CAT 3208TA timing advance unit

[Mischief Managed]

I think one of mine is bad and am close to removing it (it's a bit of work). Anyone here ever dealt with a bad one? The engines runs OK but has more vibration than the other engine at low speeds and uses a bit more fuel. When it's idling, the V belts vibrate like crazy which I think is caused by the crankshaft speed varying in every revolution. Additionally, the tach sending unit (which is driven by the timing advance unit) sends out extra little electrical pulses that trick my Aetna tach into reading high. I can see the pulses on my oscilloscope. I swapped tachometers and sending units and the problem always follows the engine.


I think one of the springs in the timing advance unit is fractured and it's advancing at too low of an RPM.



Your thoughts?

 

[Scottwb96]

no input, but I have the same engines, so curious to see what people say...

 

[High Wire]

Can you swap it to the other engine or is that more work $$$ than replacement?
Also what does Boatdiesel say?

 

[Mischief Managed]

Can you swap it to the other engine or is that more work $$$ than replacement?
Also what does Boatdiesel say?

It's way too much work to swap from one engine to the other. The work requires lifting the engine high enough to get the oil pan off and then the 130+ lb front housing has to come off carefully. Of course, the front lifting points for the engine are on top of the front housing, so after the oil pan is off, the engine had to be propped up or suspended in the air, from something other than the front lifting points, to take the front housing off. I have engine suspended by a 10,000 lb nylon tow strap wrapped under the bottom of the block right now and expect to get the front housing off today.


Boatdiesel did not have much to say about my particular symptoms, but I did speak to a master CAT mechanic and he thinks my theory is plausible for the symptoms seen. One thing I forgot to mention is that this timing advance unit was frozen at full timing retard at the beginning of last the 2021 boating season. I had to gradually increase RPM under load until it finally popped free and advanced, so there's some extra incentive to inspect it regardless. I could live with it like it is forever, but I need to replace the front port engine mount on this engine, so I figured while I have the engine lifted for that job, I might as well dig into it. I already had the gasket/seal kit for this work in my spares inventory too.

 

[Mischief Managed]

I got the timing advance unit out today and it has a broken center bearing. Not 100% convinced it was the root cause of the problem, but it sure seems likely. They don't sell the bearing separately and they no longer make the advance unit, so I'm buying a used one. Fingers crossed that it solves my issues. Once I have the new part in hand, I'll press the rivets out of the old one to open it up and see if there's anything else wrong with it.

 

[Southern Boater]

I got the timing advance unit out today and it has a broken center bearing. Not 100% convinced it was the root cause of the problem, but it sure seems likely. They don't sell the bearing separately and they no longer make the advance unit, so I'm buying a used one. Fingers crossed that it solves my issues. Once I have the new part in hand, I'll press the rivets out of the old one to open it up and see if there's anything else wrong with it.

Please keep us informed, as already mentioned, many have the different variations of this engine, and no doubt to keen to understand the different issues that arise as they age.

 

[Mischief Managed]

Please keep us informed, as already mentioned, many have the different variations of this engine, and no doubt to keen to understand the different issues that arise as they age.

Will do. This does not seem like an age/wear issue, but honestly I have no clue why it broke. This is probably the least stressed bearing in the history of engine bearings. It only deals with movement when RPM changes and only has to deal with a maximum of 7 degrees of rotation (to provide 3.5 degrees of timing advance relative to the crank shaft).



In addition to being broken, it's also very rough when I spin it in the gear, so I suspect it has galled the opposing bearing surface and was causing jerky operation.