Bought a 1984 K2500 Suburban last week. Imagine my surprise when I went to pick it up and learned the original owner had installed a Roto-Master labeled Rajay turbo. The seller, the second owner, never mentioned it in the ad or during our phone calls!

I keep reading about J code heads, but most of the discussions I've read make me think they were developed later than 1984. I have the original window sticker for the rig. The engine is the RPO code LL4 HD engine, rated at 135 HP, an increase of 5 HP over the LH6 engine, according to the Vehicle Information Kit I downloaded from the GM Heritage website. The Information Kit refers to the LL4 code engine as having Heavy Duty Emissions (sic). Yeah, I'm an information geek.

Here's what I want to know. Does this engine have the J code heads AND the improved flow intake manifold if it has the J in the eighth position of the VIN? It does.

Thanks for any help. I know I can learn a lot here.

 

I'm not positive but if I remember right the so called J heads were only in 82 and 83 J engines. They were a big valve head on the HD 6.2 diesels 3/4 and 1 tons. they dropped because they had a bad habit of cracking between the intake & exhaust valve seats. After that the difference between the J and C engines was pretty much limited to internal pump timing that was seat up on the test bench.

 

i think the early j code engines had a free flow intake with no egr.. and also cast rockers instead of the stamped steel with the plastic buttons.. and also the course thread injectors.. but it is true about the big valve heads cracking .. back in the day i always looked for the newer small valve fine thread inj. heads when doing repairs on them.. but i do like the older rocker shafts if not wore out

 

Believe it or not the stamped steel rockers far out lasted the rocker arm shaft assembles. I think the shafts were a little to soft. Because the brass bushing wore the shafts out.