Jump Start Engines – part #5


In this part we look at the Camshaft Group 1100. You can refresh your thoughts on this by looking at the 2013 story I wrote about this group:

Getting Started in 2013, Part #3, The Camshaft Group (1100)


The take away from that story is how the number system supports a wide array of choices available to builders, ranging from a reground cam  with a stock gear to a new cam with a fail safe billet gear installed for you.


I have built and tested all of the options above, and they all work.  Which one should builders use? Well, any one that appeals to them after some reading to understand the differences. To amend this, let me share some of the additional things I have worked with in cams in the last few years.


-The most popular cams in use in Corvairs remain the same Clark’s OT-10 (new and regrind) that we have been recommending for 15 years.

– I have built motors with and tested the California Corvairs CC-10 and it is a good quality cam and essentially the same output as the OT-10.

-I am having a run of cams ground to a pattern that we tested in 1997-98, based on a design done for me by the late Harvey Crane. The cam has a small advantage over an OT-10. The jump start engines will be built up with these cams. I had considered doing this before, but it took a while to find a US grinder who had the right experience and equipment and was OK with making cams for aircraft.

– I have worked with every Cam gear on the market, built engines around all of them, from the Clark’s basic gear through the $300 American Pi adjustable timing billet. I dislike the fact that the Clarks gears are likely Chinese products, but they do fit and work. The California Corvairs and Larry’s Billets are American made, but they are very tight fits on cams, and I do not recommend installing one at home. The California gear has a shallow key groove that requires the height of the key to be checked.

– Absolutely, under no circumstances, ever, hit a cam hear with a hammer to “finish install it”. This appears in Corvair car sites and is very poor advice. Cams are brittle, at the next College I will demonstrate how easy it is to crack or break one with a 16 oz. hammer.

-Here is a link to a seven and a half year old story from our main website: http://www.flycorvair.com/hangar1206a.html  Half way down, it is detailing how we put cam gears on. I note that I want the thrust washer on tight.  Below is a section from our webpage 14 moths later. When GM built your Corvair, it had a tight thrust washer. If you go on line, you can find a number of car people claim that they would prefer to have the washer loose. Although I can not pin point this as a failure issue, It is a good example of car people offering very poor advise.

If you press a cam gear on tight with an un-chamfered washer, the gear gets run out in it and is then junk.  It took many wrecked cam gears to spot why some Corvair parts sellers didn’t make the gear tight. It was the new washers made without the chamfer below that cause the gear not to sit properly if it was pressed all the way on. Their solution was to simply not put the gear on all the way and leave the washer loose. They had the washers fixed eventually, but in the last 24 months, this issue and un-chamfered washers have shown back up. There are pages of commentary on Corvair car sites about cam washer looseness, but not a single one of these notes anything about the root cause, the missing chamfer. Part of the reason why I am going to do a run of my own cams is because it is frustrating to solve this issue at my own expense years ago, but again see builders coming to colleges with cams with supplier installed gears that cost nearly $400 that again have loose washers.


(Feb. 2008) “Technical News You Can Use
Above are two cam thrust washers for a Corvair. On the lathe, I’ve cut a slight bevel to provide clearance on the side of the washer that touches the cam. My research into building Corvair engines is continuous and ongoing. The unbeveled washer is an aftermarket part supplied by several of the Corvair parts houses. When pressing on a new cam gear, this will make the cam gear walk slightly out of square at the last moment. After years of installing countless cam gears without problem, we’d recently had trouble getting several of them to seat on their cams and hold tight their washers. Ignoring this problem, people selling cams with gears on had been leaving the washer loose as a really poor fix. It took a while to determine what was causing this issue, but a slight relief on the washer makes the difference.”




Below, the Group 1100 chart from our webpage checklist:


Cam group (1100)

1101- Cam

1102- Thrust washer

1103- Key

1104- Cam gear

1105- Hydraulic lifter set -12 total-

1106- Cam lubricant

1107- ZDDP oil additive



Above, an engine being assembled at CC#22 in Texas. It is a Clarks Fail safe gear on an OT-10, and a Weseman Gen 1 bearing.  the dial indicator shows that the steel crankshaft hub that the Weseman bearing rides on is correctly installed. Barely visible are the three small Allen screws that are centered around the crank nub. By adjusting these screws and the tapered shims underneath them carefully, the steel crank hub can be zeroed to exact alignment with the crankshaft. This adjustment is not required on the Gen 2, as the bearing hub is installed on the crank in processing and ground concentric. The sole advantage of the Gen 1 is that it can be installed as a retrofit on a fully assembled engine. Most people building an engine with a 5th bearing from the start now opt for a Gen 2 bearing. More info at: http://flywithspa.com/fly5thbearingcom/5thbearingnewengine.html





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