Piston ring size

[apgodden]

I got my block back from the machine shop, I purchased oversized pistons 91.209mm.  The machine shop supplied me with new piston rings which were 90.80mm + 1mm  This were too big?

Looking online I can see 90.80mm + 0.50mm = 91.3mm.

My pistons are 91.209mm which means the +0.5mm rings will be 0.091mm too big.  Is this small amount of tolerance acceptable?

[Bob Tucker]

I'd go back to your machine shop. You need the +0.50 rings.

Im surprised the correct rings  werent included with the pistons.

You need to gap all new rings anyway. Check Youtube for how to do it.

[maca]

Few Questions

Did the machine shop have the pistons at the time to bore to?

Have you asked the machine shop to change the rings supplied?

It maybe that the ring need gapping to the finished bore.

Pistons are normaly supplied complete with rings.

[apgodden]

I got some hardly used pistons on eBay which the machine shop  recommended.

yes they had the pistons befor he bored and honed the engine.

[apgodden]

The picture is the +1.0mm ring the machine shop supplied and it over laps.

[apgodden]

5 hours ago, Bob Tucker said:

I'd go back to your machine shop. You need the +0.50 rings.

Im surprised the correct rings  werent included with the pistons.

You need to gap all new rings anyway. Check Youtube for how to do it.

Do you know what the gap should be? 

[IanS]

According to ford for a 2l pinto.

Top and centre gap is 15 to 25 thou.

Bottom 16 to 55 thou.

Cautionary tale, check that the pistons are all the same last time I got pistons 2 were high compression and 2 low compression, I only noticed after fitting and found 2 pistons were near level with the top of the block at TDC and 2 were well below deck hight, I was not pleased.

 

[Bob Tucker]

Just measure from the top of the piston to the top of the gudgeon pin/ wrist pin/ little end (name depends on your age/location!)

So long as they are all the same you "should" be ok. Go with Ians recommendations.

 I dont recall my Pinto measurements. Ive recently been building engines with 4.6 inch bores (598 cu in, 10 litres) so my ring gaps wont help you.