Tapping noise, low rpm, lower, BF15

I swear everything I have bought off craigs has had some type of issue. It doesnt matter how close I inspect them.

So my bf15 has a tapping/knocking noise just about idle coming from lower unit. If I raise throttle a couple hundred rpm it goes away. It mainly does it as I pull away from dock or slow down in no wake zone.

I just put a new 9.75 prop on as it had an 8. Im going to change the prop back to the 8 and see if it does it.

Can you guys give me some ideas of what to look for?

Update---------------It does not make the noise out of the water running on a garden hose. Going to test old 8 prop this afternoon when it cools down a bit. Blasted heat wave here in N ID

Last update. The 4 blade stock oem honda 8 pitch got rid of the problem. I want to thank all who pitched in with advice and help.

Well....I don't see any replies so I assume that your last comment was a somewhat facetious one.

If so, touche! ;>)

I was waiting (as I suspect others were too) to see the results of your plan to go back with the old prop.

If it hadn't worked, I might have suggested that you try installing a new thrust washer. Actually, I would still suspect that the thrust washer might have been at least part of the problem.

It can be hard to detect the wear on an old thrust washer until you have a new one to compare it with side by side or if you have the dimensions and can accurately measure the height.

The thrust washer is also installed BASS-ACKWARDS about 50% of the time.

The increased pitch of the replacement prop probably set up a "pulsating" thrust condition that caused the knocking noise. Something a new thrust washer might have prevented.

While on the subject, MY last comment is about prop shaft seal damage and checking the thrust washer. Because, most prop shaft seals fail prematurely because the prop and thrust washer aren't ROUTINELY removed and checked for damage and wear along with removing any debris that wraps around the shaft. Which, by the way, is typically monofilament fishing line.

I do have a discombodulated fragistat question as long as we are on the topic. I did notice that once torqued to spec i can move both props in and out about an 1/8th to a quarter inch with the honda prop being less. I think its the shaft moving in and out not the prop sliding back and forth. Does that mean i need to replce the pstw? When i move it in it feels slightly spring loaded.

Good on you catching my slight.

Also while i have your attention. The 4 blade honda prop is 8 pitch. Boat does 19mph at high rpm. The 3 blade mich. Prop is 9.75 pitch. Boat does 19/20 mph slightly less rpm. Should i buy honda 4 blade 10 or 11 pitch? Boat is 14ft mirrocraft deep sea fisherman semi v. Boat is empty with me and wife, combined weight 285.

Well, I don't know what a pstw is but a small amount of lateral movement of the prop shaft is normal. The "springy" feeling when you push it forward is also normal as that is the shift spring pushing the slider pin against the shift selector rod end in the front of the gearcase.

I don't have any specification limits to give you for how far the shaft should move because I've never seen any published. Suffice it to say if she shifts ok and doesn't make a bunch of racket then everything is probably just fine.

I don't have a lot of experience straying from the original Honda props but you might want to measure the depth of the two hubs and compare them. If they are different lengths then that would explain the difference in movement you're seeing. That and possibly a worn thrust washer.

I can't answer your question about what prop to buy but if you're looking for increased speed I don't think you have much left to gain with the 15hp on that hull. My opinion is that at 19mph you're gettin' all your gonna get with that combo. I suspect that hull needs a 40 to 50hp to get up on plane and really scoot.

Just my opinion though.

Good luck.

Pstw= prop shaft thrust washer.
Rodger that on low hp max speed with boat. Transom is rated 35hp. Im going to buy honda 10 pitch 4 blade to lower rpms. The bf 15 is sold with 8 for trolling and 10 for normal boating.

I will also replace pstw. Thanks for help.

Of course! Short hand for thrust washer! Or "tw" for REALLY short hand.

I don't know if you have an A model or a D but if it's a D, there are several prop options available. See in the link below.

https://www.boats.net/catalog/honda...hp/bf15d3-shga-2003/propeller-shaft-propeller

It looks like the A model only came with a 9 1/2" X 9 1/2" though.

I think Michigan Wheel has a prop selection guide on their website and I know several of the other prop manufacturers will answer questions about what might get you the performance you're looking for.

Good luck

jgmo said:

Of course! Short hand for thrust washer! Or "tw" for REALLY short hand.

I don't know if you have an A model or a D but if it's a D, there are several prop options available. See in the link below.

https://www.boats.net/catalog/honda...hp/bf15d3-shga-2003/propeller-shaft-propeller

It looks like the A model only came with a 9 1/2" X 9 1/2" though.

I think Michigan Wheel has a prop selection guide on their website and I know several of the other prop manufacturers will answer questions about what might get you the performance you're looking for.

Good luck

Click to expand...

Its the D. 9.25x 7/8/9/10/11. Honda only for me as the 3 blade Michigan is the road-apple that caused the issue to begin with. Also the 4 blade launches the boat to plane in about 3 seconds and the 3 blade took at least double that. No gain for 3 blade and only bad. Knocked, cavitated, no speed increase.

Here is our lake and the 8 pitch running 19mph.

Yeah, props are expensive to "try out" and confusing as to what works best. You can't return them either. But, there are some shops...very few I suspect...that will let you try out an alternative if they have a used one lying about. Finding THAT shop is the hard part.

Sometimes though all you can do is bite the bullet and spend the money to satisfy your curiosity. As you just did.

That's pretty much why I don't get into recommending prop replacement choices. I don't think I'm knowledgeable enough on the subject.

There's a line in an old song that goes:
"and if ya got money, ya got lots of props"...er...uh...wait....that's not how it goes!
But I think you get my drift ;>)

jgmo said:

Yeah, props are expensive to "try out" and confusing as to what works best. You can't return them either. But, there are some shops...very few I suspect...that will let you try out an alternative if they have a used one lying about. Finding THAT shop is the hard part.

Sometimes though all you can do is bite the bullet and spend the money to satisfy your curiosity. As you just did.

That's pretty much why I don't get into recommending prop replacement choices. I don't think I'm knowledgeable enough on the subject.

There's a line in an old song that goes:
"and if ya got money, ya got lots of props"...er...uh...wait....that's not how it goes!
But I think you get my drift ;>)

Click to expand...

I found a site that had oem honda 4 blades for 1/2 price. I got the 10 and 11 pitch. Im thinking the 10 will work with me and wife. The 11 when its me and the dog. Probably keep the 11 on most of the time.

The song that mostly matches my life would be "Send lawyers guns and money, Im stuck inside this jail". Which is in close second to "88 lines about 44 women". Must not forget "burning ring of fire".

Sorta like Spinal Tap..."goes to 11"....