Continental O200 Gear Alignment

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kc0081

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Hello, I am trying to align the gears for timing on my O200. I am confident that I have the crank gear timing marks identified (in red) but I can not find any timing marks on the cam gear . Do any of you have suggestions on how to find the timing marks on the cam gear or a way to install the cam gear correctly? Any help would be greatly appreciated!

Gear C.PNG
 

Victor Bravo

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There's a dot or dimple visible on the gear, at about 11 O'Clock on the photo you posted. That's the only thing I can see that looks obvious... but definitely take Percy's reference to the Continental manual over my assumption.
 

kc0081

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There's a dot or dimple visible on the gear, at about 11 O'Clock on the photo you posted. That's the only thing I can see that looks obvious... but definitely take Percy's reference to the Continental manual over my assumption.
Thank you Vic, that is a drop of oil. I can't find any markings at all, I thought I found one and I marked it with a marker but I am now having doubts that it is a mark.
 

kc0081

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Thank you pwood, I have referenced that before and it still refers to a punched mark. Maybe I have to do what it says and position the No. 1 cam lobes then punch mark the gear myself. The gear bolt holes are offset so it only goes on one way, its weird that it doesn't have a mark.

1628255780900.png
 

TFF

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If you have to get granular, marks correspond with top dead center of #1 cylinder. The both cam lobes for #1 should be on the heel of the cam. Crank stroke at highest, cam lobes facing opposite. They will both be at angles, but they should be equal, one high, one low.

edit. Sent before real instructions.
 

Dan Thomas

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Thank you pwood, I have referenced that before and it still refers to a punched mark. Maybe I have to do what it says and position the No. 1 cam lobes then punch mark the gear myself. The gear bolt holes are offset so it only goes on one way, its weird that it doesn't have a mark.

View attachment 113942
I wouldn't punch that gear. It may have been marked at the factory before heat-treatment, and punching it now could start a crack at the gear tooth root. Might just touch it with a small drill instead.
 

kc0081

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That's a great point Dan, thank you for posting that.

TFF, its hard for me to get my head around the position of the lobes. Here is a pic that is close to TDC, I believe. The lobe nearest the cam gear is exhaust and the next one is intake.

1628277050267.jpeg
 

TFF

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If the rod with the foam is #1, the lobes for #1 would be pointing to the opposite side.
 

kc0081

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TFF, yes the foam is #1 rod.

My problem is this, I assembled the case halves and aligned the gears as to what I thought was correct. I hired an A&P to help torque the case and verify the gear timing is correct. He stated that it looked good and I pressed on. Now, my first engine start was not very good. The engine had a bad miss. I have EGT and CHT probes on all cylinders and the front two cylinders were cold and the back two were normal.

So, the #1 and #2 cylinders are firing good. The front #4 and #3 are cold/dead.

I found that my carb was leaking and worn out. $1,000 later and a new carb and the miss is still there.

I am thinking what can it be? I believe it may be the gear timing. It actually should be easy to confirm. If I had a good understanding of the valve operation, I should be able to rotate the prop and see if the valves on each respective cylinders are opening correctly (timing is good) or not.

Here is a video of the engine run.

 

Dan Thomas

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Thatone

Plug wires on the correct cylinders?
Yup. Probably reversed. Maybe got the cylinder numbering screwed up. The cylinders are numbered from 1 to 4, starting at the rearmost cylinder, which is on the copilot's side of the airplane. #3 is ahead of that one. Number 2 is the rear on the pilot's side and 4 is the one in front of it. The lead nuts should have the cylinder numbers and positions stamped on them; for instance, B3 is for the bottom plug in #3 cylinder. T1 is for the top plug in #1. Those nut numbers are for the cylinder numbers, not the firing order.

Once the leads are connected properly it will likely run OK. But I'd be concerned about the cam timing, since it would be easy to get the gear off by one tooth. A full-power static run should be done, and the max RPM achieved should fall within the range specified by the TCDS. Now, if it's on a homebuilt, you'd have to find a TC'd airplane with the same or very similar prop to get the RPM number. If the RPM is too low, I'd suspect incorrect valve timing.
 

kc0081

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In a dark garage, I removed the top plugs and carefully pulled the prop through and seen the bottom plugs fire in the two front cylinders, and got shocked by the top wires that I was accidently touching (lol). My plug wires are not numbered, but I have checked and double checked that they are correct. Man, I would absolutely do a back flip with joy if that was my issue. Mags- I have pulled them four times and re-pinned and retimed them.

One thing that I did find, I marked the top of the prop flange 24 degrees with a marker to make it easier to see while setting the timing (a common hack), instead of 24*, it was around 25.5* to 26*. I have not retimed and did a run yet but I don't think that would contribute to the issue.

If it is a gear {valve} timing issue, it will suck, being that I have to take the assessory case and oil tank off, but it would just be a weekend adventure.
 

TFF

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With the risk of being laughed at, I wired my mags wrong and only had two cylinders running. I do mags all the time and I pulled a rookie mistake on my own engine. All I could do was laugh at my self.
 

kc0081

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Yes they are Slick mags and I used the diagram that Dan posted. TFF, I am going to run the wires down again and see, I would be thrilled {and embarrassed) if that was the case.

So, if the back two cylinders are firing good, does the consensus here feel that the gears are correct?
 
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