Marcus' Corvair conversion, 914-C6 Options

[r3dplanet]

A few years back I got all excited about doing a Corvair engine conversion for my 1971 car. The project waffled. Numbers were crunched and chewed. Thought and diagrams and opinions were drawn out over long winter evenings.

One particularly rainy winter evening, I found an ad on Craigslist advertising a warehouse full of Corvair parts including engines. So my pal Rory and I drove a hundred miles into the boonies late one rainy night to what turned out to be an unmarked, geographically isolated, former slaughterhouse illuminated by a single 60 watt light bulb. No cell phone reception, no escape. We were met by a couple of toothless brothers who couldn't stop talking about Daddy. Seemingly they only did what Daddy wanted them to do. Daddy wanted them to sell the stash of Corvair parts. Daddy wanted them to steal my Toyota cargo van. Daddy needed to approve the transaction of cash for an engine. Daddy, it turned out, was long dead. The two brothers kept trying to separate Rory and I, and the creepier of the two brothers kept demanding my car keys so he could test drive my van, despite my insistence that it wasn't for sale. For the first time in a long time, I wish I had a tazer gun on me. The brothers eventually showed us exactly what I wanted - an RD code 1965 110HP engine. Fearing for our lives, Rory and I muscled the engine into the van while the brothers went to find more stuff for Daddy to sell to us, or you know, maybe a club or some rope or a ball gag or something.

I left the $100 on the bench and tore the hell out. Rory and I laughed all the way back to town, ever so pleased that we were neither killed, nor raped, nor eaten. Plus, we were one up on a Corvair engine.

So with a provenance like this, and seeing JRust's new car, Dr. Evil's project, and 914coops Nader's Nightmare all take shape I've finally decided to get serious about my own project: the VW-Porsche 914-C6.

The "C" stands for Corvair.

[r3dplanet]

Some more progress on this long term project. I'm still working on case prep. Since the last episode, my machinist tested my crank to make sure it was still good and then had him polish it and make sure it was balanced. I also bought a new crank gear, cam, and cam gear. The cam I'm using is a reverse rotation Otto-20. I've sent these, the newly cleaned up connecting rods, and a few other parts to be cryogenically treated. Gregg Hikimian is doing the work. He's a very interesting chap and has delighted me outstanding service. He also performs all kinds of space age coatings and other treatments. While I'm waiting for all of those parts to return I had my case halves cleaned, and cleaned again. I'm going to perform a head stud test (as seen below), clean off the casting flash from the engines halves with a Dremel, and then hike hike them up to American Metal Cleaners for a trip into a heat-process cleaning specifically for aluminum. Or Aluminium if you are British.

So today I'm showing the head stud test. I found a great procedure here:
http://flycorvair.net/2012/01/28/testing-head-studs/

I followed this for the most part with one small modification. But first up I had to clean up the threads on the head studs. I'm actually considering pulling all of them and replacing them with stronger studs, but the Corvair brains I've picked are very split in their opinions. The aircraft guys all seem to do it, but the automotive guys don't tend to unless there's serious problems. I have a call in to American-Pi to see what they recommend. In the meantime, I'm passing the time with important little tasks. [Hey Marty, please feel free to chime in on this issue!]

You can see that the ends of the studs (3/8"-24 using the Roman Catholic measuring system) don't look very good. So I'm using both a die and a thread chaser to clean them up.



The thing about a six cylinder engine is that there's more studs than usual. The top row is where the damage is. The bottom row is shorter by an inch or so. The bottom studs also hold the rockers in place, and because they're constantly coated in oil these threads are in super condition.



Now it's time to see if the studs can hold 30 pounds of torque. The first idea I had was just to use one of the old cylinders and torque it down with some fasteners, but you can see that there's no way to do that since any little amount of torque would just break the fins. I thought about making a square jig to fit over all four studs and the cylinder to simulate the head, but then I remembered that I don't have any machining capability.



So I went to Plan B and cut some 3/8" steel tubing and used some hardened fasteners instead. This failed because the tubing begins to collapse at less than 20 pounds.



But finally the lights when on and I picked up some steel plumbing nipples of different lengths to match the stud length and still reveal the threads. I spun on a Tee so that I could view into the hole with a small light to see if the head stud would turn as I torqued it down. The tool completely obscures sight of the stud so this little idea worked really well.



This is the final setup. Using hardened washers to protect the case surface, I torqued down the nut to 15 pounds making note of the position of the wrench handle. Then I torqued again to 20, 25, and then 30 pounds making sure that the handle didn't travel too far to meet each target.





At the end of the exercise I had exactly one loose stud. I'll order a replacement from Clark's that measures .003" thicker on the base stud and Loctite it in unless American-Pi tells me to pull them. If that's the case, then I just wasted a Saturday. But hey, it's pouring down in rain Portland and this is what you do in this crappy weather.

[gf4c]

-snip-
I'm actually considering pulling all of them and replacing them with stronger studs, but the Corvair brains I've picked are very split in their opinions. The aircraft guys all seem to do it, but the automotive guys don't tend to unless there's serious problems. I have a call in to American-Pi to see what they recommend. In the meantime, I'm passing the time with important little tasks. [Hey Marty, please feel free to chime in on this issue!]
-snip-
At the end of the exercise I had exactly one loose stud. I'll order a replacement from Clark's that measures .003" thicker on the base stud and Loctite it in unless American-Pi tells me to pull them. If that's the case, then I just wasted a Saturday. But hey, it's pouring down in rain Portland and this is what you do in this crappy weather.

Hi Marcus

I don't recommend replacing any studs that pass the torque test when building a stock type engine. They are plenty strong IMO, no need for those expensive 7/16" studs which cost over $300 for replacing all 24 studs.

Regarding installing the replacement stud: Factory Manual recommends using anti-seize on the threads when installing into the block. If your threads are good in the block, the .003 will be very snug to install, the anti-seize will help. I use a special installation tool, similar to these:

These work much better than the double nut arrangement commonly used.

HTH
Marty

[r3dplanet]

Hey, those are cool! Where can I find them? Or the exact name of the tool?

The only reason I thought about replacing all of the studs is because of the increased displacement and power of the 3.1 conversion. I know for a stock engine there should be no issue, but with the increased power it gave me pause.

Thanks for being here!

-marcus

Hi Marcus

I don't recommend replacing any studs that pass the torque test when building a stock type engine. They are plenty strong IMO, no need for those expensive 7/16" studs which cost over $300 for replacing all 24 studs.

Regarding installing the replacement stud: Factory Manual recommends using anti-seize on the threads when installing into the block. If your threads are good in the block, the .003 will be very snug to install, the anti-seize will help. I use a special installation tool, similar to these:

These work much better than the double nut arrangement commonly used.

HTH
Marty

[gf4c]

Hey, those are cool! Where can I find them? Or the exact name of the tool?

Those ones are made by Motion Pro but I don't see any in 3/8-24 in their catalog. You might check with some of the motorcycle shops as the Harley guys need them in the 3/8-24 size (also available on ebay).

The only reason I thought about replacing all of the studs is because of the increased displacement and power of the 3.1 conversion. I know for a stock engine there should be no issue, but with the increased power it gave me pause.

My experience is the studs are not the weak link when making extreme power. (IMG:style_emoticons/default/biggrin.gif)

You mention the 3.1 conversion: If you're willing to accept a few less cc by using a 92mm piston/cylinder instead of the 94mm ones (2974cc instead of 3130cc), you can build a stronger engine IMO. The 92mm cylinder is available in a "thick wall" version; it also has a reduced spigot end diameter where it enters the case, resulting in more aluminum around the studs. Many thanks to Jeff Ballard, owner of SC Performance for this tip.

Marty