Confused about Tachometer

[Ranger01]

when i bought my boat there was a tach installed in the helm that had not been hooked up to anything, i have since replaced the engine and when i went to hook up my tach i read a sentence in my seloc manual saying that it can be bad to not have the right tach for your engine and it can seriously damage the ignition. However that was the only info it gave me. The tach goes up to 70,000 rpm and says VDO on the bottom. there are three screws in back, one for a ground the other i imagine goes to the enige and the power source. What i'm wondering is how do i know if this particular tach will work?

 

[Mark42]

Re: Confused about Tachometer

Ranger01,<br /><br />Generally I found that tachs that are not connected do not work. But you can try to connect this one, it can't hurt. It probably will work if it has an adjustment on the back that lists 2, 3, 4, 5, 6 etc. Those number match the number of poles in the alternator of the outboard. If it has this adjustment, you need to set it to the proper pole setting, then figure out which of those screws is the ground, +12v, and tach sender. Usually Evinrude/Johnson use grey for the tach sender.<br /><br />Start with the VDO website, they probably have diagrams and pole setting there.

 

[Ranger01]

Re: Confused about Tachometer

I also found that things not conected generally dont work to well, story of my life! i didnt conect it because of what my book said about it ruining the ignition if it were the wrong type, it scared me. how do i go about finding out about the pole adjustment. i dont know anything about that kind of stuff.

 

[Mark42]

Re: Confused about Tachometer

I have a Teleflex brand tach. On their website they list most all motors and the tach settings for each. Check out VDO's site, I'm sure they have something similar. BTW, VDO makes quality guages. If it works you just saved about $85.

 

[Ranger01]

Re: Confused about Tachometer

that's good to know! i did check out vdo's site and while they had a lot of different gages i didnt find anything that would tell me which unit to use them for, i will however check out teleflex's site and see if they mention it anywhere. i did fond a gage on vdo's site that was very similar to mine, it went up to 70,000 like mine did and was the only one to do so, next to it, it said 12volt only, 12 pole alt. i know what 12 volt is, i'm not sure about the 12 pole alt. do you know what it is?

 

[danlee987]

Re: Confused about Tachometer

HEY!!! I have been reading thru the threads sopping up all the great info. I was thrilled to think I might be able to add something(WITH MY LIMITED KNOWLEDGE) I am struggling thru Tach issues. I have been to a site http://www.egauges.com/Inst_PDF.asp#Tachometer <br />There are adjustments and other info listed here for VDO tachs. Hope it helps

 

[Mark42]

Re: Confused about Tachometer

12 pole alternator means there are 12 poles internal to the alternator and those poles make the pulse signal the tach reads. So the tach needs to know how many pulses it is getting per engine rotation to display the RPM's correctly.<br /><br />Generally speaking, a 12 polt alternator uses the 6 setting on the tach. Having it wrong won't damage anything, but the tach will display incorrectly. IE if it needs to be on 6, but you set it to 4 then it will be off by 1/3.