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Old 05-12-2012, 04:10 PM   #1
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2008 Astra XR
Wrench How To - Checking Valve Clearances

This is an "add-on" account of how to check your valve clearances on our Saturn Astras. Most of the steps can be found in my Timing Belt Replacement article (found here). Most of this info can also be found in the Haynes manual that covers the European version of our cars. This procedure does not cover the steps needed to "restore" (for lack of a better word) clearances to factory specs. I've included a list of tools needed and one somewhat grainy picture (sorry). This procedure should be similar to the Z18XER engines found in the Chevrolet Cruze LS and Sonic.

It is important to note that that this is a much simpler job than replacing a timing belt. No new parts are required because you are simply measuring clearances, and the job only takes an hour or two (depending on how anal you are) so it won't take an entire evening/weekend either. If you find any clearances that are outside of spec, you will have to put everything back together and think about "getting things back into spec" some other time. This is because parts will have to be ordered -- almost certainly from a central warehouse in the USA (up to a week away) -- so you can't simply leave everything apart and continue on the next day. The only thing you have to be careful of is with some of the plastic components that are attached by tabs (which can break).

**********

Special tools needed:

Feeler gauge set
Small straight edge
E10, E20 (female) Torx sockets
T20, T27, T40 Torx sockets

Parts needed:

None initially (clearances are "adjusted" by substituting followers with different "thicknesses", plus there are other parts required too)

**********

Begin by reading through the steps outlined in my Timing Belt Replacement article (found here). You obviously won't need to perform every single step in that thread, but you may want to consider performing both jobs at the same time if your weekend allows it.

To sum up, you will only need to remove the lower splash shield, air cleaner, upper timing belt cover, ignition coil pack, and valve cover to check your valve clearances. You will not need to remove the engine mount, other timing belt covers, or any belts. You might even be able to do everything without removing the R/F wheel. You should not require a new valve cover gasket, unless yours is currently leaking.

**********

On a piece of paper, draw out the engine from above, showing the four cylinders and all sixteen valves, with room next to each to clearly record the valve clearances. The intake cam is the one located on the firewall side, while the exhaust cam is the one closest to the radiator. Cylinder #1 is closest to the timing belt end of the engine, with the remaining three cylinders following in order. The picture I included below was taken from in front of the car, with the intake cam above, the exhaust cam below, and cylinder #1 to the left.

Using a small straight edge, draw a line through the center of the crankshaft pulley, intersecting the center of the crank pulley bolt and the timing mark, to place some sort of mark approximately 180 degrees opposite. It doesn't have to be perfect, but it does have to be at least close. Mark it in such a way that you won't accidentally be mistaking it for the factory mark!

Position the engine at TDC for cylinder #1 (using the factory mark). Make sure that the crank pulley mark lines up with the mark on the lower timing belt cover, and that the marks on the cam sprockets are lined up facing each other.

With the engine at TDC for cylinder #1, measure and record the clearances between lobes and followers for both intake valves on cylinder #2, and the exhaust valves on cylinder #3.

Rotate the crank pulley 180 degrees clockwise until your handmade mark lines up. Measure and record the clearances for both intake valves on cylinder #1, and the exhaust valves on cylinder #4.

Rotate the crank pulley another 180 degrees clockwise. Measure and record the clearances for both intake valves on cylinder #3, and the exhaust valves on cylinder #2.

Finally, rotate the crank pulley another 180 degrees clockwise. Measure and record the clearances for both intake valves on cylinder #4, and the exhaust valves on cylinder #1.

**********

Valve clearances should be between 0.21-0.29mm (0.008-0.011") on the intake side, and 0.27-0.35mm (0.011-0.014") for the exhaust side. If they are all within specs, you are good to go! If you have one or two that are just b-a-r-e-l-y outside of specs, you can probably let it go*. If you have more than that, or you have one or two that are quite a bit out of spec, you have more work cut out for you.

Valve clearances directly affect valve timing -- that is, precisely when each valve begins to open and completely closes. Clearances that are too "loose" will result in valves that are open for less time than intended (ie: opening later and closing sooner), while clearances that are too "tight" will cause the valves to open for more time. You might notice a drop off in power or an increase in emissions when your valves are out of spec, but I seriously doubt it. Not it if happens gradually anyway. Valve clearances almost always increase as parts wear, but sunken valve seats could cause them to decrease.

There is zero chance of causing mechanical damage when the valves are out of spec, except in the rare cases when the clearances are significantly tighter than spec (especially exhaust). This is because valves are cooled significantly during the time they spend in contact with the valve seat, which conducts the heat away. If clearances are too tight, the valves spend more time open and less time in contact with the valve seats, which can cause the valves to overheat, warp, and eventually crack. Under extreme conditions, the head of the valve can completely break off, causing significant -- and often non-repairable -- damage to the cylinder head, cylinder wall, and top of the piston!

Our Z18XER engines don't use hydraulic self-adjusting followers and they cannot be manually adjusted either. The followers come in various "thicknesses", stamped onto their underside. This means that for you to even order the correct parts, you have to take the engine even further apart (engine mount, tensioners, belts, cam sprockets, camshafts, etc.) to retrieve the followers and figure out what size they are, do some math, figure out what size you actually need, and then order those. You will also need new timing belt end oil seals (for the cams), sealant, and a whole bunch of new bolts (many engine fasteners are torque-to-yield on modern engines). If you are working out of your own garage at home, you could easily get in over your head. This set-up might seem bizarre, but I have been told that many motorcycle engines use a similar design.

So to replace just one or two followers because they are b-a-r-e-l-y out of spec, it just doesn't seem worth it. My advice would be to wait until more than a couple of valves are out of spec, or replace any that are seriously out of spec. As you have seen, the task of simply checking your valve clearances isn't that difficult or labour intensive, so if you must, you could simply check them more frequently if you are worried about one or two. Plus, it gives you a great excuse to get out of other chores around the house.


* This is my opinion only. Actual factory procedure would dictate replacing any followers that did not fall within specs. Your call.

.
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Old 08-28-2012, 02:55 PM   #2
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2008 Astra XR
Default Re: How To - Checking Valve Clearances

Very nice write-up. What would be the recommended interval for this? Also, did you use RTV to reseal or replace with a new gasket?
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Old 08-28-2012, 03:51 PM   #3
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Default Re: How To - Checking Valve Clearances

Quote:
Originally Posted by Astra08 View Post
Very nice write-up. What would be the recommended interval for this? Also, did you use RTV to reseal or replace with a new gasket?
I don't have my owner's manual within easy reach, but my Haynes states "every 90,000 miles or ten years".

I didn't use a new VC gasket, nor was any sealant required. The gasket is made from neoprene and remains flexible even at high temperatures, unlike rubber gaskets.
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Old 08-28-2012, 03:54 PM   #4
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Default Re: How To - Checking Valve Clearances

Thanks! I just read your excellent post on the timing belt replacement, so I might be tackling that soon as well, having just hit 75K.
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Old 06-29-2015, 01:28 PM   #5
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Default Re: How To - Checking Valve Clearances

I just wanted to complement ALV on yet another useful "how to" thread.

After encountering some valvetrain noise, I ran through the process this weekend. Everything was in spec, but the above was very helpful and straightforward.

I did modify the attached cam graphic to include callouts to mark valve lash, in case anyone decides to do this, they can simply print the doc and record the results.
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