Why are Harley engines so bulky?

[SmithSwede]

 I’m not trying to flame on Harley.  I’m assuming there is some technical, engineering explanation.  I’m just ignorant of that reason. 

Why are Harley engines so seemingly bulky?  Why is there such an enormous primary chain cover on the left?

Big displacement engines, like Guzzi big block motors, don’t seem to have such seemingly wasteful bulk.  Large displacement Japanese I-4 engines don’t seem like this.

What’s the deal here ?

[twowheeladdict]

What model and year bikes are you comparing?

Could part of it be that tha width of the 90 degree V-twin of the moto Guzzi engine is so much wider ar the heads?

Could it be that the inline 4 engine is so much wider at the cylinders?

Could it be that you are not comparing just the engines?  The Harley engine is quite narrow compared with the other two.

The primary is part of the drivetrain but not the engine.  The primary on my M8 107 is narrower than the primary on my twin cam 96 softail engine.

Are you comparing similar displacement air cooled engines?

[cliffrod]

My opinion, as an owner-

At this point, The architecture has as much if not more to do with tradition and trademark as function.  Until the Twin Cam brought functional obsolescence into the HD business model, HD engines/transmissions were perceived as endlessly rebuildable.  That’s Good for a customer but bad for the manufacturer. They were the farm equipment that we (Harley owners) call them because they were originally designed for hard use on & in often poor to bad road conditions.  they were also big enough to be durable, not fragile.  I believe That’s probably why there’s a crazy number of non-running old bikes of various marques from any given year lingering around the USA vs the same model year of Harley Davidsons.

Now that older architecture about marketing tradition.  The newer models have architecture that confounds traditional owners.  They don’t look like a Harley.  I bet they won’t last like one, either.  Probably why dead “ran good when parked, just needs tune up” VRod projects that will likely never run again are already becoming more common on fbmp.  Their offspring will soon be joining them.

[blu guzz]

Smith:  Keep in mind that much of the engineering on the air cooled HD engines exists as a nod to the past.  For example, in an interview, when asked why HD transmissions clunk when 1st gear is engaged, Willie G. said "because our customers like it that way".  He went on to say that the engineering talent at the company could have made the transmissions snick into gear as smooth as anyone if they decided to go that way.
My last HD was a 2006 Wide-glide that I bought new in late 2005.  It had a host of upgrades that year which is one of the reasons I wanted it.  The first 6 speed transmission and improved and beefed up axles.  It clunked going into gear which I was perfectly happy with because that was part of the HD experience.  That bike handled so much better then you would have guessed it would have given its geometry.  It was a great bike, not just great for HD.  It had just enough of the old school mixed with modern.  After 18,000 miles in a very short time, I traded on a Victory.  The Vicky had a much smaller primary drive housing btw, and had its drive belt on the outside of the engine with just a simple cover to remove should a belt break.  On the HD, the same repair is an all day affair because when they went to belt drive, HD simply used the traditional location for the chain arrangement modified for a belt which meant there was an internal component that had to be accessed to change a belt.  The Vicky was a "better" bike in almost any metric you cared to measure, power, suspension, brakng power, etc.  However, it did not have that HD secret sauce.  Most HD riders can't really quantify what that secret sauce is, soul, character?  Sounds like how we describe our beloved Guzzis.   

[Kev m]

I was gonna say that part of it is definitely a design choice for look and feel. It's a perception thing.

[Tom H]

Why the large primary cover you ask. Then also ask why the large bell housing on a Guzzi. They both have a clutch assembly in there. Why is the primary case so long? So that the clutch and the drive sprocket which are centered on the engine and trans will fit in the cover.

The engine has larger pistons for the most part than a Guzzi. The need cooling fins at least up until they went to water cooling on some. So the cylinders look bigger. The block itself is not all that big.

The clunk into first gear can be lessened or eliminated with the correct primary oil and level, clutch adjustment and pulling the hand clutch lever for a moment or two before you shift to 1st. The 1st cold start of the day if I just pull the clutch lever and kick it into gear will try to spin the wheel. If I hod the lever for maybe 5-10 seconds, you don't even hear it or feel it go into  gear.

Tom

[Motormike]

Unlike Japanese (and Moto Guzzi) Harley still uses the non-unitized engine and transmission. Two completely separate casings for each, joined together by the rather bulky primary chain case. The double-row chain Harley uses adds width, and then on the "Big Twins" they mount the clutch housing on the outside of the primary chain adding even more width.  Old Triumphs and Nortons had a similar set-up.  It gets the job done, but at this point is an archaic design they stay with mostly out of tradition over anything else.  It also explains why Harleys have "three oil" changes: Engine oil, transmission lubricant, and the primary chain oil.

[Tusayan]

Unlike Japanese (and Moto Guzzi) Harley still uses the non-unitized engine and transmission.

I’d suggest you take a closer look at various Guzzi power train designs.

[MerleLowe]

The Sportster engine and transmission are much more compact than the big twins if we throw those in the mix.  Haven't taken a tape measure to them, but I'd be surprised if a 1200 XL engine was much larger than a Shadow 750 engine.


As far as obsolescence, the TC an M8 are both quite rebuildable, and will be for as long as you want until the state intervenes and prevents repair and/or use.

[SmithSwede]

Thanks, very interesting.   I figured there were reasons !

[slowmover]

Bluster