With the flywheel and clutch installed I have some play when move the crankshaft up and down.

This is on a .12 sirio evo4 sti engine with about 1.5 gallons of 20% through it. This engine has ceramic rear bearings and steel front bearings. It seems to have more play then my novarossi 12-3sct plus that has the same mileage.

The crankshaft rides on bearings so I imagine that I might have to consider replacing something soon? Would it be the front or rear bearing? The engine runs ok right now, is it that critical?

Someone who hear my engine running pointed out that it sounded different, so he applied pressure to the heatsink and the tone changed. He told me this means the rear bearing is worn. He did this before I even noticed the play in the crankshaft.

gday, just replace both bearings no harm in doing it and then it will perform better.

Replacing the bearings is not a bad idea, but I can tell you with the Sirio engine the front bearing is more likely to go out first. The front bearing is also very inexpensive.

I was hoping to know which one to replace or if it was both. Sinks that after 1.5 gallon of 20% I would have to replace a bearing.

I've never heard of people replacing bears because of what I described. I have only heard of replacing bears because of a "gritty" feeling or the front bearing leaking fuel. Which is why I wanted to ask.

From my experience up and down movement was from the front bearing.

I also heard that sirio evo 3 / 4 bearings are only good for engine run in then they need to be replaced.