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Author Topic:   170 stainless prop problem
fitn217 posted 05-08-2004 03:31 PM ET (US)   Profile for fitn217   Send Email to fitn217  
I recently purchased a 20" pitch laser II prop for my 170 montauk 2 stroke 90. At speed the prop runs great BUT at idle speed and slow speeds the prop seems to bang around and cause more vibration whereas the standard aluminum prop is as smooth as silk. Has anyone else experienced these same problems when switching from an aluminum prop to a stainless prop?
MantyMonty posted 05-08-2004 05:26 PM ET (US)     Profile for MantyMonty  Send Email to MantyMonty     
I run the Laser II also, and it is smooth as the aluminum one. Even seems there is less of a clunk than that of an aluminum prop. Maybe I shift it from N-F-N-R differently with more water time under my belt too.
fitn217 posted 05-08-2004 09:02 PM ET (US)     Profile for fitn217  Send Email to fitn217     
Monty, I think you misunderstood. When shifting into gear it's just a ssmooth as the aluminum. The increased vibrations and banging around occur when the boat is in gear and the prop is turning at idle speed (the slowest speed possible when in gear).
fishgutz posted 05-08-2004 10:12 PM ET (US)     Profile for fishgutz  Send Email to fishgutz     
Check your hub setup if its the Flo-torqII make sure you have all the parts properly installed, the thrust washer may be on backward. Also make sure its the right thrust washer. Make sure the nut is properly torqued and the tabs on the washer bent into the grooves usually only 3 or 4 tabs can be bent. Hope this helps. If one prop works then the other should work the same (at slow speeds anyway).
Clark Roberts posted 05-09-2004 07:28 AM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
Fit, sounds like what's called "gear lash" caused by low (in gear)idle speed. The flywheel effect of the heavy SS prop is causing prop to drive the gears momentarily (sp?) and the sound is amplified by the motors mid-section. Try increasing idle rpm a bit (100-200 rpm) and that should take care of it but it may clunk a little when shifting. Also removing about an eight of an inch off each blade tip(reducing prop diameter by 1/4") may help and this will raise the max rpm by approx 100. Note: your engine idles on timing only (carbs are not involved) and adjustment is via one screw on timing link on engine's port side. Be sure you locate correct screw either by shop manual or advice from someone... soooo easy to do once you've done it! Happy Whalin'.. Clark.. Spruce Creek Navy
PS>Seems to me that 20" pitch is a bit too tall for the 90hp 2 stroker (even with the 2.3:1 lower unit ratio). If engine won't turn 5500rpm at wide open throttle (trimmed out) then pitch is too high. Rule of thumb is that one inch of pitch will net 200rpm either up or down. If you cannot reach 5500rpm then you may want to get a lower pitch as that may have some bearing on the "gear lash".
AQUANUT posted 05-09-2004 08:38 AM ET (US)     Profile for AQUANUT  Send Email to AQUANUT     
good post clark!

but I am wondering, if you are retired, where from?.

and how are you getting your hands on mercury service bulletins..and tech

most 90hp carb model 2 srokes we deliver get a screw adjustment for low idle. merc tech bulletin.
every single one of them I start in "the cement pond" runs differently at idle initially.

fitn217 posted 05-09-2004 08:57 AM ET (US)     Profile for fitn217  Send Email to fitn217     
Clark, with this prop I'm getting 5400 rpms at full throttle, with max rpm being 5500. This prop is also the one that everyone here and mercury recommends for the 170 montauk.
I don't think I will alter the prop but I will try to increase the idle 100 rpms via the timing link screw. At the present time I removed the laser II and put the aluminum prop back on.
I was curious however to see some feedback from other 170 owners who have also installed this prop and if they have the same symptoms that I am having.
Thanks for your help Clark.
Sal DiMercurio posted 05-09-2004 08:07 PM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
I agree with Clark.
Thats alot of pitch for that engine to be twisting on that boat.
Unless your engine is mounted "WAY" up, I think I'd check your tach.
Swellmonster posted 05-10-2004 11:06 AM ET (US)     Profile for Swellmonster  Send Email to Swellmonster     
My 225 EFI had the same noise at low idle, in gear. It was called clutch rattle. Switched props down to a lighter SS prop and the noise went away. I talked to several people, dealers and Merc and they called it clutch rattle.
fitn217 posted 05-10-2004 02:28 PM ET (US)     Profile for fitn217  Send Email to fitn217     
Guys the original prop that came with this motor is a 21" pitch aluminum. I chose the laser II in 20" pitch because most people here and the mercury dealer said it would be the prop for my boat.
All I want is to get the best gas mileage, good mid range cruising capabilities and good holding power in rough water as the 21" pitch standard aluminum prop blows out every so often.
My knowledge of props is nil and I know I am naive in this department but it doesn't make sense to me why I would have to change timing or shave down blades to achieve getting a Mercury prop to work with a Mercury engine especially since the dealer recommends this prop for this engine. I paid the extra bucks for the Mercury prop so I wouldn't have to deal with issues such as this.
I have heard guys mention raising the motor. Would this help me out? Like I said I don't know too much but I think raising the motor one set of holes would cause it to blow out more. I'm not interested in speed, I want good holding power and good gas mileage.
Guys, what in your opinion would be a good prop for the 170 Montauk with 90 two stroke motor, that would give me the performance I am striving for.
Bigshot posted 05-10-2004 02:38 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
You sound like you are propped properly:) I would have the dealer let you try another prop, especially being you only need to idle it. Your idle may be too low and it will act like a car "lugging" in the wrong gear.
CHRISWEIGHT posted 05-10-2004 04:16 PM ET (US)     Profile for CHRISWEIGHT  Send Email to CHRISWEIGHT     

we have a mercury 90 2s with a 22p lazer prop on an sl16 pulls 5300 @ wot 43 mph gps. so I think the 20p should be fine, our engine is mounted about 1.5 inches above the transom bottom.

have not noticed any rattling noises but prop came on this engine so nothing to compare, but I seem to remember a similar post previously commenting on just this problem and I believe most posts on the thread saying that unless the rattle was severe that there should be no problem.

regards chris.

Clark Roberts posted 05-11-2004 11:57 PM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
Aquanut, yes retired from GE after fooling them for 30 years as Human Engineer/Human Factors Engineer/Lead and Project Engineer etc. I have no access to Tech/Service bulletins and am no expert but happy to share opinions and tips with all!
Happy Whalin'... Clark... Spruce Creek Navy
LHG posted 05-12-2004 06:22 PM ET (US)     Profile for LHG    
A Mercury technician recently told me the 2-stroke 90 is really putting out about 100 HP, whereas the 4-stroke and Optimax 90's are a true 90. To meet 3 star emission standards, HP is now kept to the rating, as underrating an engine makes it more difficult to meet emission requirements (higher HP engines put out more emissions).

All of this makes the NMMA 10% plus or minus rule bad news for consumers. Now, you never get more HP than you pay for, but still can get less! As a matter of fact, to meet emissions, there is even incentive to give you less, since emission levels are keyed to rated HP output!!

This is also why the Mercury 225 EFI is known to be faster than the 225 Optimax. The EFI is really a true 240 HP, while the OPTI is only a true 225.

This is also why the performance figures on the new Nantucket show the 115 2-stroke to be more powerful than either the 115 4-stroke or Optimax. The 2-stroke is under-rated.

In a recent dyno test done on my 1985 Mercury 115 in-line 6's, they discovered the engines are still putting out 125 true HP!

This has been Mercury's approach almost since day one, but the new emission standards may now change all of this

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