Today I noticed 2 hairline fractures in the sleeve of cylinder #4. They are easily missed, but a magnifying glass shows the fractures reaching clear through to the aluminum, but only extend down to the ring wear mark where they stop.

Why would it fracture in 2 places, only go down as far as the ring marks, and happen in only one cylinder?

I'm already assuming that means this block is shot... but I'm curious if this was fairly common with D-series engines or something?

 

I can't get my camera to focus well enough... but I found this other guy's picture, which I'm using because his problem looks EXACTLY like mine.

 

I'd have to go back thru your posts, especially those showing the top of the block, right when you pulled it apart.. To see if there were any head gasket issues. It IS interesting that these sleeves would fracture like that: the steel sleeves we use in my MG race engines are more likely to hammer the sleeve seat cut into the bottom of the block, which results in the sleeve driving the lower part of that web down, as much as 1/8"! In fact, in the engine we're currently rebuilding, it also pulled down the block deck, right at the web between cylinders.

Anyway, THANKS for posting this... Judging by the date of the thread, I must have missed several posts...

 

How did the pistons and spark plugs compare between the 4 cylinders?
One possibility would be that your injector on that cylinder was not working properly and created a lean condition.
Signs of detonation would settle that argument.

 

On a DPFI?

 

This actually happened to my B2 engine also. I'm not sure how well the previous owner took care of my car but I'm guessing he didn't. Anyway I did take good care of that motor but it eventually got to the point where my car wouldn't be able to go a few miles without starting to overheat. I took it in to have the head gasket changed since all signs pointed to that but a little later after that my mechanic called me over and showed me two cracks in the sleeve just like that but a lot worse.
I can't answer your question to it being a problem in a D series though. I've got a B7 in mine now and all is well with it. It's interesting to see the same thing going on with yours and that guy's picture though because that makes 3 of us.

 

Missed that.
Even less surprising to me due to the DPFI intake manifold having the unequal length and funky turns in the runners.

 

Interesting.. does that mean that by design Dpfi'ers tend to run a fraction of a bit leaner in the 2 outer cylinders than the 2 center?

 

You're never going to get 100% stoich for each cylinder with carby/dpfi.

How many miles were on the motor?

 

133k

Here's another possibility... apparently if you overheat your engine, and then dump in cold water while it's still hot, (like some people do in an emergency) you run a chance of fracturing your sleeves.

 

^ This...