Really dumb question...

[BlueLightSpecial]

Pulled the prop off of my 280 yesterday. First time pulling it. The bolt in the center, that locks the cone down, had some messed up threads. Using a thread guage, I was surprised that the bolt size was 5/16, 18tp. Is this correct? It does thread into the prop shaft, but feels loose in the threads. I assumed, that being made in sweden, it would have been metric. Perhaps someone lost the original bolt, and replaced it with, what they thought was the correct size bolt. I would like to know, so I can run a tap through the hole in the prop shaft, and replace the bolt. One more question: My crappy seloc manual says to use anti-seize on the prop shaft. I have seen on this forum, people saying NOT to use anti-seize, use marine grease. So, Which one do I use? Thanks in advance!

 

[billbayliner]

Re: Really dumb question...

The female threads on the AQ series aluminum drive parts are US N/C threads, and are generally thread inserts [much like a Heli-Coil].
I'd not use a thread cutting tap to chase insert threads. Instead use either a roll-form tap or a very worn cutting tap, and lube it well. You are not cutting threads, you are just cleaning them up. You don't want to catch the insert while trying to chase them.
BTW, both external/internal prop shaft threads are roll-formed threads [no insert].

As for the Anti-Seize, the Marine version is what they are talking about. The automotive version is great for engine threads but it contains conductive materials that will cause problems when used below the water line. You can use marine anti-seize, water proof grease or thread sealant.

Toss that crappy Seloc and buy yourself an OEM service manual.

 

[BlueLightSpecial]

Re: Really dumb question...

Exactly, I have both thread cutting, and thread restoring taps. What about possibly just using a helicoil. I do have a 5/16-18 helicoil kit, since helicoil inserts are stainless, cant see why it wouldnt work. I will try to clean them up first, and see how it feels. Dont really want to replace the prop shaft. Thanks billbayliner, for the speedy response.

 

[billbayliner]

Re: Really dumb question...

I'd not spend too much time trying to save these threads, and risk a failure here.
The 280 prop shafts are just about a dime per dozen these days.
You can change the prop shaft without any change to any shim control values.
This is because all shimming takes place between the driven gear, angular contact bearing and the carrier shim shoulder.
In other words, the sum dimension of the gear/bearing against the control shoulder remain unchanged. The shaft does not affect this.
I know that sounds counter intuitive, but take a close look at one.

 

[SteveMcD]

Re: Really dumb question...

I won't see my 280 until tomorrow, but drilling and tapping the shaft and drilling the cone for a 5/16" might work.

 

[billbayliner]

Re: Really dumb question...

The 280 prop shafts are a carbon steel alloy. I know little about the alloy, but know that these are specially chrome plated to protect them. They are not plated forward of the seal surface area and will rust in this area if left exposed to the elements.
Drilling and tapping threads may open this up to unprotected carbon steel, and you may have rust concerns.
If you need the cone nut locking bolt, the best fix is to install a shaft that is OEM threaded.