Diameter Chevrolet 216 pistons?

[Alex van de Wetering]

I must be doing something wrong, but I can't seem to find the STD diameter of a CMP Chev 216 cast iron domed piston. The Maintenance manual does show detailed measurements of main bearings, camshaft and crankshaft journals, but no detailed info on piston diameter(?).

I am preparing to measure the parts in my engine to determine if parts are still STD, or if someone has rebuilt it in the past already. I have 5 pistons marked "BB" on top and one that is slightly different with "STD" on top, along with some markings that are hard to read. The 6 pistons seem to have the same diameter, meaning they good all be STD, but I need better measuring tools and specs to really be sure.

Does anyone know where to find detailed info on piston and bore sizes?

regards,
Alex

[Richard Farrant]

Alex,
Standard bore size is 3.50 inches

pistons were available in .003", .010", .020", .030" and .040" oversizes

[Alex van de Wetering]

Hi Richard,

Thanks for your responce. 3,5" bore of the block right? So, the piston would be slightly smaller???
Alex

[Richard Farrant]

Originally Posted by Alex van de Wetering

Hi Richard,

Thanks for your responce. 3,5" bore of the block right? So, the piston would be slightly smaller???
Alex

Well yes, you would have the piston clearance to subtract, don't forget to measure thrust to non thrust side (ie opposite to pin) of skirt. A micrometer is best way to measure.

[Mike Kelly]

Alex

When measuring the bores, you can use a telescoping gauge. Cheap gauge sets are available on ebay , you use a micrometer to place across the telescopic gauge. The best gauges are Moore & Wright made in England or similar, the modern Asian sets are OK but you get what u pay for .

Measure at the lower end of the bore, right down inside, this is where the bore wear is at a minimum . I've got new sets of Hastings rings +30 and NOS domed pistons +30 and 40 . Standard pistons , I reused the standard pistons in the C8 engine with a hone and chrome faced rings from another engine ! , only problem is a rattling gudgeon pin on one piston, hear it after warm up but its not the end of the world.

[Lynn Eades]

Hi Alex. I'm not sure how much you know, so don't be offended if you know all this.
If I recall correctly, ).010" wear, or 0.003" oval, and it's time for a rebore. Those old tollerances were the deal back in the day, for a patch up,but today they're hardly acceptable.

Piston to bore clearance is such that the bore is honed so that the piston slips on a 0.002" feeler, but locks up on a 0.003" feeler. (feeler sitting down the thrust face of the bore)
So a 0.002" piston to bore clearance.
The piston is measured on the thrust face (90 degrees to the gudgeon pin) just below the oil ring. This is the biggest measurement you get on a cam ground piston.
My info covers 1935 to 1951, but does not say anything about the difference between cast iron and alluminium pistons. Each should have a different spec.
Measuring the bottom of the bore will tell you what the bore size was, but what you need to know is what the maximum measurement is. That tells you what you have to do. For example if you have 0.012" wear, you need to find some 0.020"O.S. pistons, for your motor re-conditioner to bore and finish hone to.
For me, I would buy some good quality modern piston rings for it.