Tach accuracy question

[Tony Radford]

I'm running the MSD 6A contoller, MSD distributor and coil. My SW tach has operated correctly in the past, but when my engine was replaced, a new MSD distributor with a smaller diameter cap (the old distributor interfered with the new intake manifold) was installed. Now my tach has a 1,000 RPM higher reading and it won't zero. The tech at MSD told me that I needed an MSD 8920 tach adapter ($50) to fix the problem. Does this make sense? The wiring went back the same way it came off and the parts are still all MSD. I hate to drop the bucks if I don't need to. Any suggestions?

[CJ428CJ]

I'm running a Stewart Warner tach and an MSD distributor in my 428 and I don't use a tach adapter. The instruction manual that came with the MSD6 did list a bunch of different tach brands that would require the adapter but Stewart Warner wasn't one of them. Besides, the signal to the tach comes off the MSD 6 and not off the distributor so I don't see why changing the distributor would make a difference. But, on the other hand, I would expect the tech line at MSD to know more about it than I do.

Chris

[sllib]

Tony;
I'll be facing a similar problem soon. Just for future reference,
what intake are you using, and did it fit under the stock Unique hood?
Bill Stradtner

[Tony Radford]

Bill, yes it did fit. The intake is a Vic. Jr with a Mighty Demon carb and the 15" oval cleaner with 2" high element. I have about an inch of clearance. I can't describe how awesome the engine is, both in looks and performance. As soon as I can marry up with a good digital camera, I'll get some good detailed shots of the engine in the car.

Chris, I believe the problem may be in the MSD controller ground. The unit was grounded to the previous intake manifold, but now is grounded to one of the polished valve cover studs. It seems to work correctly intermitently. I'm going to move the ground lead to a better point and the problem will probably go away. I will post the results.

[Cracker]

Tony R. Give me a call at 770-664-7670. I want to hear about your new beast and may have some imput on your tack issue.

[HighPlainsDrifter]

Tony,
Another thing that the gauge manufactures don't tell you;

the needle movement is dampened so that the tach doesn't bounce all over the place.
This makes the tach slow to react to fast- going through the gears acceleration. I run a msd shift light with plug in pills. My 5" autometer tach is 400 rpm slow at 5,500 rpm .....The light comes on but the tach movement is only at 5 grand, so you are actually over revving your engine waiting for the tach to catch up.At a steady rate the tach is accurate.
Perry.

[Russ Dickey]

Tony:
Yes, please do post your results as I am struggling with the same tach issue. I also have the old-style SW tach in my Unique, along with the MSD coil and 6AL box with a Mallory distributor.

Sometimes it seems to be accurate, sometimes it bounces all over the place, and sometimes it's just dead wrong (like 1000 rpm wrong). I can shift just fine by ear, but it drives me crazy nonetheless.


Thanks,

Russ

[Tony Radford]

Russ, did MSD tell you that you needed a tach adapter since you are running a non-MSD distributor? Go to their web site and look at the product description. That may solve your problem. I'm running all MSD equipment. I believe I have a ground problem.

Tony, I'll call you tomorrow.

[Len Hurlburt]

Guys: Does this sound familiar:

- Unique
- MSD 6A
- SW Tach
- Mallory Distributor

I have this set-up and I swapped out the SW tach because it seemed to have a mind of it's own. Sometimes it would work, and other times it seemed to wander around. I replaced it with a new SW tach and everthing was OK for about a year. Now the replacement is starting to do the same things, although mostly on start-up. I'll be watching this thread closely. If anyone has a fix, please let us know. Len

[Cobra20646]

Len,

A fellow club member has the same problem (Unique + SW). My older Unique with a 20 year old tach 'was' working fine, but now starts reading high at times..... and rapping the glass with my knuckle seems to restore normal ops.... suspect something loose inside, but that's another problem.

Getting back to my friend, I put his tach on the bench and tested it with test equipment and the thing was accurate to within a few percent all to way up the scale. Went over all the wiring, paying attention to grounds and ground loops..... everything looks good. I suspect that there is something about the "signal" from the ignition system that the tach gets confussed over, hence the "tach adaptor" that's been talked about. It must condition the signal so that the tach sees a "cleaner" signal.

My tests have shown that trying an old fashioned points distributor makes the problem go away.... something to be said about compatablity problems between old and new stuff

Like you, I'll be looking back to this thread for solutions.

- Jim -

[Steve R]

SW = "Stewart Wornout"

[JoeLafives]

I'm running a Mallory Unilite Distributor and a their Power Coil. No MSD but I'm getting a lot of bounce. I'd heard it might be the ground.

Any thoughts about running a Unilite with an MSD 6AL?

[Dennis Mosley]

Jim,

I seem to be having the same problem that you are having with your SW Tach. Some times I'm driving along and look over at the tach and its reading way high. I tap on the glass and it goes back down to the correct reading. If you find out what the problem is with yours please let me know.

I am running all MSD and have not changed a thing. This problem just started happening.

[Tony Radford]

Have we discovered an epidemic or what?

[sllib]

I just put in my order to Alan Weaver at Unique yesterday and specified the Autometer guages, so hopefully I won't have this problem. I have no doubt, though that the garage gods have a unique set of problems in store for me...
Bill Stradtner

[Len Hurlburt]

OK, has anyone tried one of the MSD tach adapters that Tony mentioned earlier?

[Cobra20646]

Originally posted by Dennis Mosley


Jim,

I seem to be having the same problem that you are having with your SW Tach. Some times I'm driving along and look over at the tach and its reading way high. I tap on the glass and it goes back down to the correct reading. If you find out what the problem is with yours please let me know.

I am running all MSD and have not changed a thing. This problem just started happening.

Hi Dennis,

It's on my short list of things to do in the "off season", which by this mornings ride in the low 40's, is going to start any day now

Opening the thing up is not going to be easy, if it's anything like the speedo! I had to replace the glass in my speedo, and had to "un-roll" the crimp ring around the whole circumference of the thing. Can't tell where I boogered it up after it's back in the dash! I'll post something later when (if) I find anything broken inside.

- Jim -

[rdorman]

Mine seems to read correctly at cruise but when I stand on it, it reads fast. SW tach with Mallory Unilight Dist. This problem has seemed to pop up just of recent. Any experience with this issue?
Thanks
Rick

[Len Hurlburt]

Rick, It sounds like you have a variation of a common problem. I've sent an email to the tech support area of SW to see if they might be able to shed some light on this. From what I've read here it seems the only common pieces between all of us is a SW tach and a pointless distributor. Jim's comment that when hooked to a point type distributor, the SW tach reads OK. This would seem to support (for some reason) these tachs not liking this set-up. If anyone would like to forward their comments to SW, here is the email address: rthibodeau@maximatech.com
Len

[rdorman]

Thanks Len, I also sent him a note. I will post the response.
Rick