So the blog has been suffering over the past few months. I challenge myself to hone my time management skills and usually I do it fairly well. However ever since spring hit it has been a struggle to juggle all the work that needs to be done. Something had to give and unfortunately it was the blog. The garage projects continue to happen however the blog postings have not.
Even though I am still feeling the pressures I figured I better just suck it up and post something. So here it is. I had spent the last couple months catching up on summer yard projects. With the completion of the outdoor fireplace last year it was time to pick up a load of birch for burning. I had a temporary firewood holder made from 2×4 lumber and decided it was time to rework it and build it out of metal.
About 4 summers ago I had built a “built in” BBQ with a full stone surround and tile top. Over the past years the tile has taken a beating. With the constant freezing and thawing over the winter the tiles started lifting and the top was in need of a rebuild. So this spring I stripped the tile top off and built a steel one out of 10 gauge. I bent all 4 sides, built a couple accent handles, and then powder coated it matte black.
Next was onto the deck skirting. The deck was built about 5 years ago and I had always planned closing up the lower section. I stash my spare aluminum under the deck and my better half was tired of looking at it. So the deck skirting got done, no metal, all lumber in order to match the rest.
One of the garage projects I got side tracked on was some cylinder head machining for a friend’s 1973 Porsche 911. He acquired the car about a year ago and it needed a top end rebuilt so he stripped it down and upon inspection all the heads requires some repair. On the air cooled Porsche 911 engines it is common for the cylinder head sealing ring the wear a groove into the head itself. Typically this happens on the exhaust port side. The fix is to machine off about .010” on sealing surface of the head. Since the head is stepped machining of the step is also required as the same amount needs to be removed from the head surface and the step.
Here you can see the groove that gets worn into the cylinder head sealing surface. Always on the exhaust side.
When he approached me my initial reaction is that I am not set up to do this kind of machining. But as I pondered the details a little more I figured I may be able to pull it off. It was a challenge so I was game. I had warned him that he will be on the hook for any “money” mistakes I make. He already had another set of heads lined up for $2500 just in case my risky venture didn’t turn out.
In the end the heads turned out great. It took a lot of time, careful set up, and repeated measuring but I was fairly pleased with the results. I’ll work you through the process using the visual format. Let’s continue…
The project began by having to build an adapter in order to mount the heads to the lathe. I started off by finding the center of the combustion chamber. I was just barely able to grab the edges of the combustion chamber step in the jaws of my lathe chuck. Now I was able to spin the head up and mark the center on the opposite side.
With the center marked I transferred the head over to the milling machine in order to continue measuring for an adapter.
I machined an aluminum center finder in order to locate the exact center of the studs. using my DRO I was able to measure, within .0001″, the spacing between the center of the combustion chamber and the 2 studs that straddles it.
With all the dimensions calculate the rest was simple. Using a 3.5 inch chunk of 1014 steel I machined up a precision adapter that would bolt to the studs on the head and, in turn, allow me to center the combustion chamber on the lathe.
With the adapter built it was time to clean the heads up. Before machining they all got run through the bead blaster to get pulverized with #80 Aluminum Oxide
Heads are clean and ready to cut!
The heads just barely fit on my little Craftex B227 lathe. I set up a dial indicator in order to monitor my cuts a bit more closely.
The following is a video I shot cutting the heads. To many of you it may seem kinda boring but for me I think it’s pretty cool. Unfortunately YouTube cuts the quality down therefore the video is a bit choppy. I spun the heads up to just over 1600 RPM in order to perform the cutting.
I built a dial indicator holder in order to mount the tool into the 1/2″ collet of my milling machine.
Here is where the time consuming part comes in. I needed to perform 2 careful measurements. First one was the step. I was shooting for .100″ as that is what the factory spec was. I didn’t use the dial indicator as the measuring tool, I simple used it as a zero point and then performed all my readings using the DRO.
The Z axis of my DRO was the scale that did the measuring. All I did was use the Z axis of the milling machine to adjust my dial indicator to zero. then I was able to read my measurement off from the DRO. Here my machined step is well within spec.
My second measurement involved having to measure the over head height. I built a crude gauge block seen in this picture sitting on top of the vise. I would zero my dial indicator and DRO Z axis to the gauge block. Then I had a base point in order to reference all my other heads to. This dimension is incredibly crucial as a one piece cam housing sits across three of the heads. If the head dimensions aren’t equal then stresses will be placed on the cam and cam housing.
Lots and lots of measuring, here is 2 of 5 pages worth.
And here is the finished product. .010″ shaved of cylinder head gasket surface as well as the deck. Just enough to clean up the groove.
Happy to say I got all 6 heads done and dimensioned with no “money” mistakes.
GordsGarage Blog 