CL350 Electric Tach
Results 1 to 9 of 9
Like Tree1Likes
  • 1 Post By go_hercules

Thread: CL350 Electric Tach

  1. #1
    Senior Member go_hercules's Avatar
    Join Date
    May 2009
    Location
    Southern California
    Posts
    194

    CL350 Electric Tach

    I want to temporarily hook up a multi-meter to read RPM on my 1969 CL350. The meter says to hook one lead to ground and the other to the negative side of the coil. So that I don't have to remove the tank, can I just hook up to the wire off the points that lead to the coil since they are easier to get to? And in case you're curious, I want to do this to calibrate my stock tach that I rebuilt and replenished with damping fluid. Thanks.

  2. #2
    Sensei 66Sprint's Avatar
    Join Date
    Sep 2008
    Location
    Roanoke, Virginia
    Posts
    25,971
    Sorry, that makes NO sense to me.........
    Particularly because I don't remember the stock tachometer as having ANY fluid in it........
    (Well, maybe a tiny amount of oil on the bearing surfaces)
    Last edited by 66Sprint; 06-27-2019 at 04:03 AM.
    "I have a mind like a steel trap.....Old and rusty, of antiquated design, and hard to get stuff back out of...."
    Contact info: E-mail; [email protected] Phone; 540-525-5199

  3. #3
    Senior Member go_hercules's Avatar
    Join Date
    May 2009
    Location
    Southern California
    Posts
    194
    The speedos and tachs on these bikes are eddy current types, also known as drag cup types. The cable drives a cup with a magnet in it. This spinning magnet sets up an eddy current that drags an aluminum cup with a spindle shaft to which the pointer is fixed. The spindle shaft is constrained by a wound hair spring, which returns the needle and is adjustable for calibration. Along the spindle shaft, just below the dial face is a small aluminum cup, also known as a damping pot. In this pot is damping fluid, which is silicone fluid, usually with a viscosity of around 50K centistokes. If you have ever seen a needle bouncing around, or one that jumps wildly when the bike is first started, then you will know what happens when that cup is dry. The silicone fluid causes enough friction between the spindle shaft and the upper bushing to stop these oscillations. The fluid in the pot is the reason that you should never store a gauge of this type upside down - the fluid will slowly run out and get on the face of the gauge. In my case, I had re-filled this pot about 10 years ago and it has worked flawlessly until recently, at which time it started jumping around some. I refilled it and it is now dead steady once again. Most of the time when people post about this problem they are told to lube the cable, which doesn't work if the pot is empty. So when I had it apart, I put the hair spring back as close to where I thought it was before, but the RPM's seem off just a bit. That is why I want to tension that spring accurately with an external tach.

  4. Remove Advertisements
    HondaTwins.net
    Advertisements
     

  5. #4
    Sensei 66Sprint's Avatar
    Join Date
    Sep 2008
    Location
    Roanoke, Virginia
    Posts
    25,971
    Thank-you....I've now learned my something new for today.....

    Back in the day, we didn't fix them...just replaced them.....

    I've seen them (broken) apart, but ASSUMED the cup over the spinning magnet was steel.......
    Last edited by 66Sprint; 06-27-2019 at 10:01 AM.
    "I have a mind like a steel trap.....Old and rusty, of antiquated design, and hard to get stuff back out of...."
    Contact info: E-mail; [email protected] Phone; 540-525-5199

  6. #5
    Senior Member go_hercules's Avatar
    Join Date
    May 2009
    Location
    Southern California
    Posts
    194
    You're welcome. How about my original question, can I tap right off the points to measure rpm with my RPM capable multi-meter?

  7. #6
    Sensei 66Sprint's Avatar
    Join Date
    Sep 2008
    Location
    Roanoke, Virginia
    Posts
    25,971
    The points wire does carry positive power (until the points close), so the meter is acting like the static timing lights we use to determine pulses....Point wire IS coil negative......

    Again, just a guess, but sounds like it should work if the instructions say to connect it that way........
    "I have a mind like a steel trap.....Old and rusty, of antiquated design, and hard to get stuff back out of...."
    Contact info: E-mail; [email protected] Phone; 540-525-5199

  8. #7
    Senior Member go_hercules's Avatar
    Join Date
    May 2009
    Location
    Southern California
    Posts
    194
    Okay, I hooked it up directly to the points and it works fine. The lowest setting on the meter is 4 cylinder, so I have to double the reading, but it works fine. Now I am just fiddling with the little hair spring to get it just right. Luckily, the use of a clock spring with many turns makes the gauges pretty linear, so that if I calibrate it at mid range, say 5000 RPM, it stays pretty accurate at idle and at redline. Just thought someone else might want to try this someday.
    chaindrivecharlie likes this.

  9. #8
    Supporting Member Yendor's Avatar
    Join Date
    Aug 2011
    Location
    Camden County, New Jersey - USA
    Posts
    2,901
    Multiply by (4X).
    If the meter is calibrated to give you the RPM of (4) Pulses per CYCLE and you are only provideing an Input of (1) Pulse per cycle then Multiply by (4).

    Should work but the problem may be that the meter won't read well in that very low range.

    Idle speed on these bikes is approx 1100 to 1200 RPM so that means a meter reading of 275 to 300 rpm.
    1970 CB 350 CAFE - Current Project on the bench,
    1972 CB 350 K4 Red - Now a Happy Rider ! !
    1972 CB 350 K4 Green (My Sons) DONE - YES !,
    1st Bike 1970 SL 350 (Brought home in Parts - Trailer/Trunk/Back Seat - I miss that bike),
    2nd - Bike Kawasaki 750
    3rd - '73 XLCH 1000

  10. #9
    Senior Member go_hercules's Avatar
    Join Date
    May 2009
    Location
    Southern California
    Posts
    194
    Hey Yendor, you're right about multiplying by four. That's what I did but I think I stated multiplying by two earlier. From 4 cylinder on the meter to a two cylinder Honda is confusing. You would think it would be a factor of two, but the Honda twins can be thought of as two one-cylinder engines since they have their own coils without a distributor. Therefore, the factor of four like you mentioned. My meter seems to be very accurate throughout the range. The meter and the Honda tach are very linear throughout the entire range. Thanks for the pointers.

Sponsored Links

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •