83mm .04 -- What are these???????

[sammy]

I cleaned up my pistons last night. I saw a .04 on top of the pistons and assumed that these were 86mm or 87mm. I measure the diamete of the pistons and liners. It measures 83mm. The pistons have 4 rings. What size of pistons do I have?

 

[DrEntropy]

Have you measured at the top of the piston or taken two measurements at the skirt, pin parallel and 90* opposite?

 

[sammy]

I measured at the top of the piston.

 

[martx-5]

I thought that the Vangard pistons had four rings.

 

[PeterK]

Well, 86mm + .040" over is 87mm so... maybe you have 40 over 83's (84mm)

Are they from a TR2 or TR3?

 

[sammy]

They are in a TR3. The sleeves look new so who knows what they were originally used for.

 

[Andrew Mace]

It's not easy, but it is possible to bore out the liners. And presumably that's what you have: original 83mm TR3 liners, bored out .040" and fited with .040" over original-style pistons.

 

[DrEntropy]

The diameter at the top (where the rings are) is less than the skirt. Measure at the skirt, both parallel to the pin and 90* to it. Should ba a bit "oval" but the 90* reading will be close to the bore + clearance.

 

[YankeeTR]

It's pretty common to find oversize pistons in these cars.

Many motorcycle shop would have the fixture to hold the liners in a boring bar...and sometimes a machine shop would bore the liners on a lathe.

 

[Geo Hahn]

It's pretty common to find oversize pistons in these cars...

That's what mine has... no idea of who, when or why:

 

[Don Elliott]

My pistons have 4 rings. The are Hepolite pistons with 83 mm diameter (1991 cc displacement). I changed the rings after they had been running for 93,000 miles and put the same pistons and liners (newly honed) back in and it's been better than new for the next 4,000 miles.