Amount of forward shaft movement on 400DA-whats normal?

Skuza

Skuza

Well-Known Member
Nov 1, 2006
1,460
Lake St Clair, MI
Boat Info
400 Sundancer
Engines
7.4L Horizons
This past weekend I stopped by the marina to check on our boat thats still a month away from launch. I was looking at the prop shafts at the cutlass bearing and noticed that there was about 1/2" of polished shaft at the rear of the strut. The polishing is due to the force of the props pushing the shaft forward into the cutlass bearing while running and wearing or "polishing" it. While at rest this wear area comes back out of the cutlass bearing and is visible. I'm wondering how much (if any) forward movement is normal. If there is excessive movement does this mean your engine mounts are getting too soft? There was no side to side movement of the shaft in the cutlass bearing which is orignally what I was looking at. Any thoughts? Boat has 400+ hrs.
 
New one for me.............

Off hand, I'd say you better check the nut on the front of your shaft to be sure it is snugged tight and that the shaft isn't moving within the coupler. Beyond that, it is hard for me to see how you could have 1/2" of movement in the transmission or in loose engine mounts and not notice some odd sounds as the boat runs, particularly when you shift gears......a few .001" 's maybe, but not 1/2".
 
A full half inch? That's an awful lot of movement for something like this. Is it possible something was wrapped on the shaft that caused the polishing? Can you manually move the shaft by push/pulling on the prop?
 
I don't think anything was ever wrapped around the shaft and I did not try forcing the prop shaft forward manually.
I am still betting that this is being caused by the force of the props propelling the boat forward. Remember that all 21k is being pushed by those shafts. My question is the amount of movement and if its normal. I will try and get a picture so this is better visualized.
The boat runs fine with no odd vibrations or major clanking in and out of gear. Can anyone else check their shafts for comparisons? I should have walked around the yard to check out similar boats.
I'm thinking if they are moving that much they are affecting engine/shaft alignment. But how could you accurately align the motors when its done at rest and then changes while under load?
Once the wrap comes off I'll have to check the coupling. I'm not familiar with how the coupling is built and what might cause this type of movement.
 
You are "betting that this is caused by the force of the props propeling the boat......" I think I answered that. Some movement.... 001" - .002" is perhaps normal, but not .500".

Forward/aft movement in the shaft sould have no effect on engine alignment as long as the coupler is aligned in the first place.

If your shaft is moving this much, don't try to fix it with internet forum answers. Get a technician experienced with inboatd boats involved. I'd do it now before it is time to launch because you will probably have to haul out again to diagnose what is going on.

Also, I'm guessing you are in fresh water, but is there any chance there was some type of marine animal that was hitching a ride......I have seen barnacles grow on a strut while a boat sat idle for several weeks then polish a spot on the shaft as Mr. Barnacle wore away......but I have to tell you that boat was in sorry condition and I suspect you would have seen marine growth like that when you hauled out.
 
Frank, thanks again for your reply. I actually look forward in paticular to your replies due to your experience.
There are zebra mussels in our waters but I never noticed any sizeable accumulations on any of the underwater gear during the season. Interesting point though? Have to look into this further and get some pics.
 
Here are pics. Its tough to see but you can see the dark ring near the strut, thats the area that is polished. The amount is smaller than what I thought, maybe 1/4". I checked other boats in the yard and the size of the wear marks ranged from 1/16" up to about the same as ours. This was on about 10 different boats of all makes and relatively new-10yrs old or so. Any further thoughts and can anyone check theirs to compare?
 
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We also have a 400DA and there is no evidence of any forward/aft shaft movement. Double check the coupler as suggested and then get a pro to have a look as Frank suggests. This is very strange..

I just helped a friend pull a 2" x 11' ss trawler shaft that was bent 0.019 in one spot and despite some vibration under way there was still no foreward/aft movement at the strut! (interestingly, the shop straightened it to 0.002 with heat).
Warren
 
I'm getting outside my comfort zone here because photos can be misleading, but I don't think that area looks like a cutlass bearing polished it. I would expect to see a mirror smooth shiney spot....not a blackened stain. So, I'm not sure the shaft is moving forward and aft.
 
SKUZA,

I am pretty shure what you are looking at is the normal movement of the shaft when the engines "load-up" the transmission when the boat is being propelled in the water. If you open up the engine hatch and watch the transmissions when you take off from a dead start, you will see the body of the transmission "flexing" in a forward/upward motion. This motion is enough to cause the mark you are seeing on your shaft. The movement will be especially noticeable when you apply full throttle from a dead start. My 2004 340 sundancer with 8.1 vdrives had the same wear mark as your picture shows and I traced it back to the transmission flexing.

Hope this helps.
 
Frank, the black area is the area that appears slightly polished. Due to the camera and flash it came out looking dark.
I feel slightly better after seeing other boats with the same type of markings but would still like to know what the cause is. Coulda been something that wrapped around the shaft but I would expect to see marks on the cutlass bearing.
 
One other thought of the day is this...Could these marks have become evident due to the boat sitting in dry dock as oppposed to sitting in the water? Maybe the bottom settles and the shafts are pushed out of the strut showing the marks where they usually are while in the water. Couple that along with a little bit of flex and I think theres nothing to worry about. Still would not hurt to ask though.
 
Skuza said:
One other thought of the day is this...Could these marks have become evident due to the boat sitting in dry dock as oppposed to sitting in the water? Maybe the bottom settles and the shafts are pushed out of the strut showing the marks where they usually are while in the water. Couple that along with a little bit of flex and I think theres nothing to worry about. Still would not hurt to ask though.
Click to expand...

Excellent point. Your boat does not have the normal shape sitting on dry land.
 
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