Late 90's Honda 8HP 4 stroke reduced thrust in gear (engine revs up)...

[seanderson]

Long time lurker, first time poster...

So tonight we were out and decided to explore an inlet with the kicker. Started up, and away we went. All seemed normal. Then there was a (relatively fast, but not immediate fast) sound of the engine reeving up and a lost of thrust (there was still some). I immediately throttled down as low as I could, the engine rpms lowered, and we had normal low rpm thrust. Increased the throttle (slowly) rpms increased, thrust increased, as it went on the same thing happened... engine revs up, thrust decreased.

I tried putting the shifter in and out of gear (F to N to F and F to N to R... F) and the problem was still there.

I do have appropriate thrust at low rpms. It's when more throttle is applied does it sound like its slipped out of gear (although it appears there is still some thrust). Also note that when it first happened there was no sound of anything breaking; just a relatively fast (3 seconds) sound of rpms increasing and thrust decreasing. And also... engine sounds normal at low rpms in forward, reverse and neutral.

Thoughts? Ideas? Suggestions?

Huge thanks in advance!

 

[rogerwa]

Re: Late 90's Honda 8HP 4 stroke reduced thrust in gear (engine revs up)...

Sounds like a classic spun prop hub.. The splines that fit over the shaft are wrapped in a rubber bushing that fits very tightly into the main prop. Sometimes this bushig slips. You can prove it by making aligned marks on the inner part of the prop hub and the outer part. Take it out and run it. When you get back, check the alignment of the marks. If they moved you need a new prop or your hub rebuilt.

 

[seanderson]

Re: Late 90's Honda 8HP 4 stroke reduced thrust in gear (engine revs up)...

Thanks. I will take off the prop this afternoon and make markings and test this weekend. This engine also has a shear pin for the prop, I'm wondering if that has let go... will be checking that of course when I remove the prop. Hopeing that it is just the shear pin!

 

[seanderson]

Re: Late 90's Honda 8HP 4 stroke reduced thrust in gear (engine revs up)...

OK, so the shear pin was ok.

I marked the outer part of the prop and the inner as well as the axle.

The mark on the axle and inner prop were lined up (I think, the inner mark was hard to see) but the outer marking was off.

So thinking that meant a spun prop I called a dealler for a quote. And the parts guy said that this model does not get spun as it has a shear pin and that it would be something else.

Is that possible? I dont trust the parts guy 100% and I'm finding conflicting information online.

Does anyone here know 100% sure?

It's a 1997 8hp Honda outboard model BF8A.

 

[rogerwa]

Re: Late 90's Honda 8HP 4 stroke reduced thrust in gear (engine revs up)...

I couldn't tell you for sure as I don't have that model. Do you see the rubber bushing between the splines and the rest of the prop?? The Mismatched markings would tell me more than the parts guy..

 

[seanderson]

Re: Late 90's Honda 8HP 4 stroke reduced thrust in gear (engine revs up)...

There is no rubber bushings. There are two peices of metal that I'm assuming are pressed into each other, I believe that the shear pin fits into a grove in the inner portion (its not in front of me right now) and the shear pin goes into the axle (of course).

Now it looks to me that the outer portion is no longer lined up with the inner portion and the axle. So I cant see how it can be anything other than something wrong with the prop.

 

[rogerwa]

Re: Late 90's Honda 8HP 4 stroke reduced thrust in gear (engine revs up)...

I would get yourself a new prop. Put it on and if the problem goes away poof you're done. If not, return it and start digging deeper, although I cannot imagine what it could be..