I actually went through this months ago but I've been meaning to discuss it here to see what folks thought.

Engine is a 2004 5.7L Hemi for a buddy's car. First 5.7 I ever worked with. It was knocking when he got it, looked like it was run out of oil and then ran hard, lost two rod bearings. Tore it down and decided to just use the block/replace everything else in the bottom end.

He bought a brand new crankshaft, rods, pistons, rings, and all the bearings from Mopar. Prices were surprisingly cheap for the mundane stock stuff like that.

Anyway I spent some time checking it out...

Clearances:
Mains: .0028 to .003" across all 8
Rods: .002 to .0025 across all 8
Piston to wall .0012 to .0015 across all 8, normal for a cast or hyper piston, always has been

Checked the service manual, everything was in spec per Chrysler. So...being that the clearances are basically the same as a V8 from the sixties, what's up with the myth "Modern engines are built tighter"? It's really no different from my 1968 318 2 barrel in that dept.


+ or - tolerances may be slightly tighter on the machining end, which I guess I'm on the receiving end of... but recommended final clearances appear to be pretty much the same as always.

Thoughts?

That seems looser! I thought stock 440's were around .0015 on the mains.

Those clearances were even looser than old specs. 60's spec's. .0005-.0015 rod and main in my book (/6, 318-440). Hemi's were fit looser though.
I still fit mine at .0015-.002 at the loosest.

Its fuel injected, so no fuel washing past the rings and into the oil. Thats the biggest difference, and the reason why new EFI motors seem to last forever if they are taken care of.

The perfect gas burning engine should have no ring/valve leakage,needs a complete seal/combustion. Friction is the "evil" of all motion.

I think the machining is more consistent and the oil and filters are "better", along with fuel injection keeping the burn cleaner. It all adds up to a longer lasting engine UNLESS it's been run hot or low on oil, just like in years past.

I did notice when I had my old 3.5 apart it had very thin rings which would lead to less friction.

Having a degree from UTI but not even close to the years of knowledge on this board, I can offer my .02. Fuel injection and volumetric effeciency is key. Modern materials, ie more consistant expansion/contraction rates, less or no contaminants in little or no blowby, VERY effecient PCV etc systems make for an engine that contains each element of it's performance in it's allocated place, with little cross contamination. This allows for for tight tolerances that LAST. The same tolerances are generally required for an engine to function, but deteriorate quickly if cross contaminated or improperly maintained.

I had worked at GM for the last 7 years, and part of my job was setting up the final bore and final production hones as well as write the specs for them and monitor capability. I can tell you the crank bore tolerences were no worse than +/- 0.012mm, with most our lines running around +/-0.008mm and run-out was only allowed 0.025mm from front bore to the rear bore max.

Cylinder bores were only allowed +/-0.011mm and a max of +/-0.008 on the thrust wall and cylindricity of 0.013mm max and max taper of 0.007mm. And just in case you don't think it can be held, it can be, and it can be done day after day, week after week, etc. The machines use in-line feed back to constantly hold size.

Years ago, the sizes and tolerences were not this tight, but to meet the ever increasing demand for 100k warrenties, and not go broke in the process (on second thought, I guess they did go broke), all the specs were tightened over the years. If your measuring in thousandths, your already oversize....

FYI 0.01mm is less than 4 tenths (.00039) to maintain that is fantastic.

You may have guessed-no degree here. Tell me more about the reason that the new 5.7 Hemi calls for 5-20 instead of the 10-40 recommended by the builder of my 440. Is it the tolerances? Is this why the make-up of the synthetic can clean/loosen buildup that can lead to a leak?
Is it the passage ways themselves that are too tight for the 40 weight?

very interesting,
thanks for posting that

in terms of 'tight tolerance'
wouldn't one of the potential benefits
be to hold a predictable
'Quench Clearance'

Tolerances from the
bearings
con rod length
crank throw
piston deck height
piston rock
head gasket compressed thickness
... all these 'stack up'
and make it possible that the worst of the 8 cylinders will result in a quench clearance where the piston crown will impact the combustion chamber flat.

in terms of what a bore diameter should be
it may sound 'wild'
but shouldn't it be a kind of wild undulating shape
for best effect?

I say this because the North Carolina shops not only use a honing plate to simulate the cylinder head bolt stresses ... but they also heat the bores during the hone and keep secret how they vary the temperature from top of bore to bottom. The idea is to get superior ring seal at severe operating conditions, which may mean the bore size when cold varies all over the place.

Most import engines,hybird and industrial engines use high quality micro finishes on componants and block bores and use more stable alloys in there construction allowing for closer tolarences.

This is a subject that I've never thought about, but can make for some good read. From what you've said, if it's true, then my take would be that the standard person that doesn't know anything can make this type of statement about tighter clearances and be halfa$$ right. Me? I don't think they are tighter, but I do think that the machining process of parts and blocks is tighter and more accurate with the use of computers, lazers, etc. so that componets are more square and all. Now if you take all your bearing clearances and tighen them up, there will be lots of friction and heat going on within the motor that you could cook some fries with the oil it'd be so hot. So I think Detroit has them where they need to be and have had plenty of years to do the homework on tolerances to seal a motor yet allow friction to be at a minimum.

I left out an important word after micro.Parts are micro polished to reduce friction.The tolerences are closer with the types and quality of lubercations(synthetics) and cleaner blends also also reduce friction.Mirror like cylinder wall finishes and ring styles and materials have greatly improved engine life.Many of the import and commercial engines are warrantied for 100Ks miles some thing unheard of in years past.Actually we have some 600 hp Cummins diesals in our tracter trialer fleet(lowboy heavey haulers)that came with 500,000 mile warranty.engine building techonology has change,when I first started playing with cars 30/40K miles you were ready for rings,bearings, and valve job.We have many pieces of heavy equipment(dozer,excavators,etc)with over 10,000 hrs on them.One excavator(Kebelco)has 18,000 hrs with only in frame overhaul.Needless to say we have a good maintaince program.

I guess my point was, just because machining + or - tolerances are closer, and finishes are better and smoother, really does not mean the clearances are any tighter. They aren't, at least not in the case of
that 5.7.

Relative to another comment above...at one time in the '90s it was fine to run the 2.0 Neon engine on 10w30 oil. If you took your car to the dealer, odds are good that's what they would pour in. Come 2005, and you absolutely can not run anything but 5w20 per the pwner's manual. Look up the clearances for both engines, and guess what...they have not changed over time either. I'd think if there were going to be any big changes they would show up in little 4 cylinder engines first, but even that doesn't seem to be true.

It's just something to discuss and throw around, I'm not trying to prove anything but I think the myth is funny. Tolerances may be tighter, I don't doubt that, but the desired end result is pretty much the same as always.

At the OEM level, it's not uncommon to scrap a few hundred engine blocks because the bores are oversize by like two microns. MICRONS. Pieces that could have went 150,000 miles without an issue. Sounds a bit wasteful just for the sake of maintaining tight tolerances, doesn't it?

I heard a clip on the radio that says the best for modern cars is 0-30. That the 5-20 is a warm-up emissions issue that is not in the best interest of engine life.

I never broke the motor done or check specs but my brother had a 2001 ford focus. That was the start of the 5w-20 thing for ford if i remember right.

At the time it was hard to find a full synth. oil in 5w-20.

So i changed over to 5w-30 no problems then next oil change i went with a 5w-50 and had a knock.

Switch right back to the 5w-30 kock went away.