Notch dimensions for piston oil squirter relief?

[Jetmugg]

I am getting back to work on my 1.5L / Turbo build, using a turbo block.  I have a set of 1.5 pistons (0.5mm oversize) that I need to notch for oil squirter clearance.  In order to get the position and depth of the notches in approximately the correct positions, I have marked a set of used, standard pistons to use for notching practice.

Not having a set of factory turbo pistons available to me, I would like to find a recommendation on how wide and deep the factory "notch" is in a TD piston.  I'm thinking of going with a 3/8" end mill, and cutting approximately 0.400" deep (up from the bottom of the skirt).  I realize this depth dimension is probably different than for a 1.6TD setup, which uses a different rod and piston height.


As always, any help is appreciated.

Steve.

[R.O.R-2.0]

the piston doesnt travel as far down in the bore on a 1.5

so, you shouldnt need to notch it as deep either..

dont go too wild on the notch.. the 1.6 pistons have steel cast into them to keep the area around the notch from cracking..

[CrazyAndy]

it's not a 1.6, but stock AAZ notches are 15mm diameter semi-circle w/ the circle's center about 6mm off the lowest pert of the skirt, straight parts leading away from the semi-circle edges at a light angle with the straights being rounded where they meet the skirt.  Sorry for the crappy explanation, maybe a slightly less crappy pair of cellphone pics would be more helping.




EDIT: Okay, so my new smartphone's pics are't too crappy at all. 

[Jetmugg]

The pics and recommendations are good.  At 15mm, those notches are a bit larger than I expected, but a very hand reference, all the same.

Steve.

[CrazyAndy]

Don't forget to mock up the engine BEFORE doing any cutting so as to see how much the piston would contact the squirter, if it even would at all.

[R.O.R-2.0]

Don't forget to mock up the engine BEFORE doing any cutting so as to see how much the piston would contact the squirter, if it even would at all.

oh, it will, dont worry..

the piston skirts still come out of the bores at BDC..

[theman53]

another thing to possibly think of is this... the oil squirter is only .150" or so. To keep the strength of the piston why notch more than you need to? Other than time, which you aren't in a hurry yet, why don't you assemble and mark where it is on the piston width wise, then take the squirter out and mark how much more it goes down into the bore and measure. That way you are only taking off a little bit of material. Granted with heat things grow and the squirter can be mildly manipulated to move a bit before being locked downl, but overall if you have a squirter that is real thin why machine 1/2"x1/2" hole in the piston?

[monomer]

notch is .712 deep, .660 wide.

Relief between is .322 deep between notches, back side of piston.

These are OEM Kolbenschmit 1.6 TD slugs.

[Jetmugg]

another thing to possibly think of is this... the oil squirter is only .150" or so. To keep the strength of the piston why notch more than you need to? Other than time, which you aren't in a hurry yet, why don't you assemble and mark where it is on the piston width wise, then take the squirter out and mark how much more it goes down into the bore and measure. That way you are only taking off a little bit of material. Granted with heat things grow and the squirter can be mildly manipulated to move a bit before being locked downl, but overall if you have a squirter that is real thin why machine 1/2"x1/2" hole in the piston?

That's pretty much exactly the method I have used so far.  With the crank in the block, sitting on a bench, I put 1 rod/piston combo in at a time, and then rolled the crank over by hand.  When the piston skirt came into gentle contact with the squirter, then I marked the location on the skirt.  At that time, I removed the squirter from that cylinder, and continued to roll the crank over until the piston was at BDC, at which point I scribed a mark on the skirt to show the location of the bottom of the block on the piston skirt.  I have marked each of the 4 pistons in this way  This work has all been done on a used, standard piston.  When I get the whole deal figured out, then I'll move on to the new, oversized pistons.

I milled one notch last night, using a 0.500" end mill, going to a depth of 0.400" from where I first hit metal.  This depth took the notch to the thickest part of the piston wall (if you look at the skirts, you can see where the thickness steps down near the bottom of the skirt). I still haven't decided if I want to use the 0.500" mill, or another size.  I thought the same thing as you guys have suggested, make the notch more narrow.  However, after looking at the reality of the piston skirt size and the notch size, I am more concerned with a tight radius creating a stress riser in the piston skirt.  I may move up to a 0.625" end mill, trying to create a more gradual transition from the skirt to the notch.  I plan to blend out the milling cuts by hand.

Steve.

[Jetmugg]

There is a steel insert in the 1.5 pistons also, but it is located high enough (near the piston top), that the notch will only be within about 0.700" of the bottom of the insert.

Steve.

[R.O.R-2.0]

There is a steel insert in the 1.5 pistons also, but it is located high enough (near the piston top), that the notch will only be within about 0.700" of the bottom of the insert.

Steve.

the steel insert WRAPS AROUND the notch on TD pistons..

it ADDS STRENGTH to the piston and notched area..

[Jetmugg]

notch is .712 deep, .660 wide.

Relief between is .322 deep between notches, back side of piston.

These are OEM Kolbenschmit 1.6 TD slugs.

Excellent info - thank you very much.

Steve.

[Jetmugg]

Here's a pic of the first notch I cut, after opening the slot up with a 0.625" end mill.  This is on one of the "practice" pistons.  It's a little tough to define the depth of a slot cut into a sloped surface, but it is about 0.500" from the flat part of the skirt...



I'll give it a test-fit this evening.

Steve.

[R.O.R-2.0]

Here's a pic of the first notch I cut, after opening the slot up with a 0.625" end mill.  This is on one of the "practice" pistons.  It's a little tough to define the depth of a slot cut into a sloped surface, but it is about 0.500" from the flat part of the skirt...



I'll give it a test-fit this evening.

Steve.

do you have a crank and rod in the block?

i would mock it up like its going to be running..

btw.. if its the same specs as a 1.6TD piston cut out, then it will clear by a mile.. the 1.5 has a shorter stroke..

[Jetmugg]

I put the piston back on the rod, and put it back on the crank to check for clearance with the squirter re-installed in the block.  With a depth of 0.400" from where the milling cutter first touched the piston skirt, the notch would just barely clear the squirter.  I put a piece of modeling clay in the bottom of the notch to check the clearance, and there was virtually no clearance.  I could see through the clay at the point where the nozzle and notch would be closest.  I am going to take an additional 0.100" depth of cut on the NOS Kolbenschmidts just to be on the safe side. At that depth,  the bottom of the milling cut will be in the thickest part of the piston skirt.

Steve.