9.8 2008 Nissan/Tohatsu off-idle howl/screech?

[gary - k7gld]

I have a new Nissan/Tohatsu 4-stroke outboard - short shaft, manual start. It only has several hours break-in time on it, and seems to be a great and extremely quiet motor - other than a noticeable and consistent howling or screeching noise at a narrow band of RPM just off-idle.

It appears to be coming from the area of the camshaft pulley/belt, and I suspect some sort of RPM resonance - hopefully just due to being all new components, and something that will "seat in" and go away with a few more hours running time?

I asked an online Nissan tech about this issue, and he agreed with my suspicion - but I'd like to hear if other Nissan/Tohatsu 9.8 owners have also observed this - and if it DOES eventually go away? It's not real loud - just noticeable, and I'd really like it to not be there, especially on so otherwise a great and quiet motor!

I've removed the timing belt cover, and observed the belt as the engine runs - it's all centered well, and no dragging or rubbing on other adjacent components.

IF it doesn't go away on it's own with more hours use, will belt dressing help - or are there other "cures" available?

 

[TOHATSU GURU]

Re: 9.8 2008 Nissan/Tohatsu off-idle howl/screech?

We have run a bunch of them over the last 4 years and I can't remember any of them having the noise you describe. I would urge you to take it into a dealer and let them determine if you have a problem or not.

 

[gary - k7gld]

Re: 9.8 2008 Nissan/Tohatsu off-idle howl/screech?

We have run a bunch of them over the last 4 years and I can't remember any of them having the noise you describe. I would urge you to take it into a dealer and let them determine if you have a problem or not.

Unfortunately, this is a remote area, and ANY boat motor service or sales is a long ways away. Strange thing is, the "howl" is ONLY at a very narrow RPM band, just above idle - all other engine speeds are totally quiet. Only other possible suspect, might be the rope start mechanism, given that the noise SEEMS restricted to the immediate topside of the motor...

And I should again emphasize, the "howl" is NOT real loud - it's just THERE! It's the same sort of noise that's somewhat common in V-belts running too loose under load on a car's alternator or steering pump - and seemingly coming from the same sort of location on my outboard - just a different type of belt.

 

[duncannon]

Re: 9.8 2008 Nissan/Tohatsu off-idle howl/screech?

I have a 06 9.8 hp Tohatsu and a 08 8hp Tohatsu and both have a low rpm whine, just a little above idle. It is very noticeable.

 

[gary - k7gld]

Re: 9.8 2008 Nissan/Tohatsu off-idle howl/screech?

I have a 06 9.8 hp Tohatsu and a 08 8hp Tohatsu and both have a low rpm whine, just a little above idle. It is very noticeable.

AH! Thanks - maybe I'm not alone or going crazy after all!

I gather that in your case, the whine never went away as engine hours increased? It's not really a great issue - as long as timing belt whine is ALL it is!

Probably would never hear or notice it - if the rest of the engine wasn't so quiet!

 

[duncannon]

Re: 9.8 2008 Nissan/Tohatsu off-idle howl/screech?

Gary, neither motor has a lot of hours and since I'm use to the whine, I pay little attention to it. Good luck.

 

[pvanv]

Re: 9.8 2008 Nissan/Tohatsu off-idle howl/screech?

I also have this whine or howl on my 9.8 Nissan long electric remote (NSF 9.8 A3). The motor is almost new, just approaching 8 hours on the hour-meter.

It's around 2200 on the tach. Goes away at idle, and goes away above 3,000 RPM. It's not always there -- but usually is -- might be dependent on whether the motor is under heavy or light load -- not sure yet. I did not notice it at under 1 hour on the motor. Since the motor is in the lazarette well on a sailboat, it sometimes resonates through the entire cabin, and is very noticeable.

Not sure whether it's a "whistle" in the intake system or some sort of belt or bearing issue, but, so far, it doesn't seem to be causing (or the result of) any catastrophic problem. A thorough inspection has shown no problems yet.

Since it is the off season in Buffalo, I won't know more about this particular motor until May.

If anyone nails this down, I'd love to learn more about it.

 

[gary - k7gld]

Re: 9.8 2008 Nissan/Tohatsu off-idle howl/screech?

Thanks guys, for confirming my own experience and suspicion - just as the reply direct from the Nissan tech did. So far, haven't heard from the owner of a high-hour motor, to see if this goes away after more hours - but if not, I'll try some belt dressing on the timing belt to see what effect it has.

I certainly can't speak for all affected owners, and hate to create the impression or fear with prospective buyers reading all this, but this seems to be a very SMALL issue, and one that in no way otherwise detracts from a very nice and quiet running outboard!

It's far more a simple curiosity, than any serious concern.

 

[simplystressed]

Re: 9.8 2008 Nissan/Tohatsu off-idle howl/screech?

I notice this sound on mine especially after changing props. Doesn't sound like it is a mechanical issue but would be nice to deadenen or reduce the whine at certain rpms.

 

[pvanv]

Re: 9.8 2008 Nissan/Tohatsu off-idle howl/screech?

Some of the 9.8 motors have this characteristic. It has been diagnosed and tested to the Nth degree, on several motors... on my own boat... here in my test tank... by the National Service Manager in the tank at Tohatsu America... and by the Japanese engineers from Tohatsu. It has nothing to do with the timing belt. The sound is a harmonic resonance in the intake. In essence, it is a whistle, not unlike blowing across the opening of a bottle.

What we have done to get around the issue is to change props so that cruising is not at that (approximately 2,000 - 2,500 RPM) speed. In your case, stressed, you changed props and ended up cruising precisely AT that speed, so you are noticing it more. What pitch are you running?

 

[simplystressed]

Re: 9.8 2008 Nissan/Tohatsu off-idle howl/screech?

What we have done to get around the issue is to change props so that cruising is not at that (approximately 2,000 - 2,500 RPM) speed. In your case, stressed, you changed props and ended up cruising precisely AT that speed, so you are noticing it more. What pitch are you running?

Currently running the 3 blade 6.5P @ 5300rpm. Using the stock prop I don't recall it doing it last year, but I'll swap out and see. Doesn't seem to move it any faster with either prop as I'm around 6-6.5mph hull speed so not upset if I have to use the stocker...although would be nice to get optimum RPM's

 

[pvanv]

Re: 9.8 2008 Nissan/Tohatsu off-idle howl/screech?

Currently running the 3 blade 6.5P @ 5300rpm. Using the stock prop I don't recall it doing it last year, but I'll swap out and see. Doesn't seem to move it any faster with either prop as I'm around 6-6.5mph hull speed so not upset if I have to use the stocker...although would be nice to get optimum RPM's

If you are pushing a displacement hull (sailboat), you could try a 4-blade HT prop. I have a 5-pitch on the shelf, if you would like to try it. That might get you closer to 6,000 WOT.

 

[simplystressed]

Re: 9.8 2008 Nissan/Tohatsu off-idle howl/screech?

If you are pushing a displacement hull (sailboat), you could try a 4-blade HT prop. I have a 5-pitch on the shelf, if you would like to try it. That might get you closer to 6,000 WOT.

Its just an aluminum fishing boat pvanv.

Went back to stock prop yesterday and noise was gone but back to 4300 rpm at wot.

Not sure I'd the 5 pitch 4b is to little for my 1700lb boat but was getting I think 5200 with the 6.5 3b

 

[pvanv]

Re: 9.8 2008 Nissan/Tohatsu off-idle howl/screech?

Are you using a Factory tach to verify RPM? As we discussed, 4300 is a little slow. FWIW, the 3B2B645131 (8.5 DIA X 6.5 PITCH) prop was so unpopular that it has been discontinued. I understand that the 5-pitch 4-blade prop might allow you to over rev. Another possible option for that 6-7 mph range would be the 3B2B645120 (8.7 DIA X 7 PITCH)-4 BLADE (HIGH THRUST), which costs $73.15. Hopefully that would get you closer to 5,000 RPM, landing you in the correct WOT RPM range of 5,000-6,000.

 

[simplystressed]

Re: 9.8 2008 Nissan/Tohatsu off-idle howl/screech?

Are you using a Factory tach to verify RPM? As we discussed, 4300 is a little slow. FWIW, the 3B2B645131 (8.5 DIA X 6.5 PITCH) prop was so unpopular that it has been discontinued. I understand that the 5-pitch 4-blade prop might allow you to over rev. Another possible option for that 6-7 mph range would be the 3B2B645120 (8.7 DIA X 7 PITCH)-4 BLADE (HIGH THRUST), which costs $73.15. Hopefully that would get you closer to 5,000 RPM, landing you in the correct WOT RPM range of 5,000-6,000.

Im using a tiny tach to verify rpm. Still getting 6mph with stocker which is hull speed but 50% throttle isn't being used due to high prop pitch

 

[simplystressed]

Re: 9.8 2008 Nissan/Tohatsu off-idle howl/screech?

pvanv since I'm at 5300 with the 6.5 would going from a 6.5 pitch 3 blade to a 7 pitch 4 blade get the rpms up higher? Or is the 5 pitch 4 blade the better option?

 

[TOHATSU GURU]

Re: 9.8 2008 Nissan/Tohatsu off-idle howl/screech?

Everything else equal...The number of blades reduce RPM due to resistance. The 5P4B should reduce RPM about 150 RPM in theory.

 

[simplystressed]

Re: 9.8 2008 Nissan/Tohatsu off-idle howl/screech?

Everything else equal...The number of blades reduce RPM due to resistance. The 5P4B should reduce RPM about 150 RPM in theory.

I still think I would gain RPM with the 5P4B going from 6.5 to 5p?. Maybe not as much as I expected but more than 5300.

pvanv what can you get on your 9.8 with the 5P4B and the heavy sailboat?

 

[pvanv]

Re: 9.8 2008 Nissan/Tohatsu off-idle howl/screech?

I still think I would gain RPM with the 5P4B going from 6.5 to 5p?. Maybe not as much as I expected but more than 5300.

pvanv what can you get on your 9.8 with the 5P4B and the heavy sailboat?

I can hit the redline of 6000 on the sailboat, with a hull speed of about 5-5.5 knots (depending on windage against the hull). The ESG never engages (which would happen around 6200). The 7P4B was too much pitch, not allowing WOT RPM to even reach 4600. But... it's a very different boat... displacement hull... up to 8,000 pounds (depending on crew and gear)... etc. Low hp on a heavy boat means much greater effect of small changes in propeller. Running a 3-blade prop causes a lot more "slippage" on that rig, whereas the HT props "shovel" the water at slow speeds. Might not be the best setup for your boat, since it is a very different rig.

 

[Traxion]

Re: 9.8 2008 Nissan/Tohatsu off-idle howl/screech?

I have the same noise issue on my 8hp motor. I use it as a kicker motor and run a lot in that lower RPM range. I switched from the factory 3 blade to a HT 4 blade and it puts the RPM's @ my trolling speed right in the sound area. I like the HT prop, better bite for my trolling application, but the noise gets annoying.