Topic: Engine is off center to frame

[kixbox]

Hello again,

I have a situation that seems serious to me.  However, given my limited experience, I thought I’d reach out as I cannot find any info on this. 

Bike: CB750K 1978

Should the engine be centered to the frame?

Reason I ask: I am in the process of stripped the bike down for a major ‘check-everything & clean up’.  Over the weekend, I started working on cleaning the engine from the outside checking off the 3k miles maintenance schedule (and some) as I go along.  For some reason, I decided to take the Head Breather Cover for a bit of clean and polish, but I could not remover one of the screws (see picture).  Screw was blocked by the frame.  I did not want to use force, so put it back in its place. 



But it stayed with me the whole day – and it got me thinking, then after dinner took some measurements.  It turns out that the engine placement is about 0.25-0.35” off center to the left.  It seems a very small, but it is visible when I stand in the back or the front of the bike – and concerns me. 

I could be wrong, but this off center does not seem by design.  What do you think? I took some pictures (or tried to find best representation). 

If my engine is in fact not placed correctly relative to the frame, what can I do about it?

ANY advice would go a long way? I am a bit down about this as it’s a beautiful machine, in great mechanical shape and put a lot of sweat into it. 

Anxiously awaiting your input and thoughts

[kixbox]

2nd picture.

[HondaMan]

It is off-center by design! These all are (as are many other bikes). The 750K bikes are statically center-balanced by offsetting the engine to its left to compensate for the oil tank hanging out on the right side. The 750F bikes suffer a too-heavy-right side weight issue (always have) because of the heavy 4-1 muffler Honda used on that side, which interestingly has been noticed by quite a few owners who wobbled and crashed their bikes in slow-speed maneuvers.  As you learn more about the bike, you will also discover that your model (post-1975 K) also has a rear-wheel offset to the left, and the front wheel is also left of the earlier bikes, but in the center of, the front forks. 

[kixbox]

Wow...mind...blown...

I could not have figured that out on my own.  There is nothing to stress about after all.

Thanks Hondaman for the response.  Do you know the thinking behind this? I know the L-to-R weight distribution is different but did not think dimensions would be.  I learned a a key design aspect today. 

Follow up design question: as I inspected the bike’s frame yesterday to prep for paint touch up, noticed a dent (seems major but maybe not).  Do you have thoughts on the structural integrity of the frame with this dent? What could have caused it? I connected this to the offset but now I cannot be related.  Should I just live with it? As an FYI, the bike is fully stock and no cuts on frame.





PS: purchased your book a few years ago and it is the only reason I have confidence to tackle the garage build - except the engine tear down part . It’s in my work bag goes with me everywhere.

[kixbox]

Okay - good to know on the structural integrity.  Thanks for that. 

It was powder coated by PO and he told me that when I picked up the bike (4 years ago).   Him and his brother took on a restoration project and got it to I’d say 90% which is awesome. So I was aware of that, I did some spray paint touch up yesterday. 

Weird what could have caused it - I wonder if it was dropped or in an accident. 


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[kixbox]

Looks like a contact dent from the frame falling into something, perhaps during restoration. Or something dropping onto it.

Thank you.


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[DaveBarbier]

Any info on the 550 if that motor is centered in the frame? It may overhang on one side more than the other but is the center line of the frame in line with the center line of the engine? The centerline of the engine I’m calling the oil filter bolt and the center casting fins of the head and cylinders.

[kixbox]

Any info on the 550 if that motor is centered in the frame? It may overhang on one side more than the other but is the center line of the frame in line with the center line of the engine? The centerline of the engine I’m calling the oil filter bolt and the center casting fins of the head and cylinders.

Good question, I’ll leave it to the experts to address. 

I also assumed the center line of the engine is the oil filter bolt on my CB750K.


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[HondaMan]

Any info on the 550 if that motor is centered in the frame? It may overhang on one side more than the other but is the center line of the frame in line with the center line of the engine? The centerline of the engine I’m calling the oil filter bolt and the center casting fins of the head and cylinders.

Good question, I’ll leave it to the experts to address. 

I also assumed the center line of the engine is the oil filter bolt on my CB750K.


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Almost: the oil filter is not centered on the engine. Honda was very concerned about these sorts of cosmetics (marketing, ya know...), so they often did things like offsetting wheels, engines, handlebars, etc., so it "looked" right. Up until the 750F came out, they kept the 750 well-balanced and the CB500 exceptionally so. The 550 was good in the K model, but the F versions got heavy on the right side. In roadracing, this stuff mattered!