Wie geht’s Ihnen. Saw your post on pistons from Nov 2019. Have been seeing different values for piston to wall clearance on Mahle pistons for Jaguar. Dick Maury of GeorgiaJag in Atlanta says .003" which is what AE pistons run to avoid scuffing. I read that Mahle advises about .001" ( or less) The conversion from mm to inch can cause a problem for some. Can you confirm what optimal clearance should be? I have run AE, Venolia (forged high expansion), Wiseco ( low expansion forged). AE’s scuff at .002", Venolia’s scuff at .004", Haven’t taken Wiseco’s out for inspection. If I build another motor am interested in trying Mahle. Is it hyper-eutectic? Did the Mahle test engine have a torque plate used for final honing?
Danke
Douglass Harroun
Hi Douglass,
Clearance is material and casted/forged related.
The Mahle aftermarket pistons, which are sold through Barratt, are casted and AlSi12CuMgNi. These are heat treated to specification and therefore allowed a small heat expansion. The .001” is recommended and usable using and round/conicity cylinder bore. I would not going less because could cause scuff in case of any cylinder bore inhomogeneous.
Venolia for example are forged and use material 2618 (0,25% Si). Heat expansion is higher and need an adapted higher clearance. Another point on forgings is the forging process (Umforming), the higher the “Umforming” the less can be used in clearance.
Mahle is the only company which can use the same clearance on castings and forgings (using 0.005mm more on 2618 material).
Torque plate is only necessary in trying to go less .001” clearance.
Original: In 1953 Mahle built casted 7:1 and 8:1; the forged versions were used on 9:1
If you need anything further, let me know.
I had a stroke three weeks ago, came home from hospital yesterday and have some difficult in writing and spelling right, so please excuse some wrong words.
Best regards
Thomas