February 19, 2015 1 Comment
On the surface here, the issue is the fit of the cam gear washer, part number #11o2. I have covered this topic in my writing for 10 years. I have always told builders that this washer must be held tight between the cam and gear.
In a nutshell, they were always tight, but Clarks, the supplier of our specified cam switched from using US made washers to Chinese ones, and they didn’t catch that Chairman Mao’s fan club forgot to put a critical bevel on it, and if you now tried to clamp it tight, it offset and ruined the cam gear. So they decided that it was OK for the washer to be loose. Working in my shop, I solved the mystery, and showed everyone that putting a small chamfer on the washer, which took 2 minutes in a late solved the issue. Clark’s corrected this, and things went well for years, but they have recently slipped back to using non beveled washers and loose gears. If you want to avoid the issue and have a cam that is 100% made in America you can get it from us: 1100-WW Camshaft Group
To demonstrate that I have been covering this for years, read these stories, and note that they have pictures and stories in them that were first published on FlyCorvair.com 10 years ago. This isn’t a new issue. If you are building a Corvair, I suggest spending more time reading my website than internet discussion groups. Read: Getting Started in 2013, Part #3, The Camshaft Group (1100) and Jump Start Engines – part #5.
NOTE: although the pictures show a cam in a press, UNDER NO Circumstances is it acceptable to press a cam gear on cold, or EVER press down the length of the cam. The pictures are showing how the cam is held when the gear is heated and seated under pressure, but it isn’t being pressed cold. If you press the gear cold, and it moves, it IS JUNK, because you wounded it. If you press down the length of the cam, I will assure you that you cracked it (Cams are cast iron, not steel, find a junk one and hit it with a hammer and watch it break in half) Anyone who suggests hitting the gear with a hammer or pressing it cold, is suggesting you to crash your plane.
The Issue Today:
A builder is Australia read my story after he bought the cam from clarks with a loose gear. The solution is to remove and throw away the gear, chamfer the washer, and put a new gear on. But evidently that sounded expensive, so he went to the internet looking for a second opinion, a gray area, where other people could tell him it was OK to have it loose, or come up with some cheap fix. He wrote the following letter to the “CorvairCraft” group, which I am banded for life from for being intolerant of people who offer advice there, having never built a flying plane before. Here is the letter, and the response he got from Lon Wall, a Corvair car guy who has never flown in a plane in his life, the same guy who sold cast pistons to aircraft builders for years telling them they were better than forged. Read “Local Expert” convinces builder to use cast pistons. Lon’s business is basically over, but he is still around on the net to give advice. Follow it, but make your peace with God first.
On 2/18/2015 6:30 AM, John Woods via CorvAircraft wrote:
I need some practical advice regarding a recent post on WW blog regarding
the washer on the cam shaft.
I have the OT-10 from Clark’s and the washer is not clamped tight in place
as William recommends.
The washer can be rotated but there is very little side movement. I can’t
get a 0.04mm feeler gauge between the washer and the cam gear.
I’ve rotated the cam together with the crank shaft and there is no binding.
Is this acceptable to use?
I’ll email WW also, but wanted the view from his who are flying with a
similar free turning cam washer.
Reply From Lon Wall:
Hi John – This is an issue that just won’t go away!
Of course the washer must be tight. Put it in a press and press it back tight – Note – if it takes very little pressure to get it tight then you have a loose cam gear and that’s the kiss of death. To those who have said that a loose washer is ok – Then where is the published specs on allowable tolerance (looseness)?
A new cam gear is REALLY cheap insurance for the last part to fall out of the engine and a part that sets timing. Lose the gear and you lose your engine.
Note that Lon is saying it is OK to press the cam gear cold, That if it moves this is OK, note how he agrees that it needs to be tight, but his “method” of “Fixing” it is something I would expect from a car guy with a marginally existing business. He has been on CorvairCraft for 15 years offering this kind of advice, and I am pretty sure he has never seen flown in a light plane of any kind. I have covered his problem in many stories like this: MA3-spa carb pictures, Wagabond notes.
It’s your life, take your pick on where you get advice on flying Corvairs carefully, If you constantly look for gray areas, rethink that as an approach to flying planes. You will not always get a “Do Over”, and you can be certain that no one who offered unqualified advice on the net will show up to assist you in building another plane or help your family with the cost of your burial. -ww.