bertram31.com

1985 merc 454s with thunderbolt ignition.

VDO viewline tachs

Aparently these are not compatible, after two sets of guages and calls to VDO and the retailers tech line. When accurate at idle it under reads at higher RPMs and when accurate at cruise it overreads at idle.

I was told I would need an inductive sender that counts the flywheel teeth and there may be a 7/8s threaded fitting on the bell housing but maybe not.

Is it worth the trouble or should I just get a set of tachs that will work without having to go through this trouble?

Of course I did this just prior to Sandy and have no boxes for the installed guages and spent a lot of time and money having the plug and play connections for the VDOs added to the wiring harness..

Mechanic suggests just putting in a set of Farias

It shouldn't be that big a deal to install if this is it and you have the hole. Even if not, get a good bi-metal hole saw.

http://www.vdo-instruments.com/sensors/ ... kup-2.html" onclick="window.open(this.href);return false;

http://www.vdo-instruments.com/media/in ... Sender.pdf" onclick="window.open(this.href);return false;

Note that this document says the tachs have to have an hourmeter built in to work with this sender.

Peter,
I have the tachs from steve marinake's refit. They are original gas thunderbolt ignition as marked on the back. 0 to 6k.
Was gonna toss em cause they aren't worth anything really. Your welcome to em.

Bruce I appreciate the offer but I bought all new white guages, hoping to find ones that work and match the rest of the guages.

Check then with folks at isspro. Their sales and tech support have been good for me in the past.

http://www.isspro.com" onclick="window.open(this.href);return false;

Bruce,

Don't throw out those tachs just yet. Isspro also does not make a tach compatible with the thunderbolt ignition. Thanks I called them..

Pete

An alternative is to get ac taps on the altenators to drive newer tachs if they don't have them already.
Any alt shop can do it.
Just keep the belt snug.

I contacted just about everyone gauge company I could think of the only positive I got was an email from faria

Any of our Inboard or I/O tachs will work if you hook it up to the negative side of the coil.

To be honest I'm not really sure what that means.

Pete-
Have you tried Teleflex? I purchased some of these:

and expect them to be direct replacements for the Teleflex units that were in my boat like this:
..

Negative side of the coil is where the pulse comes from to drive the tach signal.
Other side is plus battery voltage. Would kill the tach.

If memory serves me on the thunderbolt ignition the tach signal comes off the module not the coil.
But not 100% , been to long since I've serviced one.

Check where your current tach signal comes from, module or coil.

Stephan,
Peters vintage thunderbolt ignition does not use a standard tach. Similar to the old sun Tachs.

Peter,
My 78 B33 has several notes in the owners manual that Bertram modified the wiring harness to work with the Thunderbolt I ignition. Neber could find out what the modification was. The prior owner replaced the Merc distributors with Mallory. When I bought the boat I found that the tachs were way off. I put all new Teleflex gauges on the bridge & found the new tachs were off also. I ran new wires from the bridge to the negative terminal on the coils & the new bridge tachs now read correctly.
Al

I installed an all new set of Faria guages on the bridge of my B31 about a year ago. They look pretty good and are very accurate. Then the first rain came. One of the temperature guages and one of the oil pressure guages fogged up. Then it rained again. The other temperature guage fogged. Then my brother washed down the boat after a fishing trip. Forgot to tell him not to get water anywhere near the bridge guages. Right, marine guages, just dont get them near water! Two oil pressure guages and one temperature guage fogged and one temperature guage half full of water. Of course none of this happened until the warranty expired. I replaced the water logged temperature guage. The tachs and the voltmeters have yet to fog up.
I just replaced the guages at the lower helm today. Teleflex Lido series. They look great and seem to be working perfectly but it has only been one day. I had the Lido series on a prior boat and they were accurate and never leaked even after heavy rain or washdown, however after two years the tack pointers deformed/curled which of course made them useless. (One of the reasons I tried the Farias this time.) All I could attribute it to is a couple of very hot triple digit Texas summers. I replaced them and whenever not in use, since they were in direct sunlight for part of the day, I placed a towel over the instrument cluster and never had the problem again. The direct sunlight seemed to be the problem but I am hoping that whatever the problem was, Teleflex has corrected it. They were all still working great when I sold that boat. I also have the same Lido series in my center console boat and have never had a problem with them but that boat stays in the barn when not in use. I will be turning the Farias on the bridge into crab trap weights and replacing them with the Teleflex in the near future.
I have the Chrysler 440s and the tachs wire into the modules rather than the negative side of the coil but they should work either way.
I just thought I would pass this along for whatever it is worth. Good luck!

Al,

The boat is a 1969 and the motors are 1985. I don't think the harness has been modified in any way.

Parker,

I've read other negative reviews about Faria on this site and is a big reason I went with VDOs against my me hanics recommendation.

If hooking up to the negative side of the coil means choosing the right wires in the harness the farias are the right solution for me. If it means I have to run new wires from engine to bridge I might as well stick with my VDOs and add the inductive sender.

My me hanic may know the answer I will check with him today. If anyone can clear that up I'd appreciate it.