Piston ring gap range

The Haynes manual is vague about the piston ring gap range, it does not at all specify the low end and it says that the upper end is generally not important (I question that) but should not exceed 0.04". That sounds a bit high because various places around the interwebs suggest 0.004" per inch of bore diameter, which is 3.6", which comes to 0.0144".

I am asking because the new standard rings come to around 0.02"+/- and the old ones were in excess of 0.04" (which coincides with the Haynes upper limit) and were leaking profusely (~80% leak, after water/ice got in the cylinders when the heads were off). I wonder if 0.02 is still too much and I should send them back and get oversized ones (0.5 mm over) and maybe file them to an optimal size to give good compression.

 

@shmn -- thanks but I am slightly confused about "maximum" vs "standard", the latter of which specifies a range whose upper limit is well below what it says under "maximum"

 

For No.1 ring, standard gap is 0.3-0.4mm. Maximum gap is 1.0mm. Maximum gap > standard gap. So you want to set things to standard gap. I do find it odd that maximum gap is so much more than standard but I've never rebuilt one of these engines so can't speak from experience. The 2TR-FE (4 cyl) just has one range of gaps (no maximum) so I'm not sure why the 6-cyl has this odd specification. Maybe someone who has rebuilt one of these can speak to this.

 

Toyota has always been generous on their maximums.
It’s almost like their maximum are literally MAXIMUM. As in the engine won’t run at that point.

You definitely don’t want them set too small (close together)

 

Standard is the reccomended range as in when building a new engine, maximum is the upper limit of wear anything beyond the maximum would be considered worn out.

 

I'm nowhere near that point.

 

but in order to be able to measure the gap, you must have the pistons out so why would anyone put the old rings back when new ones are so cheap, if they were above the standard but still below the "maximum"? which kinda makes the "maximum" only theoretical but practically useless.

Long story short, what applies to anyone (re)building an engine is the standard (more conservative) range.

 

In short standard is considered as built or new specs and maximum is considered to be the service or wear limit.
So when building an engine with new parts use the standard specs, maximum specs are only used when checking if used parts are still serviceable. It's no more complicated than that.

 

If you are looking to get into Standard NEW engine build range, you’ll need over sized rings.
If you buy .5mm (.19685”) you’ll be at .003 of clearance. That’s way too tight, and will request filing. (Like you said before).

You’re only .004” from the standard range on ring 1
And .0003 from ring 2

 

@TnShooter -- yes but why not do it right (get within the spec)? the incremental cost will be about $40 ($6 for shipping back to RockAuto and about $34 for a ring filer)

 

That is an option.
If you want to do it right (per factory specifications), you’ll need new rings and a set of files.

 

I’ve never personally filed rings myself.
But I did for a very small time work for a shop that built engines.
They used one of these to file rings.
https://www.summitracing.com/parts/pro-66785

I basically pulled engines, and put them back in.
(And I didn’t like doing that, so I didn’t stay at that job long)

 

@TnShooter -- the same (looking) tool is half that price on Amazon.

So you think that, even if I decided to be off a little (~ 0.020" gap, which is about 30% over the standard maximum), it would be fine, I just wouldn't be getting optimal compression?

 

I have no idea. @Torspd will have a better answer than me.

 

How are your cylinder bores?
You have to remember unless you have a brand new block or sleeves there's gona be some wear there which will increase your ring gap size.

 

I think they are fine but have not measured them because I don't own a bore gauge. I did hone them so they look shiny. A set of telescoping bore gauges and a large micrometer would set me back about $70, you think I should do it? Does it make sense to measure it if what in the end matters is the ring gap, and if I can get that within the range with oversize rings?

 

I mean that is up to you, if I was rebuilding an engine that had known oil burning or compression problems I would want to check the bores for squarenes and wear but if I was just refreshing one that had no known issues with oil burning or compression I'd probably hone it, slap some new rings in and call it good.

 

yeah i think i'm just going to bring my ring gap to the spec range and send it

 

Not sure if it’s the angle of pic or not, doesn’t look like a good hone to me. 2 and 3 look much different. Are you using the right size? Also how much experience do you have rebuilding engines? Not a lot of people rebuild these things