cam timing/ locking tool???
Discussion
You need the designated gap between the cam and the bucket - the spacers are there to enable you to achieve that gap.
I wouldn't expect any real wear on the spacers. Normally the gap will change either due to newish valve stems stretching or some valve recession into the valve seat (closing the gap up).
The gap is there to ensure that the valves are allowed to close and seal properly. If the gap is too small the valves won't seal properly and you'll start to burn the valve seat, lose compression etc.
So:
1) measure the gap you have on each valve at the moment, with the valve totally closed - ie the peak of the cam pointing 180 degrees away from the valve.
2) calculate the difference between the actual gap and the desired gap. ie if the actual gap is 6 thou and you want 12 thou then you need to remove 6 thou of shims from that valve. Wheras if the actual gap is 18 thou and you want 12 you will have to add 6 thou of shim.
3) Do that for each valve and then write it down!
4) If you have to make adjustments then ensure that the engine is at TDC for number 1 piston and secure the crank.
5) When you have removed the cams write down the total thickness of the shims you have removed from each valve - personally I wouldn't trust markings on them, they may have been ground down, so use a micrometer.
6) Add together the actual shims present with the required shims (which may be positive or negative) and write it down for each valve.
7) Then, add up the total number of space you need to shim up for the whole engine - ie Inlet 1 +5 thou, Exhaust 1 +2 thou, inlet 2 +6 thou, exhaust 2 +1 thou etc, etc - this will give you the total ammount of shimming you are going to require.
8) Compare The above figure with the actual ammount of shims you have and try to create the best fit of shims you have before buying any new ones - you might find that you can shim up 12 valves with the shims you already have and then just buy the right ones for the remaining 4 valves.
Hope that helps - please do take my advice in conjunction with actually reading the manual! I have shimmed up heads before on numerous occasions but have not had my Cerb long enough to have to do it on an AJP8.
Please excuse the long post - good luck!
ETA - you realise that after all this you'll check your clearances and they'll be spot on
I wouldn't expect any real wear on the spacers. Normally the gap will change either due to newish valve stems stretching or some valve recession into the valve seat (closing the gap up).
The gap is there to ensure that the valves are allowed to close and seal properly. If the gap is too small the valves won't seal properly and you'll start to burn the valve seat, lose compression etc.
So:
1) measure the gap you have on each valve at the moment, with the valve totally closed - ie the peak of the cam pointing 180 degrees away from the valve.
2) calculate the difference between the actual gap and the desired gap. ie if the actual gap is 6 thou and you want 12 thou then you need to remove 6 thou of shims from that valve. Wheras if the actual gap is 18 thou and you want 12 you will have to add 6 thou of shim.
3) Do that for each valve and then write it down!
4) If you have to make adjustments then ensure that the engine is at TDC for number 1 piston and secure the crank.
5) When you have removed the cams write down the total thickness of the shims you have removed from each valve - personally I wouldn't trust markings on them, they may have been ground down, so use a micrometer.
6) Add together the actual shims present with the required shims (which may be positive or negative) and write it down for each valve.
7) Then, add up the total number of space you need to shim up for the whole engine - ie Inlet 1 +5 thou, Exhaust 1 +2 thou, inlet 2 +6 thou, exhaust 2 +1 thou etc, etc - this will give you the total ammount of shimming you are going to require.
8) Compare The above figure with the actual ammount of shims you have and try to create the best fit of shims you have before buying any new ones - you might find that you can shim up 12 valves with the shims you already have and then just buy the right ones for the remaining 4 valves.
Hope that helps - please do take my advice in conjunction with actually reading the manual! I have shimmed up heads before on numerous occasions but have not had my Cerb long enough to have to do it on an AJP8.
Please excuse the long post - good luck!
ETA - you realise that after all this you'll check your clearances and they'll be spot on
Edited by itiejim on Friday 13th February 20:36
Many thanks for taking the time to reply. Unfortunately I'm still a little unclear about one thing. Im totally fine with the idea of valve overlap, and Im fine with everything else thats been said. However, in previous threads about setting the timing, things have been mentined like "set the timing to equal lift at TDC". Now I can understand that by putting a bigger shim under a bucket, you're effectivly giving the valve underneath it greater lift, right? If so, then it sounds like what you've got is two different ways of defining the required shim spacing; one relating to the gap between the cam and the bucket, and one relating to lift. Does this make sense to you? If this is case, then it sounds like one method is a lot more difficult than the other, as the latter requires that you know what angle the engine is at. So is there a benefit to doing it that way?
OK:
The valve clearance is set when the valve is closed - it is a gap between the cam and the bucket - it has no effect on how far the valve will lift, that is just down to the peak on the cam.
The "equal lift" bit you refer to is all about timing the cams - ie their relationship to the crank. - Having removed the cams and put in the right number of shims to get the clearances correct you then need to put them back in the correct position. The correct position is when the crank is at TDC and the cam is holding both inlet and exhaust valves open by the same ammount - hence equal lift.
This obviously has to be done for both banks of cylinders at the same time as they are both run off the same chain!
The valve clearance is set when the valve is closed - it is a gap between the cam and the bucket - it has no effect on how far the valve will lift, that is just down to the peak on the cam.
The "equal lift" bit you refer to is all about timing the cams - ie their relationship to the crank. - Having removed the cams and put in the right number of shims to get the clearances correct you then need to put them back in the correct position. The correct position is when the crank is at TDC and the cam is holding both inlet and exhaust valves open by the same ammount - hence equal lift.
This obviously has to be done for both banks of cylinders at the same time as they are both run off the same chain!
So how do you loose timing on the cam? If you keep the cam sprocket tied to the chain so that it can't jump position, and you bolt the cam back on in the same place, then how can you alter the timing? Is the cam not held onto the sprocket by four allen bolts, so that the effective adjustment between the cam and the sprocket is virtually nil? Sorry if Im being dumb, but Im really keen to understand this job, as its something I'l love to do myself some time.
Depends of they've got verniers on or not - I suspect that the AJP8 hasn't but I don't know for sure.
If it's just 4 bolts and no adjustment then yes, you're right, so long as everything is secured it should be no problem.
However, for anyone rebuilding an engine the method and correct positioning of the cam timing is necessary if you're starting from scratch.
If it's just 4 bolts and no adjustment then yes, you're right, so long as everything is secured it should be no problem.
However, for anyone rebuilding an engine the method and correct positioning of the cam timing is necessary if you're starting from scratch.
, that makes sence if you're starting from scratch. The holes in the cam sprockets are slotted for adjustment, and yes you can just put it all back how it was but there's no guarantee that its right, mine was 10° out on both banks, it ran OK like this but a lot better when set correctly!
Also make sure you use loctite on a degreased bolt and bolt hole when bolt goes back about 3 of 8 bolts on mine were a little on the loose side and had no loctite.....
Also make sure you use loctite on a degreased bolt and bolt hole when bolt goes back about 3 of 8 bolts on mine were a little on the loose side and had no loctite.....
Guys, I've put some pics on my rebuild site with reference to checking/setting valve clearances and setting the cam timing - might be worth a look. The pics also show how to find TDC, and how I made my own crank position indicator by fixing a degree wheel to the crank pulley as well as a pointer.
more pics at http://rides.webshots.com/album/212016964dytUsY?st...
more pics at http://rides.webshots.com/album/212016964dytUsY?st...
cupra20v.t said:
right ive dug out an old feeler guage, its in metric and the tvr manual gives imperial numbers 0.010 of an inch. ive converted this to mm and it comes out as 0.254mm my feeler guage has 0.2 and 0.3mm blades.
What do i do? should i just buy an imperial guage they are only £5
I would strongly recomend buying a set of imperial gauges with offset tips. I found that the angle on the tip makes it much easier to measure accurately.What do i do? should i just buy an imperial guage they are only £5
I used a set similar to these...
http://cgi.ebay.co.uk/Laser-Feeler-Gauge-Imperial-...
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