Hi all,

Curious to know if overheating will speed up the process of making the cylinders go oblong or out of round.

I've been in the process of blue printing my block and picked up another block that was already honed which appears to have tighter results than my block in the lower part of the cylinders. By that I mean it's closer to new specifications than my block unhoned.

However, the top part of the cylinders, my block is less out of round and is sitting right at service limit on 3 of 4 cylinders. The largest variance is .11mm on the worst cylinder. One the honed block the largest variance is .22mm.

This has me questioning how it can be more out of round than my block while having better results lower down in the cylinder.

An overheated condition allows the cylinder tops to go out of round easier?

 

I think I read this right, but wanted to atleast add this.
1: Overheating can most deff.ly screw up the most perfect round bore.
2: If you got a block back finish honed and it is out of round then the machinist just did the best he could and decided the compromise of P2W was getting to far then to keep working on something that is not perfectly round. And this is just the nature of the beast and the reason we have service limits.

 

OR whoever did the hone job spent a lot more time on the top of the bore during their strokes (possibly trying to get rid of a ridge). The longer you use a hone (especially flex types) the higher your chances are for honing the cylinder out of round. I have seen this first hand multiple times and many different platforms.

 

I just ripped the pistons out today out of the honed block. By the looks of the bearings, rods and mains, this is a lower mileage block.

Also I tend to think the guy honed it himself so not machinist honed but home hone job. No bore so any imperfections were already there for honing.

Also I did find a little scuffing on the pistons so that would also tend indicate that the motor was overheated at least once I believe.

Overall though, it appears to be closer in spec than my block. I just did the measurements on both blocks and both blocks are under temp at the moment at about 58° F. However, I already did my block at 68° F before so now I can just take the variance of the new block from what I got this time around from my block and either add or subtract the .01mm-.02mm difference from my 68° F measurements. Or at least that's my theory. Not sure if that is actually a viable cheat but it seems reasonable.

Of interest, the 10 dollar block I bought seems to be about .01mm to .02mm tighter to new spec than my 274K KM block.

Thanks for confirming my suspicion that during an overheat it's possible for the top of the bore to become out of round more easily.

 

Piston scuffing doesn't happen from an engine overheating, at least not in my experience. Either the pistons were reinstalled in the wrong bores or it was running lean or too much timing and was detonating. This would also explain a out of round top and not bottom, due to highest temperatures happening at the top of the piston and higher up in the bore. Either way, looks like you know everything you need to know already.

 

That's good to know. I was told elsewhere that light scuffing can occur during an overheat and could get to the point of seizing on a major overheat.

I actually do not know what all can cause it so I am going blindly by what people here tell me.

Being the block appears to still have been using the graphite gasket, I can hazard a guess it was on it's original head gasket. I think this would be a fair sign the car wasn't overheated and instead be more in line with what you were just saying about too lean or to advanced ignition timing.

Thanks for the experienced insight!

In all cases though, both this block and my block the scuffing is light as far as I can tell. The one example of severe scuffing I saw is way beyond what I see on these 8 pistons I have in my possession. Also it's almost perfectly centered between the top and the bottom of the skirt 90 degrees off the pin holes. About a quarter sized patch on all the pistons in my block and I forgot how many on this second block.

You can see pics of the ones from my block in this post:

https://honda-tech.com/honda-civic-d.../#post50444415