Question about Danno's valve bashing fix
 

Can you explain how it works?

You said it bolts to the head studs, so do you cut with the pistons still in the engine?

How do you keep from getting metal shavings in the cylinders?

Whens it gonna be available?

Pics?

What does everyone think about it?

I personally think its a very cool idea, and perhaps wise idea to turn our engines into non-interference engines. Kinda wonder how that affets performance too...

The metal shavings would be a major concern of mine. I machine valve reliefs in pistons all the time but always out of the engine. It can be done, mabye with a shield around the cutter or a vacuum type of deal, but im a clean freak when it comes to engine internals.
The other is how much it would lower the compression ratio. From what I've measured, the reliefs dont have to be cut all that deep.
I think its a good idea. just need some clarification on the process.

If you bolt it to the head studs it's most likely a spacer that just adds a little distance between the pistons and the valves. The only way I've heard of Danno talking about making the pistons non interference is by cutting into the dish a little bit and you would do that with the pistons out of the motor so you wouldn't have to worry about shavings.

From the pic he showed, he did cut a "bowl" type shape into the pistons, and he did say that the cutter just bolts to the head studs.

Danno, where are you on this one?...some people are very interested on your idea

Personally, I wouldn't worry too much about the shavings. They would only be on top of the piston, no place for them to go really. After the relief was cut, a quick shot with the air hose and they would be gone.

But heaven forbid that a little sliver get lodged in there because there goes your cylinder wall. It's much safer to do this cut with the pistons out of the motor unless you all know something that I don't know.

Yes it is much safer with the engine disassembled. However, I have seen it done on an assembled engine before.

"Can you explain how it works?"

Simple, the tool is a big block of aluminium that slides down over 4 head-studs. It has two guides that hold a cutting bit at the same angles as the valves. The bits have a depth setting to cut to the proper depth. You spin the cutting bit with a hand-held drill. Cut the pockets, suck out the shavings with a vacuum, remove tool and install in next cylinder. :)


"You said it bolts to the head studs, so do you cut with the pistons still in the engine?"

Yes, the pistons are cut while they are installed in the engine. The intention is for someone who've just had their valves bashed by a broken timing-belt to cut the pockets while they've got their head off.


"How do you keep from getting metal shavings in the cylinders?"

You put down some duct tape around the periphery of the piston-tops to seal up the gap on the edge of the cylinders. The tool then clamps down on the tape and keeps all the shavings in the pocket over the pistons.

"Whens it gonna be available?"

Some time in the next couple weeks. I'm gonna try it out on my engine first, a 944NA shortblock in a 951. :) Should be going for about $150 rental.

"Pics?"

Ok, I'll take some photos when I cut my pistons, maybe this weekend or the next week. It'll be used to write up the instructions.


"Kinda wonder how that affets performance too..."

Not much, the volume removed is about 1cc. So it doesn't even change your compression by 0.1:1 ratio.

"What does everyone think about it?"

Well, it depends upon who you ask. This procedure is commonly known as "fly-cutting" in the muscle-car hot-rod market. It's been done for many decades since the '50s. There's something about the culture of Porsche owners. They tend to be 1/2 a century behind the other car-owners in their upgrade thinking.

Most common idea is, "Porsche must've done it this way for a reason, why change it?". Well, if that's your philosophy, why even bother upgrading your car at all? It was 'perfect' when it left the factory and Porsche has not many any improvements on their car since! Most of what I do is apply current state-of-the-ar technology to our cars.

BTW - you don't even have to break a timing-belt to smash your valves. I just installed a new head on a 944-spec car this last weekend. It must've been overrevved due to a missed downshift or something. All four exhaust valves were toasted along with major dents in the tops of the pistons. But the belts were perfectly intact... :(

Actually Danno, thats last part was for everyone else to answer, lol.

but I love the idea and with the timing belt being such a big issue on the '44 I feel its a really good idea, just didn't know anything about it so I'm asking.

I almost bouncing off the walls waiting for the pics.