in-line 6 Cylinder Engines, 'straight-six'

This is news to me too. As Mack is owned by Volvo/Renault Trucks, I'm wondering if the motor/block is the same as the Penta D12? Those are a 12ltr as well.

It s the first time I hear of a failure on the Merc box used in the Rs. I had both an 99XJR and a 00 XKR. I did go thru 3 differentials in 6 years on the XKR though, for some reason Jaguar though they could use the same diff as the normally aspirated models.

Had the water pump and tensioner problems on both.. And a year after i sold the XKR I heard the buyer had to replace the engine Due to nikasil failure... BMW got bitten by nikasil too in the 90s...

Back to straight 6, the engine used from the late 80s was the AJ6 engine, different from the XK engine. Both where great and valves adjustment wasn't a real issue.

I still have my 72 E-type (V12, another great engine...), almost bought a V12 XJS last month...

No problems with the air suspension (CATS) on the Super V8. Crossed fingers as I understand it is $7grand repair. The car has 12,000 miles and is a garage queen so far.

I am in the plating business and I have done electroless nickel with silicon carbide plating (ie: Nikasil) years ago. It is absolutely bullet proof is you get perfect adhesion to the substrate. Since the Jaguar blocks are aluminum, that is the weak spot. Aluminum forms an oxide film almost immediately upon being exposed to atmosphere and plating Al is a crap shoot at best. I believe the plating was done at a plant in Wales and was very proprietary as they only plated the cylinders. Have not looked into it lately and I have had no problems with my Nikasil engines.

The PO had a turbo rebuilt under warranty and no further work has been done. The engines were marinized by American Diesel in New England. It is my understanding that Macks are popular among commercial fishing captains. The PO had an interest in a trucking company and was a fan of Mack engines.

After all of the problems everyone has stated with Jaguar's, I sure as heck wouldn't want to own one. Differential failures 3x, valve adjustments, transmission failure, $7,000 air suspension, nikasil liner issues.......thanks but no thanks.......LOLOLOL

There have been marinized macks running around for as long as I can remember. The first ones that I remember were built by Merlin and then later on I think it was some outfit named American Marine Diesel. I seem to remember Lauderdale Propeller Service being a dealer for one of the companies that was marinizing them for mack.

They did and it didn't work in their pickup truck line. Ford in their F 150's (the best selling US truck for decades) had a 300 cubic inch inline 6cylinder gas engine. It had less power and much less fuel economy than the 302cu inch v8. While the 6cylinder diesels work well, it appears the gas engines at least in the larger displacements aren't fuel efficient. I think that has to do with bore vs stroke ratio and the port designs exhaust and intake on a 6 cylinder. You're forgetting that a heavy truck, needs x amount of horsepower and x amount of torque to accelerate, get to, and stay at speed and they're not the most aerodynamic vehicles. So you're just pushing a 6 cylinder that much harder to do the same. The torque in a vehicle is used to accelerate it from a dead stop to speed, at that point horsepower is utilized and the v8's have more power in the same cubic inch package.

They should offer more diesels, and I think Ford/GM would've pursued that route much more if the EPA didn't really clamp down on emmissions on the diesels. Right now both companies diesels have to have so many different emmissions systems on them to meet the EPA mandates, that it REALLY adds to the cost of the engines/vehicle and also makes them less reliable.

My point was related to ANY application, both marine, automotive or even aircraft. The simple point being that a V8 (or an opposed) configuration, while slightly more expensive to produce than a inline six, provides smoother operation and better power to weight ratios. That applies to diesel or gas engines. The reason for this is that a straight six has a lot more cylinder block mass for a given displacement, and a heavier crank since the rods don't share crank throws. As a result, you can have a larger displacement engine with more power, or you have the option of slowing down the larger engine and having longer life. While many marine engineers "don't care" about the weight, if you strive for an efficient system, adding mass for no real reason isn't generally a good way to achieve it.

If the designer shortens the stroke he can increase the rotational speed and maintain a similar piston speed. That's the beauty of a shorter stroke design. The downside is that the valves don't get as much time on their seats and it is a lot harder to keep them cool and valve life generally suffers.

There is a strong relationship between specific output and life. Bottom line is that higher specific output engines have a shorter life. That is pretty much a fact of life and if you want really long life, you will slow any engine down and reduce the piston speed and the load on the components. What trades the designer makes in the design space and the manner in which the details are carried out also have a very strong influence on life so it's not not just a piston speed or temperature issue either.

Well, actually the XK series of engines are relatively long stroke engines were never really high speed engines. Back in 1948 they were great engines, but they became obsolete in racing, in large part due to their inline configuration. They had (for the time) advanced cylinder heads and good breathing, and did well more from that aspect than their inherent configuration. While they won Le Mans in the 50's, by early 60's they were really pretty much relegated to back marker status. Same can be said for the Aston Martin six cylinder engines. Ferrari pretty much dominated sports car racing with their V12's through the mid 60's, and they were replaced by Ford V8's and Porsche V12's. Bottom line is that since the BMW CSL of the mid 70's, there hasn't been a competitive inline engine in endurance racing. That's over 35 years ago. The fact that the XK series remained in production for a long time is more indicative of how well it was designed originally than any inherent goodness of the in line configuration.

Well actually Brian, there has been a trend to 6 cylinder engines, but these virtually all have been V6 engines and they are a lot lighter than inline engines and these also package much better in a front drive installation. When you consider the cost of tooling and how many applications you can put the package into, an inline engine doesn't make much sense. Most of those engines were leftovers from the early 50's, and, while torquey, they weren't powerful or all that efficient. It's relatively easy to quantify how much each pound costs you in terms of EPA rated mileage, and that's as good a measure as any to compare apples to apples. When you do that the much lighter V6 beats the inline six every time.

Also remember that for a given road speed fuel mileage is a strong function of displacement per mile. That is, look at the gear ratio in top gear (actually multiplied by the tire size) times the engine displacement and that will tell you how much potential there is for fuel economy (assuming similar aerodynamics). Very tall gearing in V8's can give you the same displacement per mile as a smaller engine, and very similar fuel economy. My Corvette has a very tall sixth gear, at 75mph it is only turning 1700 rpm and it gets 32 mpg on the highway at that speed. Pretty impressive for a car that gets to 60 mph in four seconds flat.

Yes, and the other trend I've been seeing a lot of in the last few years in gas vehicles is a smaller displacement 4 cylinder or v6 and utlitizing a supercharger or turbocharger for the power yet gaining more efficiency at cruising or highway speeds with the smaller displacement.

As to the corvette, I've owned many back in the day and the fuel economy they get on the highway is a sheer miracle given the amount of horsepower and torque they have. I know one thing, you can chew through a TON of fuel in the city hotrodding around though......if you're constantly bottoming out the go pedal......hehehehe

I had an old Chevy Diplomata, built in Brazil with the 4.1ltr straight six from the mid 70's. It put out 125hp and 200ft-lb on an autobox. The EPA fuel figures said it should give 18mpg but running in Antigua, often on dirt roads, at 30 to 40mph on low octane fuel, I got much better economy than stated.

Those long stroke motors just purred along, burning very little at low revs. It was only when you floored the throttle did the fuel needle move toward the E mark.

The basic Chevy "Stove Bolt" six traces it's lineage back to the late 20's. The 4.1 was designed in 1962. Good engine, but only 125 hp from 4.1 liters is pretty low specific output. A BMW 4 cyl of the same vintage could make the same power, but wouldn't be nearly as nice since it wouldn't have the torque of the bigger 6. This engine had 7 main bearings. Good for reliability, but that makes for a lot more bearing drag than a v6 with only 4 main bearings. This is another reason for the switch to V6's, when the EPA mileage is on the window sticker, the better number you can post often swings the sale. Also with CAFE standards, it helps the manufacturer to reduce the fuel consumption of any and all of his cars. While I'm sure a V6 is more expensive to produce than a straight six, they want the lighter, smaller, and more efficient engine in a car.

I know that in the older Ford F150's where they offered an inline 6 (300Cu in) and a v8 (302 cu in). The fuel economy on the inline 6's in real life was poor and less than the v8, but here are the EPA figures

6cylinder automatic city 12 mpg, combined 14mpg and highway 17mpg
v8 302 automatic city 12 mpg combined 14 mpg and highway 17mpg

Both 2wd.

I don't know about the whole bore versus stroke. I know a shorter stroke can be revved higher and has the potential to make more hp. I know this, the 302 cu in Ford v8 and the 351 ford v8 shared the same cylinder heads and such. You could always make a lot more power with a 302 over a 351 with the same mods and the 302 always got much better fuel economy due to it's smaller displacement.