timing marks on O200A align at 24 degrees when #3 on compression

[Sleepingsquirrel]

I have run across an O200a engine that I believe has been incorrectly assembled.
Runs good, but number three(3) on compression when the timing marks are at 24 degrees and points open (propeller shaft marks and top of the crankcase seam). I believe that someone has mistimed the marks on the camshaft gear and crankshaft gear.
I think that number one (1) should be on compression when the timing marks are aligned.
What gives?

 

[Henning]

Easy mistake to make. A direct 180 out isn't a problem, one tooth is a problem.

 

[Sleepingsquirrel]

I suspected 180 out. That means the prop is clocked at the wrong position. Is it necessary to disassemble the engine to correct or just keep it running?
Thanks for the feedback!

 

[jesse]

180 off would be cylinder 2 not 3?

Firing order is 1 - 3 - 2 - 4. It fires every 90 degrees of rotation. 180 would be cylinder 2.

 

[Henning]

I suspected 180 out. That means the prop is clocked at the wrong position. Is it necessary to disassemble the engine to correct or just keep it running?
Thanks for the feedback!

I wouldn't think so since the prop indexes to the crank flange.

 

[Sleepingsquirrel]

180 off would be cylinder 2 not 3?

Firing order is 1 - 3 - 2 - 4. It fires every 90 degrees of rotation. 180 would be cylinder 2.

I think the cam shaft runs at 1/2 crankshaft speed which may make a difference (180 vs 90)regardless of how many degrees out, it is it is running fine.

 

[Dan Thomas]

On a Continental the #1 cylinder is the right rear cylinder, not the right front. The timing marks on the crank flange of an O-200 will be at the bottom, not the top, with #1 at TDC, and the marks will be in line with the crank seam.

I think your engine is just fine.

Dan

 

[Sleepingsquirrel]

On a Continental the #1 cylinder is the right rear cylinder, not the right front. The timing marks on the crank flange of an O-200 will be at the bottom, not the top, with #1 at TDC, and the marks will be in line with the crank seam.

I think your engine is just fine.

Dan

I really like this answer! Thanks!. bottom not top, got it. I am dealing with a very experienced A&P he may just be yanking my chain for fun.

 

[Sleepingsquirrel]

I really like this answer! Thanks!. bottom not top, got it. I am dealing with a very experienced A&P he may just be yanking my chain for fun.

"On Continental engines, the TC mark on the propeller flange will align with the LOWER crankcase split line. These marks, when properly positioned, indicate that the number-one piston in the number-one cylinder is at top dead center. Other marks on the flange indicate degrees before or after top dead center."

Thanks everyone for the great feed back! Just wait until I see my Mechanic tomorrow! I've got to find a way to get him back now.

 

[Tom-D]

I think that number one (1) should be on compression when the timing marks are aligned.
What gives?

The timing marks are not what you time by. just the TDC &the 28degree marks.

The gears in the accessory case are just to get the cam and crank in time.

 

[Let'sgoflying!]

24 degrees

Does your data tag really say 24°btdc?
Unless you have some really old cylinders I think you are allowed 28°.
Might ID the cylinders and check the svc bulletin.

 

[Tom-D]

Does your data tag really say 24°btdc?
Unless you have some really old cylinders I think you are allowed 28°.
Might ID the cylinders and check the svc bulletin.

The original data tag will say 28, but the AD on old TCM cylinders says 24. the 28 may be stamped out to read 24 as per the AD.

 

[Let'sgoflying!]

The original data tag will say 28, but the AD on old TCM cylinders says 24. the 28 may be stamped out to read 24 as per the AD.

exactly.

 

[Tom-D]

exactly.

OK we'er good, now we replace the cylinders with ECI's. what should we do to the data tag?

There is nothing in the ECI STC that says to re-stamp the tag.

 

[Sleepingsquirrel]

Does your data tag really say 24°btdc?
Unless you have some really old cylinders I think you are allowed 28°.
Might ID the cylinders and check the svc bulletin.

tag says 24 , I'll look at the cylinders.

 

[Tom-D]

tag says 24 , I'll look at the cylinders.

What does the overhaul manual say the designed timing is.

 

[Let'sgoflying!]

OK we'er good, now we replace the cylinders with ECI's. what should we do to the data tag?

There is nothing in the ECI STC that says to re-stamp the tag.

haha, the AD came out before many if not all those cylinders were made, so there is no guidance in the AD
Unless there is a superceding AD to this third version. Or SB from the mfg.

 

[Tom-D]

haha, the AD came out before many if not all those cylinders were made, so there is no guidance in the AD
Unless there is a superceding AD to this third version. Or SB from the mfg.

Correct, so what do you do to the data tag when the ECI's were put on?

The AD was directed at the old continental cylinders, when ECI's or the new TCM and Superior's are used the AD no longer applies.

 

[Sleepingsquirrel]

Does your data tag really say 24°btdc?
Unless you have some really old cylinders I think you are allowed 28°.
Might ID the cylinders and check the svc bulletin.

Yep, 24Degrees, What cylinders are these ? Does this one qualify for 28 DEGREES?

 

[Let'sgoflying!]

If you can't tell by looking at them, check the logbooks, and:

when ECI's or the new TCM and Superior's are used the AD no longer applies.