Thinking that contacting County would be a good idea, I can’t seem to find a web listing for them other than retail sellers.
If you’ve measured the gudgeon pin position and found it symmetrical, would there be any other design element that suggests orientation other than the potential “A, arrow” on top?
I might just do that. Yes, I do feel that that small engraved/punched thing is an arrow after all, although it does look like an “A”.
Yes, I got them form David Manners Group in the UK, I could ask. At first I was going to use the MKV original style pistons, but for many reasons (including Ed’s experience down under, suggesting against the use of new long skirt / split skirt pistons) I ended up wth standard size 3.4L XK pistons.
The gudgeon pin is floating and the grooves for the locking circlips are the same distance from the edge, so yes, symmethrical.
Everything else seems fine, it’s just weather that “A” should be pointing to the front of the engine or to be 180 deg the other way, so it would read as an “A” looking from the front of the engine (like pictured.)
It’s curious that it appears to be many small punches, rather than one single punching with a letter A hand stamp.
Reminds me of a BMW SOHC 6 732i I once had, which had an oil feed tube on the head, supposed to feed oil to each rocker arm. It was stamped with what looked like an arrow in the middle, so a previous shop or owner had put it on with the arrow pointing forward. But as installed it was spraying oil an inch (2.5 cm) away from each rocker, so none were getting oil and one rocker was broke. Turns out in reading the manual it was a letter V for the German word Vorne, meaning Front. The tube was on backwards. Turned it around so the rockers got oil. DPOs!
I have not found ”County”, I did contact the company that sold me the pistons, David Manners Group and got an answer really fast, the problem being that it’s like in Eastern Finland where they always answer with a question and after that all you can hear are crickets.
So no-one knows.
The good news is that I finally got the block and the crank back, and now it’s rolling nicely with caps tightened to 112Nm and the Chevy 350 -0.020” undersize main bearings.
I hope I can figure out which way to mount the pistons soon.
Sure, but I read it (the orientation of the gudgeon pin) may be off-center by just a few thousandths of an inch. Now how do I measure that?
Also I have a fear that ”A” may stand for ”asymmethric” or it may be an arrow in which case it should point towards the front of the engine. I’m going for the latter unless I find out that’s not right.
You could make up a go/no-go set-up where you put two small round pins or dial gauges at a certain height on a surface plate or on glass, and see if they still fit the gudgeon pin holes when you flip the pistons around. If it has air, readjust and flip again. If it now doesn’t, you’ll know what the A is trying to tell you.
Hi Pekka, your remark quoted here makes me think maybe you have not measured the gudgeon pin offset. The gudgeon pin offset is the distance of the cylindrical axis of the gudgeon pin lateral to the piston cylindrical axis. Said another way, how far over is the center of the “O” of the gudgeon pin from the vertical line defining the piston center?
The thrust side is the piston side trailing the rotation direction of the crank. The thrust side is akin to which part of the turkey came over the fence last.
Thank you for the suggestions, I might just do the test and try to use a dial to measure if there is any difference or how accurately I can measure this with the given suggestions.
BUT the good news is that I did get an answer from DMG saying the the manufacturer confirmed that the “A” is indeed an “A” and is there only for showing the grading and if there are no other markings on the crown the pistons are symmethrical.
Quote " > The supplier has confirmed that the “A” marking on the crown of the piston is for the grading of the piston and, if there are no other markings on the crown of the piston, the pistons do not have to be fitted in a specific orientation,"
I think you are correct, it does look like a poorly stamped “D” with one third of the letter missing. So probably a factory internal inventory number or such as used on cylinder heads etc at engineering. Engine number was chosen and stamped later when they knew which car it was going to be fitted in (SL prefix the “L” for LHD MKIV), just as for many engines for decades later.
