40021 Ben Morgan Road, Leonardtown, Maryland 20650-2521, Copyright Retained.
One of the most, if not the most, popular marine engine timers was made by Cuno of Meriden, Connecticut. I have not been able to determine the production life span, but it does appear it began about WWI and came to an end about the beginning of WWII. This simple but reliable timer was used by a large number of engine makers on one through four cylinder marine engines. The Cuno timer was also often used as a replacement timer for marine engines that had faulty or unreliable timers. See Figures A and B.
The Cuno timer is really very simple once one understands how it is assembled. It is also apparent that a lot of marine engine buffs don't understand how it is supposed to be assembled. Hopefully this article will be of help to those having Cuno timer problems.
The Cuno timer has four principal external parts:
(1) The timer case with handle that contains the lower (angular contact) ball bearing and an internal fiber ring mounting one to four contact segments which are insulated from the case. The contact segments would be connected to individual spark coils. (One coil per cylinder.) See Figure C 'A.'
(2)The cover containing the upper (angular contact) ball bearing. See Figure C 'F.'
(3) The top cap which contains a captive ?'-10/32 thread brass round head machine screw. It is not uncommon for the captive screw to be missing and it may be replaced without being made captive. It should be noted the top cap rotates when the timer is in operation but the COVER DOES NOT! REPEAT, DOES NOT ROTATE! If the cover rotates there is a serious problem that must be corrected if the timer is not to be destroyed. See Figure C 'C' for the top cap.
(4) The timer drive shaft. See Figure C 'D.'
The 'sector' is 'G' and it is critical to proper timer operation but it is not part of the timer itself. The radius of the sector must be maintained if the timer is to be held in any chosen position from 'Full Advance to Full Retard.' The teeth of the sector can become badly worn over long term use, but it is relatively easy to repair them with a three-cornered file. Close examination of the detent shown on the underside of the handle in Figure B or D shows the effect of years of wear on the detent. In this case one can see the wear on the underside of the handle on each side of the detent. The detent on this timer is so worn down that the handle itself rather than the detent has been resting on the sector. One should note the two brass rivet heads showing that attach the handle to the timer case. Also note the clearance provided around the bearing in the bottom of the case. The rivets and clearance permit bending the timer handle down slightly to maintain pressure on the sector. The whole timer will move around slightly when the engine is running, and this perfectly normal.
It is difficult but not impossible to rebuild the detent with braze and then file a new edge to meet the sector.
The timer drive shaft 'D' will be found with either a ?' or 5/8' bore to meet up with the engine timer drive shaft. The timer drive shaft will be found even in NOS with either 8/16,' or ?' long ?'/20 Thd set screw. Do not use the ?' set screw, as it will interfere with the sector.
Figure C shows the parts of the timer. Part B is the rotor which slips onto the drive shaft part D. Part B is found in either steel or brass, but the rotor is always steel. Either works well as long as the rotor receives an occasional drop of oil. Some old time watermen would fill the timer with grease to keep down sea water corrosion problems. Immediately after filling the timer with grease the engine might run rough for a few minutes until the rotor cleared the grease from the stationary contact(s). My own experience has been that the practice of filling the timer case with grease doesn't work very well, so I just keep the rotor shaft and the angular contact bearings oiled with SAE 30 weight motor oil.
One should note the flat on the timer drive shaft part D; its set screw and the rotor all line up. This is helpful when one wants to know where the rotor is without removing the timer cover.
The bushing and spring part E is installed between the cover and the cap. The bushing has a radius that mates with the inner race of the angular contact ball bearing pressed into the cover part F. It should be noted that there is a radius on the timer drive shaft which mates with the inner race of the angular contact ball bearing pressed into the timer case. It is important that there be clearance between the bottom of the timer case and the flat under the radius on the drive shaft. The precise amount isn't important; probably not more the 1/64' is adequate. What is important is the outer race of the angular contact ball bearing not be pressed in so far that it causes the rotor to wear on the underside of the cover. The same holds true for the bearing in the cover not being pressed in so far that it forces the rotor against the timer case. If one examines Fig. D part F slight wear is present on the underside of the cover. This wear is probably due to the rotor moving up and down on the drive shaft rather than the lower bearing being pressed in too far.
Fig. D shows how the rotor fits on the drive shaft. One should note that the flat on the drive shaft stops the rotor from sliding all the way to the bottom of the drive shaft. Occasionally a rotor will be found that does not slide down to the end of the flat on the drive shaft. Generally this will be caused by a burr in the hole in the rotor. A few passes with a file should cure the problem.
Occasionally a drive shaft that has had long service will be found with two slots worn where the rotor mates with the shaft. While this may throw off the timing, one can easily compensate simply by moving the handle a little further on a four-cycle engine but it may make it difficult to control a two-cycle engine easily when 'reversing on the spark'.
It is relatively easy to build up the worn areas with weld, grind the shaft round and mill a new flat on the shaft. This is probably much easier than attempting to make a new drive shaft because the distances and radius for the ball bearing must be maintained. The weld, grind and mill approach can be done with little regard for precision measurements, as sufficient reference surfaces can be maintained as the weld need only be two small areas on the drive shaft.
In the single cylinder timer there is a small brass screw opposite the contact segment. Occasionally this will be found to project beyond the face of the insulating fiber ring. This screw can be seen in Fig. C part A. This screw should not project beyond the surface of the fiber ring. If it does it will cause two sparks per revolution of the rotor which, while of itself may not cause engine operational problems, can cause the rotor to bounce and wear the surface of the fiber ring badly.
One should also check the fiber ring adjacent to the contact, as it will wear faster than the contact and in turn cause a 'ski jump' effect on the rotor. This can result in a very weak spark, particularly at higher engine speeds.
When assembling the timer the cap should not be screwed down so tight it binds the drive shaft and cap from rotating easily.
The angular contact ball bearings are NICE 505. These may be hard to find today but any bearing dealer should be able to find an essentially identical bearing made by another maker. Just give him the NICE 505 part number.
For a single cylinder engine, any of the one to four cylinder timers may be used. Just use one contact. For a two cylinder two-cycle engine a timer with two contacts at 180 degrees is required. A four contact timer may be used by selecting two contacts at 180 degrees. For a two cylinder four-cycle engine with the cranks on opposite sides of the crankshaft, a timer with two contacts at 90 degrees or a four contact timer may be used by selecting two contacts at 90 degrees. For a two cylinder four-cycle engine with the cranks on the same side of the crankshaft, a two contact timer may be used with the contacts at 180 degrees or a four contact timer may be used by selecting two contacts at 180 degrees. In a pinch, running a two cylinder four-cycle engine with the cranks on opposite sides of the crankshaft at low speeds at a show, a three contact timer will sometimes work satisfactorily. For a three cylinder engine one needs a three contact timer with the contacts at 120 degrees. For a four cylinder engine one needs a four contact timer with the contacts at 90 degrees. One should note that some early four cylinder marine engines had a firing order of 1234 rather than the later more common firing order of 1243.
One can easily determine the firing order by examining the intake and exhaust valve operating sequences. In the typical old time marine engine the exhaust valve is closed at top dead center, and the intake valve opens 8-10 degrees after the exhaust valve closes. Further, most old time four-cycle marine engines are left handed, that is the engine rotates counterclockwise when one faces the flywheel.
Most Cuno timers are brass, but some were made of steel; most of the steel units that turn up that were used in marine applications are rusted beyond use. They are directly interchangeable.
In conclusion any of the typical vibrator type spark coil work well with the Cuno timer. Six to twelve volt AC or DC may be used depending on the coil requirements. Model T Ford spark coils work well with the Cuno timer on six volts DC.
One coil is required for each cylinder. Coil paint erosion can be reduced by starting on six volt DC and switching to 8-16 volts AC for running. Early so-called 'Jump Spark' magnetos typically put out low voltage AC that depended on how fast the engine was turning. The advantage of AC being the points don't wear as fast as on DC. One trick the watermen used was to have two batteries and with a simple three position switch (Plus-OFF-Minus). They could run on a Plus to the coil for perhaps ? hour, then Minus for the next half hour. This not only reduced point erosion, it also lengthened battery life.
Remember, rotating the tier handle in the opposite direction to rotation of the time top cap ADVANCES the spark.