M96 Cylinder Heads/Cam Covers - EBay
 

I bought a $700 2000 Boxster project. Engine “quit running” and sat for several years. I determined that B1 timing was off. Turns out part of the chain rail broke off, lodged in the sprocket and it jumped timing. All intake and exhaust valves were damaged, and need to be replaced. I was just going to buy a new head setup and bolt it on.

I looked on EBay, and there are lots of Heads for sale. Most are being sold without the cam bearing caps and cam cover. I know these are matched machined parts, and won’t work if you mix and match.

How are these parts on EBay useful, if they aren’t selling the complete set? Doesn’t make sense to me and figure I must be missing something. How could a head missing the caps and cover be worth anything?

Simple: Incomplete head are virtual boat anchors, but people line up to sell them on flea bay, along with outer similarly useless items.

Caveat emptor...……...

Whew! I thought I was missing something.

can't you line bore them and put bearings in? you can on just about any other engine.

Many motorcycle heads are like the Porsche. The parting lines don't line up on the caps if they get swapped around. And no bearing shells available, oversize or otherwise, because they didn't come with any.
I imagine a guy could find a custom mfr to make bearing shells for ya.... but sounds expensive.


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well, i presume the head and the cam cover originate as separate castings (no caps; caps are part of the cover) then are assembled and line bored at the factory, at which point they are matched to each other. so, do what the factory does, but you have to go oversized and would need to insert some bearings to bring the tolerances back down to match the cam. presume bearings are no big deal; a diameter, width, and thickness?

just did something similar for the crank and cam on my triumph, where the bearings required are just based on the oem tolerance and how much you had to remove. but truly am out of my depth here so could be way off.

Can't comment specifically on the Porsche, but the motorcycle examples I referenced earlier, this is not the case.
Single casting. Bored, and then the caps are "cracked", and separated. That's why the parting lines only match in once place.

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Yeah, pretty sure the entire unit is cast as one, then split.

that blows my mind what they can cast - that would be items 1 and 7 in the pic below are cast as one piece then split?

http://986forum.com/forums/uploads02...1562616767.gif

I don't know how these particular ones are cast, but they're usually cast separately, mating surfaces machined, then bolted together to bore the journals for the cams. This is why it's so critical that they are kept as a set. A mis-matched set would never have perfectly round cam journals.

No, I'd be talking about #1 & #5 in that pic.
The pic, though, makes it look like there are only 2 of those? Am I seeing that correctly?

Remember, I'm not the Porsche guy here, haha. But the few motorcycle motors that I'm referring to below, those caps are cast as one piece with the head, then split. That's a deviation from standard practice, in my experience though. Typically, the caps are cast, then machined, then bolted-on, then bored/honed. as one would expect.

?? go figger.

yeah, i think most of the races are part of the cover; there's just the two on each side that hold the two cams at the chain end.

https://cdn4.pelicanparts.com/techar...mall/Pic06.jpg

here's a better pic of the upper cap, and it doesn't really look like it was cast w the head then split:

https://cdn4.pelicanparts.com/techar...mall/Pic07.jpg

oh yeah.... seeing that, just forget Everything I said. Hahaha.

So, looking at that, I'm not sure I know a machinist who'd still be my friend after asking them to line-bore or hone that..... that looks like a sunnaba-B.

I believe the connecting rods on Corvette motors are single castings. They bore the hole for the crank, tap for the bolts and break them in half. It's pretty ingenious, considering you can't really bolt on mismatched caps in a rebuild. I'm sure that wasn't their concern, though. Most likely they found it a faster & cheaper process.

Those are called cracked connecting rods. A fairly common process where tolerances are critical.