TAD for Serpentine Pulley Kits - Perkins 4.107 Pulley Kit - Perkins 4.108 Pulley Kit  - Westerbeke 40 Pulley Kit





Serpentine Pulley Kit
Slipping Belt Problem on your Perkins 4.107 4.108 & Westerbeke 40 Solved

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     With more & more electronics being used on boats, the demand for more 12v DC amperage is increasing. If you are using a high output alternator on a Perkins 4.107, 4.108 or Westerbeke 40 with a standard belt, you already know the problem.

FOR PERKINS 4.107 and 4.108

    Trans Atlantic Diesels Inc. can supply an easy to fit serpentine pulley kit (6 groove) for the Perkins 4.107, 4.108 & Westerbeke 40. With this kit you can achieve in excess of 150 amps 12 volts DC without the belt slipping (providing your alternator has the capacity).

    Anyone who has tried to extract much more than 65 amps out of the original pulley and belt configuration, will know that black belt dust and squealing from the slippage are all too familiar. Over tightening the belt is not the answer as you will find out in the next paragraph.

Shown above: Perkins 4-108 with Bowman manifold and Balmar with 2 mounting foot.

Important: Tech Tip Warning!
     An over tightened belt, operated over a period of time, can cause metal fatigue on the front section of the crankshaft. This can result in failure, breaking the crankshaft at the #1 journal. This generally occurs when owners have over tightened their belt in an attempt to stop or reduce slippage. The serpentine belt will not slip using the same recommended tension as used on the V belt. See figure 2 below.


  • A. Crankshaft Serpentine Pulley p/n T336-108C

  • B. New Fresh Water Pump with Serpentine Pulley already fitted p/n T0054/336- 108W

  • C. Serpentine Pulley for alternator. (17mm bore) Fits the Balmar 60, 70 and 90 series and most common Delco Alternators and others. p/n T3781

  • D. 6 Groove Serpentine Belt p/n T060400 for 4.108
    Only for Westerbeke 40. 1 x 6 Groove Serpentine Belt p/n T060415

  • E. 1 3/8 x 3 1/2 hose to extend fresh water cross pipe to clear the wider belt (only needed if Bowman Manifold is fitted.) as pictured above. p/n T1.3750

Figure 1 Kit Assembly

  • F. Front crankshaft oil seal in case the original seal is damaged during pulley removal. p/n 0730098

  • G. Only for Westerbeke 40 Bolt and spacer kit. for Balmar with 2 mounting foot: 1 x crankshaft bolt 32162316, 1 x crankshaft washer 33124119


  • We recommend ordering a spare belt. Let us know which alternator you have to ensure we supply you with the correct size pulley, as these will vary between manufacturers. We cover the most commonly used sizes per item C above.

  • Your kit will include a new water pump with the serpentine pulley already installed.

  • For future reference, if you have a 4.107 or a Westerbeke 40, the part # for a replacement water pump using our serpentine pulley system will now be U5MW0054

  • This is a standard 4.108 pump which is fully interchangeable but has a larger diameter shaft than the 4.107 pump.

  • The part # for replacing a 4.108 pump is unchanged.

  • For our records and future guidance, let us know if you have a 4.107 a 4.108 or a Westerbeke 40.


     1. Crankshaft Pulley - Remove positive battery leads from starter motor and isolate positive lead from battery. It will be necessary to stop the engine from rotating when removing and re-torqueing the crankshaft bolt. This can be done by removing the starter motor and placing a pry bar in the ring gear teeth on the flywheel. An impact wrench can be used for removal but will not ensure the correct torque when re fitting. Remove the original crank shaft pulley retaining bolt with a 1 standard socket for the 4.107 & 4.108. For the Westerbeke 40 use a 1 1/8.socket. With the bolt removed the pulley should pull off quite easily by using two hands and pulling evenly on both sides. Do not pry against timing cover. This is a good opportunity to inspect front seal for leaks and replace if necessary, as the seal is now fully exposed. One is included in the kit. Re fit the crank pulley applying a smear of grease to the polished area on which the seal rides. 4.107 & 4.108 tighten the retaining bolt to 230 ft lbs if you have a phosphate bolt (dull finish most popular) or 190 ft lbs if you have a cadmium coated bolt (shinny).

     Westerbeke 40 Only.  Owners can purchase from us the necessary replacement larger phosphate bolt (part# 32162316) and washer (part# 33124119) to fit in place of the original one. Tighten with 1" socket to 230 ft lbs.

The Westerbeke 40 requires some additional bolts and spacers to re-align alternator to be placed as shown above.
Westerbeke 40 with Balmar 2 foot mount

     2. Water Pump with Pulley - Drain anti freeze coolant. Remove the old fresh water circulating pump. Clean the gasket surfaces, and fit the new water pump which will have the serpentine pulley already installed. (new gasket supplied). 4.108 Owners with the Bowman manifold. (as configured in the above picture) will be required to fit the short supplied hose to bring the fresh water cross over pipe forward slightly to avoid contact with the new serpentine belt. This will replace the existing hose. This does not apply to others not using the Bowman manifold.

     3. Alternator Pulley - Replace the V pulley on the alternator with the serpentine pulley. An impact wrench works well for this. Some alternators have a provision in the end of the armature shaft for an allen wrench to hold armature from turning while tightening with an open wrench. Torque may vary according to your alternator manufacturer.

     4. Serpentine Belt & Tension - Fit the new serpentine belt. Tension should be adjusted using the original alternator adjusting arm so that, with normal thumb pressure, the belt can be depressed 3/8 of an inch at the center of the longest span. (per fig 2) NOTE. The new belt will require re tightening after a few hours of operation. This check should be done while the engine and belt is warm. Continue to check tension until the new belt no longer stretches. Following this procedure, periodic checks should be made checking condition and tension.

Carry a spare!

     5. Replacing Coolant - If you have not changed your coolant within the recommended period, this is a good time to do so. We suggest a good quality extended life ethylene glycol anti freeze with corrosion protection and rust inhibitor. Once coolant is filled with a 50% 50% mix, approx. 6.6 qts., not including hot water heater, check for leaks. Be sure to vent the air, and monitor the fluid level and temperature carefully before and after engine comes up to working temperature. Caution: Do not remove cap to check level until engine has cooled down as the system will be under pressure and could cause burns.


These instructions are for installation guidance only.
All normal safety precautions should be followed.


To ensure our Serpentine Pulley Kit will work with your 4.108 4.107 or Westerbeke 40 engine, please identify which set up your engine currently has, as not all will accept the kit.

Figure 1 - 4.108 Bowman combined Header tank/heat exchanger/manifold

Shown in figure 1 is the 4.108 Bowman combined header tank, heat exchanger and exhaust manifold. This unit WILL ACCEPT our Serpentine Pulley Kit.

Figure 2 - 4.108 North American Front Tank
Shown in Figure 2 is the North American front tank as fitted to the 4.108. This configuration WILL ACCEPT our Serpentine Pulley Kit.
Figure 3 - Westerbeke 40 Front Tank
Shown in Figure 3 is the Westerbeke 40 Front Tank. This configuration WILL ACCEPT our Serpentine Pulley Kit.
Figure 4 - Shows 4.108 Low Line Tank
Shown in Figure 4 is the 4.108 Low Line tank. This WILL NOT ACCEPT our Serpentine Pulley Kit without modification to the tank. Contact us for details.

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This Page Last Updated June 01, 2020

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