Cat 3116 7SF/2BK Variants and Exhaust Brakes, Need help

[DtotheAmbrose]

I am hoping someone with more historical knowledge can help me out.

My topkick has a 7SF cat 3116 in it and the chassis was delivered to the coach builder in Jan 1991 but the chassis itself was built in 1990.

The 91 built models use the 2BK cat 3116 which it looks like part way through the production cat changed some internal parts so you could use an exhaust brake.

What I have not been able to find out is what was different, I have only seen clues to it. Jacobs exhaust brake had a bulletin come out stating you can update the 7SF to the 2BK spec and run the exhaust brake for the 215 and 250hp models but not the 165-185 hp models.

The update list Jacobs has the following parts

Qty, Cat #, Description

1, 9Y8103, Valve Cover Gasket
1, 7E0844, Oring governor sleeve
1, 6F6673, Oring governor sleeve
1, 1T1068, Oring front housing
1, 7W6552, Gasket front cover
1, 9Y4634, gasket PTO (air compressor)
6, 4P4949, Valve spring retainer
6, 6I2307, Exhaust valve spring
6, 4p7750, Exhaust valve seals
1, 6I2342, Camshaft (200hp and above)
1, 101-4557, Camshaft (below 200hp)

Based on this information I am guessing the camshaft profile might be different and something with the valve spring strength. Or possibly the camshaft was a cast model and the later units used a better material or forging.

Anyone have any ideas as to the what/why you cannot upgrade the 165-180 hp models? At some point my topkick was upgraded to a 210hp model on the serial plate but nothing was logged with Cat when it happened as they don't show anything for my serial number.

[Booyah45828]

Those exhaust brakes clamp to the turbo. So I'm thinking the reason the 165-180hp versions aren't suitable for upgrade is because the turbo is smaller then the larger hp models.

The upgrade #'s from jacobs include stiffer exhaust springs for the higher exhaust back pressure. Those stiffer springs would then require a harder cam lobe surface to resist wear. The rest of the part numbers look to be stuff needed to replace the springs. The springs are the big thing. The reason they have a 200> and a 200< cam is likely due to different lobe profiles for the high and low hp engines.

If you were upgraded to a 210 hp engine, you likely got the bigger turbo. So then to run the brake, you'd probably only need the parts in the list. If those parts aren't already present.

The big thing I remember from the 7sf to the 2bk is the dual pipe air intake. Any internal changes I don't remember.

[DtotheAmbrose]

Originally Posted by Booyah45828

Those exhaust brakes clamp to the turbo. So I'm thinking the reason the 165-180hp versions aren't suitable for upgrade is because the turbo is smaller then the larger hp models.

The upgrade #'s from jacobs include stiffer exhaust springs for the higher exhaust back pressure. Those stiffer springs would then require a harder cam lobe surface to resist wear. The rest of the part numbers look to be stuff needed to replace the springs. The springs are the big thing. The reason they have a 200> and a 200< cam is likely due to different lobe profiles for the high and low hp engines.

If you were upgraded to a 210 hp engine, you likely got the bigger turbo. So then to run the brake, you'd probably only need the parts in the list. If those parts aren't already present.

The big thing I remember from the 7sf to the 2bk is the dual pipe air intake. Any internal changes I don't remember.

I already put the brake on but was very careful not to give it too much RPM as I had some concerns after reading the jacobs tech bulletin. The stock springs must be really soft as it did absolutely nothing to slow the truck. I know the valve works if you kick it on and try to accelerate you don't go anywhere and everything behind you disappears in a cloud of black lol.

I am debating to install a 2BK or later variant in the truck with a higher HP rating as it looks like the cost to have the camshaft and other parts installed wouldn't be too far apart.

[Booyah45828]

That exhaust brake will have minimal braking effect, unless you're at high rpm with the converter unlocked or any rpm with the torque converter locked up.

The reason they spec'd stiffer springs is so as to not float the valves causing them to hit the pistons. You can get like 60+ exhaust psi out of one of those valves, so floating the valves isn't out of the realm of possibility.

That doesn't surprise me on the costs. A used 3116 is cheap and available whereas those requesting new parts for them have little demand. What you do is up to you, but if you're engine is in good shape, I'd have a hard time swapping it out for something with 300+k miles on the clock. Maybe buy the used engine for components only, and stick the upgraded parts into your engine.

[DtotheAmbrose]

Originally Posted by Booyah45828

That exhaust brake will have minimal braking effect, unless you're at high rpm with the converter unlocked or any rpm with the torque converter locked up.

The reason they spec'd stiffer springs is so as to not float the valves causing them to hit the pistons. You can get like 60+ exhaust psi out of one of those valves, so floating the valves isn't out of the realm of possibility.

That doesn't surprise me on the costs. A used 3116 is cheap and available whereas those requesting new parts for them have little demand. What you do is up to you, but if you're engine is in good shape, I'd have a hard time swapping it out for something with 300+k miles on the clock. Maybe buy the used engine for components only, and stick the upgraded parts into your engine.

The trans was locked up in 3rd when I tried it out. I found an engine decently close so now the debate of swapping the engine, whee!

[DtotheAmbrose]

Welp I am going to cheat. I found a 9Y variant from a 97 bus which is a 250hp model. I get to get more horsepower and an exhaust brake.