C145/O300 Cam-Crank timing

[cbeyer]

Is it possible to install the cam shaft and the crank shaft 180 degrees out of phase and still have the timing marks correct?

Thanks,
Cbeyer

[n2582d]

Troubleshoot the easiest stuff first.

[c170b53]

Pick of the two gears

the gear for the crank and then the cam

[cessna170bdriver]

The bolt pattern in the camshaft gear (Jim's upper picture) is not symmetrical, so it will only bolt up to the camshaft one way. The crankshaft gear (Jim's lower picture) has a hole to accomodate a dowel pin in the end of the crankshaft. If the timing marks on the two gears are lined up, the crank/cam timing has to be correct. With the mags off, you should be able to see the timing marks to verify whether they line up.

[cbeyer]

Thanks guys. You stay up way to late! You are saying there is no way they could be 180 out? Is it possible a gear is marked incorrectly or incorrect for a C145 ?
And Just for a sanity check, the piston should NOT go down when the exhaust valve is open nor up when the intake valve is open.

Cbeyer

[Bruce Fenstermacher]

What they are saying is the gear can not be bolted to either the crank or the cam incorrectly.

Can the exhaust open while the piston is traveling down? Yes if your turning the prop backwards. But I'll bet your not.

Slow down. Go back to basics. Pull a mag. Put #1 piston to TDC. Check to see the timing marks are aligned through the mag hole. If not you found your problem. If they are, move on.

[cessna170bdriver]

Thanks guys. You stay up way to late! You are saying there is no way they could be 180 out? Is it possible a gear is marked incorrectly or incorrect for a C145 ?
And Just for a sanity check, the piston should NOT go down when the exhaust valve is open nor up when the intake valve is open. Meeting with the mechanic in 2 hours, I will advise out come. He is a big fellow!

Cbeyer

It wasn't that late on the west coast, Charlie!

It's possible the crank could be 180 out, but the marks will never line up; both would be at the top of their respective gear. Blowing up Jim's photo of the crank gear, there are marks on two adjacent teeth, and the cam gear most likely has a mark on a single tooth. When the gears are properly meshed, the mark on the cam gear should line up between the marks on the crank gear when #1 is at TDC and both its valves are closed. I don't know much about any other engine types, but I'm not aware of these parts being used on other types.

[cbeyer]

Thanks all. Engine was indeed out of phase by 180 degrees plus or minus a tooth. Pulled starter from subject engine and found no evidence of timing marks on crank gear. Had to pull the starter from another O300 to verify timing marks at second bolt from dowel as in Jim's photo. Marked subject gear with Sharpie and loaded engine back into pickup for return trip to mechanic's shop.

Cbeyer

[c170b53]

Here's a better pick of the mark it may be hard to see in the engine

on the cam gear, Sorry for the poor quality, its the iphone 3 at work.

[170C]

Jim, looking at your photo's I had to wonder, is that your supervisor lying there

[c170b53]

Frank that's Dylan, he's 11 and he assumes that position pretty much all the time.
No timing marks on the gear; queue the twilight zone music

[cbeyer]

My mechanic called this afternoon to report he found the crank gear timing marks under the bolt head upon removal.

Cbeyer

[HA]

I always mark the proper teeth/timing marks with a red marker prior to assembly. Makes it easier to have "one last" easy visual check before buttoning things up to ensure better sleep.