Checking a block



I am just full of questions these days . . .

I might be going to check out possible donor blocks this weekend. How does one measure the piston to deck clearance and the bores? Do I need a special tool to do this? Is there anything else I should check out on these blocks? Where is the date code stamped on the rods? Any other suggestions of things to check.


Please . . . some most be able to shed some light on this . . .
Don't quote these piston heights. I'm not sure what they are for US 200 and 250's

Yeh, first thing is to measure or find the "blue print" block height from the centre line of the crank to the bottom of the head gasket face. Say you've got a US 250. That is 9.469 inches (A). Rods are 5.885 inches from the centre of the big ends to the wrist pins(B). Pistons may be 1.600 inches tall from the centre of the wrist pin to the top (as measured with a straight edge) [C]. Crank stroke is 3.91 inches (D) we want to find out how much the piston is recessed into the block.

Answer is A-B-C-[D/2]= Deck register

9.469-5.885-1.600-[3.91/2] = 0.029 (below the steel section of the block. Note that the head gasket could be 40 thou (0.040) above block, then the head.

As esay as ACB, ah ABS, um AC/DC .... Oh dearodeariedearieme!
I just simply used a straight edge and a digital caliper, use the end not the caliper, and set this up on the top of the deck, extended the slide and turned the motor over until top dead center was achieved and subtracted the thickness of the straight edge and you have the deck height to the top of the deck. Mine was .025" on my 200. The replacements pistons were .o2o" shorter pin height than the stock ones, so I decked the block .045" to achieve .000" deck height.
Howdy Isaac and All:

I'm not exactly sure what you're looking for in a donor block, or what the stock, worn deck height will tell you, or how accurate you need to be, but let me add some more stuff.

I carry an inexpensive, plastic, dial caliper with me if I want to be fairly accurate in gauging deck depth. Basically, I follow '63Comet's procedure. I usually measure several places around the piston, but not in the dish recess. Be sure to scrap the carbon and crud build-up away. Typically, the most consistant and accurate spot is just above the pin bosses. Highs and lows are greatest 90 degrees either side of the pin bosses due to piston rock in a worn engine.

About .025" is fairly common for a late OEM 200. Biggest surprizes are in rebuilt engines, early 144s and 170s, and 250. Don't be surprized to find as much as .150" deck height in a 250.

If you don't have a dial caliper, a feeler gauge will get you close. Lay a guage of about .025" on top of the highest part of the piston at top dead center. If it is flush with the top of the block, you got it. It it is not flush, add or subtract thickness until it is.

Most match books are about .030" thick. In a pinch, that will give you a ball-park estimate.

If you find something interesting or really odd, please share. And enjoy the journey.

Adios, David
8) a tape measure is a useful tool to get a rough bore measurement, for a more accurate one you need either a set of inside and outside micrometers, or a good dial caliper.