Counterboring of top of block

Thanks for the feedback. I agree with all the comments in relation to removing any lip before removing pistons, however, the wording in the 1937 Service Letter 25 implies the 10 thou counterbore is applied after a rebore activity. Even so, the consensus appears to be that this is not the accepted practice and that there are no known problems experienced from not having the counterbore. I will be happy with the standard 30 thou oversize rebore in my engine - thanks.

On a re-ring job , the need to remove the ridge is to prevent
the new top rings from hitting the ridge with the resulting damage.

I noticed your located in Kingwood NSW Austrailia. Terry Cockerell is located in Cooranbong NSW Australia. He is finishing up his Cord restoration. Sadly he used the EGGE machine shop pistons and they were not correct. The piston pins were 40 thousands too high up in the pistons so much that they contacted the heads. It took months of shipping back n forth plus all the fitting before he got a piston that was close. EGGE machine shop is in a new location and about 4 miles from my home. Hope Terry can help you out.


Gary Parsons

I have never heard of overboring the top of the cylinder. I think Pat is right and that referes to ridge reaming to remove old pistons. Don't go overboard in reaming the ridge and remove more than is need to remove the old pistons!
CORDially Mike

A standard practice for many older cars required a ridge reamer applied to the top of the cylinder to remove any lip. Then the pistons could be pushed out the top and not damage rings.

I have never heard of this idea. But am following this so I learn if its correct. I personally don't think its the way to do an over bore but???


Gary Parsons

Cord Service letter No 25 states that when "reboring for installation of over-size pistons, it would be necessary for your shop to counterbore the top of the cylinder block about .010 larger than the cylinder bore."

I have only just located this information after my block has been rebored 30 thou over-size. Even so, the instruction doesn't describe how far the 10 thou counterbore should extend into the block. I presume that it should not be any further than the top of the bore on the outside edge of the block to ensure there is no chance of catching to the top ring. Does anyone have any further insight into this factory 'requirement' and whether it has been found to be of value?