What makes an inline 6 engine more reliable than a V6 or V8 configuration? 3

[eouedu]

I don't want to start an engine debate but I know enough that generally straight 6 engines have a reputation for being more reliable than a V6 or V8 configuration. Just to simplify this discussion I want to stick with a discussion of older pre efi passenger vehicle and pickups engines because that is what I'm interested in. There aren't that many inline 6 engines out there but most of them have a very good reputation for being reliable.

-Cummins diesel all years but specifically the 89-98 "12 valves" are known to be very reliable
-Ford 300 straight 6 there are a lot of people including myself that would argue this is the most reliable gas motor ever produced
-Dodge 225 "slant 6"
-Jeep 4.0/4.2
-BMW inline 6
-Toyota supra inline 6
-HJ60 landcruiser diesel

Runners up:
-Toyota fj40 gas straight 6
-Mercedes 300D (inline 5 so doesn't get full credit)
-Chevy 250/292

These engines are often referred to as "bulletproof" or at the least are pretty well known for being very reliable. Especially when compared to their v6 or v8 counterparts.

Possible ideas that would contribute to the making them last longer than most V6 and V8s:

-less powerful so they aren't used as hard
-easier to access and work on therefore they are maintained better.
-less moving parts
-Power peaks at lower RPMs so it takes less to do more
-less prone to hot spots so less chance of detonation
-being upright gives more lubrication around the cylinder walls because gravity isn't working against the high side of the cylinder wall
-being upright applies the same theory for cooling and every other part where gravity could be fighting a v engine
-more bearings in the crankshaft (ford 300 has 7 main bearings)
-better balanced
-more surface area exposed to air and more open engine bay for it sheds heat better
-less nooks and cranies for old oil and engine particles to hide when the oil is being changed
-less parts of the engine hidden that aren't as well lubricated and/or cooled
-I don't believe any of the above mentioned engines have timing belts, it's either a chain or gears

If anybody has anything to correct or add feel free.

 

[dgallup]

From Tmoose's link above: Used-car shoppers should also realize that even the most complained-about engines represented less than 1 percent of those made, so the odds of avoiding such a car are in your favor.

So to me, when 99% of the engines don't have the problem, it is not a design issue. There has to be some other contributing factor(s). Either poor quality control, poor maintenance, unusual environmental conditions, something other that a design flaw or more would have the problem.

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[Compositepro]

My 2004 6 liter Powerstroke started started having problems at 50K miles. It was hauled away this last weekend with 140K on it. I bought a diesel truck because of their reputation for durability. It used to be you could run diesels on used motor oil. They are now made to such high tolerances that a tiny piece of grit can cause a cascade of failures that disables or destroys the engine. The 6 liter used 20 quarts of oil, which also operated the fuel injectors so oil cleanliness was essential. It had 10 micron and 5 micron fuel filters in series. It used a special grade of coolant that was expensive and hard to find. All maintenance and repairs were expensive. I spent $4000 replacing the oil cooler and EGR cooler with an after market "Bulletproof Diesel" kit, when these went bad. These were well know problems after the engine was out a few years.
I bought a gas truck to replace it. At the time, I read that diesels were a $5,000 option compared to gas engines, but when looking at prices on the market it seemed more like $15,000. My experience with Ford dealer service in my area was horrible.

 

[oldfieldguy]

Hailing from the days of the 'shade-tree mechanic" and the 'points-plugs-condenser' routine - your REALLY motorhead buddy owned a timing light - and fifteen thousand miles on a set of bias-ply tires, I don't want to roll back the clock, not ONE bit.

old field guy

 

[dgallup]

I think I still have a timing light somewhere.

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[RodRico]

My old Acura TL is still running strong with 240,000 miles on its 3.5L V6. I never had even a minor problem with it. I loved it so much, I bought the 2017 Honda Accord with the same engine precisely *because* it had the same engine. Sadly, Honda/Acura dropped the engine from passenger cars in favor of turbo fours in 2018. As for old versus new, I sure don't miss cleaning and gapping plugs and points, adjusting valve lash, and replacing clutches, but I do miss how they helped build a *relationship* with my cars. My 30 something nephew (who once raced sprint cars) got in my 1993 RX-7 the other day and said "I miss these old school cars. They've got soul." I think he's right. New cars are certainly "better" but I feel no connection with them.

 

[waross]

Well for a real comparison, does anyone have reliability statistics on a Detroit Diesel 2-71, 3-71, 4-71 and 6-71 versus a Detroit Diesel 6V-71, 8V-71, 12V-71 and a 16V-71?


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[VEBill]

Experiences will differ.

Many drivers would toodle around gently, never mashing the accelerator pedal to the floor and never exploring the rev limiter.

'Reliable' in such a light duty context is merely an indication that the engine doesn't have any serious design or build errors.

Other drivers would be full throttle and at the red line several times just going to work in the morning.

'Reliable' in the severe duty / abuse context is much more illuminating.

By way of example, when I was young I owned a Dodge Dart with the 225 Slant-6 engine. I recently learned that the Slant-6 red line was supposed to be 4500 rpm. Oh dear. I recall assuming at the time it was 6000 rpm, and treating it as such. For years...

'Reliable'

 

[berkshire]

A straight 6 engine not discussed here is the Volvo B30 engine which started life as a carb engine and in its last iterations before it was dropped in favor of a V6 was EFI. The engine had a reputation for reliability and would regularly run 200,000 miles before overhaul. It is also interesting that the V6 that replaced that engine was a terrible engine, prone to head leaks and camshaft failures.
B.E.

You are judged not by what you know, but by what you can do.

 

[berkshire]

Before somebody comes back and mentions it, I know the B30 was prone to crankshaft failures when people tried to soup it up, because of torsional resonance in that long crankshaft.
B.E.

You are judged not by what you know, but by what you can do.

 

[BrianPetersen]

The V6 that replaced the B30 inline was the PRV. I don't think it's crappiness had anything to do with its cylinder arrangement. It was simply a crappy design.

 

[GregLocock]

I used to look through CANBUS data for real customers. In something like 7 million minutes of operation nobody exceeded 5000 rpm. Obviously my car didn't have a recorder on it! I was actually looking for the distribution of real life braking accelerations, that was interesting and useful.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[PackardV8]

Anyone who thinks straight sixes are magically reliable and that Subarus are reliable hasn't been around many automotive machine shops.

Most of the old iron straight sixes mentioned were somewhat reliable because they didn't make enough power to hurt themselves.

Every job shop gets a steady flow of Subaru cylinder heads. They blow the gasket, warp the head. The local repair shop has learned how to pull both heads, bring them in, we mill them without removing the valves, pressure test, out the door and back on the car in the same day.

As far as the original VW air cooled engines outlasting the car, I've personally never seen it happen, but then I didn't live in the rust belt in the VW heyday. Maybe if the body rusted out really quickly. However, it was another engine designed unable to make enough horsepower to hurt itself. If the oil cooler was kept clean and the oil changed regularly and the valves kept adjusted, they would run a while. But like the Subaru, it was possible to swap a VW engine in the driveway in an afternoon.

My 2004 6 liter Powerstroke started started having problems at 50K miles. It was hauled away this last weekend with 140K on it. I bought a diesel truck because of their reputation for durability. It used to be you could run diesels on used motor oil. They are now made to such high tolerances that a tiny piece of grit can cause a cascade of failures that disables or destroys the engine. The 6 liter used 20 quarts of oil, which also operated the fuel injectors so oil cleanliness was essential. It had 10 micron and 5 micron fuel filters in series. It used a special grade of coolant that was expensive and hard to find. All maintenance and repairs were expensive. I spent $4000 replacing the oil cooler and EGR cooler with an after market "Bulletproof Diesel" kit, when these went bad. These were well know problems after the engine was out a few years.

FWIW, there is some truth to the above. Yes, Ford had some issues with the 6.0., but a '04 gas truck worked as hard as a 6.0 can work would have been dead years ago. Yes, the 6.0 EGR system is simply a flawed design; pumping corrosive exhaust gases through a thin radiator shared with the engine coolant was inexcusable. They all failed; some sooner, some later. When they do, it blows out all the coolant and put the truck out of service instead of just needing service when convenient. I've replaced the EGR cooler one time and am still driving my '04 6.0 every day with 185,000 on it. No, the coolant isn't especially expensive or difficult to find. Good fuel filters are a good thing. Lots of oil capacity in a heavy duty truck is a good thing. The 6.0 has the easiest to service fuel, oil and transmission filters I've ever encountered in sixty years of doing maintenance. You forgot to mention the variable vane turbocharger will rust up if not driven hard and regularly.

When the 6.0 began having teething problems, some looked back fondly on the more reliable 7.3 it replaced; yet another example of an engine being reliable because it didn't make enough horsepower to hurt itself; more iron than output. The 6.0 made fifty more horsepower with better fuel economy and met emissions requirements.

jack vines

 

[BrianPetersen]

Jack, you must be talking of the VW air-cooled engines. Those were from an era where 60,000 miles was considered normal service life. (So, for that matter, are quite a number of the engines that have come up for discussion in this thread.)

From the water-cooled era - The VW "2.slow" - 2 litre 4 cylinder 8-valve iron block - is another engine that doesn't make enough power to hurt itself. VW managed to screw some of them up by installing some piston rings upside down, which made them oil-burners, but otherwise they didn't break. Even if the timing belt was neglected and broke, at least the early 8-valve engines were non-interference. Unfortunately, that engine offered neither power nor gas mileage, and so it's not on the menu any more.

 

[PackardV8]

Jack, you must be talking of the VW air-cooled engines. Those were from an era where 60,000 miles was considered normal service life. (So, for that matter, are quite a number of the engines that have come up for discussion in this thread.)

From the water-cooled era - The VW "2.slow" - 2 litre 4 cylinder 8-valve iron block - is another engine that doesn't make enough power to hurt itself. VW managed to screw some of them up by installing some piston rings upside down, which made them oil-burners, but otherwise they didn't break. Even if the timing belt was neglected and broke, at least the early 8-valve engines were non-interference. Unfortunately, that engine offered neither power nor gas mileage, and so it's not on the menu any more.

For true, Brian. I edited my first post to clarify that point. For those of us old enough to remember when they first arrived, "VW" has only the one referent. The more recent fifty years are muddied up with Audi, Porsche, SEAT, Bentley, Bugatti, Lamborghini, Ducati, Skoda, et al.

jack vines

 

[enginesrus]

PackardV8, my experience when an Al head with OHC warps, well that warp happens after the fasteners are removed and then the cam or cams won't turn. If they are machined flat in that released state then when re fastened wouldn't the cams be locked from the bores still being warped or misaligned? Just curious how that all worked out.

 

[Tmoose]

Yeah, not surprisingly the OHC cam bore alignment drives the best repair sequence.

Here is a description of a common commercial method using heat.

http://www.enginebuildermag.com/2014/10/head-surfacing-straightening/

Here is a description of why straightening cold, in a hydraulic press might be better sometimes.

https://www.alfabb.com/bb/forums/en...199054-heat-treatment-repair-warped-head.html

 

[waross]

This started as a comparison of straight 6's versus V 6's and V 8's.
Possibly the best comparison is the Detroit 71 series and the Detroit 71 series.
A lot of the same parts are used in the straight 2 cylinder, 3 cylinder, 4 cylinder and 6 cylinder engine as are used in the V6, V8, V12 and V16.
Many of these engines share the same pistons, liners, heads, valves, blowers, con rods and a lot of other parts.
I have never heard any comments or anecdotes regarding the reliability of straight 71 series versus the V 71 series.
What experience have others had with the comparable reliability of these engines.
Surely this is one of the best example of apples to apples that we will find.
Any comments and/or first hand experience?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[SwinnyGG]

Well if you want to talk Detroit Diesel... Once upon a time, many moons ago, when men were men and giants walked the face of the earth, I worked at Detroit Diesel as an engineer in the warranty investigation department, where our job was to determine root cause of failures.

I worked on major warranty campaigns across several platforms, including Series 71, 40E, 6.2 and 6.5 liter, eventually Series 60 and then very early development work on DDXX engines, and even some ancient 110s at one time.

I never worked on a campaign on a production platform where a major component failure was the result of component design shortcomings related to engine configuration.

The Series 71 especially is a platform where a large number of configurations are possible from a relatively small number of individual parts; V engines use heads from smaller inline engines (Series 71 V16, for example, uses cylinders/liners from every other Series 71, along with 4 Series 71 inline 4 cylinder heads).

The vast and overwhelming majority of problems with these engines are the result of controls problems. Frozen pumps/injectors, failed sensors, emissions gear, etc etc. I can honestly say that across dozens of campaigns across these platforms, all of which were successfully solved for either single cases or engineered changes to a design, there was not one case where a problem was tied directly to architecture.

 

[Lou Scannon]

Well, that just goes to show, at least, that the designers of the 71 series knew how do design a Vee engine as well as an inline engine.
Such as they are, I guess the balancing challenges for a 2-stroke engine are generally less than a 4-stroke engine.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

 

[BrianPetersen]

An inline-four 4-stroke wants to have the two inner pistons moving together and the two outer pistons moving 180 degrees opposite to have an even firing order. An inline-four 2-stroke wants a crossplane crankshaft (90-degree firing intervals). An inline-six 4-stroke has a symmetrical crankshaft front to rear (two
mirror-image groups of 120-degree spaced crank throws) to have an even firing order and is almost vibration-free. An inline-six 2-stroke wants cylinders firing 60 degrees apart to have an even firing order. No two cylinders will hit TDC at the same time.

A google search of a picture of a 4-53 crankshaft suggests that it is a crossplane (90-degree firing intervals). A google search of a 6-71 crankshaft suggests that the front group of three has crank throws 180-degrees opposite the rear group of three with cylinders 3 and 4 180 degrees apart, cylinders 2 and 5 180 degrees apart and 120 degrees offset from the inner pair, and cylinders 1 and 6 180 degrees apart and 120 degrees offset from the others.

I know the inline-four crossplane-crank configuration requires a crankshaft-speed opposite-direction balance shaft ... see 2009-on Yamaha R1. I don't know if the Detroits spun fast enough for it to matter.

A google search of a 6V53 indicates that it has a 60-degree bank angle with common crankpins for the corresponding cylinders in the left and right bank and there is a big counterweight on each end of the crank outboard of the outer main journals.