liftin the head help needed

[wdkingery]

Hey guys i just pulled my head today.. i thought i had blown the thing up using ether for the past .. 30 starts. eventually it got tough to start on ether even..? so i figured it was real bad, white smoke was getting thick. well, i have yet to see the rings as i don't have the oil pan down yet, but the walls don't appear to be scored from cracked/broken rings, although i didn't drive it long after the deadly white smoke.

so my questions are:
good way to check piston protrusion? i'm figuring to use my dial indicator some kinda way.
good way to check for bend rods? it is possible i bent a rod with ether, causing the white smoke.
good way to check cylinder ovalness or any real cylinder measurements? i remember in school we had a T shaped dial indicator to check that number.. yeah i don't have one of those.

2500 miles on the motor oil yielded impressive results. i expected insane carbon buildup; it wasn't actually that bad. the heat shields had exactly the same size hole that the injector shoots out, and on my low compression cylinder apparently the heat shield clogged over entirely (which was likely my white smoke there at the end, and my hard starting.) but down in the pre-cups was little or no cake. the cake is a yellowish-brown dust essentially. you can find it on the valve heads, in the precups, on the bottoms of the pre cups.. but there was no real build up anywhere. i'd say i can do 25k miles before a problem, with good compression.

i'm fixing to purchase all autohausaz.com products; rings, head gasket and bolts only $67.  are my bolts stretch? i have no way of knowing.

thanks for any info you can provide
Pix in the morning

[rallydiesel]

Definitely check protrusion. You need a good dial gauge and a magnetic holder. You need to put a straight-edge (preferably machinist quality) across the bore and rotate the crank until the piston top hits it. Place the dial gauge probe right against the straight-edge so it is on the highest point of the piston. Zero the dial. Remove the straight-edge. Rotate the crank slightly until you get the max measurement. Repeat for all cylinders.

Check with Bentley for specs. Good chance the ether bent a rod and you are not getting complete burning and the white smoke. White smoke is usually unburnt diesel, coolant occurs less often and has a different smell.

[745 turbogreasel]

I go TDC, lay a straight edge across the piston, and measure down to the block on both sides in at least 2 directions.  It's a pain, everything has to be very clean.

Any cyl that is less protrusion probably has a bent rod, as would not reading the same across the wrist pin.

If it ate a glow plug or anything, you might have to file a piston top or two flat first.

[wdkingery]

I don't think I had enough compression nor enough starter (gasser) to bend a rod anyway. 2 bottom rings broke in half = white smoke. Could swipe a credit card through most of my rings. Bearings looked good.

[CrazyAndy]

Do what RD and TG said about the straightedge measurement method.  You might still find something, and now is the time to do those measurements.  As for cylinder out-of-round or "ovalness" as you put it,  put a new piston ring in a cylinder, cover the rest of the hole with the piston or a similar-sized coaster or something, and shine a flashlight from the pan area (if you want to take off your pan for this that is).  Do that both at the top, bottom, and middle of the stroke.  Also don't forget to measure the ring end gap; that is the main determiner of if you will need overboring in the future as well.

Pix coming?

[wdkingery]

I guess I could throw up a couple of pictures.

[Toby]

Be sure to check for cracks in the main caps and cracks radiating from the main cap threads in the block. Dye check the main cap bolts or pitch them.

[pointynoggin]

I'd like to comment on piston protrusion.

Cold pistons are cone shaped so the pistons will rock in the cylinder.  This makes getting a repeatable measurement impossible unless you measure along the center of the block in line with the wrist pin.

when I did mine I used feeler gauge set and steel ruler.  you can use adjacent pairs to get within a couple thou of the upper limit of the gasket specs.  set the ruler across the piston and if you can slide the pair of gauges thru you're good to use that gasket.

Bentley does not address the rocking piston issue and the pic shows the dial gauge not over the wrist pin.

Using this method I choose a 1 notch rather than a 2 notch and I have no probs.

[745 turbogreasel]

Oh yeah, this won't tell you if you bent all 4 rods the same, but  what's the chance of that?

[CrazyAndy]

I'd like to comment on piston protrusion.

Cold pistons are cone shaped so the pistons will rock in the cylinder.  This makes getting a repeatable measurement impossible unless you measure along the center of the block in line with the wrist pin.

when I did mine I used feeler gauge set and steel ruler.  you can use adjacent pairs to get within a couple thou of the upper limit of the gasket specs.  set the ruler across the piston and if you can slide the pair of gauges thru you're good to use that gasket.

Bentley does not address the rocking piston issue and the pic shows the dial gauge not over the wrist pin.

Using this method I choose a 1 notch rather than a 2 notch and I have no probs.

This is a very good point that I had not considered.  I'll have to keep that fact and procedure in mind when setting up on measuring for my own HG.  Thanks for sharing.

[Toby]

I'd like to comment on piston protrusion.

Bentley does not address the rocking piston issue and the pic shows the dial gauge not over the wrist pin.

That is because it is pretty much of a non issue. Put a dial indicator on top of the piston and try to rock it sometime. Unless you have lots of bore/piston wear you won't see anything om a .001 DI.

[pointynoggin]

been there, done that.

New build, new KS pistons with skirt to wall clearance .001". Pistons will rock.  I had values ranging mid one notch to low 2 notch.

Over the wrist pin was high one notch and that is what I used.

Maybe they won't rock when carboned up?

I was worried enough about the rock I pulled the pistons to check the clearance.

[Toby]

If you could rock the pistons with new rings in a new bore they messed up clearancing the pistons. It happens all the time when they don't read the papers that come with kraut pistons.

[pointynoggin]

please excuse me repeating myself.

Cold pistons are cone shaped ish.  Typically pistons for this engine are .02 smaller at the top then at the skirt. The fit is .0012 at the skirt to cylinder wall.

If someone wants to do the trig they could calc the hieght variance due to rocking.

[Toby]

The pistons aren't .020" smaller on any portion that contacts the cylinder wall. You are measuring the ring land area that is relieved and does not contact the cylinder wall. With new rings on non worn out pistons, you should not be able feel the piston rock unless the bores are quite worn. Rather than doing silly things with coasters and flash lights why not just measure the bore with a dial bore gauge. Used examples aren't that expensive. Kraut pistons are atypical in terms of shape. Most of the rest of the world uses very slightly tapered pistons from the bottom of the skirt to the top of the skirt, just under the rings. Most German pistons tend to be barrel shaped and are clearanced just under the rings, instead of the bottom of the skirt. If you clearance them like most everything else they are loose in the bore and exhibit slight piston slap. You probably won't notice it in a Rabbit, but I have seen MBs rattle more after a rebuild than when they came apart when the machinist did not read the spec sheet in the piston box,