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Engine Specific Info and Questions => IDI Engine => Topic started by: kevinm on March 24, 2011, 08:23:53 pm
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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...
(http://i276.photobucket.com/albums/kk17/kmahon01/CIMG0159.jpg)
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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.
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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.
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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.
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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.
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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.
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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
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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.
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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?
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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?
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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...?
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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. :-X
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Why are diesel bore tolerance so tight anyways...?
compression
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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. ;D
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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
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The pros on here all say that boring it bigger than spec is about like starting out with a half worn block and any machine shop that doesn't want to do it to bentley specs should be avoided.
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The pros on here all say that boring it bigger than spec is about like starting out with a half worn block and any machine shop that doesn't want to do it to bentley specs should be avoided.
Indeed.. The idea behind the looser spec for performance is simply to reduce friction.. Pretty much like is done in GASSER race motors.. However, since a diesel needs that compression the tighter, the better it's gonna last...
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The pros on here all say that boring it bigger than spec is about like starting out with a half worn block and any machine shop that doesn't want to do it to bentley specs should be avoided.
Indeed.. The idea behind the looser spec for performance is simply to reduce friction.. Pretty much like is done in GASSER race motors.. However, since a diesel needs that compression the tighter, the better it's gonna last...
and diesel fuel is a lubricator anyways.......at least it used to be.
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Actually most gassers that run a lot of piston clearance are using forged pistons which expand when they heat up. If you ever listen to a motor with forged pistons start up, they'll have massive piston slap for the first few minutes until things start to heat up and it will gradually diminish as the engine comes up to temp and the pistons expand.
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DankCorry why the concern... Have you got your motor up and running yet and had low compression?
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The pros on here all say that boring it bigger than spec is about like starting out with a half worn block and any machine shop that doesn't want to do it to bentley specs should be avoided.
Show me an engine thats worn an exact amount the full length of a cylinder-and in all axis's. ??? And give me the address for Bentley warrenty claim center. :P
If you bring me stock VW replacement pistons-I'll feel safe giving you .001.
If you bring me Mahle's-I'd do it-but give you plenty of warning why I'd be worried.
If you bring me Prothe pistons made in some country i never heard of-I'd make you sign something that you know more about the thermal expansion quailties in a piston that only costs a 1/4 of stock-and you trust your judgement over what pros in the trade have seen time+ again.
Scuffed pistons suck. And if it happens, its ALWAYS the machine shops fault. :'( NEVER the customers. ::)
Don't lose any sleep on your .0015 clearance-its what I built my own engine to.
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DankCorry why the concern... Have you got your motor up and running yet and had low compression?
Nah man just the bottom end im in school now totally away from where my engine is. ill finish it this summer. Im kinda worried now since this discussion about low compression
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I'm with sdwarf, don't loose any sleep over it.. I've simply thrown a set of rings at engines approaching the half million mile mark, and get a few 100,000 miles out of them with little trouble..
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.0005 in bore size equates to .0015 more ring end gap-don't lose sleep. And people seem to take the .003 number as a "fail" number-what it means is "you started with .001-you now have.003--so your cylinders have worn .002 from where you started."
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The pros on here all say that boring it bigger than spec is about like starting out with a half worn block and any machine shop that doesn't want to do it to bentley specs should be avoided.
Indeed.. The idea behind the looser spec for performance is simply to reduce friction.. Pretty much like is done in GASSER race motors.. However, since a diesel needs that compression the tighter, the better it's gonna last...
and diesel fuel is a lubricator anyways.......at least it used to be.
yes, it did USED to be..
i found some old high sulfur diesel not too long back, about 3 gallons of it, ran my car till it was about out of fuel then dumped in the HSD, and as i was fueling the car (with the engine running) i could hear it clattering less.. and it felt like it had a slight power increase..