We are talking about two different operations here.
Shimming the tables is to do with getting the upper tables (surface planing in the UK, jointing in the US) co-planar.
Adjusting hte sprockets is to do with getting the lower table (planer in the US, thicknesser in the UK - hence the confusion about the term "planer") right.
You won't find the sprockets until you get the machine on its back or upside down.
I had a 636. One day I was sitting in my lounge. My workshop was the other side of the wall. I heard an almighty crash. A cupboard full of metal (nut's bolts and the like) fell of the wall and knocked over the 636.
I asked the insurance company to fix it, it needed setting up again. No, they would just send a replacement, which was the 637.
The 637 arrived. It was a Friday Afternoon job. Poor paintwork, nothing straight and true, thicknessed board 0.5mm different over a 125mm width. Just unusable.
Called Kity Support. It wasn't called Kity - something beginning with S, I forget - but they did the support work for them. They sent an engineer. He took a look. "Never seen one of these before".
My heart sank.
"But I used to service Chinook helicopters"
OOOOOOOOOOOOOOOOKKKKKKKKAAAAAYYYYYYYYYYYYYY
He took it away. Several weeks passed. I had no receipt that he had taken it. I was starting to worry.
Eventually it came back. It was PERFECT. He had spent 16 hours on it. That must have cost the agent more than the value of the machine. But it was perfect.
A year or two back it started to get very noisy. I changed the head bearings, but the problem was a plain bearing in the drive chain. A mate made me a new bronze bearing and now it is right again.
I wish it had longer tables (they are 600mm). But I've never actually regretted buying it. A good little workhorse.