Cosworth pistons?
Cosworth pistons?
I am pulling down a 75 860GTS engine & have just got the front piston out. Inside it is marked DM0031 & COSWORTH, etched onto the gudgeon pin boss is PA0493/1. Any ideas as to what I`m dealing with? Bore size is 86.8mm & I think it`s forged.
KERRIN
Seems to me to be an oversized Cosworth piston.Sorry I couldn't help myself.I do remember Cosworth making pistons for bevels a long time ago but I've never seen one. Is it a flat top or is there a dome? If it is in good shape you could probably find rings for it and reuse it. You will need to measure the thicknesses of the rings and find a match in a mfg. catalog like Hastings or Deves.
Guess I walked into that one, but I probably could`nt have resisted it either! As I`ve not seen a stock 860 piston its kind of difficult to compare, but looking at photos I`d say that the skirt is shorter & there is more of a dome than standard. The dome is also asymetrical with a shamfered side adjacent to the plug. The pistons look like new, very little carbon & no discolouration underneath so if the clearances check out OK I`d hope to reuse them & the rings. With these pistons, 40mm carbs & worked over heads someones put a lot of effort into hotrodding this poor old 860. Not checked the cams yet but it would be nice if they`re stock. PS sorry about the multiple post earlier, thought I was editing not resubmiting.
KERRIN
I think the only valvespring cams available for the 860 were a regrind and that was in the pattern of the Imola cams. The timings on them were kind of sudden for use with valvesprings.Higher compression pistons were popular and easy to do and many people cleaned up the ports while they had the heads off.After you have it back together you can check the cam timing events with a degree wheel to see what you have. The timing data is in the owners manual and in the service manual.You may find the 40mm carbs to be a bit much for street use as consistent idle is elusive.