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Just installed new timing chain and sprockets. The Detroit service manual states and I quote:” Install the crankshaft gear and position to 12o’clock. That means rotating the crankshaft to that position. Now, install the camshaft gear & chain & turn to the 6 o’clock position. That means rotating the camshaft to that position without connecting to the crankshaft. Now, install the chain with the colored links matching up with the dots on the crankshaft & camshaft (according to the book this be TDC on # 1 cyl.) Now rotate the crankshaft 2 revolutions. If the camshaft & crankshaft timing marks don’t line up IE: 6 o’clock & 12 o’clock, Realign the camshaft sprocket.”……………Scuez my egnertz but this makes absolutely no sense. First when the engine was originally stopped odds are the # 1 cyl. was not at TDC on the compression stroke. Then, when the crankshaft and camshaft are rotated individually so the sprockets are at 6 o’clock & 12 o’clock respectively, how in the Sam Hill does one know that #1 cyl. is at TDC on the comp. stroke?????????
This being an “interference” engine I sure don’t wont to “shell” it out when I start it.
Thanks for your indulgence.
Respectively,
Srwa
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Turning the crankshaft to 12:00 puts #1 at TDC.
Turning the camshaft to 6:00 closes both valves on #1, making it the compression stroke.
If at any point when turning either shaft you encounter any resistance that you think may be valve against piston, STOP. Step back, look, and think.
Turning the camshaft will of course entail moments of significant resistance as you open valves.Appreciate your answer.
The camshaft & crankshaft position sensors tell the computer when to fire each cyl., but not sure how that exactly works.
Well, after double checking everything, I put it all back together today.
It cranks but wont start. Set code PO340, no camshaft signal detected by the pcm……….Also, engine “lopes” when cranking, which suggests that the timing is 180 degrees out.
I must be missing something………..all suggestions are appreciated.
SR/WA
I have attached a picture of what the timing marks should look like when everything is lined up. Did you replace the camshaft sprocket? I have seen cases where depending on model year the tone wheel on the cam sprocket will be different and it will cause problems if the signal to the computer is not what it wants to see.
Thanks for the picture………..Have that pic. in the service manual along with the instruction that I posted at the beginning. Installed sprockets & chain exactly as instructed. Turned crankshaft 2 revolution, timing marks lined up IE: 6 & 12 O’clock correctly. Also, checked #1 cyl.with a screw driver; ” appeared” to be TDC….Did that twice……..As I posted, when I initially tried to start this beast it kinda/ sorta “loped” & set code PO340, “no camshaft signal detected by the PCM”…….I just removed the camshaft sensor, re-O’ ringed & checked the spacer & reinstalled it……Now, I’m gonna go try to start it……..Be back……and thanks again.
SR/WA
Forgot, did replace the camshaft sprocket, looks exactly like the original, except there is no arrow where it is stamped TDC.,but the keyway is the same.
The cam gear should have a shroud on it with little windows in it. My question was are the windows in the new and the old cam gear exactly the same. I know you said it was the same but I would look closely to make sure. Those windows are what make the cam sensor produce a certain signal that the PCM is looking for. It is possible for the new cam gear to bolt on to the engine but have different sequence of windows on the gear. I’m assuming you didn’t have the cam sensor code before.
Also don’t know if you watch any scanner danner videos on you tube but I believe he has a case study on this very thing on his channel. He has lots of videos like eric. you would need to do a search to find it. It may help you.
I answered your last post a couple of hours after you posted. “Apparently” it was lost somewhere in the “ethernet”, what ever that is. Anyway, I put everything back together as the book instructed IE: 12 o’clock on the crankshaft & 6 o’clock on the camshaft. Am getting compression after one 1 revolution of the crankshaft, which the crankshaft is at 12 o.clock & the camshaft is at 12 o,clock.
No matter how the camshaft sprocket is rotated, without the chain back to the 6 o’clock position, then the chain installed the compression stroke happens at the 12 o;clock position on the camshaft sprocket.( the crankshaft sprocket is always at 12 o’ clock.
QUESTION: IS THIS RIGHT?
Thanks;
Ken
Well, the camshaft rotates at 1/2 crankshaft speed, so after rotating the crank 360°, the cam will have moved only 180°. So, getting both timing marks at 12 o’clock after 1 full crank rotation seems correct.
However, the business with compression occurring when the cam timing mark is at 12 o’clock seems odd. The compression on #1 cylinder should be happening when the timing marks are in their initial state: cam at 6 o’clock and crank at 12 o’clock. (Intake and exhaust valves for #1 cylinder will be seated.) After 1 crank rotation, when the cam is at 12 o’clock, the #1 piston will be at TDC again, but on the overlap period between the exhaust and intake strokes. Both the intake and exhaust valves should be open, and their shouldn’t be compression in #1 cylinder.
Perhaps you’re mis-understanding something in the assembly instructions, or the instructions are wrong. It wouldn’t be the first time a technical reference was in error.
Agree, with all that you’ve stated. The shop service manual that I quoted, verbatum, at the beginning does not mention anything concerning compression stroke. Also, I have access to a “copy” of the commercial version of AllData, ( don’t tell anybody),…….it states exactly what the the service manual says. I bought the service manual just after the warranty ran out on the van, cost $110.00.
I do not, in the worst way, want to take the rocker arm cover off…thats gonna be a pain.
Why am I going to all this trouble someone screams? Because my wife has an emotional attachment to this beast. Must admit, this is the best riding & handling vehicle we’ve ever owned.
I’ll turn 81 Wednesday…….Maybe. Getting increasingly difficult to get up once I get down.
Thanks again for your answers.
,SR/WA
After thinking about this for quite awhile I believe I have be approaching this from the wrong angle. Maybe TDC on the comp. stroke really doesn’t matter as long as the crankshaft sprocket is at 12 o’clock & the camshaft sprocket at 6 o’clock when installed as the book states.
The reason is the computer controls firing of the # 1 cyl., and all other cyls. when the camshaft position sensor sends signals to the computer relative to it’s position on the camshaft sprocket, this being in conjunction with the crankshaft position sensor….See attachment
And also, look at the camshaft sprocket, It’s in the 12 o’clock position because of the steel dowl pin on the camshaft. Only one way to install the sprocket. After many,many,many tests, comp. stroke happens at 12 o’clock no matter how many times it was installed at 6 o’clock. Which kinda/sorta reinforces my previous theory.
Am I way off base??
Thanks for your indulgence,
SR/WA
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