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Finding TDC


Conn47D24

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Today I have a question on the cycle of rotation / firing .

 

Lots of threads but just to be clear I need some help please.

 

I have the # 6 inspection plug out and have inserted a screw in rod ( old miller tool ).

 

I rotated the engine with the starter and saw the rod go up and stopped.

 

Using an inspection camera I can see the :

 

# 1 cylinder  - Exhaust closed , Intake slightly raised.

 

# 6  cylinder - Exhaust slightly , Intake closed

 

Question:   What action is taking place next here ? 

 

Am I just BEFORE TDC or just AFTER TDC ??

 

Thanks all !

 

Clay

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PA

I have the dizzy out and trying to get it set after rebuild. 

I am having tough time rotating the engine by hand and was wondering how close i may be to #1 being at TDC.

plugs are all out but the 1 &1/8" socket keeps slipping off the crank hub. 

Do i need another touch off the starter or around again ?

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IF on removal....you did not remove the oil pump....the base line is still an ESTABLISHED condition on your engine....you put in the distributor..it should fire up...if not, slightly lift the distributor and rotate the rotor 180 degrees....one of the two conditions will be correct.....

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Think its too late for that.

 

Engine was demantled completely for rebuild. Pump , dizzy both out . I am starting (  no pun)  from stractch.

If i continue the rotation a bit more  from where I am now, does that close both valves in 1 & 6  ?

 From what I've read on other posts that's the condition I am trying to attain so I can set the oil pump and distributor. Is that corect?

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Think its too late for that.

 

Engine was demantled completely for rebuild. Pump , dizzy both out . I am starting (  no pun)  from stractch.

If i continue the rotation a bit more  from where I am now, does that close both valves in 1 & 6  ?

 From what I've read on other posts that's the condition I am trying to attain so I can set the oil pump and distributor. Is that correct?

 

Timing marks pictured is current position as I described above.

20190224_134305.jpg

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I would only pay attention to cylinder number 1. As mentioned, it takes two revolutions of crank shaft to complete cycle.  

 

So intake valve opens as piston drops, to let air/fuel into cylinder, then intake closes and piston starts to come back up.  When piston is at top, that is top dead center and ready to fire that cylinder.

Edited by thisoldtruck
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8 hours ago, Conn47D24 said:

I have the # 6 inspection plug out and have inserted a screw in rod ( old miller tool ).

 

I rotated the engine with the starter and saw the rod go up and stopped.

 

Using an inspection camera I can see the :

 

# 1 cylinder  - Exhaust closed , Intake slightly raised.

 

# 6  cylinder - Exhaust slightly , Intake closed

 

Clay

 

If the #6 piston is near TDC then the above cannot be the case. Either #1   OR  # 6  inlet and exhaust  valves should be fully closed.

 

You may not have installed your timing chain to the cam and crank gears correctly.

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I thought it took 720 degree's of crankshaft rotation to complete one 4 stroke operating cycle

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Basically he was 2 strokes away from TDC on cylinder number 1 and cylinder number 6 already fired and was in process of exhausting itself, so cylinder number 2 would be next in line for firing right at this stage. 

 

Whatever state number 6 is in, really doesn't matter because cylinder number 5 is next to fire after cylinder number 1 anyways. 

 

 

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Pull the #1 plug- Put your thumb over the hole and crank the engine till you feel compression pressure then stop cranking- look at the timing marks and pointer-  rotate the crank till pointer lines up with "0".  If the timing gears and chain are installed properly, you are now at top dead center compression stroke on #1 cyl.  Install the dizzy with the rotor at 7 o'clock and there ya are.

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14 hours ago, Dodgeb4ya said:

I thought it took 720 degree's of crankshaft rotation to complete one 4 stroke operating cycle

This is correct. 2 upstrokes consisting of a compression and an exhaust and 2 downstrokes consisting of a power and an intake. Each stroke is 180 degrees multiply that by 4 for 720 degress or 2 full rotations.

Edited by Silverdome
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Yes... two revolutions of the crankshaft... not four.

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I  always keep in mind that distributor R.P.M. is one half of engine R.P.M....(engine R.P.M. 800 = distributor R.P.M.400) ?

Edited by T120
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Did this problem get resolved, I believeThe valves may be open if the timing chain is done wrong or the valve adjustment is wrong. With #6 @ tdc either #6 or #1 should have closed valves. I would check the valve adjustment

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16 minutes ago, Hickory said:

Did this problem get resolved, I believeThe valves may be open if the timing chain is done wrong or the valve adjustment is wrong. With #6 @ tdc either #6 or #1 should have closed valves. I would check the valve adjustment

 

THIS MAY BE INTERESTING..ON OUR WEBSITE....

 

 

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Hi PA,

 

I did the assembly.  

 

Still haven't had time and weather to get out and investigate further.  

 

I'll try to turn it over and feel for compression at # 1. If this works out perhaps my doubts about the valves being fully closed is moot.

 

then I'll get it back around to  # 1 and set the oil pump and dizzy as per the manual and info here.

 

The it's up to the Gods !

 

?

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This is the life expectancy of your engine you are risking, if you are not confident enough in your abilities to find TDC Compression Stroke with it buttoned up remove both the head and timing chain cover and set it properly......this way you can "see" everything.

If your are indeed at TDC and your marks line up on timing gears but your dizzy doesn't point 7 o'clock then you must pull it and try 180 test, if that still won't line up you must Clock the oil pump to ensure the dizzy points 7 o'clock presto everything is good.

Button up and move to the next agenda.....all that peace of mind for the cost of a few gaskets and a little sweat equity.........

Edited by Frank Elder
left out cover
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  • 2 weeks later...

Before removing the timing cover I want to ask this.

 

After researching this site and Youtube , I have turned the crank  further and now have # 1 top as indicated by  BOTH the # 6 inspection hole rod, AND the

 

position of the valves.  I have watched as I turned the crank the valves closing with my video camera.

 

That said, # 1 BOTH tappets move freely by hand.  # 6 the Exhaust moves freely and intake will not.

All 4 of these valves are closed yet this one tappet is never the less firm.

 

Is this condition correct for TDC ? 

 

OR,  should all 4 tappets be free ?

 

Last call before I open this mother back up again.

 

Thanks ALL 

 

Clay

Edited by Conn47D24
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Forget about what's going on with #6...I think that is confusing you.  What makes it go is the piston in #1 is at top dead center with both valves closed, pointer at '0' and the rotor pointing at 7 o'clock.  With ignition, compression, correct firing order and fuel, it should fire right up.  

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