Robertschas

I need help again. You guys have hit my last problem right on the head so here we go again. 1995 Dodge 3500 with 12 valve Cummins. It has an oil leak on the front of engine right behind the water pump? Leaks only when the oil filler cap is on, almost like a build up of pressure in the engine: i mean it pours out! Take the fillier cap off and the leak stops. Not the front main seal as it is not that low. You can actually see (from the top) the oil seeping out of a space where the water pump fits on the block when the engine is at fast idle. Again, taking the oil cap off and the leak stops. Engine only has 116K on it so can't be blow by , can it?
Thanks for you help.

dslpower

Sounds like a classic symptom of the Killer Dowel Pin. Has the pin on yours been tabbed?
If not then most likely the dowel pin has worked out of the block and fell on the cam gear and got wedged in between the gear and housing, cracking the aluminum timing gear cover.
You will have to remove the water pump to check and see if that has happened.

Robertschas

I guess i don't know what i am doing here as i don't know where or what that dowell pin is for. What does it hold on? Is it behind the timing chain cover? If it did come out how do i prevent it from doing that again? Come to think of it, the mechanic that looked at it did say the leak was because the seal between the engine and chain cover was bad.
You seem to know a lot about these engines and maybe you can recommend a good repair manual that gives lots of details on this thing. Chiltons was the best at one time but can't locate any of their manuals anymore for some reason.
Thanks.

xmr

do a search on this site for KDP ( killer dowell Pin) You will find more info than you can imagine. Plus there are some good photos and how to info. You will also find some ways to repair that no manual will give you.

Robertschas

OK. Thanks a lot. Pictures are worth thousands of words when you don't know what you are looking for.
thanks.

VACHZHD

look here for one of the best summaries of how to do the repair I've seen - complete with photos... Good luck.

http://www.tstproducts.com/DowelPina.pdf

Robertschas

Man, that is a cool site. That is exactly the kind of instructions a person like me needs. Could not have been better.
NOW, i saw the pin and it is exactly where my oil leak is, but the leak is to the left of the pin on the outside of the case right about the level where the freeze plug is but a little lower near that next notch in the case. Could it be that the pin worked out so far or maybe all the way? If it worked out all the way is the oil coming thru the pin hole? Guess my question really is, where is the oil coming from and how come it doesn't stay inside the case rather than exiting?
thanks.

infidel

These instructions are on how to prevent the problem from occuring. It sounds like it has already happened to you, you're too late.

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. Sounds like this is what happened to you

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.

Robertschas

OK. We are on same wave length here. The engine runs great and the oil leak only happens when i put the oil filler cap back on. There are no visable cracks in the aluminum housing so i guess it' still OK. Next question is how is oil getting to the outside? When i put the oil cap back on and rev the engine, i can see the oil coming out between the aluminum case and the block about where the freeze plug is. Could it be that the dowell has dropped to the pan and the oil is being forced out the dowell hole?
Guess i will find out for sure when i tear it down.
Thanks

infidel

When a loose dowel pin does it's damage the crack that oil leaks from it almost always under the fan pulley where you can't see it. No oil flows from the dowel hole, it's into the solid steel on the engine block.
This is what the damage looks like and what's involved to fix it>
http://www.cumminsdatabase.com/read.php?id=111

The fact that the leak is worse when the oil cap is on leads me to believe you have two different problems going on, the leak and excessive blowby. The blowby could be caused by a plugged up blowby tube, a vacuum leak, valves out of adjustment or bad rings.

dslpower

Quote "When a loose dowel pin does it's damage the crack that oil leaks from it almost always under the fan pulley where you can't see it."

Yep, thats where mine is cracked, dowel pin fixed but I had to JB weld and silicone the housing. At the time I did not want to pull the cam to put the new housing on.

Jeff in TD

If you look in my gallery, you will see a couple of photos of where the gear case cracked in a company truck I was using.

Though it's my understanding that they don't usually blow out that bad (where you can see the gear inside), it will give you an idea of where to look...

Robertschas

INFIDEL,
Excellent article and demo. Best i have ever seen. Tells me exactly what i need to know and answers my questions. My special thanks to you and also thanks to all who contributed to this problem.
Chuck