ihave just recently been to my local auto spares dealer for an air filter for my cavalier and they asked what engine i had in (which is a 1.7 td) and they said it took two filters one for the bigger box just behind the drivers side headlight and one for the rocker cover mounted box. i have looked in my manual to see if this is right and it doen't show two filters nor does it describe it in the maintainance intervals i am wondering if fitting two air filters could in affect choke the the engine. any thoughts?
{Subject header amended to include make of car, as mentioned in the sticky threads above. DD}
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by the way it is the isuzu engine if that makes a difference
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When GM cobbled together this animal it came with its own air filter in the box on the manifold. Rather than 'design' a new arrangement to pick up cold air from the front of the car for this stop-gap model they simply hooked into the existing air filter box. I have seen filters in either box but I think the box on the wing remains empty. Whilst tempting to fit both for added filtration I think you might upset the airflow.
Andrew
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Simplicate and add lightness!!
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If you choose to use only the air filter near the rocker box, I would suggest that you check it more regularly than suggested in the service schedule. For some reason, they seem to clog up very quickly, and I used to change mine, on my 1.5TD Nova, every 6K or so.
The other thing to keep an eye on with these engines is the tappet clearance. They close up, and this leads to poor starting, and reduced performance.
Number_Cruncher
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hi n.c am i right in saying that this is done through the use of shims?
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Indeed, they are shimmed, but don't let that put you off checking them.
The inlets should have 0.006" clearance, and the exhaust 0.010". The inlets tend to close up, sometimes so far that there is no clearance at all.
You don't need any special tools to change the shims, they are quite easy to get out.
Number_Cruncher
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so i take it i need a set of feeler gauges to do this operation. as for taking them out i wont disturb anything critical will i? i suppose i could dislodge the shims with a feeler gauge? it sounds to me tough if any of the inlets are closed up completly i'll need to compress the valve spring a little? also is there any tell tail signs to look out for as to diagnose a wongly spaced shim before i take the rocker cover off? just going through all the variables beforehand!
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Yes, feeler blades are the tool of choice for clearance checking. If you need to reset the clearances, you will also need a micrometer to measure the thickness of the existing shims, becasue you need to know the thickness of the existing shims to determine what shims you need to replace them with.
You won't disturb anything. The only bolts you need to undo are those to take off the rocker cover.
You won't dislodge the shims. When you see what they're like, it will all make sense.
If the inlets are fully closed up, there is no clearance to measure, so for the first iteration, you would select shims 6 thou smaller than those that are already in there.
Checking the clearances should only take you half an hour or so -easy job.
Number_Cruncher
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hi number cruncher, respect! you are a regular fountain of knowlege. i will check them as soon as i have got the time maybe at the weekend. thanks for the info
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err.. where would i get a micrometer? are they expesive? just thought they were a specialists tool. the shims have the thiknesses written on the underside dont they? or do they wear off after a while?
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You are right about the micrometer - it isn't something that you will use every day.
However, if your clearances are OK, you won't need one at all.
You are right about the shims being marked. But, wear can remove the marking, and make the shim thinner than its marking would suggest - it is best practice to measure them.
If you find that you are going to need to change the clearances, you will also need to find out how you are going to obtain your new shims, and how you will be charged for them.
Some garages will try and charge a lot for this work, so it may be worth your while buying a cheaper (Draper?) micrometer just for this job alone. IIRC, a previous backroom poster was going to be charged over £100 for this work.
Number_Cruncher
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Micrometers can be had quite cheaply;
cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&category=...1
for example. BTW, Mitutoyo is a well respected maker of engineering metrology products - not a cheap brand.
Number_Cruncher
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When I had my Isuzu engined Cavalier,I asked for an air filter for it,and when presented with it,said that it was the wrong one for the airbox behind the headlight,to which the guy told me that there wasn't a one in there,only one on top of the rocker box.
So that is the one you want.
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