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High RPMs
https://www.smwebhead.com/phpBB3/viewtopic.php?f=6&t=13260		 Page 1 of 1
Author:  zeberifo1 [ Sun Jul 27, 2014 12:18 pm ]
Post subject:  High RPMs
Hi everyone, so a few days back on a somewhat rough Lake Michigan, getting up on plane seemed to demand very high RPMs. I can't remember the exact gauge reading but I believe I was at almost 5500 RPMs getting up on plane. This made me nervous so I didn't stay up that high. Temperature and oil pressure appeared normal. Not more than 3-4 boat outings ago, I had the oil changed, drive maintenance and compression checks done. I did run aground a little bit in lake kalamazoo in saugatuck, but I believe it was only mud or sand and I never really got stuck. Any ideas? Could the prop in fact be damaged? Thanks!
Author:  Surface Interval [ Sun Jul 27, 2014 2:53 pm ]
Post subject:  Re: High RPMs
Are you sure the tach is accurate? I have an '02 268 with the 5.7. Gi and my tach reads high occasionally. I usually tap or swat the top of the dash above the tach 2-3 times and it returns to normal. With original propellers you would not be able to turn 5500 rpm at top speed. It most certainly would not rev that high just getting on plane. The tach is known to do this once in a while with others on this site also.

On the positive side you can use it as a demonstration of how the captain runs his ship with a firm hand :lol:
Author:  rpengr [ Sun Jul 27, 2014 5:35 pm ]
Post subject:  Re: High RPMs
It certainly sounds like prop damage. Assuming you did not grind the tips down to a much smaller diameter (which would look very noticeable), so the next thought is that the blades were bent forward towards a flatter pitch.
Author:  Bliss36 [ Sun Jul 27, 2014 10:23 pm ]
Post subject:  Re: High RPMs
Surface Interval wrote:
Are you sure the tach is accurate? I have an '02 268 with the 5.7. Gi and my tach reads high occasionally. I usually tap or swat the top of the dash above the tach 2-3 times and it returns to normal. With original propellers you would not be able to turn 5500 rpm at top speed. It most certainly would not rev that high just getting on plane. The tach is known to do this once in a while with others on this site also.

On the positive side you can use it as a demonstration of how the captain runs his ship with a firm hand :lol:


+1 Mine does the same exact thing so I just tap it a couple of times like Suface Interval said and it drops into normal range. My Floscan meter has a digital tach that I watch instead because the factory analog one is so erratic.

On a side note if you did run aground I would recommend(personal experience) pulling the boat and checking your outdrive oil for water/damage especially if you have a trailer and can do it yourself. It would be cheaper to find out now rather than later if you do in fact have any damage, and if everything looks good then at least you won't have to worry about it.
Author:  kd4pbs [ Mon Jul 28, 2014 11:36 am ]
Post subject:  Re: High RPMs
It could be that the prop hub is damaged, causing the drive shaft to slip inside the rubber hub. Another possibility, which you certainly don't want it to be, is that the drive coupler is on it's way out. That would be the least likely thing though, as when they go, they usually GO... as in there's barely any torque being delivered to the prop while in gear.
Author:  Surface Interval [ Mon Jul 28, 2014 12:15 pm ]
Post subject:  Re: High RPMs
I would recommend the following:
1. Verify that your prop is not substantially damaged. If possible, pull the boat out of the water and check the outdrive for oil quantity, briefly pull the drain plug and see if water comes out, then reinstall the plug.
2. Verify tach reading at idle in neutral. The tach should read somewhere between 600 and maybe 900 rpm. The engine is tuned to idle somewhere around 650rpm. Put it in gear and verify tach reading. This should be about 600-700 rpm.
3. Going to full power the tach should read 3000 rpm or just a bit more as the boat is trying to get up on plane. You might see approximately 3500rpm as you pass through 20 mph on the speedometer.
4. LISTEN to the engine. The maximum rpm range is 4600-5000 rpm. If the engine sounds normal, it probably is. If it sounds like it is screaming at 5500 rpm (500 rpm over redline) then you do have a problem. I doubt that a spun prop hub or coupler problem would last or give the results you are describing.
5. If your rpm readings are very far above these numbers I'm pretty sure the tach is acting up. I have heard it described on this site and other sites. Smack the dash above the tach a couple times or so, and maybe consider a new tach sometime in the future. In the mean time, go have fun. Summers are too short in the north country. Hope this helps.

Gary
Author:  rpengr [ Mon Jul 28, 2014 12:19 pm ]
Post subject:  Re: High RPMs
Add:
6. Respond to this thread and let us know how it turned out.
Author:  zeberifo1 [ Mon Jul 28, 2014 1:54 pm ]
Post subject:  Re: High RPMs
Thanks everyone. When the kids and this lousy summer allow, I will try smacking the tach and go from there. More to come!
Author:  zeberifo1 [ Fri Aug 08, 2014 8:22 am ]
Post subject:  Re: High RPMs
Hi everyone. Following up on my OP.
Holy sensitive Tach display! I hit it several times with my thumb and it goes up or down! When I was happy that it appeared normal, I would stop. Thanks for the info! Is this something that can be repaired or just a "bug" with the vista?
Author:  ric [ Fri Aug 08, 2014 8:49 am ]
Post subject:  Re: High RPMs
I would like to chime in that I'm also part of the "tap the tach to make it read correctly" club.
Author:  JeffLW [ Fri Aug 08, 2014 9:33 am ]
Post subject:  Re: High RPMs
I also tried the tap method last week and my tach works great now. :lol:
Author:  kd4pbs [ Fri Aug 08, 2014 10:50 am ]
Post subject:  Re: High RPMs
There are basically three grades of gauges I've found on boats. Well, four if you put the integrated system such as the VDO cluster or those clusters one finds on 80's era Bayliners...
-Low-end cheap plastic ones. These are typically not very water/moisture proof, and look as cheap as they really are. I had these on my '87 Galaxy 2100 and my first boat; a 1978 Cobia (complete with it's OMC 800 stringer and 350). They aren't very accurate (especially the tach), but I believe the reason the tach isn't so accurate is due to moisture getting into the electronics. Since there is a switch on the back that sets the # of cylinders for the engine, the corrosion causes issues with the switch. Some of these tachs also have a potentiometer to calibrate the tach. I've never seen one that was spot-on, but I've been able to easily calibrate it to make it spot-on (at least at one point in the range, which I usually set at 2800 RPM).
-Mid-grade plastic/glass/metal ones. My Vista came with these. My Signature 24 also had some of these made by VDO, but Chaparral decided to make that panel a little less-standard in that the gauges didn't have bezels; they were a nice attractive flush fit with a little bit of convex shape to cut glare, but were plastic and crazed a bit with age and UV exposure. The ones in the Vista had actual glass (it looked like it anyway) crystals, metal surrounds and decent looking faces. The electronics, however seem to be the same as what's in the cheap ones. I replaced the gauges on the Vista with a new set of these that don't have gold trim around them due to issues with a couple of the gauges not working. Had to calibrate the tach right out of the box; it was ~10% off from reality. This leads me to believe that most manufacturers simply slap the tach in the panel and hook it up without verifying calibration. Again, being not totally sealed, the tach is typically the one to act up first (there's more electronics in the tach than any other gauge).
-High-end gauges that easily cost the same amount for one gauge as a person can pay for a whole set of the mid-grade gauges. They are typically oil or glycerin filled, large, and attractive. Since they are filled, they are very well sealed against moisture. They typically have anodized trim available in every gaudy color of the rainbow. We all know that the more wild colors one can put on a boat, the faster it goes, so that seems to be why these gauges are most popular with the GFBL boat crowd. I swear they even consider the gauges' appearance in boat show contests. As for the accuracy, I imagine they're a bit better than the other styles, but I don't know for sure, nor do I ever plan to find out. They also tend to leak the contents of the gauge all over the place after a little age gets on them, garnering tons of anguish from their owners that a drop of oil has suddenly appeared on their holographic insert dash panel.
Ultimately, those gauges all use the same sensors to drive them, and looking at the longevity issues with leaky oil-filled ones, I can't see where one style lasts much longer than another.
I guess what I'm saying is either just tap the gauge from time to time, or replace it with whatever your wallet decides is best.
That being said, I am far from an expert on the subject; these are simply my observations.
If it were me, I'd just tap the thing from time to time, as I tend to use my ears as a tachometer more than I use the tachometer as a tachometer.
Author:  zeberifo1 [ Sat Aug 09, 2014 12:10 am ]
Post subject:  Re: High RPMs
Thanks for the replies!
Author:  hail mary [ Sat Aug 09, 2014 8:56 am ]
Post subject:  Re: High RPMs
Yip I have same problem tach started reading 1500 to 1800 higher on full throttle and bit higher on idle :?
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