tacho/rev counter - solutions

[mk1vdub]

I've noticed quite a few threads on this and have read some old ones on how to run one from the alternator, and the electronics went over my head pretty much straight away :roll:  :lol:  I also wasn't too sure about it due to the possibilies of the belt slipping and the readings changing as the belt wears. So I did a little bit of searching and came across this:

http://www.tinytach.com/tinytach/diesel.php

it looks pretty good for the price (which works out about £35 to me, although I haven't looked into the UK distributor, or shipping costs) and looks like it will be much more acurate, and for others like me a very simple soloution  
I did wonder about making my own using a timing strobe which uses the same sort of transducer cliped over a fuel linebut that would only really be worth it if I could find one second hand for less than the tiny tach...
anyway I just thought I'd share that with you all as it may be of interest to some of you, if I do go ahead and get one I'll be sure to write a little report on how well it works and post it up

cheers
Paul

[dieselpower]

hey,
i have a tiny tach on my dirtbike. and even tho it works good to set my idle and to veiw my cruzing rpm's, i wouldnt recomend it for your car. first of all, they arent back-lit, so it would be useless at night. second, its digital so unless you are a math genius, it's hard to tell the rate of acceleration using it. they also have about a 1 second delay in them while it figures out rpm so it realy isn't useful unless you are at a constant rpm.

another idea is taking the transducer and modifying it onto a gas tack somehow. now a gas tach uses 2 pulses a revolution whereas this would only be 1 every 2 revolutions. so you could hook it up to a 1 cylinder motorcycle tach if you could find one, or build a circuit board to multiply the pulses somehow.

hope that helps

Mark

[mk1vdub]

cheers for the reply mate,
I did wonder exactly how good it would be. I had already thought of converting it to run a gas tach, I'd definitely prefer an analogue needle and lighting and I'm sure I could make it work with a bit of thought, the second delay is a bit of a bugger though.

[dieselpower]

hey,

does anyone kno how this works?
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=42291&item=4359080992&rd=1
do u think there could be useful parts on that to hook up to an analog tack in the car?


Mark

[mk1vdub]

thats basically what I was talking about in my first post, the timing strobe - it shold have the same sort of transducer which clips over a fuel line the signal fires the strobe which you point at the flywheel and look at the marks

[2mn2]

Try:
http://www.4crawler.com/Diesel/CheapTricks/Tachometer/index.shtml

[VWRacer]

The more electronics inclined may wish to check out this DIY page for not only making a non-W tach for a diesel VW, but also integrates a MK1 GTI instrument cluster, with its 7000 RPM tach.

Link.

[dieselpower]

thanks for the link,
couldn't the same idea be used if you took the disk and made 2 - 1/2" bumps on it then used an abs sensor to pick up the signal instead. then you wouldn't have to worry about cleaning the disk and sensor all the time and the whole thing would be protected by the timing belt cover.


Mark

[GTD.]

I wanted a tach for my 91 GTD (SB Engine), mk2 GTD tachs are like hens teeth, so I fitted the clocks from a mk3 Mechanical TD of a AAV? or 1Z engine.

VDO list a 52mm 5k revcounter that will work with a w terminal, that you could fit in the center console if you remove the blanking plate.

What electrcal system have you used in the SB conversion ce1 or ce2?

[Northern RD]

Try:
http://www.4crawler.com/Diesel/CheapTricks/Tachometer/index.shtml

I`ve tried and it worked well with the factory tach I installed but the trigger set-up is too complicated to suit my tastes. My solution was to use the photo-interuptor from a 1.8L distrubutor and a 2mm notch machined into the crankshaft pully. It`s worked well for 137,000+km despite having road trash tossed up on it and i BELIEVE I still have to circuit some where if anyones` intrested and if they`re handy with this sort of thing,..
N.

[racer_x]

hey,

does anyone kno how this works?
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=42291&item=4359080992&rd=1
do u think there could be useful parts on that to hook up to an analog tack in the car?


Mark

The Snapon Lummy-Mag uses an optical pickup. You remove one of the glowplugs and screw an optical pickup in the hole. The flash from combustion provides a signal to the tach/timing diagnostic device.

On the subject of using a gas tach on the diesel, I've wondered about using a hall effect or magnetic type pickup in the plug at the back of the injection pump. That would get one pulse for each cylinder firing because the plunger in the pump moves once per combustion cycle. That would be analogous to the coil connection on the gas cars. I'm just not sure how easy it would be to get a pickup in there considering the pressure in that chamber behind the plunger.

[Northern RD]

hey,

does anyone kno how this works?
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=42291&item=4359080992&rd=1
do u think there could be useful parts on that to hook up to an analog tack in the car?


Mark

The Snapon Lummy-Mag uses an optical pickup. You remove one of the glowplugs and screw an optical pickup in the hole. The flash from combustion provides a signal to the tach/timing diagnostic device.

On the subject of using a gas tach on the diesel, I've wondered about using a hall effect or magnetic type pickup in the plug at the back of the injection pump. That would get one pulse for each cylinder firing because the plunger in the pump moves once per combustion cycle. That would be analogous to the coil connection on the gas cars. I'm just not sure how easy it would be to get a pickup in there considering the pressure in that chamber behind the plunger.

That was my thinking. Rather than go to the troble of mounting the trigger disc on the pump, mounting the sensor in the belt cover, and the rest of it, it occured to me that there might be an easier solution. My fist thought was to use the timing mark on the flywheel but one day while servicing a Canon photocopier it struck me that the way they generate thier own timing signal, which was with a cut-out disc and photointerrutor moted on the main motor, that THAT was close to what I wanted for a trigger circuit for a tach. The end reult was something that reads the crank speed without having to multply up and divide down etc.
I must admit though that taking a signal right from the pump is an intreguing idea though,...
N.

[VWRacer]

That would get one pulse for each cylinder firing because the plunger in the pump moves once per combustion cycle.

The "Tiny Tach" mentioned in the opening post does exactly this, so why try to reinvent the wheel?

[racer_x]

That would get one pulse for each cylinder firing because the plunger in the pump moves once per combustion cycle.

The "Tiny Tach" mentioned in the opening post does exactly this, so why try to reinvent the wheel?

Actually, the "Tiny Tach" has a transducer that fits on one of the fuel lines to the injectors. It produces a signal every time that injector gets a pulse of fuel, once every two engine revolutions. That's part of why that tach doesn't care how many cylinders the engine has. If it's a 4 stroke diesel, the transducer generates one pulse per 2 engine revolutions.

[VWRacer]

Yes, that's exactly my point. The guys above are talking about using a Hall or magnetic pickup, which, since either produces a small dc pulse which is converted to a tach signal, is functionally identical to what the Tiny Tach does.

Unless the objective of the exercise is to 'reinvent the wheel'...if so, then by all means have at it!