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Tractor Pulling Discussion Forum

using a tachometer

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1951G

01-26-2005 10:35:43

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I posted a message few days ago about purchasing a tachometer. Now I have one but I'm not sure I'm using it correctly. It's a digital type with the laser and reflective tape. I cut about a 1/2" piece of tape and applied it to the outside edge on the end of the crankshaft on my unstyled JD A. When I crank the engine and hold the tachometer about 1 foot away, it gives the reading, but goes up and down. I haven't noticed the engine surging or not idling at a consistent speed. Is there something else I need to do in order to get correct reading? Thanks in advance.

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856puller

01-27-2005 15:12:53

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Re: using a tachometer in reply to 1951G, 01-26-2005 10:35:43

i have noticed that if there is any paint chips or other colors, rust,ect that will throw my tach off. i will paint or clean the area well first.

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1951G

01-27-2005 07:30:46

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Re: using a tachometer in reply to 1951G, 01-26-2005 10:35:43

Thanks for everyone's replies. I ended up putting the tape on the edge of the flywheel and holding tach about 1 foot away. Also, did this in the shade to avoid the bright lights. By doing this, I got a consistent reading.

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rkm

01-26-2005 19:45:36

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Re: using a tachometer in reply to 1951G, 01-26-2005 10:35:43

It helps if you are in the shade. Bright light will cause the tach to give erratic readings

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REDEYE

01-26-2005 17:14:07

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Re: using a tachometer in reply to 1951G, 01-26-2005 10:35:43

i have heard of these tachs and was just wondering where i could get one. and what are the types to stay away from, the ones that have interfernece problems with ignitions.

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1951G

01-28-2005 07:05:51

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Re: using a tachometer in reply to REDEYE, 01-26-2005 17:14:07

Redeye,

I got mine at a place called Tool Central. You can also get them from various sites on the internet by typing tachometer on a search engine, like google.com and it should come back with companies that carry these.

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super 70

01-26-2005 16:00:07

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Re: using a tachometer in reply to 1951G, 01-26-2005 10:35:43

You are supose to put tape on clutch pulley JD book will tell you that to check rpm

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deadeye

01-26-2005 14:34:41

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Re: using a tachometer in reply to 1951G, 01-26-2005 10:35:43

Make sure that the tape you put on is the only one on there. It may have been checked before at a pull and you could have more than one piece on at different spacings. Seen it happen at Sigourney once....deadeye

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ToddF

01-26-2005 13:51:10

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Re: using a tachometer in reply to 1951G, 01-26-2005 10:35:43

It may improve the accuracy of the reading to move your tape to the outside of the flywheel rather than on the end of the crank. You also can back away from it 3 or 4 feet and still get a good reading if there is interference from the ignition that affects it. We use one that sounds similar at work to check fan blade speed, it works pretty well. For the fan blade we generally don't even need the reflective tape, just shoot the blades and divide by the number of blades to get the correct RPM. I also believe that for slow speeds, and I don't recall what they consider slow, that you can put multiple pieces of tape on (2 @ 180 degrees apart, 3 @ 120 degrees) to help improve accuracy and settle the number from fluctuating quite so much. You then divide the output by the number of pieces of tape to get RPM.

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ToddF

01-27-2005 07:35:48

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Re: using a tachometer in reply to ToddF, 01-26-2005 13:51:10

I might add to above that the spacing between multiple pieces of tape is not super critical because the tach. is averaging over time, thus placing them "by eye" should work fine.

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jd b puller

01-26-2005 13:43:09

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Re: using a tachometer in reply to 1951G, 01-26-2005 10:35:43

you put it on the crank?

Clean off a small spot on the edge of the flywheel - the part that faces you when you are in the seat. Now you need to hold the gizme about 1/4-1/2" away from the flywheel so that it can read the tape when it comes around. You can also put it on the belt pulley if you want.

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Red Paint Gotta Pull

01-26-2005 13:19:54

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Re: using a tachometer in reply to 1951G, 01-26-2005 10:35:43

You will get a up and down reading if a 2 cyl JD is idleing because it will run up and down. Idle it up until it kinda smooths out and check it then

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CASEPOWER

01-26-2005 10:51:04

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Re: using a tachometer in reply to 1951G, 01-26-2005 10:35:43

Try to get as far from the magneto, dist, coil, or MSD box as you can. Try to check your PTO and see if it stays consistent. If you have a diesel around check it, there is no spark interference on a diesel. You may have one of many that won't work right on a spark engine.

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1951G

01-26-2005 11:07:13

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Re: using a tachometer in reply to CASEPOWER, 01-26-2005 10:51:04

Thanks Casepower, I'll try the pto. This tractor is setup with the magneto and I'm on the opposite side where the flywheel is. Unfortunately, I don't have any diesel tractors to use. Knowing my luck, I've probably got one of the problem tractors that won't allow you to check it.

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01-26-2005 13:39:01

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Re: using a tachometer in reply to 1951G, 01-26-2005 11:07:13

Put the piece of tape on the biggest diameter available, EX. the outside edge of flywheel, this helps some times make sure to hold the tach. perpendicular to the centerline of the shaft your checking.

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