Connecting Rods

The following is from a posting by WW and still needs editing:

If you take your core engine apart, everyone ends up with six pistons on rods. After pulling them off, try to keep the correct caps with each rod. Once you have them out you need to choose how to have them rebuilt.

Like dealing with the crank, there are a lot of different ways to go, but I am going to keep it simple here and outline the two most popular paths, both of which I have personally used a number of times, both of which are fully accessible to anyone no matter where they are.

The first route is to send your rods and pistons to Clarks. The reason why I mention sending them both is that it takes a hydraulic press of 5 to 10 tons and a little jigging to take the rods off the pistons. Most builders don't have access to this. If you take them to a local machine shop, you will likely have to make two trips and you will probably pay the same price as Clarks charges for removing them, about $35. Just put them in a Large US mail Flat rate priority mail box, and send them. The $14 shipping is better than running around town. If you do have a press, you can knock the pistons off the rods and save the cost and $5 on shipping because the rods by themselves will fit in a medium flat rate box. Yes, you can get really creative and pull the pins out with a 1/2" threaded rod, but this is best saved for a real Mad max moment. I used this technique to take a #3 piston out of my '67 corvair with the engine still in the car to prove to Kevin it could be done, but lets stick to practical ideas.

Clarks sells a set of reconditioned rods, Part number C-9203 that we have used in several dozen engines. The Catalog also shows a part number C-9203ww, which is the same thing. I just set the second designation up with Clarks so that a person asking for "the part WW uses" gets the correct choice from the several different Clarks options. These rods Cost $259 after you send in your cores.

As mentioned, Clarks gets $35 to press your pistons off also. These rods have ARP bolts with 1/2" six point nuts, they are rebuilt and they are balanced. I have used these in all kinds of engines, and they work well. This should be considered the base line for aircraft use.

If you are buying your pistons from Clarks, you can also have them put them on these rods for another $35. If you are building at home, this is a good option. If you are headed to the College, we will use a rod heater and I will install your pistons there as part of the event.

(There is 50% of the cost of attendance saved right there.) If you want to make progress, off to the shop and get that core torn down, and get the box in the mail on your lunch hour on Monday.

Option #2: Box your rods and pistons up and send them to Roy's Garage. Roy also rebuilds rods. I have used Roys rods in a lot of Corvair engines as well. All of our 2850cc kits have Roys rods, and my own personal 3,000cc engine has them also. They are an upgrade over the 9203s. Roy's are 100% magnafluxed, the are end for end balanced (this means their CG location is the same) and the have the high end ARP 'Waveloc' bolts, and they use 3/8" 12 point nuts, which are easier to install. These Rods are $400 a set, but for an apples to apples comparison, Roy includes pressing your old pistons off and putting your new ones on. For comparative purposes they are $65 more per set that the 9203s. If you are on a budget, Go Clarks, got a bit more to spend? Roy's rods are money well spent. Take your pick, either one is infinitely better than letting the weekend get away and having the possibility of progress drift out of your grasp. This isn't just pep talk, I have two cores in my hangar I am going to pull apart this weekend, and their rod cores will be shipped out on Monday.

Other possibilities:

Clarks high end, 'Lightened' rods. I have never tried these. I am sure they are good, and they are about the same price as Roys. In comparison, I would go with Roys because the waveloc bots and small nuts are more important than a small weight reduction in a 4,000 rpm engine.

New rods; Several places sell them, but they are made in China, and I will spare every one my broken record speech on Chairman Mao's aviation quality issues. Be aware that the Chinese are notorious for producing fake hardware. even if you see an ARP stamp on the head of the rod bolt, I would not believe it on a product from China. I don't make this stuff up nor read it on the Internet. My oldest friend works for Grumman and they get warnings all the time about it, and they have found bogus hardware in the lift equipment about to pick up 100 million dollar aircraft assemblies. These rods have flown in Corvairs, and the bolts that were delivered with them were genuine ARP, but that could change with the next batch and their is no good way for builders to know. Just avoid these things.

Other sources; Two engines I built that flew a long time had rods built by Ray Sedman at American Pi. Nice stuff, and they had polished beams.

This detail is important on very high rpm engines. Other than this, the rods are essentially like Roy's and are the same $400, but they do not include the pressing of the pistons.

Other sources part 2, local machine shops. This is a bad idea. The only time I have ever had a rod fail was 10 years ago, when we were using Gary's skycoupe as a test mule. A local shop, supposedly very good, had done the rods for us 50 hours earlier. The shop owner was fond of pointing out that his sons worked for nascar teams. After the skycoupe landed without incident, we took the engine apart and found out that the local shop had used a non radius, very sharp tool to cut the tops of the rods. You couldn't see it on assembly because these spots were under the heads of the bolts. The Bolt and nut stayed torqued, but the rod broke right through the sharp corner. The guy was offended when I showed him the rods and asked if his sons sold tee shirts or if they were groundskeepers for nascar, because no one in his family could be an engine guy as far as I was concerned.

Special Historical Corvaircraft Note: If you are new to corvaircraft, check this out: In the bottom of my tool box is a post made to Corvaircraft by Rad Davis about how his father taught him how to polish and balance rods. A very neat piece of old school know how. I liked it enough to print it an keep it.

Here is what is remarkable: It is now 11 years old! The archives don't even go that far back, but it is worth taking the time to really appreciate what a well run resource we have here, and now something of an institution. If your out there Rad, hats off to you.

Thats enough talk on rods, time to go bend wrenches and get your cores ready for shipment. If 1am is a little late for shop work, Then go to my website and sign up for College #21. Make a command decision, it is what aviation is all about.

Thank you.

William Wynne