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robrike
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45 Posts
Discussion Starter · #1 ·
Wow!! I finally got my vibratach today and measured my RPM's on my 10323. I had it set by ear prior to getting the Tach and I was shocked to see my "ear" setting. Almost 4000 rpm at full throttle. :Stop: I dialed it back and it would hardly run at first and smoked but I added a couple of clicks and it runs right at 3100 rpm. I had mowed three or four times and it ran at this rpm some of the time. Most of the time I would run it about half throttle.

Any chance this did any long term damage? I was using Opti 2 and MMO and now have Stihl Synthetic in the gas. I am noticing the famous surge at this lower level of rpm and especially at idle. May end up drilling out the pilot and possibly main after one mow as is. I thought I was just lucky that I did not have surge but at 4000 rpm I guess it is hard to surge.

Vibratach was very easy to use by the way. You really notice the wide swing of the wire when you get it out the right length. Really happy with it.

Rob
 

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LAWN-BOY-AHOLIC
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1,349 Posts
It is doubtful that you did any damage to the engine by overspeeding it. If it is still together all is well. The surging can be overcome by the usual jet enlargement, just be sure to go slowly as it only takes a small amount of increased diameter to increase the flow of fuel and richen the air/fuel ratio. Vibratachs are really cool huh! I would not be without one. The neat thing is: no baterries, cables to hook up, etc. Low tech, reasonably priced, and plenty accurate for our needs, who could ask for anything more?

Besure your air filter is clean before drilling out the jet(s) that can influence the ratio.
 

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robrike
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45 Posts
Discussion Starter · #3 ·
Yeah, I really like the vibratach. Extremely simple to use. I have two other mowers that are crapsmans with Tecumseh engines and I think I will check the rpm on those too. No reason other than to just see where they are. Really amazing little device.

I figured if it had not torn up by now it was probably clear of damage. Never really had it under a tremendous load. Just sounds so different at this lower speed but tomorrow I will take it for a test run and see how it does.

Rob
 

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443 Posts
No way would I trust one of those wiggling wire gadgets! I've only seen one used, at a garden tractor pull where it was the "official" instrument. They had some RPM limit on the engines and half the machines were getting disqualified based on that piece of junk. My son had his 318 there and got told that the Onan was making 5,000 RPM. The governor was just as it left the factory, there was no way it could have lived for a thousand hours, vitrually all of that at WOT, if it was turning that fast. A lot of guys said the same thing, it defied logic, but the "official instrument" ruled the day. My son, and a bunch of others, packed up rather than screw with their governors. We checked the tractor with three different electronic tachs and they all read within 50 RPM of the factory claim of 3,600. So much for the official BS wiggling wire.
 

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5K Poster!!!
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5,142 Posts
I have learned with the help of an electric motor tach.....with the engine running I put the tach on the top nut and the tach measures the shaft speed which tells me the rpm. After you get an idea of the true rpm you can adjust most engines rpm by ear.

I have never used the vibratach but I've heard they are legit, but I've been skeptical...
 

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2 stroke enthusiast
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6,568 Posts
I'm leary as well with a 'vibrating wire' telling me how fast it's spinning. I'll stick my digital, inductive style instruments. If I could compare them side by side, then my opinion may change. I just don't see how vibration can be related to gauging rpm? What if the blade or crank is slightly bent? Seems all these factors would have a major role in an accurate reading.
 

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I'm leary as well with a 'vibrating wire' telling me how fast it's spinning. I'll stick my digital, inductive style instruments. If I could compare them side by side, then my opinion may change. I just don't see how vibration can be related to gauging rpm? What if the blade or crank is slightly bent? Seems all these factors would have a major role in an accurate reading.
It's all based on rotary motion and it depends on something being slightly out of balance. It reads whatever is the most out of balance and since it's all based on 360 degree revolutions it can determine the swing. If your engine was perfectly balanced, it couldn't work.
 

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2 stroke enthusiast
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Do these need to lay horizontally flat to read or can they be held sideways too like for chainsaws or other engines with horizontal cranks?
 

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Do these need to lay horizontally flat to read or can they be held sideways too like for chainsaws or other engines with horizontal cranks?
You can measure anywhere you can make good contact. The angle that you have the sirometer to the direction of the vibration will determine the direction the wire swings though. I like to put it as perpendicular to the crank as possible to get a horizontal swing. Here is some information that might help.

http://www.underhoodservice.com/Article/40240/shaken_not_steered.aspx
 

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It's going to read whatever shakes the most... It might not be the crank...
Correct. That's why they are best for small engines that are not running PTO's or have other rotating things that might have greater vibrations.
 

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Premium Member
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5,747 Posts
I have learned with the help of an electric motor tach.....with the engine running I put the tach on the top nut and the tach measures the shaft speed which tells me the rpm. After you get an idea of the true rpm you can adjust most engines rpm by ear.

I have never used the vibratach but I've heard they are legit, but I've been skeptical...
I made a similar suggestion a while ago and was widely criticized for it. You are correct, you can set RPM on a one or two cylinder engine if you have something to compare it to. This is exactly what a Vibratach does, but it uses a piece of spring steel instead of your ear drum. I can, however, see where it would not be as accurate on a smooth running opposed twin as it would be on a single cylinder engine. For the ultimate in accuracy, I have an old Jacquets Indicator which is actually a watch movement that counts revolutions for several seconds, and is accurate to 2 RPM.
 

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I have a MAC Tools electronic inductive timing light with a digital tach that reads both 2 & 4 stroke R.P.M.s. Will this work on small engines? :confused:
I never tried it on my Lawn Boy.

It works on 2 stroke outboard engines with and without a distributor.

john boy
 

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robrike
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45 Posts
Discussion Starter · #14 ·
John Boy, if it works on a 2 stroke outboard I would be inclined to think it would work on the Lawnboys.
Mitch, thanks for the link to the article. I was impressed with how wide the swing was on the vibratach, certainly easy to learn to read. I did not get to try it on my other mowers as I spent the day taking door casing and trim off to get a new sofa my wife bought into the room it belonged in. Old houses had narrow doors back in the 30's and 40's.

I did not mean to ruffle any feathers on the vibratach. If you have the access to a digital I would certainly use it. I just wanted something inexpensive and reliable. I may take my mower to a shop and have the rpm checked just for comparisons sake, doubt they would charge much to take 2 minutes to read it. With all the parts business I give them it is the least they could do. :fing32: The guy is pretty cool anyway. If I get time to do that in the coming week I will post my findings back here.

Rob
 

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The voice of reason !
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2,720 Posts
Never tried a Vibratach but I use an Lutron optical tach that I've had for years doing my RC hobbies and it extremely accurate plus it doubles as a basic DVM.

The only time I've ever had any false reading was using it on an all white engine in bright sunlight, and the fix was to put a strip of electrical tape across the fan screen and all was well.

P.S. there are also lots of other brands of optical tachometers used in RC that are very reasonably priced the best I've found other than the Lutron is Hobico $14.99
 

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