Newb Questions

[vt951]

you are prolly looking at it at BDC instead of TDC.
you're either dead on or way off.
irregardless, you do seem like you're a few teeth off by the pic.
did the po remove the gear tower?

Well, the only line I see on the harmonic balancer is lined up with the mark on the tab, so I should be at TDC, right?

I just called the PO, and he replaced the injection pump, but said he did not remove the gear tower. He basically just unbolted one IP and bolted on another, so the timing gears would not have moved, right?

The whole story is: He bought the truck with a blown engine, replaced the engine with one from a salvage yard, he drove it about 80 miles, but it didn't run quite right, so he cleaned the injectors, then it wouldn't start, then he replaced the IP, still wouldn't start, then he gave up and bought a newer truck.

 

[towcat]

rotate the crank one more time.

 

[91f2504x4]

Well, the only line I see on the harmonic balancer is lined up with the mark on the tab, so I should be at TDC, right?

I just called the PO, and he replaced the injection pump, but said he did not remove the gear tower. He basically just unbolted one IP and bolted on another, so the timing gears would not have moved, right?

The whole story is: He bought the truck with a blown engine, replaced the engine with one from a salvage yard, he drove it about 80 miles, but it didn't run quite right, so he cleaned the injectors, then it wouldn't start, then he replaced the IP, still wouldn't start, then he gave up and bought a newer truck.

The crank gear has 1/2 as many teeth as the cam gear therefore there will be two times in which the crank will read TDC but only one is correct, of course this is because it is a 4 stroke motor. Just rotate the crank around one more time and it should put you in almost the exact right place.

If you see what I mean, it takes two turns of the crank to equal one turn of the cam.

 

[vt951]

Ah, now I get it. Sorry, guess that's engine 101.

 

[vt951]

Ok, so I rotated it around another time, and the dowel looks like it's in exactly the right spot now. I can take a pic, but it looks just like yours, towcat.

 

[vt951]

Alright, I went ahead and took some pictures, and maybe it is off a little bit. Is that enough to cause start up problems?

 

[towcat]

from the looks of it, you are very possibly off one tooth.

 

[vt951]

So, it's still possible that it's out 180 degrees, right?

Maybe the PO never did drive it since swapping in this motor. Maybe the reason the motor was in a junk yard is someone screwed up the timing gears when they were working on it and gave up on getting it running.

Is there a way to check if it is at TDC vs. BDC?

 

[Agnem]

To find TDC, I usually pull a glow plug and put my finger over the hole while manually barring the engine over. When the presure on your finger quits, you found it. Of course I have no idea how you would get it within 1 or 2 teeth though.

 

[towcat]

So, it's still possible that it's out 180 degrees, right?

Maybe the PO never did drive it since swapping in this motor. Maybe the reason the motor was in a junk yard is someone screwed up the timing gears when they were working on it and gave up on getting it running.

Is there a way to check if it is at TDC vs. BDC?

you would be runnng, but the motor would be running backwards.
easy way to check is to do Mel's suggestion.

 

[vt951]

Now that I think about it, there's no question of whether I'm at TDC or BDC. If the line on the harmonic balancer lines up with the line on the tab, then I'm at TDC. Rotating the crank 360 degrees just put me at TDC again.

I think the real question is whether the injection pump is timed to inject at the compression stroke or the exhaust stroke, isn't it?

You must be registered for see images

 

[towcat]

Now that I think about it, there's no question of whether I'm at TDC or BDC. If the line on the harmonic balancer lines up with the line on the tab, then I'm at TDC. Rotating the crank 360 degrees just put me at TDC again.

I think the real question is whether the injection pump is timed to inject at the compression stroke or the exhaust stroke, isn't it?

you're correct about the TDC mark if you are a 2stroke.
BDC is the reference to the piston being at the top of the exhaust stroke.
injection happens as the piston approaches the top of the compression stroke.

 

[vt951]

Oh, I see. So, bottom dead center is kind of a misnomer on a 4-stroke.

And, now I can see how Mel's method would work, because the valves are closed on the compression stroke, so you would feel pressurized air on your finger, but on the exhaust stroke, the exhaust valve is open so you wouldn't feel any pressure.

 

[towcat]

Oh, I see. So, bottom dead center is kind of a misnomer on a 4-stroke.

And, now I can see how Mel's method would work, because the valves are closed on the compression stroke, so you would feel pressurized air on your finger, but on the exhaust stroke, the exhaust valve is open so you wouldn't feel any pressure.

bingo

 

[vt951]

To find TDC, I usually pull a glow plug and put my finger over the hole while manually barring the engine over. When the presure on your finger quits, you found it. Of course I have no idea how you would get it within 1 or 2 teeth though.

Seems like I would have to do this on a particular cylinder, since they hit TDC at different crank positions, right? I'm guess #1?