Topic: 650 cam in a 550 - ride report

[Ryan 550k]

Hee, hee......I'm 8

Thanks Jimmy.  Sometimes I just need a break down......I'm learning as I go.  I barely knew the first thing about engines before learning about a bike, and that was about a year ago.  Gotta start somewhere!  I took a look inside the 82 cylinder head and found the tach drive, so I've got that.  Thanks again for your time.  I'm starting a thread concerning the best way to replace valve gaskets in my 550.  I imagine you may have a thing or two to say, so look out for it if ya like.

[tinyrobot]

I am working on this swap right now as well.  I need to file the oil wall in the head a bit for clearance with the 650 cam lobes.  I am also getting a slight resistance with a skip, so maybe a lobe is hitting the bottom as well.  I haven't but the new cam in some v block to check that it is straight and dandy yet though.

[mlinder]

We are working on the same swap with R550's '78 cb550.
Something of interest: The early GS550 carbs seem to be an almost even swap as far as intake spacing is concerned. THey are very nice carbs, fully adjustable (as in, can buy all the jets and needles and easily swap them),.
We will let you guys know how it goes.

[FunJimmy]

Something of interest: The early GS550 carbs seem to be an almost even swap as far as intake spacing is concerned. THey are very nice carbs, fully adjustable (as in, can buy all the jets and needles and easily swap them),.

Are these Mikuni carbs?
What throat size are they?

Thanks
FJ

[mlinder]

Same as these:

http://cgi.ebay.com/ebaymotors/78-GS-550-Carbs-GS550-GW_W0QQcmdZViewItemQQ_trkparmsZ72Q3a1205Q7c66Q3a2Q7c65Q3a12Q7c39Q3a1Q7c240Q3a1318Q7c301Q3a0Q7c293Q3a1Q7c294Q3a50QQ_trksidZp3286Q2ec0Q2em14QQhashZitem400043741190QQitemZ400043741190QQptZMotorcyclesQ5fPartsQ5fAccessories


Dunno size, will check this weekend.

[InTheStreet]

If either the donor cam or your bike has over 10,000 miles you should check the rocker arms too. They sort of wear as a set.,.. not super critical and most people won't care, but I hate to mix worn parts with new. In my case both had low miles but I used the 650 rockers too because I had them.

Are the 650 and 550 rocker arms directly interchangeable, or is there some level of modification needed to make the change? Are they the same ratio and what-not? (Being vague because I don't really know what questions I really need to ask.)
I guess I am also curious if you ended up going with the 650 springs when you did the swap. Is that possible with the different sized valves?

[FunJimmy]

Are the 650 and 550 rocker arms directly interchangeable, or is there some level of modification needed to make the change? Are they the same ratio and what-not? (Being vague because I don't really know what questions I really need to ask.)
I guess I am also curious if you ended up going with the 650 springs when you did the swap. Is that possible with the different sized valves?

When I installed a 650 cam in my 550, the head was ported by MRieck and had higher lift springs installed.
The rockers where stock 550 rockers.
I did have lobe clearance issues that needed some massaging, but it's my understanding that not all heads have this problem.

[kayaker43]

If either the donor cam or your bike has over 10,000 miles you should check the rocker arms too. They sort of wear as a set.,.. not super critical and most people won't care, but I hate to mix worn parts with new. In my case both had low miles but I used the 650 rockers too because I had them.

Are the 650 and 550 rocker arms directly interchangeable, or is there some level of modification needed to make the change? Are they the same ratio and what-not? (Being vague because I don't really know what questions I really need to ask.)
I guess I am also curious if you ended up going with the 650 springs when you did the swap. Is that possible with the different sized valves?

If you are removing a used cam from a 650 , its always best to also use the 650 rocker arms with the cam as a matched set. The 500/550/650 arms are all the same but its just good practice to keep used parts together because they have matching wear patterns. This also means keeping each rocker arm with its matching cam lobe.

Mine dropped in with ample clearance on all lobes to the head casting but a few people have interference that's easily corrected. I used the old 550 valve springs with no issues.

[Bootlegger56]

I had to notch my head just like Jimmy's in the pic.  I did not swap the valve springs or rockers however as my donor and recipient were both low mileage bikes.  I was impressed with the gains over stock but could not attribute it all to the cam.  I did a carb overhaul, HM ignition, dyna coils, a set of crossover short headers and a drive ratio change.  Considering the performance and condition of the bike before the modifications, I am sure the other factors added value as well......This is my first 550 and after a couple of weeks of riding it; I understand why people like them so much.  I wish I could have swung a HM or one of the other member head reworks but I forced myself to stay within budget.

[InTheStreet]

Wow, thank you guys for your responses.  It is a huge help to have the users of this site as a reference. 
Kayaker responded to the PM I sent and said the same thing about the rockers.  He said he used the 550 valve springs (more just including that for others' future searches).
Your answers have made me think of another question I have had in my head when I was supposed to be doing work (at my job):

What should I do about cam bearings? 

Keep the 550's, put in the 650's, buy new, mic' each one and order specific bearings, something else I haven't thought of?

[FunJimmy]

What should I do about cam bearings? 

Keep the 550's, put in the 650's, buy new, mic' each one and order specific bearings, something else I haven't thought of?

Nothing. Because the cam runs in aluminum bearings in the head.
Not replaceable.

[Rgconner]

I know someone in Fresno that can probably cut and reweld new bearing surfaces in the head if there is no other option.

Does it for ruined rotary valves on Vespa's, where the bearing surface is much larger and harder to weld without warping.