Cam/ rear lobe timing question
Discussion
4.5
Can someone please reassure me!
I have completed my valve clearances and when reassembling the cams I followed the previous hole punch marks on my cams and cam caps that enabled the rear lobes to be level again. Can I confirm that with my rear lobes level the corresponding rear cylinder should be at exact TDC?
I have a funny feeling that my chain may be “off” and causing my poor running issues, especially when under load at 1800 to 2200 revs. I have replaced with new my spark plugs, ignition leads and coils and the issue is still there. It did not run this rough before I did the clearances.
So with my rear lobes level the rear cylinder will not be at TDC if this assumption is correct? I stupidlly did not mark the chain sprocket to the cam and therefore it may be throwing the timing out.
Can someone please reassure me!
I have completed my valve clearances and when reassembling the cams I followed the previous hole punch marks on my cams and cam caps that enabled the rear lobes to be level again. Can I confirm that with my rear lobes level the corresponding rear cylinder should be at exact TDC?
I have a funny feeling that my chain may be “off” and causing my poor running issues, especially when under load at 1800 to 2200 revs. I have replaced with new my spark plugs, ignition leads and coils and the issue is still there. It did not run this rough before I did the clearances.
So with my rear lobes level the rear cylinder will not be at TDC if this assumption is correct? I stupidlly did not mark the chain sprocket to the cam and therefore it may be throwing the timing out.
Wolvesboy said:
I’ve tried the bubble method - nowhere near getting it to work. Might try a balloon instead.
Why not? Remember you have to use the opposite cylinder to the one you want to time.. So 8 uses 2 and 1 uses 7.. It is a very easy method. Just make sure the tube is well seated, and keep dipping the other end in the fairy liquid..I deleted my posts as I just did my shim/timing today and found previous posters more confusing than helpful. However this one is, just read trackcar comments (aka Jools, expert).
https://www.pistonheads.com/gassing/topic.asp?h=0&...
Having done the odd bank, TDC on #1 meant valves 7 & 8 were on overlap, not 1 & 2. They were set to 1.5mm but now zero, will turn engine tomorrow and make sure they've kept it.
Fine tuning the cam is a real pain! I'd like to know how people do the fine cam tuning.
https://www.pistonheads.com/gassing/topic.asp?h=0&...
Having done the odd bank, TDC on #1 meant valves 7 & 8 were on overlap, not 1 & 2. They were set to 1.5mm but now zero, will turn engine tomorrow and make sure they've kept it.
Fine tuning the cam is a real pain! I'd like to know how people do the fine cam tuning.
Edited by Chimp871 on Sunday 5th May 06:30
It doesn't matter what piston you use.
Choose a bank of the engine. Choose a cylinder to work on.
Use your preferred method of finding tdc .. if you're using the bubble method you need the valves on the cylinder being used to be closed, if using the dead stop method they can be closed or on overlap.
Mark off TDC on the front pulley against something that isn't going to move (i put a pointer on the aircon tensioner bolt nearest the pulley.)
Now, if you've used the bubble method or found TDC with the valves closed, rotate the engine one full turn until the valves are on overlap . Now set the followers equal lift by undoing the cam bolts and rotating the cam relative to the pulley.
Rotate engine 2 full turns and re-check that chain tension foibles hadn't skewed the initial setting .. adjust cam pulley-to-camshaft as appropriate.
Forget trying to do time in 7 when at TDC on 1 and all that stuff .. use the same cylinder throughout the whole proceedure.
then go to the other bank, choose a cylinder, and repeat.
Choose a bank of the engine. Choose a cylinder to work on.
Use your preferred method of finding tdc .. if you're using the bubble method you need the valves on the cylinder being used to be closed, if using the dead stop method they can be closed or on overlap.
Mark off TDC on the front pulley against something that isn't going to move (i put a pointer on the aircon tensioner bolt nearest the pulley.)
Now, if you've used the bubble method or found TDC with the valves closed, rotate the engine one full turn until the valves are on overlap . Now set the followers equal lift by undoing the cam bolts and rotating the cam relative to the pulley.
Rotate engine 2 full turns and re-check that chain tension foibles hadn't skewed the initial setting .. adjust cam pulley-to-camshaft as appropriate.
Forget trying to do time in 7 when at TDC on 1 and all that stuff .. use the same cylinder throughout the whole proceedure.
then go to the other bank, choose a cylinder, and repeat.
Chimp871 said:
Fine tuning the cam is a real pain! I'd like to know how people do the fine cam tuning.
Some cams have flats on so you can turn the cam with a spanner - easyHowever mine don't, so I adjust by turning the crank instead
Start with the cam timing a few degrees advanced, then turn the crank so that the rocking lifters are level
Now just loosen the sprocket bolt slightly (I only use one because the timing cover will obscure the others), and turn the crank one degree, tighten bolt and check by turning crank 360
Turn another 360 in order the adjust again, repeat until the crank is at TDC when the checking
The trick is to loosen the bolt just enough so the chain tension isn't lost, but the cam doesn't move when you turn the crank
Also you need to start with the cam slots at the correct end so that they move towards the centre during the adjustment process
I'm not claiming this is a particularly quick method, but it works for me
^^ that's fine paul, a bit longer-winded but ultimately a system that works for you.
What I will say is don't get too anal about fine tuning the position, you can be say 3 degrees out before you make a truly measurable change in power.
Also I use the equal lift method because you can do it without a DTI, and it's repeatable and relatively easy, but you might not actually want your own cam timed in at that figure, but in the absence of a dyno and many hours of testing it does at least get you something that is known to work very well, and you can do it at home with no special tools.
What I will say is don't get too anal about fine tuning the position, you can be say 3 degrees out before you make a truly measurable change in power.
Also I use the equal lift method because you can do it without a DTI, and it's repeatable and relatively easy, but you might not actually want your own cam timed in at that figure, but in the absence of a dyno and many hours of testing it does at least get you something that is known to work very well, and you can do it at home with no special tools.
Shocked mention was made earlier about the hammer shown in the workshop manual pics.
But this is actually a well established and time trusted method of 'nudging' a camshaft and, when familiar with the technique, it is possible to acheive the desired incremental movement very quickly and without disturbing any other shaft.
I have personally timed many cams this way having first been shown it by a venerable builder of race Aston engines.
Naturally there are a couple of caveats; firstly that only the (end of the) wooden shaft contacts the cam lobe, and secondly that only judicious force is used (or, indeed, is ever needed). As with all mechanical skills, it is something that you sympathetically develop a feel for, much in the same way that you develop a feel for tightening a bolt.
But this is actually a well established and time trusted method of 'nudging' a camshaft and, when familiar with the technique, it is possible to acheive the desired incremental movement very quickly and without disturbing any other shaft.
I have personally timed many cams this way having first been shown it by a venerable builder of race Aston engines.
Naturally there are a couple of caveats; firstly that only the (end of the) wooden shaft contacts the cam lobe, and secondly that only judicious force is used (or, indeed, is ever needed). As with all mechanical skills, it is something that you sympathetically develop a feel for, much in the same way that you develop a feel for tightening a bolt.
spitfire4v8 said:
It doesn't matter what piston you use.
Choose a bank of the engine. Choose a cylinder to work on.
Use your preferred method of finding tdc .. if you're using the bubble method you need the valves on the cylinder being used to be closed, if using the dead stop method they can be closed or on overlap.
Mark off TDC on the front pulley against something that isn't going to move (i put a pointer on the aircon tensioner bolt nearest the pulley.)
Now, if you've used the bubble method or found TDC with the valves closed, rotate the engine one full turn until the valves are on overlap . Now set the followers equal lift by undoing the cam bolts and rotating the cam relative to the pulley.
Rotate engine 2 full turns and re-check that chain tension foibles hadn't skewed the initial setting .. adjust cam pulley-to-camshaft as appropriate.
Forget trying to do time in 7 when at TDC on 1 and all that stuff .. use the same cylinder throughout the whole proceedure.
then go to the other bank, choose a cylinder, and repeat.
Now that is a brilliant explanation. Thanks very much - I’m completely in the clear now and even though I have precise markings on my cam and cam caps to suit the rear lobes method, I now completely understand the whole process. Choose a bank of the engine. Choose a cylinder to work on.
Use your preferred method of finding tdc .. if you're using the bubble method you need the valves on the cylinder being used to be closed, if using the dead stop method they can be closed or on overlap.
Mark off TDC on the front pulley against something that isn't going to move (i put a pointer on the aircon tensioner bolt nearest the pulley.)
Now, if you've used the bubble method or found TDC with the valves closed, rotate the engine one full turn until the valves are on overlap . Now set the followers equal lift by undoing the cam bolts and rotating the cam relative to the pulley.
Rotate engine 2 full turns and re-check that chain tension foibles hadn't skewed the initial setting .. adjust cam pulley-to-camshaft as appropriate.
Forget trying to do time in 7 when at TDC on 1 and all that stuff .. use the same cylinder throughout the whole proceedure.
then go to the other bank, choose a cylinder, and repeat.
Thanks everyone else too!
Awesome stuff!
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