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.