Topic: looking for info on 1979 cb650 to 1974 cb550 cam and head swap

[randy5307]

i have a 1974cb550 and i was told i could use a 1979 650 cam as well as the head to add cheap power. will this work and if so will there be any modifications needed? any help would be appreciated thank you..

[mlinder]

You will lose a lot of compression unless you also use the 650 pistons.

Ask paulages about it, though, see what he says.

[randy5307]

thank u for the info..

[mlinder]

650 bore and stroke is 59.8 mm x 55.8 mm.
550 is 58.5 x 50.6 mm

You'd have to bore the 550 jugs to accept the 650 pistons.

Notice the 650 has a much longer stroke than the 550. You'd have to check for piston height.

[randy5307]

what if i just use the 650 cam?

[mlinder]

Then you just use the cam, and the 650 tach. You have to switch the 550 cam gear over to the 650 cam. It's a bolt-on.

[randy5307]

sounds easy enough.. is it worth it for the power i will gain?

[mlinder]

Ryan (R550) did it recently, and yeah, I absolutely noticed a difference in performance.

Granted, he also did a hone and re-ring, so some power was regained there, too, but yeah, I think the cam made a nice difference.

[randy5307]

yes i am planning on also upgrading to a 605 kit maybe i will improve power there also.. thank u so much for ur info