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'66 911 #304065 Irischgruen
Ex-'71 911 PCA C-Stock Club Racer #806 (Sold 5/15/13)
Ex-'88 Carrera (Sold 3/29/02)
Ex-'91 Carrera 2 Cabriolet (Sold 8/20/04)
Old 10-23-2007, 11:42 AM
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John, Your attention to detail rivals the best. I can't wait to see the finished product.

btw, I have an additional question. Charles Navarro mentioned coatings for the pistons.

Quote:
"Depending on a few variables, piston coatings usually run about $50/piston, when you include thermal barrier and skirt coatings. That same $50 gets you coated ring lands too if Calico does them."

John, I noticed that your skirt coatings do not include the ring lands. Is there a reason you did not get the crowns coated? I am about to get some pistons coated for my new build and I wondered... Which coating goes on the ring lands?

I could see that the thermal barrier coating would help spread the heat load at the rings. At the same time this means the rings could run hot by not being able to dissipate their heat to the piston. Does anyone know where these coatings are applied? Does the thermal barrier coating stop at the edge of the crown or the edge of the top ring land. Maybe it goes past both compression rings and the oil ring gets the anti-friction coating.

Thanks

jamie
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Old 10-24-2007, 07:26 AM
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I usually don't apply a thermal barrier unless it's a high boost / CR application OR the lighten combo with the under crown milling has been applied to the piston, to give it some extra strength, not that it is needed.

John's pistons were coated by JE; they don't offer a ring coating. They only offer a hard anodize option for the ring lands, and it's big $$$, and overkill.

I usually use Calico if I have time to wait for the pistons to be made, then coated, then have the cylinders match honed to the cylinders; usually adds about 4 weeks onto the process since I can't get that much of a head start on the cylinders then.
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Old 10-24-2007, 07:53 AM
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Jugs


Hey John,
Those look great!

Sorry if I'm late to the show, but you don't mention here what you did about your cylinders.

Did you hone and true the original ones and have these custom-made to fit?

What alternatives are there for us early '65-66 2.0 guys if we want to keep our original-looking cylinders?

Thanks.

Mitch McCloskey
'66 911 #304093
Old 10-24-2007, 08:12 AM
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Most if not all original 2.0 cylinders can be perfectly re-conditioned by taking them out to 81mm, then fitted with JE's, as done above. I bored and honed the cylinders to 81.00mm then made up the JE's to fit. Not something I do everyday, but glad to help preserve reuseable parts for the sake of originality. I usually do this for the 356 guys and for 4 Cam p+c's.
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Old 10-24-2007, 08:18 AM
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Mitch, I owe you a response on Webasto heaters, I haven't forgotten.

Charles, I thought it was the other way around, didn't you have JE make the pistons and then Millenium match-honed the cylinders to fit?
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Ex-'91 Carrera 2 Cabriolet (Sold 8/20/04)
Old 10-24-2007, 09:20 AM
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Quote:
Originally Posted by john_cramer View Post
Mitch, I owe you a response on Webasto heaters, I haven't forgotten.

Charles, I thought it was the other way around, didn't you have JE make the pistons and then Millenium match-honed the cylinders to fit?
FWIW, this is exactly how my Birals were done. JEs delivered, then cylinders match honed.
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Old 10-24-2007, 09:44 AM
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John, can't remember now which way I did it for you. Usually, if JE coats it, I don't have to match hone. I specify the final bore size to which the cylinder is honed and tell that to JE with the clearance desired. The skirt coating is then applied .00025-.0005" thick on diameter on the piston, which as far as I am concerned, does not affect how I set up the clearance on the bores.

With Calico on the other hand, I specify the coating .001" total on diameter (smallest they can do), but sometimes it comes thicker and sometimes I have had customers who use Calico after the fact end up with zero clearance (not a good thing), so that's why I wait to set the finish hone to until the coated piston can be measured.
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Old 10-24-2007, 10:19 AM
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'66 911 #304065 Irischgruen
Ex-'71 911 PCA C-Stock Club Racer #806 (Sold 5/15/13)
Ex-'88 Carrera (Sold 3/29/02)
Ex-'91 Carrera 2 Cabriolet (Sold 8/20/04)
Old 10-27-2007, 11:22 AM
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Setup was to hold the piston in a 90 degree V-block with the indicator in a height gage. The V-block was moved along the surface plate (my granite countertop which I took the time to calibrate so I don't have to haul the 35 pound surface plate out all the time!) and the measurements taken at the indicator's lowest reading point, which is the diameter.
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'66 911 #304065 Irischgruen
Ex-'71 911 PCA C-Stock Club Racer #806 (Sold 5/15/13)
Ex-'88 Carrera (Sold 3/29/02)
Ex-'91 Carrera 2 Cabriolet (Sold 8/20/04)
Old 10-27-2007, 11:23 AM
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Here is a piston after smoothing out the crown with a die grinder and blue scotch-brite roloc discs. I also used a buff with some tripoli but to really polish the dome I will need to use my bench polisher, which I doubt will inhibit carbon formation much. I will probably run this the way they are, they look very good. Those droplets are just WD40. I wrapped the piston ring area in a couple layers of blue tape and put a rubber glove over the skirt so no abrasive could get stuck in the grooves. I will clean them prior to install to be sure.

No sharp edges, and the ridge on the crown is gone, without reducing the mass appreciably (will check with the scale) or removing enough material to alter CR.



Compare to the before pic:



Thank you to Henry Schmidt for the guidance on the "crown massage" technique and tools.
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'66 911 #304065 Irischgruen
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Ex-'88 Carrera (Sold 3/29/02)
Ex-'91 Carrera 2 Cabriolet (Sold 8/20/04)

Last edited by 304065; 12-29-2007 at 10:21 AM..
Old 12-29-2007, 10:18 AM
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Henry, what do you think? Keep polishing?
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Ex-'88 Carrera (Sold 3/29/02)
Ex-'91 Carrera 2 Cabriolet (Sold 8/20/04)
Old 01-02-2008, 12:29 PM
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Hi John
Because the purpose of rounding the sharp edges is to improve flow at overlap, I might consider a slight larger radius. Your work so far looks good.
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Old 01-03-2008, 07:14 AM
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Thanks Henry! Would you have a photo of one you have done as a guide?
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Ex-'88 Carrera (Sold 3/29/02)
Ex-'91 Carrera 2 Cabriolet (Sold 8/20/04)
Old 01-03-2008, 07:19 AM
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I did a search for engine pictures on my computer and crashed the system at 7219 pictures. At that point I stopped searching. If you just make the flat area between the two edges you have polished one continuous curve that is the best you can do. Because you are not looking for every last performance gain, I would probably just leave it as you have it.
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Old 01-03-2008, 09:07 AM
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"Because the purpose of rounding the sharp edges is to improve flow at overlap, I might consider a slight larger radius. Your work so far looks good."

......And also to reduce hot spots in the combustion chamber that could cause preignition. Maybe it's just me, but I still see edges and outside corners on the dome. Can you settle for slightly reduced compression ratio in exchange for removing material from sharp corners?

Sherwood
Old 01-03-2008, 11:25 AM
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Sherwood,

In the before pic there are definitely areas that could cause preignition-- the edges of the valve pockets and the strip between them all have knife edges. I rounded these off on all the pistons.

I'm loath to remove any more material because the compression is right where I want it at 9,5:1 but even if it were necessary I would be hesitant to do it by hand-- I think it would be worse to have varying dome volumes and varying compressions among the cylinders than the edges that are there now.

For comparison purposes, here is a photo of a Mahle 906 piston. Very similar edges to the valve reliefs and of course the tall ridge between the reliefs that divides the combustion chamber in half.

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Ex-'88 Carrera (Sold 3/29/02)
Ex-'91 Carrera 2 Cabriolet (Sold 8/20/04)
Old 01-03-2008, 11:56 AM
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