Confusion over 550 engine and frame numbers

[bbrian66]

Hi All - I have acquired two project 550s - the first of which I'm now restoring. I'm struggling to understand the frame and engine numbers to know exactly what I have. I'm sorry to bring this up as I see this is a frequently recurring question. I've looked at the the various forum answers and the charts in the manuals and I'm still not 100% clear.

The frame numbers seem to be clear: CB550F-1023938 - pretty sure this is an F1; and CB550F-2110300 - pretty sure this is an F2.

The tricky bit is the engine numbers. The engine in the F1 is 1134990 which I think is an F2 engine number.

The engine in the F2 is 2028203 which I think may be a K3 number.

I acquired the bikes separately so the engines have not been mixed up before. I'd be grateful for any thoughts on these.

Thanks!

[deltarider]

Hello Brian. The answer is in the various CB500 and CB550 parts lists. You need to go here: https://www.honda4fun.com/materiale/documentazione-tecnica Scroll down.
In the first 4 pages of each parts list, you'll find the frame- and enginenumbers listed with extra info bout the carb nummers and to which markets that specific model was exported to. This is the best way to identify your model. You only need to do it once.

[Johnny4428]

Hi Brian, seems like you may have a mixture of frames and engines there. Just looking at one of your frame numbers and comparing with my bike I am working on at the moment and mine is - 1023928 which is just 10 numbers away from yours could have come out the factory same day! Identified as being from a 1975 F1. My engine number is 2019211 which is from a 1977K3. Good luck with your bikes.

[bbrian66]

Hello Brian. The answer is in the various CB500 and CB550 parts lists. You need to go here: https://www.honda4fun.com/materiale/documentazione-tecnica Scroll down.
In the first 4 pages of each parts list, you'll find the frame- and enginenumbers listed with extra info bout the carb nummers and to which markets that specific model was exported to. This is the best way to identify your model. You only need to do it once.

Many thanks Deltrarider - this is much clearer than anything I've seen previously.

From this it seems I have a late F1 engine that was correctly in the F1 frame, and that the engine that came with the F2 frame is indeed a K3.

[bbrian66]

Hi Brian, seems like you may have a mixture of frames and engines there. Just looking at one of your frame numbers and comparing with my bike I am working on at the moment and mine is - 1023928 which is just 10 numbers away from yours could have come out the factory same day! Identified as being from a 1975 F1. My engine number is 2019211 which is from a 1977K3. Good luck with your bikes.

Hi Jonny - 10 frame numbers apart! What are the chances of that?

[bbrian66]

I now have a dilemma. I am rebuilding the F2 back to completely original specification, or as close as I can get it. If the engine is a K3 engine then that's not going to work. I see that any number of empty crankcases are available on the web - will the K3 internals fit into an F2 crankcase? Or do I need to source a complete F2 engine?

Thanks.

[Bryanj]

All 550 engines are the same except the lasy ones have pinned rocker shafts but you cant tell that from the outside, to rebuild in new cases you will probably need new ,expensive and difficult to get, main bearing shells.
Personally i see no problem with a different engine number, you are rebuilding with a mix of parts anyway and not even Honda can tell you what engine number was in what frame

[bbrian66]

All 550 engines are the same except the lasy ones have pinned rocker shafts but you cant tell that from the outside, to rebuild in new cases you will probably need new ,expensive and difficult to get, main bearing shells.
Personally i see no problem with a different engine number, you are rebuilding with a mix of parts anyway and not even Honda can tell you what engine number was in what frame

Thank you for this response - its a very good point you make. It would certainly simplify things.