VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1933-1936 '36 207 ring job

Hi all, I've recently started overhauling my 207 and was told from an engine shop that I needed .020 rings. I had the block in their shop and watched him measure the bore so I know it is correct. So I purchased a set of .020 rings and proceeded to check the fit according to the original shop manual, which said to place the rings half way down the cylinder and check the gap. When I did this they wouldn't fit, the cylinder apparently has a taper. My question is do I need to get my cylinders bored or do I file my rings to make them fit half way? They do check out fine if you put them about 1" down the cylinder without filing. I really appreciate this Forum, a lot of technical info that I need, thanks for your help, Ken.

The cylinder bore needs to be the same from top to bottom. If not then the rings will flex going up and down the cylinder. That is not good! Also the pistons need to have a 0.002" fit to the cylinder both at the top and bottom.

Did the engine shop measure the cylinders top to bottom? They should have. If the cylinders are straight then the rings should have the same gap top to bottom. If not then you will need to bore the block and fit new pistons.

Ken, Chipper's reply to your question was great. However in this case I'd like to expand on it based on my experiences. I was trained to measure bore diameter at 3 levels( Dad was a machinist), 2 inches from top and bottom and at middle. At each level you take 4 readings 90 degrees apart front to rear/ side to side. This gives you taper and roundness for each cyl. The repair manual gives good advice on how to interpret this data. No reasonable amount of honing can correct for more than .002-.003. After that you rebore and fit new pistons like Chipper said. My innate cheapness has caused me to violate that advice on two occasions and I regretted it- poor ring seating, uneven compression and oil consumption. A shop that suggested you use .020 rings without boring doesn't have your best interest in mind. With all the money and work you have invested why not do it right?
Dan

Thanks Guys, I do appreciate your expertise, that's why I came to VCCA. I was afraid that was going to be your answer though, but like the old Fram commercial, pay me now, or pay me later. So it looks like I'm going to pay them now. Any good suggestions on where to go for replacement piston and rings? Thanks again, Ken.

I will send you a PM. Click on the flashing envelope.

Ken
The machine shop may have measured the bore and found the problems you had would need .020 oversize to correct hence the non fitment at this stage.
A engine rebuilder I worked for used that as standard practice.
Tony