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Cam gear not marked

Mconner7

Well Known Member
I am working on assembling the accessory section and I see no marks to time the cam gear to the idler gear. Are there any tricks for figuring which cam gear teeth should be marked with an O ?

I took this picture during the disassembly process.
 

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Is that not it at 4 o’clock?
….Ops, looking at the wrong gear!
 
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One of the idler gears on my IO-540 was so poorly marked, it took careful observation and comparison under a lighted bench top magnifying glass to find.
 
Post 3 shows what you should be looking for. Your picture is at an angle with gears and slinger in the way of getting a clear view. I think I can make out the O on the crank gear. You need to pull the idler gear and clean it the crank gear and camshaft gear teeth with solvent and search for the O's engraved in the teeth as shown in post 3.
Ryan
 
I had this on one of the idler gears (markings gone). Found a pic of the gear online and used this to count teeth from a reference point and then scribed the markings on the gear.
 
Split the Overlap

If it really comes down to doing it the old fashioned way, a cam is timed correctly when the valve overlap between intake valve closing and exhaust valve opening is at exactly top dead center. This is true for just about any four stroke piston engine most of us will encounter. There are a very very few exotic racing engines the are not timed like this. The caveat here is you need the valve lifters pumped up to be accurate, so it's tough to get it right on say, a newly overhauled engine. If it's been running recently, shouldn't be a problem. In my long ago misspent youth, a friend had a Lycoming on a newly-bought Super Cub that just didn't develop the power it should have. It ran fine, smooth and all that, but just didn't turn up. We checked the timing as above, found it was wrong, pulled the accessory housing, unbolted the cam gear, moved it one tooth (we could see the marks clearly), put everything back together and it was perfect. Go figure.
 
All together today, I used my disassembly photos to sort it out….
 

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