'68 Sporto no turn overo

[jt912]

[304065]

John, those pistons look identical the ones I took out of my '66. The chalky material is, of course, corrosion. The pistons taper toward the bottom of the skirt so it makes sense that that's where it would form.

If you are considering re-using the pistons and cylinders, the first thing I would check would be the ring groove width. Somebody installed new rings on my pistons back in 1982, but the groove had worn oversize, so almost all the compression rings were broken. You don't appear to have any broken rings, good!

The cylinders don't look bad, but a careful inspection to see if there are any low spots is in order. A bore gage is useful for this-- many people use an outside micrometer to set the gauge to the factory wear limit and then use this in the cylinder to find the low spots. I did the same thing, and found it useful to chuck the mic up in a micrometer stand to hold it while I set the bore gage. Of course you could use something like a ring gage to set the bore gage, but that could be expensive. More expensive and accurate would be something like a Mitutoyo Holtest or an Intrimik, it depends on how crazy you are (I am quite crazy.)

These are the spots I would check first:




Those Biral jugs can be bored to 81 for around $300 for all six. That's what I did. Of course you would need 81mm pistons. The replacement pistons are actually heavier than the original Mahles, which tells you a lot about the engineering back in the day. Here's my thread on this, you may have already seen it.

Jugs and Slugs: Confessions of a JE Piston owner

Well, at least you now have a clear path forward. Splitting the case will allow you to replace the intermediate shaft bearings, that's a plus.

Thanks for the photos, these are a great contribution to our community here.

[Fritter]

Same thing happened on my spare 68 engine. I had to cut one cylinder off with an angle grinder. My pistons looked just like yours. Good thing is I have a STD STD counterweighted crank. Not sure what I will do with the engine.

[jt912]

So progress is as follows. The rings on the frozen pistons were caked tight with crap. So much so that they didn't spring out like the others. So with some patience I used a .002 feeler gauge and worked it like a saw between one side of the ring and the piston. I was able to free up the rings enough were I could pop them loose with a fine nail set. So all the rings are out.
Today was the make it or brake it point. Got all the case bolt/nuts off and went to town on seperating the case. That was one gut wrenching sound. Crack!!! I was fearful of breaking something on the case (I tapped using a block of oak on the points shown in Wayne's book). I was relieved to see that faint black line where the case was giving way. It actually came apart much easier than I imagined. From my untrained eyes I think things look pretty good inside. The most peculiar thing is the bearing have spots on them? Not sure what causes this. Any ideas?
Next step is to have a local Porsche mechanic come over and help me size things and figure out where to send what.

[jt912]

[304065]

That looks like normal bearing wear. Can those be the original factory bearing shells? Pretty cool.

The real test will be the extent of wear on your intermediate shaft bearing surface. You can send the case to have it modified to take the shell inserts from the later case. It's pretty expensive and requires modification of the intermediate shaft. It may not be necessary, but easy enough to find out.

One thing that is neat about original early engines are the wire mesh windage trays.

Nice detail of the 6G headmark on your oil pump nut. Save all the nuts and bolts, these headmarks are no longer available and the only source is original engines like yours. You should see a lot of 8G "V" nuts for "Verbus," search here for "headmarks" if you are into that sort of thing.

Great photos, looks like a normal 2,0 teardown so far.

[Fritter]

Looks good. Measure that crank, I bet it's STD STD.

[jt912]

Getting back to the story. Like some many others before me, this turned into a while-you-are-in-there type rebuild. Today I finally witnessed the first signs of it going back together. I would have enjoyed putting it back together, but the shop (a one-man show) that has overseen the machine work is going to to the re-assembly. I will update as I get pictures, but the freshly machined and new parts sure are pretty!

[jt912]

...and the story continues. Skipping all the unnecessary details, I've picked my engine back up to finish it. Things didn't work out with the gentleman doing the re-assembly. So I got it back at the point of aligning the chains. Gotten everything checked off and now am at the point of finishing the rocker assemblies.
Quick rundown of what was done. Cylinders cleaned up and taken to 81mm w/ new pistons. Old pistons were not re-useable. Cams weresent to Webcam to work their magic on. Crank was polished. I think it also was turned to first under. It was right at the wear limit for standard. Rockers resurfaced and bushed. I recall something about the bushing being bored slightly off-center for a slightly longer stroke. (IIRC) New parts and pieces everywhere. Included are a couple shots of the current Zstate of affairs. I make two Z-blocks of my own design that worked very well, were quick to make, and were cheap ($2 scrap steel, $3 in knurled knobs, and $2 in screws). Used the two-dial method which I would recommend. Also tried to figure a way to get more consistant readings while timing the cams so I set the Z1 mark at case mark and mark on the fan housing. Then I taped on lined paper and used the lines to help me be more consistant. Was able to achieve 3.16mm overlap for both sides. Supposedly there are photos of the progress photos up to the point I took back the engine. I took some when I would stop in to see him working. Hopefully they show up for the records of the assembly of this engine.