Hi all, As I am measuring my QV pistons, I found an interesting mismatch between the measurement and the workshop manual: Here is the workshop manual: Note the distance between the bottom of the piston to the top of the upper ring groove (43mm): And here is the measurement at 43mm from the bottom of the piston: Well, not quite matching. 2 solutions: - the referencing (43mm) is just for the measurement of the piston diameter and has been misplaced on the drawing - my piston is not a 308 QV piston. The marking is 8093 USA, but cannot find a reference online. Opinions? Cheers, Sly
I've found lots of mistakes in the workshop manual. I noticed the firing order is incorrect in manual as well. Always double check and verify by another process if possible.
Umm.. you aren't measuring to the same place. You are measuring to the top of the middle ring land not the top of the top ring land. At least in the picture you sent.
Yes, on purpose. The caliper is set at 43mm and measuring from the bottom of the piston. The bottom to top of the upper ring groove reads 48.44mm (instead of 43).
Just an opinion, but based on the style of the drafting, I'd go with this as the purpose of the dimensioning however, by scaling the measurements on the drawing, I'd say that the error is that the "43" should be "48" (the "9.5" and "29" distances scale well in relation to each other, but both indicate the "43" distance is "48"). Also, on the drawing the top ring and second ring diameter is clearly smaller than the skirt diameter (which is should be because a ~0.5mm difference is a lot; whereas, the "9.5" diameter and "29" diameter down on the skirt are different by just 30 microns).
Even though it's a slightly larger piston, here's the same figure for the 328 piston diameters from the FNA 328 tech specs that (although not at the exact same heights) follows the same strategy of: 1) top ring area, 2) top of skirt, 3) bottom of skirt with about the same relative diameter differences: Image Unavailable, Please Login
The WSM is an interesting document. For instance, those dimensions you are citing, may be useful if you want to fabricate a piston but what purpose do they serve someone who is simply rebuilding his existing engine?
