My Take on Cylinder Head Studs for Aircooled Engines

[Neil Harvey]

Originally Posted by Walt Fricke

Re: shuffle pinning.
The machinist I used to use said the issue with shuffle pinning was the register if the hole pairs. He didn't think standard methods (pre-CAM) were accurate enough, and even one pin a bit out of line by a thou or so made splitting the case a pain.

He would bolt the bare case together, remove a through bolt, drill down one of the case holes to the OD of the bushings until he was at the right depth in the other case half. This produced a perfect register for the shuffle bushings.

When done with them all, he made aluminum bushes to install where the outer case was opened to get the hole back to stock there. I don't know if he over-overbored where these outer bushes went - a step to keep them in place. I only figured this out years later by examining the case outsides and noticing what had to be a bush. I can see how a stepped washer could do the same thing.

Care is needed with the depth of some shuffle bushes to avoid compromising oiling holes. Using the 935 type through bolts as shuffle pins looks like it avoids oiling issues, as no inner bushes are needed.

Any competent machinist should be able to install shuffle bushings.

I like Neil's hex ends on his studs, and having a sort of bullet nose avoids the sometimes frustrating, if minor, issue of getting the washer and nut to slip into place down in the hole.

Understand exactly where you are coming from.

For years we fitted hollow dowels and drilled for the oil galley hole. It was always a nightmare to do the machining. Every hole had to be indicated in as they were all over the place. Then we had to fixture up the other side and transpose all of the positions. Some holes were slightly bigger than others which meant the interference had to be decided after the hole was opened. A huge amount of work and every time we had to line bore as the case never did seem to go back straight.

We knew we had to do something when we designed these big displacement engines. It didn't take long to figure out we needed take another route. Having built many of the earlier 962 race engines that used the doweled through bolt we decided to do the same. In our opinion, it removed the line bore question and all of the machine work is from the one side only. The case can be assembled and held in place. Very similar to what you have said happened in your application, except we don't have to fit sleeves.

I'm all for making it as easy as possible. Assembly of the engine is easy as is disassembly. Once the bolts are removed, the case splits really easy.

I'm not that clever, and other really good options are probably out there. That's the great thing about this world, we have options and can chose the one we think is best.

[Jeff Alton]

Neil, great post and well written. I like the way you approached the topic. I also appreciate you being upfront with materials and not outwardly comparing your product with others already available. New respect for you and your company (of which I already had a high level).

Sadly, this thread is at risk of going down the porcelain fixture like many other's have....

One question... Why not use a metric thread? It pains me to see parts made for vehicles built in metric come with SAE thread/hardware.... I know you had reasons. Small point and likely not relevant to many on the board, but just a question. We produce our own in house suspension components all with metric threads/hardware. Not really a comparison and the engineering level is much lower on the parts we produce (though still to aerospace quality). Small point, but for some reason important to our shop. Won't stop us from buying mind you.

Cheers

[Neil Harvey]

Jeff,
The choice was purely an economic one. We have made 12pt nuts and washers at 5000 a time. These are made from Titanium which was a material we would chose as well.

The choice was to use parts we already had. We supply the cylinder hold down nuts and grease to use.

[Focker]

@Neil - Sounds like majority of 12pt nuts are SAE vs. Metric. Is that correct? IIRC the 12pt nut on ARP rod bolts is SAE as well.