What do you use for a straight edge when measuring squareness of block?

[lemming303]

I want to check some measurements myself before I decide to send my motor off as it only has a few thousand miles on it since it was rebuilt. I was thinking a long section of cold rolled steel maybe? What do yall use?

[Chryco Psycho]

That won't be accurate , even if you use the same rod & piston in each corner who says the crank throws are perfect , the rod length will be different on each rod especially if the rods have been resized once or more .
Steel is rarely straight glass is better

[jimynick]

If you're going to go that way, bite the bullet and buy a machinists straight edge. I bought one locally for less than $50. Try the tool suppliers like Harbour Freight or something similar. CP's right about the glass thing, but by the time you buy enough band-aids, you'll be 1/2 way to the proper tool. 

[Moparal]

I use a starrett straight edge.

[72cudamaan]

A  centerless ground round bar is what we use. You are only measuring at a minute point and it won't nick nearly as easy
as a regular straight edge will.

[lemming303]

Thanks yall. Harbor Freight has one? If I go shopping, what exactly would I call this? Just a straight edge? Thanks for the help. I don't mind making the investment; I doubt this will be the last build I make lol

[quapman]

The "ruler" part of a combination square is as straight as it gets, but I doubt one from Harbour Freight would be accurate. As stated above "Starrett" makes a high quality scale/straight edge. There are other brands as well....Brown & Sharpe comes to mind. You'll need a set of feeler gauges, too, to check between the straight edge & head or deck.

Glass? You're kidding, I hope.

[lemming303]

I've already got the feeler guages, just need the straight edge.

[73EStroker]

If you are measuring squarness of the block then you measure relative to the centerline of the crank. Quite a process if you do not have the right equipment. That way all compressions are perfectly equal given the crank throws being equal. That is one of the steps of blueprinting. You mght be referring to wanting to measure to see if the decks are flat - no??? Then straight edges work fine.