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stooy

Check your shaft alignment !

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stooy

G'day Guys,

A few weeks ago my brother and I purchased our first Malibu a 2007 VLX with the monsoon engine. On our first trip out less than 2 miles from the boat ramp the prop shaft broke for no apparent reason, we hadn't hit anything etc. Needless to say we were very annoyed !

When we looked into it, it turned out the shaft alignment was incorrect. I think (if my memory serves me correctly) our engine was out of alignment to the shaft by .012" the factory spec is no more than .003" Over the 315 hours our boat had run this had caused the shaft fatigue fail.

We have since replaced the shaft, repaired the prop and re aligned the engine and all is well.

Here are some pics of the broken shaft.

BrokenPropShaft.jpg

BrokenPropShaft1.jpg

Moral of the story make sure your mechanic does his job and checks your shaft alignment at the 20 and 300 hour services!

Second Moral, if this does happen to you remember to lift your v drive cover and put your hand over the hole where the prop shaft has dropped out from, water comes in very quickly!

Cheers

Stewart

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TalleyHo

Ouch!

Is there any practical way for an amateur mechanic to visually verify this? I've crossed the 300 hour mark and have been doing my own maintenance while we get our finances in order. I'd prefer to avoid having to figure out how to deal w/ an expensive repair like this one. I'm assuming the dealer has a nice tool to verify something within that tight a tolerance.

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obski

I've had that happen twice. It was the from a misaligned engine.

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Ndawg12

I know you need a feeler gauge to check shaft alignment but what about the engine? I would love to see a full comprehensive write up on engine and shaft alignment in the resources section.

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stooy

It's not too complicated, I found a PDF of a Mercruiser manual my brother used to do the job.

Basically you unbolt the shaft coupling and use a feeler gauge to confirm the gaps at the top, bottom and two sides.

I will see if I can find the link to it.

Cheers

Stewart

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jkendallmsce

Ouch!

Is there any practical way for an amateur mechanic to visually verify this? I've crossed the 300 hour mark and have been doing my own maintenance while we get our finances in order. I'd prefer to avoid having to figure out how to deal w/ an expensive repair like this one. I'm assuming the dealer has a nice tool to verify something within that tight a tolerance.

not unless your eyes can measure down to 0.001 inch.

Get a feeler gage...they're pretty cheap, and much cheaper that haivng to replace the shaft. the whole process to check alignment takes 1/2 hour...if the alignment is ok.

Edited by jkendallmsce

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Ndawg12

not unless your eyes can measure down to 0.001 inch.

Get a feeler gage...they're pretty cheap, and much cheaper that haivng to repalce the shaft. the whole process to whck alignment takes 1/2...if the alignment is ok.

do what now? Please explain..??

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REW

do what now? Please explain..??

Feeler gage, any autoparts store will have one. Basically it is a set of standard thickness sheets of metal that are marked with the thickness of the sheet. not very expensive and easy to use, just keep sliding thicker pieces in until you can determain the thickness of the gap. Get you hands on one and you will understand.

the alignment is measured at the top and bottom of the shaft coupler when unbolted. The gap should be the same all around, if it is not then you can adjust the motor mounts to make it right.

I have seen this proceedure somewhere but I can't remember where.

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Woodski

It has been posted on this site, I did that quite a while ago but don't remember the specific topic.

Unbolt the coupling, make sure one side or edge is touching and measure the gap 180 degrees across with a feeler gauge (needs to be .003" or less). You will want to do this in at least two planes (vertical and horizontal). I also check to see if the engine is at the correct height by sliding the coupling off and on the flange and make sure you don't have to force the coupling up or down to slide it on (you will have to lift slightly to offset the weight of the coupling and shaft). If you determine the alignment is not correct, you adjust by the 4 engine mounts. The engine mounts allow you to raise/ lower/twist the engine itself with the upper and lower nuts on each of the 4 motor mounts, simply adjust in the direction needed. Rotation is also adjustable to correct for misalignment via the engine mounts. Remember to peen the anti rotation tabs back down when finished. Good luck, take your time the first time.

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Mechmaster
billb

OK, I don't mean to be dense, but sometimes I just can't help it. :) What is controlling the gap in the coupler when the bolts are loosened? It seems like the two pieces would separate based on how far out the bolts are backed out. So you could back the bolt on the top out .005 more than the one on the bottom and the gaps would be different, right? I'm sure some of this will get clearer when I look at it on the boat, but I'm having a tough time figuring out what is controlling the gap. I get that the gap needs to be the same all the way around.

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Woodski

Bill, You are correct when the bolts are loosened the coupling can separate itself. You can simply use one bolt to bring that edge together but do not tighten more than finget tight because you don't want to put any compression load on the coupling. You can always do the same using two feeler gauges and measure the difference, but a single one is much easier with one edge of the coupling touching.

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areamike

Hmmm..and to think, I only clicked on this topic thinking it was not kid friendly based on the topic title...

"Check your shaft alignment !"

How sick am I ? :unsure:

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nyryan2001

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nyryan2001

or grab a pair of vice grips and clamp on so your junk doesnt sink to the bottom with a $500 propellor attached.

163488736_65ac03b232_z.jpg

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stooy

My Trouble was it broke while driving so it slipped down before i had the chance to get a hand on it. Fortunately it only hit the rudder and didn't sink to the bottom.

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WoodyBC

My Trouble was it broke while driving so it slipped down before i had the chance to get a hand on it. Fortunately it only hit the rudder and didn't sink to the bottom.

(Wondered how you had both pieces) :clap:

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