Marks from rings in bore after piston install?

[kevinm]

All other bores look fine and pistons installed without problem.  Any ideas why im seeing two glazed marks down the length of the bore only after a few turn by hand?  These are new Kolbin pistons/rings and im installing them on a freshly machined block which i measured to be .0015 bigger than piston.  Rings gaps all looked good too...

[kevinm]

It just came to me!...  I think this may have been caused when i mixed up the 1 and 4 connecting rod end caps and turned the motor a few times.  The rod probably cocked to one side causing the ring to rub?  Does this sound plausible... To confirm, maybe i should put some marker on the bore and see if its still doing it now that the correct rod cap is in and tight.

[dankcorey22]

Make sure you load the oil on those pistons and rings when you install them! Even if you let it set over night pore some oil in the bore if you plan on turning the engine over.

That piston protrusion looks like quite a bit, but it might be just the way the camera is.

[kevinm]

as for the protrusion i measure .030 or so with a vernier a.k.a varynear. Ill measure with a feeler gauge and straight edge tomorrow and get a better reading..  So why do you recommend being so generous with the oil anyways?  Ive heard too much oil and rings dont seat properly. 

[theman53]

I would guess that it was there the entire time. The rings probably just scraped the surface enough to make it visable. I used assembly lube in, permatex red bottle, in the bores and on all surfaces. I didn't have any problems with ring seat. I think some say leave it dry some say lube...I say the first start everything needs lube. BUT if you don't the oil splashing around will be up there in less than 10 crank revolutions so it probably isn't a big deal either way.

[DJPyro]

Always always always use oil when assembling your engine. Assembly lube is fine too, but I personally perfer just using motor oil. Coat the whole outside of your piston, skirt, rings, everything except the combustion face, lots of guys dunk them in a bucket, I just slather with my finger... You need oil on those cylinder walls or you'll have issues. I usually give a quick wipe or a little squirt around the cylinder wall, wet the side of the piston, and then slide it home, same thing on the bearings, dry on the back, oil on the front before you bolt things together.

Those marks shouldn't cause an issue but if you don't have any oil in there get some around that piston wall before you keep turning it over.

[the caveman]

The issue of whether to install pistons and rings is a matter of opinion, but i have found more and more engine builders are going the dry route. My last 2 diesel builds and more importantly [ at least to me] the build of my 2.2 l air cooled Beetle engine. On the 2.2 i used Total Seal second rings and they supply a powder that is used to check that your bores are bone dry before installing the pistons. I did that, and other than an initial bit of smoke, it quickly cleared . And this is an engine that had to be ran at 2000 rpms for 1/2 to seat the cam and lifters at first start up.  I then did something stupid without realizing before too late. After only driving it for less than 1000 miles and stored it for winter. The next summer i looked for the best oil i could find [ at the time i couldn't find any Royal Purple, Brad Penn or Joe Gibbs] so i used Valvoline racing synthetic. Well that was a mistake. After a couple of hundred miles it started smoking blue real bad. Tore it down again, cleaned and rehoned the cylinders, put the pistons in dry. Started it up on a dyno an couple of weeks ago and had zero smoke and blowby . As far as the 2 diesels i build ,both are running clean, smoke free [other than full throttle black!] with no blo by and no oil consumption. Just to say that there may be more than one way of doing it, but i will be doing mine dry from now on. Sorry to highjack the thread

[dankcorey22]

Thats just how i learned to build an engine at school. Use alot of oil. And plus it sounds less harmful when rotating the engine over rather than dry. It doesnt make since doing it dry the rings might scratch the cylinder wall.

[rabbitman]

If this is a 1.6 the piston cylinder clearance should be .001", not .0015". Is there a reason why it got bored out too big?

[Vincent Waldon]

I ocassionally get small lines like that during a rebuild... first time it happened I thought I had broken a ring and pulled the piston... everything was fine.  I did notice that the line corresponded to where a ring gap was (one piston had 3... each at 120 degrees) so have decided that it's an off-shoot of me using lots of oil and perhaps fresh-cut ring ends.

In any event, unless the ring is actually broken in your case it's likely harmless.  Any reason to suspect you broke a ring as you installed that piston?  Did you use a hammer to get the piston to go down?

[kevinm]

the piston tapped down fairly easily when lubed up and in a ring compressor.  As for it being cracked i probably would hear an awful sound and be hard to turn.  As for the bore being .0005 larger, the machinist told me that's how he honed it for the last guy that did a performance build?  I went with it...  Nice Diamond CNC Hone too...  Why are diesel bore tolerance so tight anyways...?

[sdwarf36]

Its perfectly normal--i see it everyday. as much as one would like to think that the rings are perfectly smooth+ even, they never are. Its just showing up the mild high spots on the rings. (I seem to get it more with Total Seals-but that may just be cuz we use them more often.)
 Old school WAS drown everything in oil-not any more. I put a few drops of oil on my finger+ wipe it on the top 1" of bore--and a few drops smeared on the skirts. Someone smarter than me wrote that "you want to duplicate running conditions as soon as possible on fire up"-- and never in normal running is everything covered in a bunch of oil.
 I've had 2 motors smoke out of the last 200 I've built-and both of those had Total Seal VERY liteweight rings ($900 a set!!) and were the only 2 I used the "magic dust' on. 

[macka]

Why are diesel bore tolerance so tight anyways...?

compression

[rabbitman]

Why are diesel bore tolerance so tight anyways...?

compression

I looked it up to make sure.

MK1, gas and diesel (separate bentleys): new=.001", wear limit=.025"

MK2, gas and diesel (same bentley and it didn't specify gas or diesel: new=.0012", wear limit=.003"

The high compression in the diesel is actually because of the high CR.

[dankcorey22]

i had mine bored at .0015 also my machinist said it would be better for performance also..  maybe i should have gone with the bentley