MG MGB and MGB GT Tech Talk
This is stamped on top of engine next to each cylinder on the tappet side. I crudely measured and I'm wondering if it means it's been bored 20 over. My measurements were 3.18 and the standard bore from what I've researching is 3.16. I read somewhere that it's a good idea to mark the top of the block when an engine is bored. Am I on the right track?
Look at the tops of the good pistons that you yanked. If there has been an overbore they should have a note to that effect stamped into each of them.
Jack
IIRC from many years ago, this mark was used for fitment tolerance range. Piston would also be so marked. All Std bore.
Assuming, for the moment, the total tolerance/range of fitment (fit of smallest piston fitting into largest bore to that of largest piston into smallest bore--all dimensions within "standard") is 15 thou then one might mark the bores 1-2-3 based on where they were in the tolerance, and the pistons similarly so that when assembled "1" piston to "1" hole the actual fit would be within 5 thou, similar "2" piston" with "2" hole, etc. instead of the 15 thou one might get wioth a "1" piston in a "3" hole.
I may not have explained it well
Mac,
The explaination was a bit fuzzy. In my case I have #2 pistons in a block labeled with #3. What would that do for my 'tolerance'?
Ken
Clean the top of the pistons you removed and you should find a number stamped into the top edge of the piston. If they are oversized.020 thou. .20 would be stamped in the top edge.
Mac is right, but for a engine needing rebuilding, just consider these marks as it telling you, you have a virgin deck surface. The bore gauge will tell you the bore size, and no a dial caliper stuck in the top of the bore won't cut it.
Its called selective fit,,in mass production there are slight variations plus or minus from
standard (allowable ) EX : TR liners marked F ,,,G or H .
Hap refers to a "Cylinder bore gauge". I'd never seen the term before, so I looked it up for all of us (that don't know better) :)
http://buy1.snapon.com/catalog/item.asp?P65=&tool=all&item_ID=64640&group_ID=1588&store=snapon-store&dir=catalog
http://www.sears.com/shc/s/p_10153_12605_00918960000PvName=Tools&cName=Auto&MechanicsTools&sName=Auto%20Specialty%20Tools&psid=YAHOOSSP01&sid=ISx20070515x00001c
Obviously, NOT a $15 H-F tool. Their's list as:
http://www.harborfreightusa.com/usa/itemdisplay/displayItem.do?itemid=94873&CategoryName=&SubCategoryName=
Learned something new tonight!