaveyDave]

UPDATE:
I did a vacuum test with he help of a buddy and his Mityvac on Friday. Here's what we did and what we found:

Setup:
1. Removed the spark plugs (safety first)
2. Connected vacuum pump to gear case upper port using the fill pump adapter. We first verified the connection to the adapter wasn't leaking. We assumed the threads were sealed - which proved correct.
3. We applied about 25 inHg vacuum to the gear case.

Procedure:
The idea here is to test all three seals: propshaft, driveshaft, and shift linkage.
1. Spun the prop several times and tried to wiggle it up/ down and side to side. Did this several times but no leak indicated on the vacuum dial by a drop in vacuum.
2. Shifted between Forward-Neutral-Reverse. The dial would indicate the change in volume due to the shift linkage going in/out of the gear case but returned to the same vacuum level when we shifted to neutral.
3. Time to test the driveshaft seal. We first put the engine in forward and spun the prop. Vacuum dropped. We then tried it in reverse and it dropped even faster when we spun the prop. This wasn't expected since it shouldn't make a difference as the driveshaft is spinning the same way. Any thoughts on why that might be? My only guess is that the pinion bearing is wearing and that is allowing the pinion shaft to move a little due to the side loading imposed on it through the forward and reverse gears. The side loading is going to be different between forward and reverse.

 

[Faztbullet]

The 2 piece driveshaft model will leak if rotated due to it not being held in line by crankshaft.

 

[WaveyDave]

@Fatzbullet Agreed! So, I left the lower unit on the engine for these tests. Looking at the tolerance stack-up of this assembly I'm amazed it seals at all.