I will attach some photos, so you can see what it looks like inside, that front cover.

It will probably require both an air compressor and a new gear(with new internal splines) to get the noise reduced.

We would pull the radiator out to do this, but it might be able to be done from the side, BUT that dang gasket between the front cover and the front housing CAN BE a real pain to clean off.

One nice thing, is that no special tooling is needed to install the front crankshaft seal into front housing, during reassembly. {but those 5 studs are spaced differently, so get it lined up, before you push it on OVER the plastic applicator, that comes with the new crankshaft seal (comes as an assembly, do not separate)}


If you choose to do it, be careful removing and reinstalling that front cover. there are two roller bearings, that must slide in and out of recessed bores/pockets in the front cover. going back together, i seen guys get them cocked and not pushed in all the way, and they put in bolts and ran them in, and broke the front cover= in too big of a hurry and too quick to use an air impact wrench, too. (need to lightly tap with a deadblow hammer, on reassembly) [also, wipe oil on those inside bores/pockets, before assembly, too.]

3176B acc drive picture 2.mdi (45KB - 26069 downloads)

3176B front housing group 2.mdi (107KB - 49424 downloads)

generic photo of 3176B air compressor 2.mdi (47KB - 2027 downloads)

I like the C-12 engine better, BUT that a lot of miles(and no records) = probably close to an overhaul, but some go past 1 million miles, too. I suspect those million engines are run for at least 10-16 hours daily [= less wear once things are warmed up] 

The 3176B engine, can leak oil at the cam gasket between the front housing and the Alum. spacer deck, to repair , it would require the complete removal of the camshaft , fuel transfer pump, top end components, everything up front(radiator, fan, front cover, idler gears, front housing, etc.) It is a big job. 

Yes, head gaskets can seep on both engines, and allow coolant to enter the oil pan, they both can have water pump weep hole, get clogged up and also can push coolant into oil pan, too. Remember, not every engine does this, these are just some things that can happen.

When I look at trucks, I then to look at ones that are easier to work on = Because, I'm going to be the guy that does the work. LOL
I don't like engines that are 1/2 way under the cab, for that reason.

Remember, I only work on engines, not the whole truck.
 I'm not afraid of either truck, even if you had something terrible go wrong with the 3176B, then a C-10 or C-12 would fit right in its place. (basically, same outside dimensions)
I do like the lower mileage of the 3176B, so if the price is right, and you can save back, say $3000, for some possible big repair, then it would work.
 It does sound like you will have a little less Hp with the 3176B verses that C-12 you mentioned = don't know if that you bother you much. Also, some of the oil leaks, that can occur, on the 3176B are just unsightly, not always necessary to repair.

I currently, don't have access to prices for the air compressor or front drive gear, not till Monday(At work). You can just call your local CAT dealer and get that info, too. I don't of any other parts place to buy the gear, other than CAT, But I don't need to look elsewhere ,either.

I'm not around any other engines, so can't give opinions on them, but always hear decent comments about Series 60, and N14.
I like C-15 (year 2000-2002);
3406E (1995-2000; since most of them have had cam changed and improvements, by now); 
C-12 (or C-10) are fine, too (CAT fixed oil leak and seepage areas that can occur on the 3176 engines.)
3406B and C mechanical engines are great, but drivers miss those nice items like cruise and more powerful jakes, on these older engines. 
 

You know people really bad mouth the 3208 engine, but if you talk to some of our school bus companies, they were rather happy with them, they actually kept a few around as their backup, because they will start and run when needed. I do feel, once they increased HP on them too much, it did really lose some reliability.



Ps: Thanks for the serial number, too. I am more comfortable to look up any parts, so I get the right part/price, If you haven't already call your CAT dealer.

That 3176B engine(9CK24089) left the factory at 300 HP at 1800 rpm, BUT the owner may have had it uprated to a higher HP.

3176B models can go to 365 HP, BUT may require turbo, injector, and software changes

C-12 models can go has high as 430 HP

That C-12 355/410 is a "multi-torque" rating(MT). There are multi-torque 1,2, and a 4 . (thus i don't know what is programmed into it) What that means, is when the truck is driving in the top gear = it is a 410 hp, but 355 hp in all other lower gears ( this would be considered multi-torque 1=MT 1)
Then MT 2 = top 2 gears = 410 hp
Then MT 4 = top 4 gears = 410 hp.

C-12 models can go 1650 ft lbs of torque at their highest level
3176B models can go to 1350 ft lbs.  [Note: all these changes require more money! on either engine]


The nicer items of the C-12 engine;
 are they basically cured the oil leak at the front cover, the engine block is solid cast iron verses that alum. spacer deck= less oil leaks,
 the very last/later C-12 CAT actually added more cast iron to the head and the block (at the head gasket area) thus the head gasket had just a little more material to crush(=takes a different gasket)
The cylinder head injector sleeves, in the C-12, are more robust; They don't use copper sleeves, like the older 3176 engines.
The joint between water pump and oil cooler is improved, with the C-12, but 3176 can be updated.

I only know to buy CAT parts for the air compressor, don't know of any aftermarket "improved" air compressor. We only use CAT parts.

135 psi, isn't terrible, but on the air governor, there is a black cap, to remove, then loosen jam nut, turn screw to lower/increase pressure, then retighten the jam nut.

I would check engine/OEM motor mounts. for that shaking you descibed(may be worn out or loose)