Possibly Dumb Question about Freshening Up an Engine

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harrisonm

harrisonm

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In the last 50 years, I have rebuilt quite a few engines. Most were complete rebuilds with professional machine work, but two were freshen up builds. On the two freshen ups, I bought new bearings and rings that matched what was in there. For instance, If I freshened up a 340 that was 0.030 over in the bores and 10 10 on the crank, I would buy new 0.030 rings and 0.010 bearings. I would reuse the old pistons (I was luck both times that the pistons were OK) after thoroughly cleaning them. I lightly polished the crank journals and lightly honed each cylinder. Both engines ran great. One was a Chevy 327, and the other was a 340.
Here is my question. New 0.030 over rings might be a bit loose in a 0.030 bore that has miles on it. In this case, could a person buy 0.040 over rings and file fit them to properly fit each individual cylinder and then place them on the pistons and install them?
 
The problem will be at the bottom of the bore where ring travel stops. There will be no wear or very little wear there, which means o'size rings might tighten up & seize in that spot.
 
If you can get .040 rings to fit on a .030 over piston you’re going to have too much piston to wall clearance. Do you have a lip at the top of the bore that you can feel with your fingernail?
 
Too big a ring for the bore filed way down will likely make the ring wavy in the bore.

Get a set of file fits for the bore you have, usually .035 over or so.
 
harrisonm said:
In the last 50 years, I have rebuilt quite a few engines. Most were complete rebuilds with professional machine work, but two were freshen up builds. On the two freshen ups, I bought new bearings and rings that matched what was in there. For instance, If I freshened up a 340 that was 0.030 over in the bores and 10 10 on the crank, I would buy new 0.030 rings and 0.010 bearings. I would reuse the old pistons (I was luck both times that the pistons were OK) after thoroughly cleaning them. I lightly polished the crank journals and lightly honed each cylinder. Both engines ran great. One was a Chevy 327, and the other was a 340.
Here is my question. New 0.030 over rings might be a bit loose in a 0.030 bore that has miles on it. In this case, could a person buy 0.040 over rings and file fit them to properly fit each individual cylinder and then place them on the pistons and install them?
Click to expand...
You couldn't use stock pistons in a 0.030 overbore. That is way excessive clearance and the pistin would rock and slap too much to hold a proper ring seal.

Also 0.030 over rings would have excessive clearance on the inner diameter on stock pistons, as they are made for 0.030 over pistons.

If you just did a rehoning job and the stock pistons were in good condition standard rings would be OK.
 
harrisonm said:
In the last 50 years, I have rebuilt quite a few engines. Most were complete rebuilds with professional machine work, but two were freshen up builds. On the two freshen ups, I bought new bearings and rings that matched what was in there. For instance, If I freshened up a 340 that was 0.030 over in the bores and 10 10 on the crank, I would buy new 0.030 rings and 0.010 bearings. I would reuse the old pistons (I was luck both times that the pistons were OK) after thoroughly cleaning them. I lightly polished the crank journals and lightly honed each cylinder. Both engines ran great. One was a Chevy 327, and the other was a 340.
Here is my question. New 0.030 over rings might be a bit loose in a 0.030 bore that has miles on it. In this case, could a person buy 0.040 over rings and file fit them to properly fit each individual cylinder and then place them on the pistons and install them?
Click to expand...
Just get .035" over file fit rings.
 
crackedback said:
Too big a ring for the bore filed way down will likely make the ring wavy in the bore.

Get a set of file fits for the bore you have, usually .035 over or so.
Click to expand...
Ya treed me! What he said^^^^^ !
 
They have to be file fit IF you plan on filing them for two reasons. For the correct ring tension and for the correct finish after filing. File fit ring are made to be filed so the ends won't keep flaking off.
 
Bewy said:
The problem will be at the bottom of the bore where ring travel stops. There will be no wear or very little wear there, which means o'size rings might tighten up & seize in that spot.
Click to expand...
The .040 ring in a .030 worn bore will seize once the engine heats up, not to mention probably breaking from tension stress on a .030 piston.
 
RustyRatRod said:
For the correct ring tension and for the correct finish after filing.
Click to expand...
The tension will vary throughout the cycle in an uneven bore, what is the clearance at the bottom of the bore? It won't be the same as the top.
 
fishmens67 said:
The tension will vary throughout the cycle in an uneven bore, what is the clearance at the bottom of the bore? It won't be the same as the top.
Click to expand...
He'll just have to do the best he can with what he's got if he's not boring it.
 
I don’t think u can get file fit rings for a cast piston. They are a thinner ring and be sloppy in the ring lands. I may need to bore it to the next bigger size and get new pistons to your liking.
 
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