I did a ring gap measurement at .013 delta, on my small blocks worst bore. I am trying to decide if it needs to be bored. Any recommendations? Please help!!!

What was the bore measurement in relation to the pistons from each hole?

If you are trying to freshen the engine using the old pistons and new rings have an engine builder mike the bores ID and the pistons OD.

If the builder tells you it is within limits have the ridge at the top of the bore removed and finish hone the bores.

I bore an engine to true things up and only bore the least amount to get things "blueprinted". You want as close to perfectly round bores as you can get, parallel to each other and center lines 90 degrees to the crank throws.

So much depends on the condition of your engine that is why I suggest having an engine builder look at what you have.

It is not uncommon for racers to do a leak-down test and decide that freshening the engine is in order but those engines are otherwise in perfect condition.

When I was a kid we would do things like run a "dingle-berry" hone down the bores to smooth things up, put in new rings, touch up the valves, and away we would go.

I don't recommend that today but then I tend to over do things like specifying a torque plate installed when the final bore finish honing takes place.

It is a labor of love so enjoy what you do and don't take any unnecessary chances.

John

It sounds to me like .013 inch is OK; I use the rule that there should be .004 inch of end gap per inch of cylinder bore. So, any bore greater than 3.25 inch would be happy with this gap. More importantly, the quality of the bore finish should be checked. If the bore looks good with a light hone job, then new rings should do the job for you. If it will not hone cleanly, a bore job is in order.

I guess that by "I did a ring gap measurement at .013 delta," you mean the gap was 0.013" bigger at the top than at the bottom? Wouldn't this roughly equate to a taper of 0.004? Old rule of thumb was that bore taper of 0.007 or more called for a bore job. Less than 0.007" could be honed and re-ringed.

I have a 400 grit ball hone that's been working good for me for many years. Great with moly rings, but I had to order it from Brush Research Mfg. in California. Was near $100, as I recall.

Tom

The gap between the piston skirt and bore is .003. I will have the shop look at everything, before I decide, but it is my decision because I want to assemble it. The ring gap delta, is the groove depth from top edge. The taper is actually less. I sounds like I can get away with hone job. Should I use the original pistons?
Thank you for the input........

typically re-use the pistons on a re-ring job.

I still haven't got the idea on your ring measurement. I thought you saying that you put a bare ring in the cylinder at the bottom where there is no wear and measured the end gap, then put the same ring in at the top of the bore just under the ridge and measured again, got 0.013" difference in the end gap. Is this not right? If it is you would have about 0.004 taper and plenty OK for a ring job.

Tom

Yes thats correct, I also checked the end gap from the top of the cylinder, to the deepest part of the groove to see what the bore wear is from the original bore, as well as the taper. I don't know if this makes sense, or is even necessary. In any event, it sounds like if I ridge ream and hone w/new rings, it will work. Should wait and buy the rebuild kit after the shop looks at it?

Danno
If you only have 4 or 5 thou taper, there's probably no need for ridge reaming. Ridge reamers commonly make marks and gouges in the cylinder walls that can't be removed with minor honing. Were the old pistons hard to get out? If the total taper is 4-5 thou, then the ridge is only 2-3 thou max. Shouldn't be a problem.

Tom

Thanks Tom, the pistons popped out ok. I'm going to take it to shop and have them take some measurements. Unfortunetly I am limmited with the tools I have. (I hate it when that happens!).
Thanks for the background info, it will help me when I talk to the shop. This is a great site!!!!!!!