Outdoor Power Equipment (Lawn Mowers, Snow Blowers, Chain Saws and more) Discussions

Hi all,

I need to adjust the RPM of my Tecumseh L-Head (9 HP / 318 cc) engine that I bought in 2007.

For that purpose, I plan to purchase "digital photo (laser) tachometer".

From my understanding this tool works by sticking a piece of reflective tape on a rotating part of the engine (such at the shaft near the pulley where the belts are located). The tool then counts the number of time this piece of tape passes in front of the laser beam in one second and multiplies by 60 to display the RPM.

Did anyone ever used such a tachometer? If yes how are you satisfied with this tool?

Also, I need to know the RPM values that this engine should be adjusted to at: full throttle and also when idling. Do anyone know these RPM values.

Hi there.  The MTC department of my plant uses them to verify screw speeds on our extruders.  They work fairly well.  I haven't heard too many complaints and their readings usually agree with the encoders.

Just wondering why you wouldn't use an electronic digital tachometer.  They're around $25.00 to $50.00 and are very simple to use.  It usually has just one wire that you wrap around the spark plug wire.  That's it. 

 http://redingtoncounters.thomasnet.com/item/all-categories/del-51-electronic-lcd-hour-meter-maintenance-meter/5140-0311?&plpver=10&assetid=g2

Max rpm is 3600.  Min rpm will be between 1500 to 1700 depending on how well your engine likes to idle.  I have an ohv B&S engine.  The lowest I can get it to idle is 1650 rpm but that might be due to the throttle setting from the factory.. 

Hi Borat,

The laser tachometer is also not expensive (http://www.amazon.com/Digital-Laser-Photo-Tachometer-Non-Contact/dp/B000EUT9ZS).

This tachometer can be used on any rotating machine, as long as you have access to a rotating part where you can stick the reflective tape.

It works with gas engine, diesel, and with electric motors.

briggs and stratton makes a tach that has a thin wire that slides out of a base plate and disc .you place it firmly by hand and hold it in place why you slowly rotate the disc which advances the wire out of it. the wire oscilates back and forth and when it reaches it's widest vibration position it has an index between the plate and disc that tells you the rpm's.you can use it on anything you can place it on that has a rotating shaft.they use them for blower speed indexing on furnaces also. it is suprisingly accurate.

A pocket size RPM meter that is compact, competent and inexpensive. It will tell you the RPM of any piece of revolving machinery by transforming vibrations into revolutions per minute on a gauge that is simplicity itself.

NEW Genuine Tachometer This is a NEW in the box Briggs & Stratton tachometer. Works on most types of engines such as Tecumseh, Kohler and many others. Range: 800 - 50,000 RPM 14 - 750 Cycles Directions Included. 19200 Works on most types of engines such as Tecumseh, Kohler and many others. Range: 800 - 50,000 RPM 14 - 750 Cycles Directions Included. 19200 Works on most types of engines such as Tecumseh, Kohler and many others. Range: 800 - 50,000 RPM 14 - 750 Cycles Directions Included. 19200

I have one of those wire type tachs.  Mine's made by a German outfit Treysit.  I have a diesel power plant at my camp and I'm totally impressed with the way that thing works.  I set my power plant at 1800 rpm by that thing.  I think I'll get one of those hand held laser units though.  Being a power plant, a steady 1800 rpm is essential.  I know the Treysit unit shows 1800 rpm but reading the scale it could be off by 100 rpm or so and I wouldn't know it.  The laser unit will give me a definitive reading.    

Borat:

    The 51 tach looks good and does not require a battery if I have that right.  It picks up energy to run from spark.  I'm looking a tach to put on various machines to check stability and RPM sag under various loads.  That would require a lot of install and removal and tax the sensor wire.  Do you think it would stand up to that?  Have you seen any better since you bought yours for the same ballpark price?  

   The Tiny-Tach looks ok and the bat go for several years so probably ok also.  Not sure about that pickup either.  If anyone has one please post what you think about the robustness of the pickup.

   If anyone has a suggestion of something better or more functional please post.

I picked up one of these a couple months ago.  It seems decent, but I have not used it much.

http://www.amazon.com/gp/product/B002Z32OHW/

trouts2 wrote:
Trouts:

Is this what you're looking at? 

http://www.contractorstools.com/redington.html

I have one of these (Readington model 5140-0311) as well as a Tiny Tach.  Both devices are quite ruggedly built.  The Readington unit reads higher rpms than  the Tiny tach does and it also has a slot in the back of the unit where the impulse wire is placed while taking a reading.  That make is easier to move around.  For my purposes, I just put a piece of suitably sized wire on each machine I want to monitor and just move the tach from machine to machine without having to take the wire off of the spark plug lead.  Another nice feature of the  Readington tach that I have is that it reads up to 20000 vs 9999 of the Mini Tach.   I don't like the idea of batteries either.  If you can get one that's powered by electrical impulse, that's the way I'd go. 

Yes, 5140-0311, Inductive Model- Surface Mount, Inductive, Hours with 1:1Tach

I looked at that tach because of your reply in post #2. 

The Tiny-Tach goes to 1,9999 and the 0311 to 7000.

Both have batteries in potted cases so not replaceable. 

The 0311 is 15 year, the Tiny 5 year but prior posting on Abbys say the Tiny's battery lasts much longer.  I'll snoop around for one without a bat.

The 0311 literature on hookup wire they call "Lead wire" only shows one end.  That looks like a plain wire which wrappes around the plugwire a few times and has an allegator clip end to clip onto back onto the lead wire.  The other end is not shown.  Can any wire be used?  What is required on the other end?  Do you have to have something connected to the wire or do you just connect bare wire to something?  Is there a hole you stick the wire into?

The Tiny talks about coax wire for the pickup.  Maybe they have a length of coax and a short wire for a setup like the above soldered to the end of the coax.  What about the other end of the coax?  How is it connected to the device?

Can both use a plain wire on both ends?   I have coax I can strip if there is no elaborat connectors requires on the ends.

The model 51 uses any wire that can be squeezed into the slot on the back. 

The Tiny tach that I have uses two normal pieces of wire that are permanent parts of the instrument.  One wire goes to the spark plug lead and the second wire is a ground.  I prefer the single wire unit.

Can't tell you any more because these are the only two units I own.  I don't know anything about units that use coax.   For me, my preferences would be:  a) no battery, b) single wire), c) removable wire.    

  It might be that what I read was about a newer model.  It mentions the coax. 

Strange language "transmits" versus carries.  There is no transmitting going on. 

I doubt the "winds around" refers to coax but since coax is used and so few wires involved coax is probably in there.  Probably most of the length of the pickup wire is coax and then some flexable wires going to the center wire and a grounding clip on the coax jacket.  ?? No pictures no explination. 

So your's has two wires running directly into the unit and not able to connect and disconnect.  I guess if something breaks it's ok as long as it's not too close to the device body. 

New Standard TT2A - TINY TACH™
RPM reading adjustable from 1 spark per 2 revolutions to 8 sparks per revolution. One TINY-TACH™ now works for most gas engines.
RPM display from 1 to 19,000.
RPM update time 1/2 second.
Hour meter records total actual running time on your engine.
Job timer can be reset to record run time for record keeping.
Coax cable transmits signal without EMF interference.
1 Antenna cable winds around your spark plug wire to give you the RPM reading – clean and simple to attach. Signal strength can be controlled by the antenna wire.
Standard cable length is 6 feet. Additional length can be added at the factory for $10. If not standard, please specify total length needed in the "comments" section at the end of the order page.
TINY-TACH™ unit is potted to prevent damage from moisture and vibration. Lithium battery life 5+ years, not replaceable.

I think you mentioned having one at a camp which I assume is unheated.  So they take cold ok at least -30F?

I found one in China, no bat, cheap - $18 includes shipping, tach and hour.  Probalby clones of.....

Never had a problem with cold temps.  I had the Readi-alert on my snow blower for a while.  It always worked regardless of temp.

$18.00 is  good price.   You can buy 2.5 of those for the price of the one I bought. 

In using the laser tach, there must be an unobstructed view of

the piece of tape. If the tach gets interupted in "seeing" the tape,

the readings will be inaccurate. BTDT

T.J.

Can any reflective tape be used?  There's fake chrome tape.  Will that work?  I'm thinking of using it to meter rakes and impellers.  Not sure if tape on am impeller would reflect back in the right way.  I think you would have to have the tape on a surface square to the meter.  That might be tough to do on an impeller.  For a rake it would be easy.

The laser ones usually come with some tape.  I have heard of people cutting the tape into strips, but not peeling the backing off then using scotch clear tape so they can reuse them instead of buying more tape.

trouts2 wrote:
I have read that people using  the shinny duct tape works perfect. I believe any shiny material will work.

To check the impeller rpm with a laser tach.  I'm guessing you would probably have to take the reading looking down the chute, or take the chute off.  Either that or I think you could get an unobstructed view shooting in right above the auger gear case.

Amazon has a number of them for sale. With reviews

   I just ordered a $15 lazer tach and an $18 small inductive tach.  I doubt it will come with tape.  I have a roll of very shiny silver back tape which I hope works.  Bottom fishing and hoping for the best. 

  A small pack of tape costs $41. 

I installed a TinyTach to adjust RPM and accumulate hours. The inductive connection couldn't have been easier. One thing I didn't expect was the RPM drop under just light loads. Full throttle no load is 3700 RPM. Under a little load it drops to 3500-3550. Under really heavy load it's down to 3000. It seems as though it dials in more throttle the farther it gets away from it's unloaded RPM. But even though it's down to 3500, it should have plenty of power to pick back up to 3600. It doesn't sound like it's at full throttle even when it's running at 3500 rpm and minimal load. Thoughts?

JimmyM, 

   What you have described sounds normal but the terms do not pin down specifics.  A governor will keep an engine within a no load ball park of the throttle setting i.e 3/4 or full.

   Under “light” you see a drop to 3500 (200 rpm for you).  You do not know how much the governor influenced things already to keep the engine at 3500 rpm. It was already adjusting the throttle before getting to 3500 trying to sustain 3700 then 3600 then stopped trying and leveled off at 3500.  You see 3500 on the tack and say why can’t it bring it back to your 3700 setting.  It already tried and could not. 

   It’s max torque is back somewhere around 26-2800 (guessing).  The torque curve is falling rapidly after 3200 (again guessing) and a faster rate at 3600 and for you even more  at 3700. 

    The engine will have a tough time trying to sustain 3700 because there is not much torque up there.   A light load drops it.  There will be and increasingly smaller drop (less rate) as you  head into the higher parts of the torque curve.  Light loading does not have too hard a time of lowering rpm.  It has a tougher time each 100 rpm you drop with increasing load as you are climbing back up the torque curve (less rpm).  That will keep going until approx 2800 rpm where you will be at max torque, most governor influence (effective influence given the design – jet port opening). 

So light load and quick drop at the top end and as you go down more resistance to drop as you get into the higher torque regions.

You did not notice the governor’s interactions going from 3700 to 3500.  By the time it got to 3500 and showed up on your tach it was done correcting and could not correct (govern) anymore. 

 

Got in two laser tachs.  One for $8 and the other $25.  Both cheapies matched readings on a variable fan blade.  Also got the $18 induction tach.  It’s looks the same as other tachs with S1 S2 buttons, records hours and rpm, single wire hookup, records hi, lo rpm, and has angled side mount plates.  All from Amazon.  The induction tach tracks with the vibratach from idle to full throttle in a few motors so it seems fine also.  Both lasers seemed to work fine with reflector sections cut from a roll of shiny silver tape.  

 Tried out the tach on a crummy motor.  It sagged under load to 1800 and could not pull itself up.  On a good motor under load the droop was to 2800 where it tossed well and could sustain the load without overly struggling i.e. driven hard but taking it ok.

trouts2 wrote:
What you say makes perfect sense. I didn't realize that the torque curve fell off so quickly in that RPM range. You would think that having the Torque peak at round 3200-3400 would be more advantageous than having it at ~2800. My blower is really slugging away at 3000 and that may be very near it's peak since I really have to push it to get it under 3000 rpm.

I installed a tach on a  ST824 i found it to be a worth while add on.At max load in different types of snow it really lets you monitor rpm sag.Its a great tool for  giveing you  a good idea of the condition of your engine. If you can manage  to stay at or above your peak torque RPM your engine is in pretty good shape         ving y

Its a easy hook up and was 2 wires in my case !

It's good to know what your engine is up to under varying loads.

I use the same tach to monitor engine rpms on various machines.  On machines where the engine is concealed, I usually just put the required wire(s) on the spark plug and ground then feed them outside of the engine compartment and leave them there.  When I want to take an engine reading, I just attach the tach with a pair of Mar connectors. 

They are a nice little tach for cheap money. Although the refresh rate is a little slow its good enough to get the job done !

Relics,

   Could you cut and resize your pictures to 640 to they don't blow out the forum line formatting?

I think Relics tach is like mine.  His was $16 and mine $18.  That body tach with the S1 and S2 and mounting flanges is all over the net with various names and prices from 14 to 60 dollars.  Most don't have a maker name.  Mine don't.   They all seem to have the same functions but various lead and wire connects.  Some have potted non replaceable bats and some replaceable.  I'm beginning to think they are all the same.

Mine came with a one sheet "manual' which says exactly this (below) for setting the rpm sensor type.  Does anyone have exactly that on their how to set rpm sheet?

TO SET THE TACHOMETER (SPARK PLUG FIRING REVOLUTION):Press and hold the S1 button for 4 seconds.  The LCS will display 01(spark plug fires twice per revolution), 02(once per revoution), 02(every other revolution), 04(hour only, will not display RPM).  Once you find your desired spark plug firing pattern, release the S1 button. The LCD will blink for 8 to 10 seconds and return to total hour meter mode.  The default for the standard model is 02(once per revolution).

The tack is ok and sync's for readings with a versatach which is one of the vibrating wire tachs.  I have three of them an they are all the same and match reading across all three.  The update is slow taking 1/2 second to 3 seconds at times.  This gets to be a problem when trying to read sag.  Often with speed change the thing will post way out of range numbers but come back in over time.  Sometimes when starting it takes the gage three to several seconds to get the rpm right.  I'm wondering if all these tachs respond the same and in fact are all the same internals with a few minor changes i.e. the guts of the reader are all alike. 

Borat, what is your's like?  Does it get instantanous readings and always on the money or does it goof up and sometimes hunt for a few seconds for the right rpm especially with speed changes? 

"Borat, what is your's like?  Does it get instantanous readings and always on the money or does it goof up and sometimes hunt for a few seconds for the right rpm especially with speed changes? "

Normally, refresh rate is probably between .5 to 1 second and is generally accurate.   Mine are getting old already and the batteries might be starting to lose some power.  On really cold days ( colder than below 0F, the lcd is a bit slow.  The tach is refreshing the readout but the lcd cannot seem to respond quickly enough thus causing partial number drop outs.  Overall, I can still get enough of the readout number to know  see the engine speed.   

   Some guys claim they can get much longer than 5 years but possibly they were tractor guys posting from Arizona.  The general spec is 5 years and probably true for a mild temp place or heated garage. 

   Mine were advertised as able to change the bats but their all potted and no instructions on how to change the bat.  Some guys on the net have changed the bat on one that looks like mine with the S1 S2 buttons.  They say it's fairly easy but the soldering of the bat delicate. 

   I'll keep fiddling with the wire hookup placement and number of turns.  Maybe this is the time to switch to an R plug to reduce noise.  Some of them come with shielded hookup wire.  It might help to cut the sensor wire close to the reader and put on thin shielded wire which I have.  Yours and relics have a ground wire and probably a better setup.  The choise was replaceable bat and no ground clip.   

UPDATE: 3/29/2011.  The three cheap tachs (not the lazer tachs) for $18 came without a ground wire and worked but were fuzzy.  After installing a ground wire inside the gage they worked fine.  The response is good and they are on the money compared to the vibratach which is very accurate.  I've quick disconnect wires on all three so can plant them on any machine I put a wire on perminantly.  An aligator clip is used on the wire from the gage to ground.  They all read the same when put on a machine. 

There are many variations of these tachs which are like the one posted by relics.  They all have the same basic board inside but there are 4 board revisions that are around.  Also, some come with a ground wire some don't.  Some are listed as replaceable battery and some not.  Some say they are potted and some not but all the same design.  Mine were listed as potted but not potted.  Mine were also listed as battery replaceable which they somewhat are.  There is no battery compartment and the case is sealed.  You have to open the case with a knive to get at the bat.  The bat is soldered along with having some silicon type glue.  Not a big deal to replace the bat but not exactly what I expected.  Still for $18 they are a good deal and accurate.

I see what you mean Dave i will have to play with those pictures and see if i can get them smaller.I noticed the battery in my tach is glued in.It looks like i could get it out though.For cheap tachs even with slower refresh rate i found measureing sag was ok.I tryed to pick areas were i went at least 10ft and mostly longer.I did have to use a small flash light as most was done after dark.Than i noted my average was between 3050 and 3300 sag rpm from 3600