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tappets and idling


Jazzman

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If they were a long way out, yes it will. Without hurting my brain at this time of day, I can't remember if that proves they were too big or too small before. Taken to its extreme, if they didn't open at all (or didn't close at all) the engine wouldn't run at all!

Check your ignition timing, and once that is right set your tick-over back to normal (I say do the ignition first, because correcting that can alter the tick-over quite a lot).

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It's worth checking the valve clearances at regular intervals; every 6 months or 12 months depending upon usage, so that you can keep an eye on whether there is any valve seat recession happening. Knowing when you last checked them, and how much they have changed in the last so-many-miles is ideal to see if you have recession problems, especially if you are not running an unleaded head.

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sparky_spit wrote:
It's worth checking the valve clearances at regular intervals; every 6 months or 12 months depending upon usage, so that you can keep an eye on whether there is any valve seat recession happening. Knowing when you last checked them, and how much they have changed in the last so-many-miles is ideal to see if you have recession problems, especially if you are not running an unleaded head.


How do you go about checking valve clearances?

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Tom here's my quick instruction guide:

1) Take rocker cover off

2) Put car in 4th gear and take handbrake off whilst parked on level ground

3) Get your feeler gauge

4) Roll the car forward (pushing the front wheel) and watch the valves move up an down

5) Move the car forward until you see a valve open (rocker depresses pushrod) Rock car back and forth until depression is at its maximum

6) Measure the corresponding valve clearance using the rule of 9 (if valve no3 (counting from the front of the engine) opens measure clearance of valve no6)

7) Clearance should be 10thou if you run a standard camshaft. if you have a different camshaft then set using whatever are the recommended valve clearances

8.) Adjust using a 1/2" spanner to release locking nut and large flatblade screwdriver to turn adjuster - turn the adjuster and nip up locking nut and remasure gap - you want there to be a little pressure on the movement of the feeler gauge

9) After checking and adjusting that valve mark that valve (e.g. with a blob of grease) and move onto the next valve

10) Make sure you have adjusted each of the valves

11) Replace rocker cover with new rocker cover gasket if necessary

You can leave the car in neutral and use the fanbelt to turn the engine but rolling it backward and forward in 4th gear is easier. The whole thing should take 20 minutes. This should be explained in your Haynes manual or similar workshop manual. I do this every 6 months and have not found much adjustment required. Just remember the rule of 9 (for a 4-pot). When valve X closes (that you wish to measure the clearance of) valve 9-X will be opened and you are looking for the point of maximum opening (i.e. depression) provided by the camshaft pushing on the cam followers and pushrods thence via the rockers.

I hope that makes sense.

best of luck, Neil

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Instead of rocking/moving the car, why not turn the engine over by using a spanner on the end of the crank(assuming fan not pres) or on the pulley of the dynamo or alternator. Take out the plugs to lessen the fight against compression etc.

Rule of 9 for a four pot, rule of 13 for a six.

10 thou gap when the engine is cold, different gaps if high lift cam fitted.

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I never understand these rule of whatever - it involves simple maths which is far too much for my brain when there is a much simpler method...

Below is a 6 pot... 12 valves... imagine a mirror in the middle (in fact there is a perfectly spaced rocker cover stud).

o = valve open (down)
x = adjust

Code:
x- -- -- -- | -- -- -- -o<br />-x -- -- -- | -- -- -- o-<br />-- x- -- -- | -- -- -o --<br />-- -x -- -- | -- -- o- --<br />-- -- x- -- | -- -o -- --<br />-- -- -x -- | -- o- -- --<br />-- -- -- x- | -o -- -- --<br />-- -- -- -x | o- -- -- --<br />-- -- -- -o | x- -- -- --<br />-- -- -- o- | -x -- -- --<br />-- -- -o -- | -- x- -- --<br />-- -- o- -- | -- -x -- --<br />-- -o -- -- | -- -- x- --<br />-- o- -- -- | -- -- -x --<br />-o -- -- -- | -- -- -- x-<br />o- -- -- -- | -- -- -- -x<br />


Note; they don't go in that order! Just watch for which valve is going down as you turn it over...  in fact you will have two open valves at one time.

It should take 10 mins max on a 6 pot :)

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Good point! Same thing but with 12 not 8 as depicted above!

I started off drawing it for a 4 cyl!

I told you maths was not my strong point :)

Code:
x- -- -- | -- -- -o<br />-x -- -- | -- -- o-<br />-- x- -- | -- -o --<br />-- -x -- | -- o- --<br />-- -- x- | -o -- --<br />-- -- -x | o- -- --<br />-- -- -o | x- -- --<br />-- -- o- | -x -- --<br />-- -o -- | -- x- --<br />-- o- -- | -- -x --<br />-o -- -- | -- -- x-<br />o- -- -- | -- -- -x

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The easy way for me is to do it on a tune-up day when you're taking the plugs out anyway for inspection, gapping, replacement, whatever.
With the plugs out, it's easy to turn the engine via the fan (close in, so you don't bend the blades).
Pull the plugs, put the car in neutral with the parking brake on, sit on the wheel and off you go.

Which valves to check whenever is probably different on the 4, but on the 6 it's easy:  when the 1st valve is down at the front, you check the 1st one at the other end; when the 2nd valve from the front is down, you check the clearance of the 2nd valve from the other end, etc.

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Just to pick on a point earlier on in this thread, it's not a good idea to try setting ignition timing when the tickover is too high- the mechanical advance mechanism may have cut in and give you a false reading. Slow the tickover down first, then check timing and adjust, then reset tickover again if necessary.

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Re- using feeler gauges,,,what Neil said... except for genuine accuracy you should really use 2 feeler gauges. Say you are setting the gap for 10 thou, you should really use a 9 thou and a 11 thou gauge, The 9 will be loose in the gap, the 11 won't go in. Doing it this way eliminates any errors around how much "grip" on the feeler there should be if you are only using one gauge to set the gap.

Most people think this is being pedantic and a waste of time and effort. But try telling a very stern electro-mechanical engineering instructor that, as a spotty 16 year old apprentice.

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sparky_spit wrote:
Re- using feeler gauges,,,what Neil said... except for genuine accuracy you should really use 2 feeler gauges. Say you are setting the gap for 10 thou, you should really use a 9 thou and a 11 thou gauge, The 9 will be loose in the gap, the 11 won't go in. Doing it this way eliminates any errors around how much "grip" on the feeler there should be if you are only using one gauge to set the gap.

Most people think this is being pedantic and a waste of time and effort. But try telling a very stern electro-mechanical engineering instructor that, as a spotty 16 year old apprentice.


completely ageee with the two feeler method

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Hello all,

just to mention that setting the valve clearances by the manual gives the least amount of engine turning, especially as two valves are adjusted simultaneously (at least on the six cylinder engine). The rule of thirteen works but takes twice as long if you only do one at a time.

Another point if the rocker tips are worn it is impossible to set them accurately whether with one or two feeler gauges.

Alec

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I use the following:

Open          Check     

1 and 3          10 Inlet & 12 Exhaust     
               
8 and 11          2 Inlet & 5 Exhaust     
               
4 and 6          7 Inlet & 9 Exhaust     
               
12 and 10          1 Exhaust & 3 Inlet     
               
2 and 5          8 Exhaust &11 Inlet     
               
7 and 9          4 Exhaust & 6 Inlet     

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Valves can be adjusted in pairs for all engines because both valves must be closed when TDC is reached at the end of the compression stroke.

Every time this occurs there is another piston at TDC with both valves rocking (i.e. at the end of the exhaust stroke, when the exhaust valve is closing and the inlet is opening).  Therefore the easiest way for me is to get a pair of valves rocking and adjust the valves of the corresponding cylinder.

For a 4 cyl engine the matching pairs are 1 & 4, and 2 & 3.

For a 6, they are 1 & 6, 2 & 5 and 3 & 4.

Useless bit of info - the rule of 9 never used to work with Fords because they used a different firing order (1-2-4-3 instead of 1-3-4-2).

Second useless bit of info - Vauxhall Viva and Chevette valves were adjusted with the engine running.

Steve

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Hello Shenderson,

"Every time this occurs there is another piston at TDC with both valves rocking (i.e. at the end of the exhaust stroke, when the exhaust valve is closing and the inlet is opening).  Therefore the easiest way for me is to get a pair of valves rocking and adjust the valves of the corresponding cylinder."

Surely that cannot work as the valve(s) that is(are) being adjusted are done when the x-13 valve is fully open not just off closed. There is a ramp from the base circle to the flank of the cam so your method must surely be inaccurate?

Alec

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