Need help with my confusion :)

[robinlh]

Ok ... I have a 1989 Bayliner with a Force 125hp L-Drive ... and a couple of questions. First, I know that there are only 2 props I can use ... FP686 which is 19pitch and FP685 which is 17pitch ... not sure which I have now but I will look in a few. Which would any of you recommend?

Thru hub exhaust or not ... thru hub to mean would be THRU the hub of the prop ( could be wrong ) ... the exhaust on my current is above (or appears to be to me) the prop. But when I look up the above 2 part numbers for the prop ... "some" sites show it as thru hub exhaust.

What parts need replacement besides the prop itself? The prop nut? washers? ...etc etc?

And finally ... any special tools I need to have on hand?

Thanks as always guys!

Robin

 

[Silvertip]

Re: Need help with my confusion

Without any data to work with we can't tell you which prop is best. Your engine needs to run at the manufacturers recommended rpm band at wide open throttle. Since you have not provided maximum speed and wide open throttle rpm we have nothing to work with. It may be neither prop is acceptable. Through hub exhust is exactly that -- exhaust exits the engine through the hub of the prop. Make some wide open throttle runs with both props and note the maximum speed and rpm for both. Then post back with the results.

 

[robinlh]

Re: Need help with my confusion

I will see what I can do. WOT is not what it should be right now (we are working through the trouble shooting process). But, the prop is bent which isn't helping things. Right now, "top speed" is about 22mph (I am waiting for my son in law to call back with the rpms at WOT) He is going to check compression. In essense it's running good, but not as fast as it should be. (I better stop, cuz this is the prop thread).

I've attached a picture of the prop ... I can't find anything on it that tells me which one it has now.

Which brings my other question ... if the exhaust isn't through hub, why do these 2 props FP686 and FP685, both show up under the thru hub exhaust?. I was hoping to order a new prop and at least cross the bent prop off my list ... but it's seeming like it's not so easy.

Help.

 

[Silvertip]

Re: Need help with my confusion

I'm certainly not an expert on your engine but it appears yours is not a through hub exhaust as it appears by the picture exhaust exits in back of the prop. However, that does not mean the prop can't be a through hub style and it would appear in your picture that it is. If you don't have the engine running right, do not start looking for props. The prop you have is not bad enough to prevent getting the engine running right.

 

[Frank Acampora]

Re: Need help with my confusion

Some Force outboards used a dual exhaust lower unit; exhaust exited through the prop hub and through the exhaust snout. To the best of my knowledge, the L-Drives were not dual exhaust. I could be wrong though; be aware that the L-Drives were a completely different animal. However, if the L-drive is similar to the outboards, if the water pick-ups are on the torpedo (gearcase) in line with the prop shaft and behind the prop hub, then it is a single exhaust with no thru hub exhaust.
The thru hub exhaust prop should work on any lower unit (before Merc changed 'em). The splines, hub diameter (4 1/4 gearcase), and hub length are the same for all earlier outboards.