280 Fill Port and Prop Cone Bolt

'Messing with my newly acquired used 280...it's a little different than the 250 currently on my boat.
The 280 didn't come with a prop cone bolt - it looks to be 5/16 18 UNC? Would any stainless allen be OK? How long?
It's nice to have the fill port on the 280, but unlike most oil fill ports I'm familiar with, this one seems to be too high to overflow at the proper level...that level would be well above the flat part of the dipstick - or maybe the dipstick is from another model? Dipstick or fill port?

Yes, the spinner center locking bolt is 5/16" NC, but since I'm not near my shop, I can't tell you the length.

As for the fill port, give the new gear oil a few minutes to rise up into the hollow cavity of the vertical shaft, then take your dip stick reading.


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The factory center bolt has a blob of nylon in the threads near the end to act as locking mechanism ala a "nylok" nut.
Rick is correct about filling, but I should add that on some dipsticks the oil level is almost impossible to see with some light colored or almost clear oils. This is worsened (at least on my dipstick) by the fact that there is no crosshatching on the dipstick to make the oil easier to see.

FYI...... the nylon device also creates a weak area in the bolt. Should it ever become corroded in place, it will most likely snap at that location.
I prefer the older style without the nylon locking device.


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I know about the hard to read dipstick...especially if the level s below the dipstick and the true reading is disguised by oil bleeding in from the sides. My engine dipstick is kinda like that - it only reads correctly from one side. So...I use a 500 watt shop light to get the level reading from the dipstick and I check both sides. The oil level on the acquired drive is at least 1/4" below the fill hole but shows about 1/2" above the high mark on the dipstick. That's why I was asking about whether the fill hole overflow or dipstick should be used.





As for the cone bolt - I got a 2 1/4 and 2 1/2. I won't know if these are correct until I try to mount the prop. I just want to be sure I have enough meat in the threads for the bolt to work properly. I did play with the cone and bolt a little - if the bolt is just a hair loose, when the cone backs up to the bolt it binds up tight...not convinced I'll need threadlock?

And speaking of props - has anyone seen one like this? It got banged around during shipping with the 280 and is aluminum. I just never saw one with the rectangular openings before, and there are no stampings to indicate pitch? I don't plan to use this prop -- just curious about it.

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jeffnick said:

I know about the hard to read dipstick...especially if the level s below the dipstick and the true reading is disguised by oil bleeding in from the sides.
Try making some cross-hatch marks on the flat area... it may help you see the oil.

The oil level on the acquired drive is at least 1/4" below the fill hole but shows about 1/2" above the high mark on the dipstick. That's why I was asking about whether the fill hole overflow or dipstick should be used.
The correct gear oil (30W engine oil for the s/p drives) quantity will read at about half way up the flat area.

Not sure what level your red arrows are pointing to. Oil at this level would indicate over-full!
The transmission wants air space as to accommodate heat expansion. (the slinger pump will ensure upper gear/bearing lubrication and cooling)

View attachment 10597

As for the cone bolt - I got a 2 1/4 and 2 1/2. I won't know if these are correct until I try to mount the prop. I just want to be sure I have enough meat in the threads for the bolt to work properly. I did play with the cone and bolt a little - if the bolt is just a hair loose, when the cone backs up to the bolt it binds up tight... not convinced I'll need threadlock?
In theory, with both the spinner and the center locking bolt tightened, the two "un-like" thread pitches won't allow the backing off of either.


And speaking of props - has anyone seen one like this? It got banged around during shipping with the 280 and is aluminum. I just never saw one with the rectangular openings before, and there are no stampings to indicate pitch? I don't plan to use this prop -- just curious about it.

This is a short hub prop with the large blades..... sometimes called the "Elephant Ear" prop.
The slots in the outer propeller hub are there as to have access for folding/bending the locking tab washer ears over into the castellated area of the spinner.
With exception to the 250/270 drives (exhaust housing outlet conflict), this propeller will fit 275, 280, 285, 290 and SP s/p lower units. (SP = drive type....... s/p = single prop)

Not that you asked....... but keep in mind that the prop shaft spacer/line cutter size is determined by the drive designation........ not by the propller style.
250, 270, 275 prop shafts require the short spacer/line cutter.
280, 285, 290 prop shafts require the long spacer/line cutter.
When correct, each nets the same length of exposed prop shaft and splines.

Click to expand...

re: "I know about the hard to read dipstick...especially if the level s below the dipstick and the true reading is disguised by oil bleeding in from the sides.
Try making some cross-hatch marks on the flat area... it may help you see the oil. "

I tried doing this last spring the day before launch with a file. Not particularly successful. Next spring, will bring dip stick home, chuck it in a bench vise and have at it with my DeWalt sander and 80 grit paper.