Weird injection port observation, kinda FREAKY

[Aponty]

I recently bought a beautiful 1 owner 1981 300sd with 155k miles. I’ve been slowly going through it to make sure its engine and transmission will keep going another couple hundred thousand miles.
Did a compression test, ranging from 380 to 410 psi across all cylinders both hot and cold, so I feel good about spending some money on her.
Today I pulled off the injectors to have them tested. Went relatively seamlessly, heat shields stayed in the head. I was hooking them out and discovered that the opening into the prechamber is much wider on cylinder 5 than on all the others. Is this normal?? Seemed to weird to not reach out to the community.
Please advise!!
Attaching some pics. The smaller opening (approx 7mm)represents cylinders 1-4, the bigger one is cylinder 5 (approx 10-12mm).

[engatwork]

Looks like the one with larger hole is missing the heat shield. The heat shield is still in place on one with smaller dia.

[engatwork]

Meant to mention that complete piece the injector screws into can be removed too.

[rwd4evr]

It looks like there's a heat shield in there still. The early reusable ones are flat on the injector side not recessed like what you buy now. I would try to dig at that a little and see if it pops loose. I've had cars come in where someone stacked two heat shields (assuming by accident).

Sent from my SM-G991U using Tapatalk

[rwd4evr]

Originally Posted by engatwork

Meant to mention that complete piece the injector screws into can be removed too.

Yes that's the precombustion chamber. It's possible that it's been replaced and has a different oriface than an original mb part.

Sent from my SM-G991U using Tapatalk