01-01-2021, 07:44 PM
(01-01-2021, 05:09 PM)Jfro5687_imp Wrote: No-one seems to be truly ‘happy’ with the service they get at dealers or at the very least we are skeptical they did it right. With tolerances so absolutely tiny (I believe +/- 0.03mm) I often wonder if its the actual process of using the feeler gauge that fuels the controversy. It’s very much a subjective task. Is my ‘just right’ the same as yours or would you go ‘no too loose’ for example. Probably, I would expect a main dealer to make more effort with results (a la Tev62) however I could also be very suspicious of a neatly produced document (Billy BS). Given the choice I would prefer to see the scruffy oily notes and speak in person to the technician that did it. They can’t win in a way. I’m fortunate that this dilemma is some time off for me, just out of interest is there anyone on the forum that’s actually had a burnt (exh) valve or had running problems as a result of not getting valve clearances checked? We all know it can happen, but has it?
I don't think so really, you are overcomplicating the measurement, it is not about the feel of a blade when given a range tolerance. What most decent shops would do is this:
Manufacturers specification is say 0.15mm - 0.20mm. (Sorry, going metric on this one)
Can he get a 0.15mm blade in? Yes/No. No=valve closed in below spec, go down blade sizes to find fit/no fit value for the gap then mark for adjustment. Yes=good on lower spec move on to maximum value. Then he uses a 0.20mm does it go in? No=good, it must be below the maximum spec, move on to the next valve. Yes=better check larger sizes, if 0.21mm does not go in = all good, move on to the next valve, if it does it's out of spec, mark for adjust. So far there is nothing about the “feel” of a blade, they either fit or they don’t.
The mechanic is not bothered as to the actual measurement of a valve that is in tolerance, it is either pass or fail, he only cares that it is within the manufacturers tolerance. It is this tolerance that is often misunderstood. When a manufacturer gives a tolerance for the valves they are doing so in the knowledge that another valve check is due say 20,000 km later. If all your exhaust valves were at the limit of the range, in my example 0.20mm they should be ignored and left as good, no adjustment necessary. There is no requirement to try and get the clearance to the middle or near middle of the range, that is not your target.
You can say oh well I know my clearances will loosen or close up over time and I’m going to take that into account and adjust for it now. Well you are just creating work for yourself and you are making a big assumption on how that valve will wear, will it be the seat that wears or the cam lobe? The manufacturer knows if you measure 0.2mm and leave it as in spec that at the next valve service it might be at 0.23mm. That is fine, they have taken that into account and are not worried about it. Similarly, if you were at the lower end of the range of 0.15mm they don’t mind if you leave it there as they don’t feel it will change significantly enough to warrant taking corrective action if you follow their service interval. If you open it up 20,000km later at it is at 0.13mm they are not concerned, you adjust it then.
The only time you might decide to use a shim to get to the mid-range is when you actually have to adjust, it is a reasonable position to take. But continually re-shimming your engine to hit mid-range at every valve service is a huge waste of time, it really is not necessary and was not the manufacturers intention. It is for this reason a shop may ask for extra time if you demand all of the valve clearance measurements, it is a fair bit of extra labour to get the exact values of a valve in range, especially if you have 16 valves.
The takeaway from this is: if you are within the range, leave it alone. Older cars/bikes with screw & locknut had a specific value rather than a range because they were easy to adjust. Shims are harder to adjust hence the range given, anywhere, absolutely anywhere, in the range is good until the next valve check.
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