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Old 03-15-2012, 08:47 PM   #1
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Portable Tachometer

So I was telling my friend who is a motorcycle mechanic that my tachs were not accurate.* I planned on using the fluorescent light / tape on the flywheel method to figure out when I was taching various speeds when the timing was right.

He tells me "what the fu*& are you doing?"* I have a portable tach that you can push up onto the flywheel.*** It is an amazingly simple device, and I plan on using it to calibrate my tachs which I suspect are off by some.

And in a related question -- since the tach comes from the alternator, and since a belt drives the alternator, can a loose belt cause bad tach readings?* My thought is yes.
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Old 03-16-2012, 04:59 AM   #2
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RE: Portable Tachometer

"and since a belt drives the alternator, can a loose belt cause bad tach readings? My thought is yes."

Yes , belt slippage will be a hassle , your alt tach readings will vary with charge and belt wear , heat and tension.

But for most cruisers "close" works fine.
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Old 03-16-2012, 12:58 PM   #3
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RE: Portable Tachometer

Often you'll find that the tach in the picture will have a pointed tip for use with shafts that have an indentation for a puller or on a regular tach drive fitting. Getting the point to sit and stay in position on a bolt head such as is found on the front of a Lehman engine or most other diesels to get an accurate reading will be more difficult. A photo tach will easily allow you to check and calibrate your tachs. Ask around your marina and I bet you'll find one that you can borrow. It will probably come with the owner who will help you and make the whole job easier.
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Old 03-16-2012, 03:34 PM   #4
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Portable Tachometer

Quote:
2bucks wrote:
Often you'll find that the tach in the picture will have a pointed tip for use with shafts that have an indentation for a puller or on a regular tach drive fitting. Getting the point to sit and stay in position on a bolt head such as is found on the front of a Lehman engine or most other diesels to get an accurate reading will be more difficult. A photo tach will easily allow you to check and calibrate your tachs. Ask around your marina and I bet you'll find one that you can borrow. It will probably come with the owner who will help you and make the whole job easier.
*never had a problem with mine...just have to get the hang of it and use the other "foot" that looks like the bottom of a door stop and has a flat face.

as long as you have it n hand..calibrating your tachs is a good idea...but that's the thing with alt driven tachs...your never sure if they stay calibrated.


-- Edited by psneeld on Friday 16th of March 2012 03:35:50 PM
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Old 03-16-2012, 08:39 PM   #5
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RE: Portable Tachometer

Quote:
2bucks wrote:
Often you'll find that the tach in the picture will have a pointed tip for use with shafts that have an indentation for a puller or on a regular tach drive fitting. Getting the point to sit and stay in position on a bolt head such as is found on the front of a Lehman engine or most other diesels to get an accurate reading will be more difficult. A photo tach will easily allow you to check and calibrate your tachs. Ask around your marina and I bet you'll find one that you can borrow. It will probably come with the owner who will help you and make the whole job easier.
*I don't know what a photo tach is...* I read on this forum that you could take a flouresecent light which cycles at 60Hz and a piece of tape on the flywheel*and when it makes a straight line at 1800.* I could never get that to work.* The motorcycle guy laughed at me (as some people here might) so I'll try his portable tach since it won't cost me anything.* But from what I understand, there are different "tips" for this that might make it easier.*** Thanks for the help from all responders.
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Old 03-16-2012, 11:58 PM   #6
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RE: Portable Tachometer

If you want a digital laser tacho get on flea bay they sell for about 16 bucks and delivered in a few days.

Bloody good value IMHO
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Old 03-17-2012, 04:00 PM   #7
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RE: Portable Tachometer

Quote:
psneeld wrote:2bucks wrote:
Often you'll find that the tach in the picture will have a pointed tip for use with shafts that have an indentation for a puller or on a regular tach drive fitting. Getting the point to sit and stay in position on a bolt head such as is found on the front of a Lehman engine or most other diesels to get an accurate reading will be more difficult. A photo tach will easily allow you to check and calibrate your tachs. Ask around your marina and I bet you'll find one that you can borrow. It will probably come with the owner who will help you and make the whole job easier.
*never had a problem with mine...just have to get the hang of it and use the other "foot" that looks like the bottom of a door stop and has a flat face.

as long as you have it n hand..calibrating your tachs is a good idea...but that's the thing with alt driven tachs...your never sure if they stay calibrated.



-- Edited by psneeld on Friday 16th of March 2012 03:35:50 PM

*That's a great solution. If you have a flat foot for it and can find it. I don't think I've ever come across one that had anything but the pointed one.

Ken
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Old 03-17-2012, 04:07 PM   #8
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RE: Portable Tachometer

easily found on ebay-

pointed tip

Stewart Warner Hand-Held Tachometer Rubber Tip 96798

flat foot tip

Stewart Warner Hand-Held Tachometer Rubber Tip 96799
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Old 03-18-2012, 07:35 PM   #9
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RE: Portable Tachometer

Nice..* You guys are awesome!
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