Prop question on a 270

[Robert D]

Working on a '72 Chris Craft Lancer, previous owner had it re-powered with a Yamaha 5.7 at a dealership back in '94. (It's a 350 Chevy engine, with Mercruiser manifolds, distributor and such...and a Yamaha ID plate on the rear of the block!) Outdrive is the original 270 with a short shaft. (I'm aware the long shaft is recommended for V8 power....I'll take it easy on it and see how it does before I throw money at replacing the drive!) Anyway, been restoring things like the deck, new carpet, new seats, new wiring, new carburetor, gauges, bilge pump, crank mounted raw water pump, some gel coat work, etc, etc. I'm looking at the prop, it looks original and was about to have it repaired. (Minor damage on the edges of 2 blades.) However, the Michigan number on it is SMC 566, which comes out to a 14 x 12. This would suggest to me it is for a 4 cylinder Volvo application, way too small for this engine. Is my estimation of this correct, or am I wrong? I'm thinking a 260 hp engine in a 19 foot boat should be running something like a 14x21? I'm about ready to take the boat for a sea trial, wondering if I should adapt a 14 x 21 stainless long shaft prop I have sitting around? (I have a couple metal lathes.....can make whatever spacers and thrust washers necessary for a perfect fit.)

Appreciate anyone with specific Volvo knowledge to chime in with your thoughts.....

Also, the shaft threads seem to be a 5/8 x 11 tpi.....I was surprised to find a 5/8 x 11 bolt fit the cone nut! Well, haven't double checked it yet, but I would expect Volvo to be metric?

Note: The drive is the 1.6 ratio.

 

[bluewavecaptain]

Re: Prop question on a 270

My Volvo 280 drive has a 14x19 prop on a Ford V8. It's pushing a 2 ton 25 foot Carver Santa Cruz. Not sure if I would mess around with putting that SS prop on. If so, make sure it has the right amount of splines. Also, make sure there is no play on the prop shaft. If I were you, I'd check out Ebay. Always tons of volvo props on there. The size and pitch of the prop depends not only on the engine, but on the size and weight of the boat. If your boat is maxed out on throttle and still struggles getting up on plane, then you need a prop with a higher pitch. Think of two types of wood screws. A course thread screw takes less turns to screw into the wood than a fine thread screw. If the boat was used for fishing, the PO might have chosen a prop with less pitch to obtain a slower speed at low RPMs. IMO, I would take the boat out and try it out. Try to pick a slightly windy day so you can see if the boat will plane on rougher waters. If your boat handles the way you want without the engine working too hard, I wouldn't worry about it.

 

[captmello]

Re: Prop question on a 270

The prop shafts are the same length, its the props that have the long or short hub. However the way they attach to the shaft is different. The short hubs us a cone, spacer, lock ring setup, and the long hub props use a cone, and center bolt that screws into the prop shaft itself. So if your prop shaft is not threaded on the end your stuck with the short hub prop. Unless you want to drill and thread the shaft...

In this link it shows both setups in one pic. Thats a bit confusing...

Lower Gear Unit: 832701 : 832701 - 7742840 - Volvo Penta

I have a feeling this will be heading to the prop forum, but fwiw, I've got a 350 in a 20'runabout and I use a 21" pitch prop. a 10" isn't going to be right. Maybe recheck the numbers on the prop or bring it to a prop shop to confirm the pitch.

 

[jerryjerry05]

Re: Prop question on a 270

Does the drive still have the Volvo tag still on it?
It's in the area where the shift cable goes through from the front.
Before you spend lots of $ take the boat for a ride?
Check performance?
You should be able to get to about 4400rpms.Then prop up or down from there.
A 14x12???? or you have the #s transposed?
I have a stainless 19 if interested.L or R

 

[Mullin]

Re: Prop question on a 270

My 4 banger volvo aq125a/270 came stock with a 14r19. I also have a 17 and 15 pitch prop, don't use the 19 anymore, even at sea-level. It's a short shaft model, don't know if that pitch is what you want but I'd consider selling it.

 

[Robert D]

Re: Prop question on a 270

Thanks for all the replies! I verified the pitch on the prop the previous owner had on there, so I called him down at Lake Tahoe and asked him about it. He preferred the prop for trolling...said at an idle, it would just creep along, but said you have to be careful with the throttle so as not to over speed the engine. Said the original prop was a 14 x 21, and he trashed it on some gravel.

I tend to go overboard on fabricating things, so here's what I did: I ended up spending the afternoon on my lathe, making a proper thrust bushing from some solid round bronze, so the stainless prop comes right up to 1/16th of an inch to the lower unit housing. A thick stainless steel washer on the back side, custom made so I have just enough threads to tighten the 5/8 x 11 stainless nut and the end of the shaft is flush with the end of the nut. The I drilled the nut for safety wire. I took the prop shaft and drilled and tapped it for a 5/16 x 18 lock bolt. I used a stainless steel allen head bolt. I made a piece that goes over the diameter of the 5/8th nut, and drilled the head of the allen bolt for safety wire as well. (Old habit from working on F-15's years ago.....) Machined a groove in the 5/16th's bolt for an 0-ring, to ensure no water enters the threads in the end of the shaft. Some blue Loctite, tightened it down against the 5/8th's nut. Proceeded to safety wire the 5/8th's nut to the 5/16's lock bolt, running 8 twists per inch. (Per McDonnell Douglas specs on the F-15D model I should add?) Lock bolt...in case the blue Loctite doesn't hold, can't unscrew as it's safety wired to the 5/8ths nut. The 5/8th's nut can't rotate unless the lock bolt gets unscrewed......I have pretty good confidence my prop is quite secure I'll keep the 'trolling prop' in the ski locker with other assorted spare parts.