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I know my tachometer to be reading high and would like to know the error. I cannot get any sensible results from the inductive pick up that came with my Maplin multi-meter, possibly due to high performance plug leads? I have a digital photo-tachometer. Any ideas where best to take reading? I tried a search but could not find this topic addressed.

 

Tim

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Hi Tim,

I would install the reflective tape (or a big white piece of tape) on the disk at the front of the engine where your timing marks are and the V-belt is running on.

Here is a video with some background of how it works:

 

(I hope the link shows above if not, then google it on You-tube.com)

Enjoy.

Waldi

Edited by Waldi
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I bought a digital photo tacho for precisely this check on my TR. (bought from Maplins) On a 4 cyl there is limited places or space for the reflective strip to attach and remain attached whilst revving and reviewing. You need 2 people also to do the check.

 

The Maplin digital photo tacho works fine compared to my hand held Smiths chronometric tacho - I compared readings of lathe chuck speed (nice flat area on chuck to attach the tape to and single central point for probe of Smiths unit) and they were as good as the same reading.

Smiths Item:-

https://1.bp.blogspot.com/-FDHkkfMWkzA/VFtiuTbnLrI/AAAAAAAAJW0/mPDqRJVOz_Q/s1600/Smiths%2BAT%2Bhand%2Bheld%2Btachometer%2Bset.1%2B004.jpg

 

Peter W

 

PS All this said and done, this job is easier done on the bench rather than on your lap in a TR - recalibrating your standard rev counter will involve removing the needle and refitting it in the correct place to suit your requirements. In my youth I worked in an instrument repair shop and my memory says that the standard TR rev counter and speedo, if the needle is set correctly, are not too far wrong. You need to decide the important speed readings and set the needle at those. ie with a known 3000 rpm input to the instrument, fit needle pointing at 3000. Then check at say 5000 and be aware of any discrepancies.

Edited by BlueTR3A-5EKT
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It didn't

Funny, the link is shown in my screen, tried several times, different ways, I give up.

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If you know someone with a Snap on timing light you could check it that way. They are top quality and accurate. Btw is your tacho the standard TR4a cable driven unit, and does it waiver or is the needle steady?

 

Kevin

Edited by boxofbits
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Tim,

 

If you have a satnav (gps), it will give you accurate road speeds, and from that you should be able to calculate engine rpm, knowing the diff ratio and tyre sizes.

 

It used be a look up on the mintylamb site, but that has dissappeared. I did keep a hard copy of the results based on 3.7 diff and 185x70 tyres, which gives 3000rpm in direct 4th as 60.8mph.

 

Otherwise this may help: https://wahiduddin.net/calc/calc_speed_rpm.htm

 

Mike

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Funny, the link is shown in my screen, tried several times, different ways, I give up.

I think there is a problem now with embedding you-tube videos in posts.

 

You were linking to this:

youtube.com/embed/QVSQLfnKytk?htm15=1&fs=1

 

If you paste that into a browser with the usual prefix it does seem to work.

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If adhesive tape will not stick, how about SnoPaque? Its a densely white paint, used to correct typed errors on paper but stick well and dries fast. probably unobtanium in this digital age, but any white paint might do.

 

John

Edited by john.r.davies
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here is a TR based XL spreadsheet. Oh no it isn't, you cannot upload XL files to this forum.

 

You can get it here

http://www.buckeyetriumphs.org/technical/Calculator/road_speed_vs_engine_speed_calcu.htm

 

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