Performance  Est. 1986

Specializing in Diesel Service and PerformanceText Box: To schedule an appointment for this service call...


Dowel Pin Awareness

 If you have heard of “dowel pin issues” on the 12 valve Cummins 5.9 with the P7100 Bosch injection pump then you may already have taken care of your truck. This dowel pin issue applies to all ’89-’98 12 valve Rams with Cummins engines and many other non-Dodge Cummins 12 valve engines. If you have not heard of the issue, or you heard yet have done nothing and you are the owner of one of these vehicles, listen up.

A dowel pin failure could destroy your engine completely or do no damage at all.


The aluminum front gear housing on the 5.9 Cummins is precisely located on the front of the cast iron engine block using dowel pins. The dowel pin is about 5/16 inch diameter by 3/4inch length made of steel. During engine assembly the dowel pins are driven into holes drilled in the block such that about half their length protrudes. Matching holes in the gear housing permit a precise fit of the housing the block. Several cap screws are used to hold the housing to the block. The problem with the dowel pin occurs because the hole in the aluminum gear housing was drilled through. During engine operation vibration could cause the dowel pin to work its way out of the hole and fall into the gear case. When the dowel pin falls, it can drop right to the oil pan or land in the gear housing, causing no damage at all. On the other hand, the pin can be caught in the camshaft gear and forced into the aluminum gear housing, breaking out a big chunk of the housing which would cause a huge oil leak and an expensive, time consuming failure.


Worst-case failure is when the dowel pin goes between the cam and crank gears, or cam and injection pump gears, breaking the gear off the camshaft. The camshaft stops rotating instantly causing valves to stop operating, leaving some valves open and some closed. The crankshaft continues to rotate for a few seconds, slamming pistons into valves, and possibly ruining block, crank, rods, cylinder head, and valve train. Almost no reusable parts in this case, a complete engine swap could be required.


If you are the owner of one of these 12 valve 5.9 engines and you haven’t taken preventive action, we suggest you take action before the vehicle strands you in a bad location with an expensive repair bill.


Mac’s offers a “Dowel Pin Kit” that includes the parts to access the dowel pin, positively lock it in place so that it does not come out. Installing this kit requires removal of the engine fan shroud, fan, damper, and front gear cover to gain access to the dowel pin. Once the dowel pin is secured, a new crankshaft seal included in the kit is installed in the gear cover and all parts are reinstalled. Installation takes 3-4 hours.