A Boring Job "line bore"
 

Been wanting to try out these old factory tools for quite some time. They belonged to my dad he got them in the 80s I think. I’ve been a Porsche mechanic for a while now and have sent off all my cases to either Ollie’s or C.E.
I recently got some training from the DI of andial and he encouraged me to go ahead and use the old tools instead of sending out my cases. Here are some photos of my first - a ‘68 normal.
Here’s a link to a video of the freshly assembled engine, everything worked out well. https://photos.app.goo.gl/zhX4gehU62VGRrgf7
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http://forums.pelicanparts.com/uploa...1691000866.jpg
http://forums.pelicanparts.com/uploa...1691000901.jpg
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Congratulations! It looks like it the bullet and stepped to the next level of engine building! Nice job.

Rahl

Are you boring it back to standard or oversize?

That’s super cool. I’m also interested in the above question. Did you mill the case halves before you bored it or was it bored for oversized bearings!
Beautiful targa BTW

The tool just hit the high spots.

Like John said the tool just hits the high spots. The case was .004” tight at the #1 bearing so after the cut the tunnel measures within the specification.
The tool has the capability of cutting oversize but the way it was explained to me the tunnel would have to be pretty bad to call for an oversized cut.

I didn’t touch the case mating surfaces…would like to learn more about that though. I think the cases that get closed like how Ollie’s does it is a benefit because you (they) can make the tunnel perfectly round after and the surfaces are flat so less chance of leaks.
The cylinder base surfaces got milled flat though! And thanks the targa is my bosses car she’s a beaut

You lap the case haves. Compound on a glass plate.

My experience with line hone, to max spec, + .019mm is a loss of bearing crush. Use to do this on race motors, and at tear down the ends of the bearing shells in the main line are all hammered from movement. If your not going to the max, you’re probably fine. This was on 3.0 cases, I just stoped doing it.

That’s one method .. when I was in school they told us that’s how ed pink does it. I imagine it removes next to nothing which would have its pros and cons

You’d be surprised how much you can remove.

Then the intermediate shaft bore closes up. Got a tool for that?

I don’t but I know where to get it, it’s basically a smaller version of the big one. I talked to Ollie’s about how the open up the 2nd IMS bearing on mag cases to accept a bearing and they told me they just do it on the mill.

Hey John, and all the other smarties, can you give me your further in the trenches bit of experience?

I called a local shop in my area, and asked about shaving the high spots and he was very reluctant to even consider it. There are not many people rebuilding Porsche Engines in my neck or the woods.

What have you seen as far as actual percentages of cases (Line-Bore) that do and don't need be shaved, vs ones that do need to be cut to either oversize or machine the case halves and then line-bore to standard bearing, vs nothing to do when checking the line-bore?

I was ignorant when I rebuilt my 1972 911T with a Mag case 30+ years ago and did not think about checking let alone machining the cases. As I recall I did plastic gage the clearances and the standard size crankshaft the I had micro polished, and all the clearances were good, and the crankshaft spun easily. I checked it with just a bit of oil on the bearings.

I guess my subconscious is asking if I could get away with it again. And said subconscious is thinking I might if I do check and have the same results, I had 30 years ago. Is my subconscious all wet and should I slap for even considering it?

The conservative approach is to just send it to Ollies or California Motorsports and have them check it and machine, as necessary. The cost to check is $95, and the $95 would not be charged it the case needs to machining.

Ok, as I am writing the post, the rational mind has taken over and considering the amount of money I am going to have in the engine, it makes the flavor of the question moot. Come on, it is only another $500...

I still have a question about the three possibilities for forecasting and budgeting my overhaul.

Well, you could put in a new set of mains, lay the crank and torque up the through bolts and see if the crank turns nicely. Some do, most don't. Or if the main bearings are still looking good, consider reusing them, in original order of course. Not a big fan of just hitting the high spots and leaving the untouched areas. How round can that be?

Thanks John, I just curious, I'll drop the crank in and see what I got. Machine shaving is against my grain as well.

Porsche dude: this is for your ‘83 3.0 right? The aluminum 3.0 and 3.2 have proven to be very durable. Unlikely that machining is needed and unlikely that new main or conrod bearings are needed. Just check for free movement and Plastigage the bearings. You have read about the poor quality in some sets of Glyco bearings. If the originals are in tolerance I would keep keep running them. The magnesium cases are not as rigid, so if you have any doubts about the main bearing fit, getting that measured is a good idea.

There is an inherent advantage to continue using the bearings. They have already bedded-in together and demonstrated durability. In the olde days of “poured bearings” machine shops used to pour the lead into the steel or iron bearing saddles and then hand scrape them down to a little less than the desired tolerance. Then the engine operation would push the lead around a bit and smooth them out. Therefore it was better to leave good bearings alone than to rebuild them. Of course, modern shell bearings are made with much greater precision (well, they are supposed to be) and the Babbit surface is much thinner, although it still gives a little bit, but the principle still stands. Leave good bearings alone. You may introduce new problems by changing them.

Not real round. I’ve measured quite a few cases cut this way between what I’ve cut with my tool and what I’ve got from C.E. In the past. That being said yes it’s not perfectly round but it is more round than it was before and eliminates the chance of a tight spot in your clearance. I had my concerns at first but those were put to rest when I went through a training with Dieter who’s been doing it this way for a long time. In my opinion the real benefit of shaving the case and boring back to STD is not the fact that the tunnel is perfectly round but the case halves are perfectly flat once again and won’t leak. I still use loctite 574 and it’s hit and miss on the mag cases that haven’t been flattened

Thanks guys. appreciate the input and advice.

I just spoke with Walt at Competition Engineering in Lake Havasu about the machine work i’m considering. A synopsis of my questions.

Rod Big Ends: Even with ARP bolts, he has rarely seen out of round 3.0 & 3.2’s that haven’t had abuse and someone screwing them up. Little end are the same. I am 100% that that the engine has never be apart.

Case Line Bore: Again he has rarely seen a 3.0 and 3.2’s case that need machined.

Crankshaft: They generally ware very little if not abused.

So my path forward is to send the case to be inspected, and cleaned. Have them inspect and polish the crank. Resurface flywheel and balance with the cover.

How many miles on the engine? If under 200K, Don’t even split the case. Refresh the heads, maybe install a new cam, inspect and recondition the rockers, the top end back on and run the snot out of it. Save your time and money for an “ultimate rebuild”.