Hi John Could you take the front cylinder cover of and use a DTI acting on the piston face? Ive done this myself a few times and found it to be the easiest and most accurate. Andy ----- Original Message ----- From: "John Pagett" <john_pagett@xxxxxxxxxxxxxxxx> To: <modeleng@xxxxxxxxxxxxx> Sent: Sunday, February 19, 2006 2:53 PM Subject: [modeleng] Finding dead centres on a loco Just to start something off... I've got to determine the lengths of the rods which run from the return crank to the expansion link on my Sweet Pea fitted with ouside admission Walschaerts' valve gear. To do this I have to set the engine on front and rear dead centre. I've seen the method where you mark a point on the wheel and a point on the slide bar when approaching dead centre, rotate past dead centre to the point where the mark on the slide bar is in the same place relative to the crosshead, mark the wheel again and divide the distance between the marks on the wheel to find dead centre. First question "Is this the best way?" Secondly, "how do you divide a curve into two equal parts?". I can do a straight line with a rule and dividers, but as I see it half of the construction space is in thin air outside the wheel! Any thoughts gents? TIA JohnP MODEL ENGINEERING DISCUSSION LIST. To UNSUBSCRIBE from this list, send a blank email to, modeleng-request@xxxxxxxxxxxxx with the word "unsubscribe" in the subject line. MODEL ENGINEERING DISCUSSION LIST. To UNSUBSCRIBE from this list, send a blank email to, modeleng-request@xxxxxxxxxxxxx with the word "unsubscribe" in the subject line.