• Causes of Boat Starter Motor Failure

    Water intrusion is the #1 cause of starter failure. If water gets pumped into the motor portion of the starter from the flywheel, it will not drain out. Rust and corrosion will destroy the inside components of the starter.

    The #2 cause of starter failure is water ingestion into the engine. Leaking exhaust manifolds, gaskets and risers are often the source. Damage to the mounting pads indicate the starter has been loose on the engine; possibly caused by water ingestion into the cylinder. Although the engine may not experience a complete hydro lock, if enough water is on top of the piston to raise the compression to a high level, the starter bolts and mounting pads will be stressed beyond normal load conditions.

    Drive Gears are another common cause of failure. Do not condemn a drive until it has been tried in actual operation and proven faulty. The Folo-Thru type drive currently used on many starting motors has brought about difficulty due to a misunderstanding of operating and lack of information on proper servicing. This fact has been reflected by the number of drives returned for warranty which are fully operative.

    The Folo-Thru drive is designed to lock and remain in the extended or engaged position until the engine starts and reaches approximately 400 to 500 RPM. The drive to flywheel rotation is fifteen to one. When the engine is turning at 400 RPM, the starter drive gear is turning 6,000 RPM. If the drive is locked in the extended position it has to be reinstalled on the engine and the engine started or the drive must be turned in excess of 6,000 RPM by a wire wheel mounted on an electric bench grinder to make it disengage.

    The reason the pinion locks in the engaged position is to assure the starter continues to crank until the engine has started, thus preventing false starts. This is accomplished by using a spring loaded pin which rides on one of the pinion screw threads and drops into a hole when the pinion is in the fully engaged position. This locks the pinion in the engaged position. When the engine starts, the flywheel of the engine drives the starter pinion. A clutch mechanism is built into the pinion to protect the starter from excessive RPM.

    The clutch allows the pinion to turn faster or overrun the armature shaft. When the engine reaches 400-500 RPM, the pinion spins fast enough to create the needed centrifugal force to throw the spring loaded pin out of the hole in the shaft and allow the pinion to disengage.

    This information is from the ARCO Starting and Charging Catalog which can be found on this website.

    Comments 2 Comments
    1. Centani's Avatar
      Centani -
      I own a 1986 Chris Craft 17' I/O drive. With a 1985, 181Cid 140hp Mercruiser I4 ....I don't have a lot of experience working on Marine Engines.

      Today when I took the starter out (bytheway thatsmine W/theSelinoid ontop) and looked at the flywheel it looked all wet, at closer inspection it looked like the bottom 1/3 or so was sitting in water, I thought this awfully peculiar, am I wrong ?

      Centani
    1. charlie54's Avatar
      charlie54 -
      I hope someone can help me. I left the lights on and ran the battery down. I got a new battery and put it in the boat and when I went to start it there was nothing. it didn't even click. the light and horn work but nothing at the key. can anyone help?