Centaur compression ratio

Adding up the sizes on the drawing I get that the piston should be Flush the end of the liner at TDC

Bed 4.500" + Hopper 2.250" + Liner lip 0.125" = 6.875"

Crank Throw 1.000" + Conrod 4.312" + 3/16 + Big End Bearing 0.375" + Pistion 1.000" = 6.875"

Looking at your photos the wrist pin does not look to be in the middle of the pistion

Edited By JasonB on 30/12/2018 12:29:51

JB,

Yeahbut, the other pic, with the piston t’other way up, looks like the piston pin is closer to the other end.

Hoptical illusion at work?

Jason - While it doesn't affect your argument I can't get your figures to add up to your second total??

Edited By Nick Clarke 3 on 30/12/2018 09:53:48

Thank's Nick, it was a typo on the bearing which should have been 0.375, I've edited the post.

NDIY, It does look a longer piston in the other photo, ring and distance of pin from ring groove looks about the same in both. Drawing has a 2" long piston with the pin centrally placed eg 1" from either end.

Just looked at the ME series and that gives the conrod as 4 7/16 + 3/16 and overall as 4 5/8 but sheet drawing shows 4 5/16" + 3/16" but with a total length of 4 5/8" which is 1/8" different!

I know it's to late now for you, but I took the length for con rod / piston off the job when making my Centaur, the piston finish's flush with end of liner.

Shortening the Con rod will produce more side thrust on the piston, and so more friction. It will accentuate the tendency for the piston to "rock" within the bore clearance, which could lead to problems with the piston skirt and the rings, risking scuffing!

My advice would be to shorten the top land, if possible. If the drawing calls for a taper, it would be advisable to maintain the clearances, to minimise the risk of problems.

H T H

Howard

At the risk of teaching granny to suck eggs.

You don't hold the Piston in the chuck to face off the crown.

You make a dummy Gudgeon pin, with a radial / diametral tapping on the centreline.

You then turn up a stepped "bung to be as close a fit as possible to the bore at the bottom of the piston, and drill it to clear a drawbar with the same thread as in the dummy Gudgeon pin. Having done this do not disturb anything..

Insert the dummy Gudgeon Pin, place the Piston on the "bung and clamp it in place with the drawbar. It should now run concentric, so that the crown can be faced off to reduce the compression height of the piston to the correct dimension above or below the top of the liner.

Howard