Help- want a shop tachometer By imnts2 (Read 787 times)

[imnts2]

I need a shop tach so I thought I would be smart. Harbor Freight has a very nice looking self powered VOM with a tach/dwell function and an inductive pickup for a nice price so smarty me grabbed one.

At Idle it looks right. Reading 60 X 10 x 2 +1200RPM. BUT WHEN I CRACK THE THROTTLE OPEN THE READING CHANGES VERY LITTLE. NOT AT ALL CORRECT.

Simple to hook up. Turn it on, connect the inductive pickup in to the unit and clip the pickup on the Spark plug wire. It has selector positions for 3, 4, 5, 6 and 8 cylinder engines (meaning the pickup should be connected between the coil and the distributor) So I select 4 cyl. Since GY6 engines fire every turn of the flywheel and a 4 cyl engine distributor based ignition system fire 2 times every turn of the crankshaft, jut double the reading.

Any ideas of a fix? If not, any ideas of a shop tach that will work on a GY6? Anyone using one? Would something like a Innova 3568 work?

Thanks
lefy2

[sprocket]

NO.. the tach won't work on a one cylinder engine...

just get a Tiny Tach.. they are self powered...

.tinytach.com/tinytach/gasoline.php" rel="nofollow" target="_blank">.tinytach.com/tinytach/gasoline.php

[cruiser]

Sprocket has good advice. Here is another supplier of small tachs.

[jct842]

What I intend to buy is an optical tach. What you do to measure is put a white tape or paint strip on some thing rotating, like scooter flywheel or a lathe or milling machine. I want to be able to use it for every thing. It is a couple notches down on my list of things I must have. john

[imnts2]

jct - I considered an optical tack. You have to uncover the flywheel and focust on that. Just about impossible to get a reading of RPM at WOT going down the highway.

[imnts2]

Sprocket. I know you know 1000 times more about these machines than I ever will and you give so generously of your time and talent I really have been hesitating to ask you to expain

But humor me please.. For all my life I have never been able to simply accept "not - it won't work go get something else" I have to know why it won't work. lol

Sprocket, darned if I know why an inductive pickup won't work on a 1 cylinder engine? Are you telling me a timing light with an inductive pickup will not work on a one cylinder engine also? Surely that is not true is it?

Enlighten me.

lefty2

[jct842]

As the thread title says SHOP TACHOMETER,..........that's what an optical tach is. I have a milling machine and a lathe and a host of other devices that spin and I want to know how fast they run as well as a scooter or two in the shop. I have one of the ENM tachs of my Chinese 150. They are not much of a shop tach as they have to have a wire wrapped around the spark plug wire and alternate readings between time running and rpm. I have mounted mine on the scooter permanent. john

[imnts2]

Hi John.
I do not disagree that an optical tach is a usefull device around a shop (and it sounds like you have a machine shop not a puny little place it the garage to fix a few scoots) and it would be appropritate to call it a shop tack. Nor do I wish to debate about the meaning of the words "shop Tachometer" I really do not care what it is called. I want some thing to use in my work on scoots that is relatively quick to move from scoot to scoot to use when I am servicing a variety of scoots for a variety of problems and I want to be able to test drive the scoots when it is appropriate to do so with an acurately calabrated tach attached (use some rubber bands to hold it in place). I am sure if you are familiar with scoot repair you understand why I need a portable and accurate tack that does not require I hold it to read the flywheel or some other revolving part while running a WOT on the highyay.

Thanks for the thoughts. I really had looked into an optical instrument but it will not do my job. I would add, If you are going to use it on an AIR COOLED scoot you don't want to run it at near full throttle long without the flywheel cover and air baffles intact for more than a minute or two.

Cheers
lefty2

[tvnacman]

Feb 18, 2012 20:23:43 GMT -6 cruiser said:

Sprocket has good advice. Here is another supplier of small tachs.

I have this style tach it works with delay its responce time lacks . It seems to lag a few seconds behind , its fine on steady rpm's . When the rpm's are changeing its not too great .

John

[jct842]

Yes and I get the same type of readings as tvnacman, very slow to respond to change with that ENM tach. A good one with rapid response is going to cost a lot more for sure. It would be nice to find one like a dwell meter/tach that would work and attach quickly. I would mark the variator instead of the other side of the engine for the while line. That side of the engine is not so much of a pain and needs to be opened more often any way to clean and change rollers and sliders. john

[cruiser]

This type of tach is used by a lot guys that add motor kits to their bikes. I have an ENM tach on my bike and it works OK with very little lag.

[imnts2]

Thanks a lot guys. Finally I am learning what I suspected. i

[imnts2]

Thanks a lot guys. You have given he question enough attention to tell me that most of the cheap tacks are slow responders. OK but have lag.

But I would not call the tiny tach or JNC a "shop tach" suitable to be sitting on my Mac tool chest for professional use in servicing customers scoots. They are rather cheap and meant to be permanently mounted.

But I still have no idea why spocket says the tach I bought will not work on a 1 cylinder engine. I doubt he is taking about the simple task of accounting for the fact that the ta ch is not calibrated for a single cylinder instead of a 4 or 6. I think he knows I am smart enough to figure that out.

Nor if an instrument like a Innova 3568 will work

Again thanks

Cheers.
lefty2

[jct842]

.amazon.com/Electronic-Specialties-328-Tach-Plus/dp/B002Z32OHW/ref=pd_sim_auto_1" rel="nofollow" target="_blank">.amazon.com/Electronic-Specialties-328-Tach-Plus/dp/B002Z32OHW/ref=pd_sim_auto_1
.amazon.com/dp/B000UZO0L0/?tag=money84-20" rel="nofollow" target="_blank">.amazon.com/dp/B000UZO0L0/?tag=money84-20

either of those should work in the shop for you. tape the first one down for on the road testing.