[ScotZ]

When looking at a crank bearing ( the cap side). How can you tell if it is spun or not. I just replaced my rear main seal and the bearing in the cap feels good to me with no scatches. There are a couple of ,what look like small pencil marks but you can not feel them. They are about 3/8's of an inch long. Milage is 127K. I have ask a couple of people that I trust, if they should be replaced or not. My answers have gone from a definate "Yes" to "No way it's fine" but when pressed nobody really can tell me where they draw the line on replacement. I do not want to take this engine out to be line (aline) bored. Whatever its called. If I do not have to. Right now I just have wrench time in it and a few bucks for gaskets and seals. This is not my primary means of transportation. Just a top down weekend wheeler....What are your thoughts?

[KyleS]

I'd say no you don't need to replace the bearings. I've torn down a few perfectly good engines and you are going to get what looks like scratches you can't feel in any engine no matter how well its maintained. A picture would really help to decide but when a bearing actually spins the little clip type thing on it that holds it in the cap lets go and the bearing is able to spin around the crank and it doesn't take long for the whole engine to go. If you had an actual spun main bearing you'd know it.

[ScotZ]

Thanks KyleS. I like hearing from someone with experiance.

Thanks Again

[bwiencek]

A couple questions:

1) how was your hot idle oil pressure before tearing down? (worn bearings will typically show up as lower oil pressure)

2) what does the little "tab" on the bearing look like? (a spun bearing will be flattened out. From your description you're looking at how to assess condition and not question if it's spun or not...

Go to the local parts store, ask them for the bearing clearance spec on that engine, then ask them for plastigauge. Put a piece on the bearing, torque, remove, read clearance. For detailed instructions go here:
http://www.plastigaugeusa.com/how.html One thing to note is that I'm wondering if the clearance will be a little off due to the crank being pulled down by gravity into the cap. Might try checking with something pushing up the flywheel into the block side of the bearing.

If the clearance is a little too large then you can usually get "Service bearings" in the .001" and .002" undersizes to take up some crank clearance.

If the bearings are smooth, and should be a dull gray color with no grooves or shiny spots on them they should be fine as long as the clearance is good.

[KyleS]

I forgot I had this picture when I was typing my respones, its a little grainy since I took it with my phone but this should help give you an idea. This is a spun main bearing out of a LT1. Notice the deep grooves and burnt looking spots. Also notice how the little tab is completely missing. Hope this helps.

[vadslram]

Tab missing = spun or spinnable= Change bearing end of story. The only questions left are, why it spun? and is the crank shot?
The picture looked like the crank was good, not too burned.
Do you know the full history of the engine? an overheat could bind the bearing as would putting oversized bearings where they don't belong.
If you have the bottom end off now have the crank trued and balanced, get all new bearings and count yourself WAY ahead.

[ScotZ]

Thanks to all. You guys are great. Today I got my bearing to a good friend of mine who is a Porsche mechanic ( I still trust him ). He told me I had no worries. Thanks for all the input.

Scot