using oversize rings on stock pistons

Machine shop is telling me that I need to use new pistons. If that is the case, then why are oversize rings made? Potential issues?

engine is a 351 w and needs to be bored out either .030 or .060. My friend who is brokering the deal has had conflicting reports (ase certified and cant answer questions)

Oversize rings are for oversize pistons. They will not work on STD pistons. If you bore it .030 over, you need .030 over pistons and .030 over rings. Best bet is to supply the machine shop with the pistons and rings so they can hone the cylinders to match the pistons and ring set of your choice. Most oversize piston sets come with matching rings and wrist pins. Give them the rods too so they can press the wrist pins for you.

What Toyman said.

I had an RD350 that had oversized rings on stock pistons after a small overbore. Piston slap was pronounced, but it did run. Lord knows what wear was inflicted on the bore and piston skirts! Always listen to your machine shop guy on things like this: it's what they do for a living.

You young punks don't know nothin' about cheap engine building. Used to be sold what was called a '10 up' ring. This was back in the olden days, if the cylinder bores were worn less than .010 from the standard bore you 'knurlized' the standard pistons to 'swell' the skirt, then used a ring set which was good up to .010 over stock (thus '10 up').

But yeah, if you are having the block bored you need OS pistons and matching OS rings. It concerns me that you can't seem to get a straight answer on the required oversize. Any competent machine shop will check the bores for ovality and taper, then recommend an overbore to clean up the wear and of course the piston must match the bore diameter. Ex: if the stock bore diameter is 4.00" and the measured wear is .020" then the cylinder should be bored to 4.030" to clear all the worn spots out and the new pistons/rings will need to be sized to fit the 4.030" bore.

Jensenman wrote: You young punks don't know nothin' about cheap engine building. Used to be sold what was called a '10 up' ring. This was back in the olden days, if the cylinder bores were worn less than .010 from the standard bore you 'knurlized' the standard pistons to 'swell' the skirt, then used a ring set which was good up to .010 over stock (thus '10 up'). But yeah, if you are having the block bored you need OS pistons and matching OS rings. It concerns me that you can't seem to get a straight answer on the required oversize. Any competent machine shop will check the bores for ovality and taper, then recommend an overbore to clean up the wear and of course the piston must match the bore diameter. Ex: if the stock bore diameter is 4.00" and the measured wear is .020" then the cylinder should be bored to 4.030" to clear all the worn spots out and the new pistons/rings will need to be sized to fit the 4.030" bore.

thanks J-man. Most likely not the engine shop issue, but my friend not asking the questions when I ask him. I will most likely call the engine shop directly for the correct answers.

Thank you to everyone for the quick answers. I will tell you more later when I get back.

Thats the current (or was) Spec miata "trick". Use .010 over rings on std bore / std pistons. File to fit.

Seems counter productive to me, less tension rings make more power ;)

Kendall

I forgot all about the knurled pistons. We used to do that on a simple rebuild. Just new rings checked for end gap.

Yeah, you just had to make sure you removed the upper 'ridge' worn into the cylinder bore using a 'ridge reamer'. Otherwise, the top ring would hit the ridge and bust the ring. IIRC, for a while Perfect Circle? had a top ring with a radiused profile which allegedly could be used without ridge reaming. I seem to remember you HAD to use new rod bearings; if the rod bearings had too much clearance the piston could still travel high enough for the ring to hit the ridge. Me, I was too chicken to try it, rather not have to tear down the motor again if it didn't work.

Ridge reamer:

Jensenman wrote: Yeah, you just had to make sure you removed the upper 'ridge' worn into the cylinder bore using a 'ridge reamer'. Otherwise, the top ring would hit the ridge and bust the ring. IIRC, for a while Perfect Circle? had a top ring with a radiused profile which allegedly could be used without ridge reaming. I seem to remember you HAD to use new rod bearings; if the rod bearings had too much clearance the piston could still travel high enough for the ring to hit the ridge. Me, I was too chicken to try it, rather not have to tear down the motor again if it didn't work. Ridge reamer:

A buddy of mine "rebuilt" the old Mitsu 4 banger in his ChryslerCo minivan without using a ridge reamer. I don't think he changed the bearings. The van ran great up until it started to use oil at an alarming rate. Then the engine caught fire and the van burned to the ground in the middle of nowhere on I90.

I have a head scratcher, have a 289 in a '69 Mustang, wrong engine so don't want to bore etc as looking for a 351 to rebuild just want to be able to drive it for now. Thing is plugs were burning light brown but wouldn't start cause valves were bad so since I pulled the heads thought I'd re ring and since end gaps were excessive thought I'd put .020 rings in the standard bore/pistons. This worked out great till I came to the oil expander. Now I'm stumped as to what to do with the expander for the oil rings. First thought I'd use the old standard ones but couple are broke. Than thought I'd shorten them by a few thousands but don't know by how much to shorted them or could just go buy new standard rings and have excessive end gaps again but spent 8 hours filling down the .020 rings. So anyone have any ideas about the expander for the oil rings ?   

This is uncharted territory...if the standard ones looked like they might work maybe order a cheapo stock-size ring set and use ones from that? If this engine runs half-decently and the rings stay in the pistons, you should consider yourself lucky...

In my experience  of looking for Windsor motors for the last few years I would just grab decent motor.  With all of the LS, Coyote, and power adders going on it appears that there are lots of old push-rod engines just collecting dust in peoples garages.   I just sold two roller 5.0 engines for $300, one had an B or E 303 cam in it.  Also picked up a sweet 306 short block for $600.  Spending time and money on iffy stuff just seems wasteful to me, but I'm cheap and have almost no time to spare so doing things twice is out of the question. 

If you're not overboring you should use stock size rings. The thing here is that the ring gap doesn't matter all that much. If you've got bore wear then yes your ring gaps will be larger than stock, but how much larger than stock do they have to be before anything bad happens? In my experience, a LOT larger! I've pulled apart an engine that had no issues where all the ring gaps were .036-.050.  On the last two turbo motors I did i made my top gaps .028 and .036 with the 2nd rings looser. No issues noted. So, in my opinion you create more issues trying to shove an oversize ring into a stock bore and then (hopefully??) measuring ring gap and filing up until it's acceptable, vs just using stock rings and dealing with slightly larger than stock gaps.  Especially if you could have put that time/money towards the next motor you were planning to install anyway. 

I wouldn't bother simply reringing a common engine like that. Either rebuild or replace. As noted above, you should be able to find a good running Windsor for a couple hundred bucks. A full tear down gasket set, rings, and a decent ball hone will cost that much.  And this is assuming the bores in your engine aren't tapered, out of round, or barrel shaped. 

Canoe. 

Its a 9 year old zombie thread, guys. 

In reply to SVreX :

I think most of us realize that.  Is Starman a canoe?  Or just someone involved in Thread Necromancy?

In reply to Cooter :

The Mod Squad already sunk the canoe, which is why you don't see it.

In reply to Jerry From LA :

Which doesn't make much difference since we are answering Starman's question now. 

In reply to Cooter :

Okay, then.  Starman, check the bores for taper and ovality, have the block bored oversize if necessary, and get pistons and rings to fit. As stated previously, hand the set of slugs you want to use to your machinist so he can finish-hone the bores.  It's a Ford V-8 so you can find cheap parts for it if you just need to get it back on the road. Consequences of a failure means a lot more money and man-hours so do those deep-inside parts right and forget about them.  If you're a couple thou over, you can re-ring with proper sized rings.  However, they'll put more pressure on the ring lands and wear them out faster.  When that happens, you'll probably break a ring and it's engine time again.

My 2 lira.

Kendall_Jones said:

Thats the current (or was) Spec miata "trick". Use .010 over rings on std bore / std pistons. File to fit.

Seems counter productive to me, less tension rings make more power ;)

Kendall

I reringed a Toyota 2GR engine.  (Had to deck the crap out of the block because one bank was sagged .004" in the middle, and while the pistons were out, well, why not?  Easier than finding out that the massive overheat that cooked the block also detensioned the rings)  Top ring spec is something like ..009-.013" gap.  The brand new rings measured at .031" gap.  I bet rings for a .010" over engine would be just about right with a tiny bit of filing.  Ring manufacturers tend to err on the side of expecting people to slap the parts in without actually measuring, so non-"file fit" rings are usually really loose.

It runs just fine, makes good compression, has good power, doesn't smoke or burn oil.  Makes me feel a bit better about the Audi engine I have where I gapped the top rings at .026".

A "speed secret" that I have heard is that a given bore usually makes more power on the second set of rings that it sees.  But people always give the bore a little hone "to help the rings seat", which completely negates that...

iceracer said:

I forgot all about the knurled pistons.

Heh.  Knurled pistons...