Mini Mad
Posted 26 September 2020 - 11:21 AM
Thanks Spider,
I have to take ownership of this not you.
My 1981 motor should have the A+ timing cover plate. I thought I even saw the bulge. Anyway all good. I'm glad I don't have the tensioner and that the guy I bought this motor actually put a double row timing chain in.
I'm always ordering parts anyway so thinking of getting new lifters.
Brad
..is NOT a girl!
Posted 26 September 2020 - 12:06 PM
I'd keep the original cam followers unless they're obviously past it, for the same reason they shouldn't be mixed up. If they're badly worn the cam could well be too.
I think having the dots align on no. 4 just made it a bit easier to install the dizzy drive on the production line by sitting the cam lobes more out of the way.
Up Into Fourth
Posted 26 September 2020 - 01:19 PM
Nick I put this new dizzy in recently and when I did it I thought it was as at TDC and the rotor was at 2 oclock. So spark plug wire 1 is firing at 2 oclock not 8 oclock.
Do the dots always align up at TDC on the compression stroke? Maybe I put the cam 180 degrees out 18 years ago. Is this possible which I find hard to beleive since my motor has been running so well?
Thanks
Brad
Mini Mad
Posted 27 September 2020 - 08:34 AM
Nick I put this new dizzy in recently and when I did it I thought it was as at TDC and the rotor was at 2 oclock. So spark plug wire 1 is firing at 2 oclock not 8 oclock.
Do the dots always align up at TDC on the compression stroke? Maybe I put the cam 180 degrees out 18 years ago. Is this possible which I find hard to beleive since my motor has been running so well?
Thanks
Brad
Gazza, no matter how many times I rotate the engine the dots won't align at TDC on no.1. They align at the firing stroke on no.4 like Spider stated.
Maybe it was a design feature they factored in like Ethel said?
Brad
Edited by maystro, 27 September 2020 - 08:35 AM.
Speeding Along Now
Posted 27 September 2020 - 09:04 AM
Moved Into The Garage
Posted 27 September 2020 - 09:15 AM
I don't know why it is, but that's how the A and I think B Series are - when the dots are lined up No. 1 has finished the exhaust cycle and starting inlet, No. 4 is firing.
Can I ask an idiot question? I thought that when the dots lined up the cam was timed in.. At, say, 106° before tdc, so no1 piston will not be at tdc but coming up to it??
Actually, no.
No. 1 will be at the top of the Bore and only just starting an Inlet Cycle, The figures like 1060 and 1100 etc refer to when No. 1 Inlet is at full Lift, which is when the piston is some way down the bore.
Speeding Along Now
Posted 27 September 2020 - 09:21 AM
I don't know why it is, but that's how the A and I think B Series are - when the dots are lined up No. 1 has finished the exhaust cycle and starting inlet, No. 4 is firing.
Can I ask an idiot question? I thought that when the dots lined up the cam was timed in.. At, say, 106° before tdc, so no1 piston will not be at tdc but coming up to it??
Actually, no.
No. 1 will be at the top of the Bore and only just starting an Inlet Cycle, The figures like 1060 and 1100 etc refer to when No. 1 Inlet is at full Lift, which is when the piston is some way down the bore.
ok so it is true to say that when the dots are in line no 1 will be at tdc ...
Moved Into The Garage
Posted 27 September 2020 - 09:55 AM
I don't know why it is, but that's how the A and I think B Series are - when the dots are lined up No. 1 has finished the exhaust cycle and starting inlet, No. 4 is firing.
Can I ask an idiot question? I thought that when the dots lined up the cam was timed in.. At, say, 106° before tdc, so no1 piston will not be at tdc but coming up to it??
Actually, no.
No. 1 will be at the top of the Bore and only just starting an Inlet Cycle, The figures like 1060 and 1100 etc refer to when No. 1 Inlet is at full Lift, which is when the piston is some way down the bore.
ok so it is true to say that when the dots are in line no 1 will be at tdc ...
Usually TDC refers to the Piston not only being at the top of the bore, but also on the Firing Stroke, so in this case, no.
Speeding Along Now
Posted 27 September 2020 - 10:03 AM
Mini Mad
Posted 27 September 2020 - 10:10 AM
No mate, that is what I just found not to be the case.
Read thru the thread.
Brad
Edited by maystro, 27 September 2020 - 10:23 AM.
Speeding Along Now
Posted 27 September 2020 - 10:16 AM
No mate, that is what I just found to be the case.
Read thru the thread.
Brad
I tried but I got too confused!
Moved Into The Garage
Posted 27 September 2020 - 10:21 AM
Sorry, to be clear, when the dots are aligned number 1 will be at tdc on the firing stroke?
No.
Number 4 Cylinder is.
Mini Mad
Posted 27 September 2020 - 10:29 AM
No mate, that is what I just found to be the case.
Read thru the thread.
Brad
I tried but I got too confused!
I hear you mate 
Mini Mad
Posted 27 September 2020 - 11:28 AM
..is NOT a girl!
Posted 27 September 2020 - 11:35 AM
For balance reasons the crank is symmetrical 1& 4 are at tdc when 2 & 3 are at bottom tdc. Tdc is a convenient datum (piston's highest point*) to use to align the rotating parts in the correct angular position. The valve timings are fixed by the cam lobes, so there are 2 possible correct positions because the crank will pass tdc twice before the cam does a lap to get back to where it started. It's arbitary whether 1 or 4 is starting its power stroke, but making a choice means you can add extra datums (pulley dot marks) so you know the cam's position to get the distributor timing right too.
To time a cam finding the crank tdc first allows to to turn it the correct amount so when you get the cam lobe to its tdc the crank & cam will be optimally synchronised.
Apologies if that sounds patronising, not trying to teach anyone to suck eggs - just running through the thought process that helps me get my head round it.
*actually the crank won't be vertical unless the bore axis is directly above the crank axis, but datums are just somewhere obvious & reliable to measure from.
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