shaft alignment DIY ?

[DAKA]

I am only just getting used to Shafts after outdrives and need a bit of help please.
A cummins mechanic taught me a shaft alignment short cut and I am interested if this method is designed to be a permanent fix or just intended as a quick check........

With the flexible coupling attached, rotate the shaft by hand until it is free.
If it is too tight to move by hand then adjust the mount.

Its very quick to check and very quick to adjust as it saves undoing all the coupling bolts, any comments as to how reliable it is ?

I replaced a rubber mount that looked to be worn and then lowered the mount by 5 mm to allow free rotation, could the 5mm too high mount have caused the rubber to wear ?
There wasnt any noticeable vibration save hard astern.
How significant is lowering a mount 5 mm ?

 

[PaulGooch]

Personally, i think it sounds like it'll get you close enough for a quick fix. I don't think it's a substitute for doing it properly.

 

[RAI]

You may need to check your adjustment after the mounting has settled.

 

[DAKA]

Thats a good point, I 'll get it checked professionally after 5-10 hours use.

 

[volvopaul]

When re engining for example I always start say doing an R n D coupling , like yours by pushing the shafts together with no bolts in, then setting up the flanges with feeler gauges in the gap top to bottom, left to right etc, rotating the shaft to check for no twist in the coupling.

You can then fit the bolts and pull the couplings together, you will see that 1 bolt has a dome headed nut, thats where you can then push in the feeler gauges and take measurements from, ie bigger gap at top the rear end needs lowering, but remember by taking the trouble to set it up withount the bolts in and then pushing together you wont be far out so dont go winding the mounts up and down much, as you will loose the settings you had before.

Do top to bottom an get within the bes you can, then left to right ie 3 oclock and 9 oclock, if thats out then you need to push the whole engine either left or right at the front of the engine mounts, you then of course have to check all 4 points again.

If of course you have a boat like a Trader or Broom with say 1 metre of shaft from the stern gland then there isnt much you can do there is that much shaft whip up and down when the shafts not attatched to the gearbox coupling.

 

[Neil_Y]

Sounds like a good check to me.

If you think about a heavy bendy shaft supported on a piece of rubber (assuming you have rubber bearings) that may have a very heavy prop on the end, the shaft is unlikely to be that straight when sat in the boat. It will also be lower than its running position due to the fact it's sat on the rubber and not a water film and the rubber has some give.

So the accuracy all depends on what position the shaft is in.

Add to this that when you are running in gear the thrust will push the back of the engine causing it to move on its mounts and every wave you hit will cause the engine to move it's all a bit hit and miss. More important for quiet and smooth shafts is the ammount of shaft support and bearing tolerance so you hold the shaft straight and prevent whip.

I for one think the focus on accuracy to less than 0.10mm at the coupling may not be the whole answer to smooth quiet shafts.

 

[macnorton]

You need one of these (or a Purnumeter) to check the engine and shaft (when disconected)are at the same angle,
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=200537192374
Then raise/lower all the mounts together until the flanges line up, it is worth getting it spot on and not that hard to do.

 

[aquapower]

I use a dummy coupling bolted to gearbox and measure round it with a feeler guage as described above, The dummy coupling is a solid coupling machined to be the same as the R&D with the register both sides, without this you would have to remove the prop to get the shaft coupling near enough to the gearbox flange and as alignment should be done in the water would involve a lift out.
The only other problem is if you have the stripper or spurs type rope cutters then you would need to make sure they went back ok after moving shaft back.

 

[hlb]

WE always end up getting a collar made, slide the collar onto the shaft, then bring the shaft as near to the gear box as possible.

When the collar will slide up and down the shaft and the gear box shaft, they must be inline. Simple.

 

[Neil_Y]

I like the collar idea hlb, works the same way as the clearance fit bearings as a bearing carrier check, if it slides in easily the two tubes/shafts are aligned.

 

[hlb]

I've seen mechanics spend hours with feeler guages, then swear the shafts bent. round and round in circles.

Get a collar made, job done in no time. Theres no way you can get it wrong.

 

[DAKA]

Can you elaborate on the collar please........

Do you remove the shaft coupling so the collar fits onto the shaft, and what about the other end, my gearbox has a cone shape plate with holes in it, I dont think that comes off, and cant see how a collar would fit over it



I was going to post in a few days when I have had time to take a photo of the damaged rubber mount.

The 'cummins short cut' alignment method I previously suggested returned a result where one mount was 5mm lower, on checking my vernier thinghy and before and after diagrams I found one measurement was taken from the centre of a centre bolt where the second one was taken from the lower edge of a centre bolt, end result the 'cummins short cut' produced an alignment within a nats cock of the previous tradition method.
Its clear the 'cummins short cut' wouldnt be much use for starting from scratch on a new installation but for a DIY check while floating every other year or after prop fouling , it appears to be a useful check.