Topic: Motor differences 550K & 550F

[Hot500]

Are there any ? Tried a search but found zip. I'm thinking maybe a different cam if anything. Did the 550s run the same carbs as the 500/4.

[fmctm1sw]

Are there any ? Tried a search but found zip. I'm thinking maybe a different cam if anything. Did the 550s run the same carbs as the 500/4.

According to a part number search, the cam is the same.  I researched that when I was (is) trying to figure out why my 550 won't run.  I have the valve cover from a 550F on my top end and I recall 4 studs in there that didn't go to anything.  I may or may not have pictures...

[lone*X]

Carbs are quite similar from 500's to 550's thru 76, although different version numbers.  Needles and air screws are different but jetting is the same.  They are interchangeable.  77 and later were different and used the PD carbs that included an accelerator pump.
As far as I remember the only real mechanical difference in the 550K and F's was the final drive ratio.  Others my know something I don't but they were both pretty close.   You can do some comparisons if you go to the FAQ pages.  Some people have a hard time finding them.

http://www.sohc4.net/?q=faq

[fmctm1sw]

Here's what I was trying to describe.  Do you see #29 & #15 in the top photo?  That's an F valve cover.  The part number listing has no entry for either one.  The bottom is a K cover.  Doesn't look like it's there.  It's been a while since I had my top end apart but I'm sure I noticed that.  Doesn't seem to have any effect tough..

[lone*X]

fmctm1sw, are you referring to the addition of the 4 locking screws/nuts that locked the rocker shafts to keep them from rotating and wearing the aluminum shaft holes to ovals?  That change came about sometime during the 76 model year and applied to both the K and the F.  Well documented here.  The 4 nuts visible on the later valve covers is the sign of the upgraded part, like below.

[TwoTired]

The engines are identical, apart from some rolling changes, to the cylinder cover and minor clutch pack differences.    Internal drive ratios are identical.  All used 17T front and 37T rear sprockets.

The carb bodies are the same, but vary with internal jetting, according to the exhaust system used, and some minor attempts at making the engine more emissions friendly.

The 77 and 78 CB550K had yet another exhaust type and PD style carbs that were the most emissions friendly.

The US model Cb500s ARE different inside, though some parts interchange.  The carb style was the same as early CB550s, again with internal jetting changes to account for displacement differences.  Trans/clutch were different with an internal final drive ratio different, too.  Sprockets were 17T front and 34T rear.
The 500 to 550 evolution was far more than just a displacement increase fixing many issues that the Cb500 was saddled with.

[Hot500]

Thanks for the replies guys. That tells me everything I needed to know. 

[Deltarider]

All used 17T front and 37T rear sprockets.

With exception of the CB550K3 [ED] that had 34t rear. Overhere Honda wanted to market that model as a touring bike and the F2 as the sportier version.