OPDA & TDC

[JKP]

As long as you didn't have cam/crank codes, it was running OK, you can just drop it in. You only need to test for compression if the engine was rotated with the OPDA out, OPDA gear sheared, etc. The FSM literally has 2 procedures, to cover this.

If you put in 180 out by some chance, it will throw the cam/crank mismatch code. If you do that with a distributor engine, it won't start.

And no, it won't hurt anything if you put it in 180 out.

 

[HiHoSilver]

Sorry for not mentioning. Replacing the original opda with a Crown as I have read about issues with the original one. Engine is running ok now. Was thinking if the original opda was pinned, the TDC would be on the compression stroke. Since the opda rotates once for two crankshaft rotations, the engine running ok, the opda pinned, and the engine at TDC, believe it would be on the compression stroke. Am I wrong? Thanks.

 

[JKP]

Go to Resources and download the FSM....

 

[HiHoSilver]

Thanks.

 

[MikeE024]

How do you know it's original? How do you know it was installed correctly the last time it was installed? You didn't say why you're installing a new one so we have no way to know what the situation was before you started.

No 1 can be at TDC ON compression or TDC on exhaust. Compression is what you need. Timing marks don't know the difference.

Nobody said this so I will. When you install the OPDA, no. 1 has to be at TDC ON COMPRESSION. Just hold you thumb on the plug hole and feel for compression. Then line up the timing marks. Otherwise, you have a 50% chance of being 180 out.

IMO, it's super valuable for you to point this out.

In addition to using your thumb, you can thread a compression tester's adaptor hose to cylinder #1 (that you rent from an auto part store) and then attach a balloon over the other end of the adaptor where the gauge normally threads on.

Alternatively, you can also install a long screwdriver and have someone keep it straight and tell you when it's coming up. I don't love that route, but I trust it more than a device that screws in and has a stem that raises on the compression stroke...which worked but for me was bent when I removed it.

 

[g.hayduke]

IMO, it's super valuable for you to point this out.

Alternatively, you can also install a long screwdriver and have someone keep it straight and tell you when it's coming up. I don't love that route, but I trust it more than a device that screws in and has a stem that raises on the compression stroke...which worked but for me was bent when I removed it.

You can watch the timing marks to know it's "coming up". But that tells you nothing regarding compression vs exhaust.

 

[HiHoSilver]

JKP, Would the engine run with the opda being 180 out? Thanks.

 

[MikeE024]

You can watch the timing marks to know it's "coming up". But that tells you nothing regarding compression vs exhaust.

Agreed.

That's why I added the alternative methods in case that person doesn't have someone they trust to go by thumb pressure.

Align the marks and feel or look for compression on cylinder #1.

 

[g.hayduke]

Agreed.


Align the marks and feel or look for compression on cylinder #1.

What does compression look like?

 

[MikeE024]

JKP, Would the engine run with the opda being 180 out? Thanks.

That's the wrong question to ask.

Pin your OPDA before removal, and then install it at TDC on the compression stroke of cylinder #1.

Then align your Cam/Crank difference to as close to 0* as you can and do the relearn. For example, a Thinkdiag2 device will provide the difference info.

 

[JKP]

JKP, Would the engine run with the opda being 180 out? Thanks.

No reason it shouldn't, but it would throw a cam/crank mismatch. It will run without the cam sensor in limp mode.

 

[HiHoSilver]

Finally installed new Crown opda. Job was easy except for hold down latch and bolt. Didn't think I was going to live long enough to get it back in. The engineer that designed ought to be deported to El Salvador. Anyway, engine running normally, no codes, and phase angle at -0.5 degrees. Thanks JKP and I appreciate all who responded to my post. Thanks.
(Well, I finally did something right when there was a chance of doing it wrong. I just disproved my old coach when he told us: "If you did it right, there ain't no chance of doing it wrong.").

 

[MikeE024]

Finally installed new Crown opda. Job was easy except for hold down latch and bolt. Didn't think I was going to live long enough to get it back in. The engineer that designed ought to be deported to El Salvador. Anyway, engine running normally, no codes, and phase angle at -0.5 degrees. Thanks JKP and I appreciate all who responded to my post. Thanks.
(Well, I finally did something right when there was a chance of doing it wrong. I just disproved my old coach when he told us: "If you did it right, there ain't no chance of doing it wrong.").

Thanks for the zingers