Yamaha 2002 115hp 4-Stroke - Question At Idle Speed

[gearyg]

For the first time, I ran my engine on the muffs (I usually only flush it using the attachment). At start up and idle, it sounds fine, but when I shift it into forward -or- reverse at the idle position, I hear a clunking sound, kind of like there is "play" in the transmission or gears, I can also feel it when I touch the engine. However, once I begin to accelerate, it goes away.

Is it that there is no pressure being applied because it is out of the water? And when I increase the RPM's, it is spinning fast enough to eliminate the play?....hope this is normal...thanks.

 

[Yamajoe]

Re: Yamaha 2002 115hp 4-Stroke - Question At Idle Speed

That is normal, the clunk is louder when you engage the shift slowly; use a deliberate fast motion when you shift into gear.

 

[gearyg]

Re: Yamaha 2002 115hp 4-Stroke - Question At Idle Speed

Thanks for the reply Yamajoe. The "clunk" sound is "continuous" while in the idle forward/reverse position (prop spinning)...so it will be clunk clunk clunk clunk etc...until I engage at a higher RPM (so basically it will clunking the entire time it is in that position) . I apologize if I was not clearer in my earlier question, but I understand that it it will clunk when I first engage, but that sound continues, are you saying that this is normal also?...thanks.

 

[rodbolt]

Re: Yamaha 2002 115hp 4-Stroke - Question At Idle Speed

yep, its the propshaft speeding up with inertia remember you only get a powerstroke every 180 of crank rotation so the shaft speeds fluctuate, its worse with a stainless wheel.
if it bothers you remove the prop.
but why shift out of the water ?

 

[andymach23]

Re: Yamaha 2002 115hp 4-Stroke - Question At Idle Speed

When I bought my F40, the dealer ran it on the hose to check it over. When he engaged gear it made a noise like a rattle from the gearbox. When he connected a F100 on a boat that was in for servicing it made the same noise. This was at idle revs. He sent away for a new lower unit from Yamaha as a precaution. When it was fitted it rattled the same.

I concluded that it must be the way the box is. I asked at Yamaha and posted on here about it but did not get a consensus.

I have 120 hours on the motor now with no problems.

Hope this helps

Andy

 

[rodbolt]

Re: Yamaha 2002 115hp 4-Stroke - Question At Idle Speed

ok. ill try simple physics once more, on a 4 cylinder 4 stroke yamaha 1 and 4 move up and down together as do 2 and 3. when one is compressing gas before fireing it tends to slow the crankshaft as 4 has an open exuast valve and 2 has an open intake and 3 is almost at the bottom of its power stroke., if the crank slows, the driveshaft slows, heavy prop is under no such slowdown and rotates the clutchdog teeth,splined to the propshaft, slightly ahead of the dog on the mating gear, now, WHHHOOOOOSHHH bang, cylinder one fires, the crank rapidly accelerates, now the drive shaft speed is faster than the now slowing propshaft, whack, the dogs hit again. process repeats when number 3 is on its way up, then 4 then 2 then 1 then 3 then 4 and so on and so on. the flywheel helps but can only be made so heavy .take the prop off and the noise disapears, ya outta hear some of the V76 motors that only run on 5 cylinders idle on the muffs with a 15X19 wheel.
so yes on certain engines, especially 4 strokes as power impulses occur every other time the piston comes up, some rattle in gear out of the water is normal.
if it bothers you you have 2 choices, remove the prop or dont shift when flushing.
as that EFI motor doesnt cut cylinders in nuetral there is no reason to ever shift while flushing.
only HPDI kills 2 cylinders in nuetral.

 

[gearyg]

Re: Yamaha 2002 115hp 4-Stroke - Question At Idle Speed

Glad to know that it is normal, it actually makes sense now that I think about it and incorporate Rodbolt's responses. Unlike my old boat, I never had to run my Yamaha out of the water, so the first time that I do, I hear a stange noise and begin to freak out about all the $$$ that I may have to spend.

Thanks everyone for the guidance and this forum has been awesome!