Hi,

We just took this engine apart it was out of the car for 3-4years now and now when we started to do rebuild we found out this thing, black spots on two of cilinder walls, engine was build before to every spec. that was written for B seria, pistons are from Endyn 82mm NA(high) and bores were done to their spec. and engine had less then 20k km done on it when I took it out of the car and it was runing nice and strong.

none of the gauges (oil, watter temp. from autometer) weren't indicating that in anytime engine was overheating !

Photo of misty black spots:



Anyone knows what could of caused this to cilinder walls,
every technical opinion is welcome, cause we're building it with better materials now and it will be seeing even more "abuse" then before (as high rpm and compression goes)

edit: and you can fell a little wave when you're going through darkest spots with finger !!!

Thanks

 

That's from sitting for 3-4 years. If you plan on "abusing the motor" more than before, I would take the pistons out, and have the bores checked to make sure they are still within spec. Better to be safe than sorry.

 

FYI, maximum cylinder taper is .002, but don't be surprised with oil consumption at this spec. If a block was bored properly, it usually won't have fluctuations greater than .0001 while running a dial bore gauge down the cylinder walls.

 

we won't just put it together, we'll take everything apart and check everything bearings (crank, rod), cilinder walls, condition of pistons, rings etc

then when we'll have all info. we'll decide if it needs rebore (as min as it can get cause it's already on 82s) and new hone, or just new hone.

it's just that we'd like to know cause for this happening to this engine so we'll know what to look for when building it again, so there wouldn't be the same mistake done twice.

 

Sure is clean for 20k Km.

The only time I've seen something like that happen was with coated pistons and a ball hone job. Even then, it didn't quite look like that.

 

looks like the marks left after lightly honing a cylinder that had a bit of surface rust!

could there have been moisture in there and the engine has been turned over?

 

you can nearly see where that light surface rust is still there at the very top of the cylinder where the rings dont reach!

 

we had the block checked by very good mechanic here and the reason for that is, deposits from car beeing still for a while and then turned on and driven and then again sit for a while and the same procedure on and on, that's why it's just on two cilinders and in different levels (height). On cilinders that had open valves so the moisture could get in, so nothing we can't sort with light sand paper 1000 grit and just clean it and light leftovers will be taken off by rings.

car was driven like 3-4 times a month cause it was 2nd car and mainly used for races.

There was some surfice rust on top cause engine was taken apart and layed for 3-4 years now but we fixed that now, nothing big just surfice rust, inside cilinders there is no rust.