Upper cylinder ridge question....

This is my first new post since I have been a member. I am an avid searcher!
I cannot seem to reach a definitive answer although I know the engine pros will have the solution.

On a used cylinder, what is the ridge composed of? Is it the original overbore metal or is it the material "pushed" up by the movement of the piston rings?

I don't have our mics around anymore to measure the ridge, so is it the oversize or new metal displaced by the rings?

The ridge is very slight, can barely catch it with a fingernail and is only present in cylinder #7 on a SBC. Pistons are .030 over and look to have minimal wear.

I am hoping to save this engine as our local machine shop has gone bellyup, and I am on my own with this one.

 

The ridge is the original bore (or overbore) diameter, unworn because the top piston ring is below the top of the piston and does not travel the full length of the upper portion of the bore. There is a tool designed to 'cut' the ridge out and that should always be done BEFORE removing the pistons, so as not to damage the ring lands of the pistons that could occur if driving the piston out with the ridge in place.

Ideally you would have precision measuring equipment and be able to measure the piston, the bore diameter top, middle and bootm, to check for excessive clearance and/or taper.

If the bore or piston is not excessively worn, you could just hone the cylinder, install new rings on that piston and 'button it up'.

Without measuring equipment, you could do that anyway and take your chances, but the results may be not so durable.

Ray

 

My opinion.....the "ridge" is actually the remains of the original cylinder wall. It looks like a ridge because the rest of the cylinder wall has actually worn away due to the rings rubbing on it for all those miles. Since the rings do not go all the way to the top of the cylinder wall (look at a piston to see the space between the top ring and the top surface of the piston)......in fact, the distance from the top of the top ring to the piston top, will actually be almost exactly the same as the width of the "ridge".
The ridge may also be a little layer of hardened carbon, but most will be remains of the original cylinder wall.

 

I bought a ridge-reamer and a set of inside mics when I did my '50 flathead. I got them from Harbor freight, and the cost was reasonable. You have to be careful with the ridge-reamer, but then again, you should be careful with any metal cutting tool; just don't try to cut to much at one time. As to the mics, since I was just checking for taper and out of round, they were good enough. Like above, I ended up cutting the ridge and honing the cylinders and re-installed the pistons with new rings. There was a little more piston to wall clearance than was recommmended, but if this engine lasts 10,000 mile, it'll be long after I'm gone, so all is good.

I think this why rings are supplied a bit oversize so you have to file the end gaps to make them fit. That way, you can get by with a "sloppy" fit on an engine thats not going to see a lot of hard use.

 

Thank you, Ray, and all, for the prompt reply!

I gently removed the pistons after stamping the caps and pushing them out by hand. Wasn't too worried about the rings since they will be replaced , of course. The lands are fine as the ridge is minimal.

Now to decide on weather to rebuild this one or spring for one of the many deals on crate motors that are available! I've never seen such deals on remans but still enjoy building my own.

 

You can measure the bore wear just below the ridge without using any hightech expensive equipment. Put a ring in the bore - square it up with a piston from the top.
measure the ring gap. Push the ring to the bottom of the bore, measure the ring gap. Devide the difference in the gaps by 3 (well 3.142 if you wish to be pedantic) and this is the wear on the bore diameter
And yes as stated the ridge is the unworn origonal diameter of the bore.

 

The rings used to cut the cylinder leaving an unworn ring at the top. Carbon would build up too because the piston and rings did not wear it away.

Sometimes if you scrape away the carbon the ridge is only half as bad as it looked. It was allowable to rering and not bore the cylinders if the taper or wear was no more than .007. There were special rings that allowed you to rering even if the bore was worn .010 or more.

Since the mid 80s cylinders don't seem to get worn as much. Low tension rings and moly filled rings don't cut the cylinders the way the old chrome rings did.

 

you enjoy building your own engine but dont know what the ridge is? Metal pushed up? I hope you dont work on the brakes.

 

You need to rethink cutting that ridge before you rering. That ridge does not have a sharp corner at the bottom where it meets the wall. It is a slight radius. The new rings will have a sharp corner. Upon starting the motor the sharp corner will smash into the radius and possably break a ring or piston land. I know, alot of guys have have put it rings without cutting the ridge. Ever wonder where that "tick" came from after starting a "new" rebuild? You have it apart now. Do it right. Cut the ridge.


Norm

 

Even installing the pistons with new rings on them is not good if there is any ridge left. It can damage the rings as they slide over that ridge. Ridge reamers aren't all that expensive and only take a few minutes to do the job. I bet Autozone and Advance have them for loan also.

Don

 

Yes, the majority of the ridge is a carbon build up, not actual cylinder wear. This comes out easily with the ringe reamer, make sure you have it seated squarely and take very little bites, you'll be able to see your progress.

I haven't run into a set of what we used to calll "radical rings" in a long time, those you mentioned for cylinders with taper or an out of round condition.

Bob

 

Thanks Don and Norm, the ridge will be removed for sure. Our bore gauges disappeared when another mechanic was overhauling his engine.

This is my fourth hobby engine build to date and all are running fine. They went away when the vechicles were sold and the owners are local.

And yes I do brakes, my work crosses the country on a daily basis, if there is a failure I would not be employed. However I do not know everything and ask questions if I'm not sure on something. If the tools were not missing I would have known the answer.

I will use the ring gap to measure the taper and take it from there. Some days the last thing I want to look at is a car or engine and try to do what was once enjoyable.