Topic: CB650 camshaft interference in CB550 head

[Kevin400F]

When swapping a higher-lift cam into a CB550, be sure to check for interference with the head casting.  I recently acquired an OEM 650 cam to wake up a CB550 track bike engine I'm building, and encountered the interference shown in the photo below.  Evidently, the casting core shifted a little on this particular head; another CB550 head I checked has adequate clearance.

Interestingly, the original CB550 cam had about 0.005" clearance at this point, so the issue went unnoticed during factory assembly.

[Jay B]

Any issues with the tach drive? I've read on here the tach will be off with a 650 cam.

[Kevin400F]

The tach drive gear on the 550 cam has 3 teeth, while the 650 cam has 5 teeth.

The driven gears have different part numbers (12431-323-000 for the 550 versus 12431-426-003 for the 650), but the driven gear holder is the same.   The 550 driven gear has 10 teeth, so there's no way the 650 can be exactly the same reduction ratio.
(3.33:1)

Does anyone here know the tooth count of the 650 driven gear?  It it is 16 tooth (3.2:1 ratio) or 17 tooth (3.4:1 ratio) it is close enough for me.  Otherwise, it looks like I'll need to come up with a 650 tach.

Thanks

[cb650]

I can count the teeth when it warms up some and I find a drive.   Do have a tack if need be.





                           Terry

[turboguzzi]

Kevin
On top of the cam to casting clearance issue, make sure you also drop the cam on the rocker cover and check that the lobes arent rubbing against the underside ot the rockers.

Happened to me with a megacycle and caused quite a lot of headaches when trying to degree the cam until I found out. If the cam does toruch the rockers simply grind away some material from them.

Cheers
TG 

[paulages]

kevin-- i have both cams, heads and tachs at my shop. i'll do a little poking around today and see what i can come up with.

[Aaron Richard]

I know this is an old topic but, I think I might be running into this problem. exactly where should I be grinding off material? pics would be helpful if anyone has some.
Thanks

Kevin
On top of the cam to casting clearance issue, make sure you also drop the cam on the rocker cover and check that the lobes arent rubbing against the underside ot the rockers.

Happened to me with a megacycle and caused quite a lot of headaches when trying to degree the cam until I found out. If the cam does toruch the rockers simply grind away some material from them.

Cheers
TG 

[paulages]

I know this is an old topic but, I think I might be running into this problem. exactly where should I be grinding off material? pics would be helpful if anyone has some.
Thanks

Kevin
On top of the cam to casting clearance issue, make sure you also drop the cam on the rocker cover and check that the lobes arent rubbing against the underside ot the rockers.

Happened to me with a megacycle and caused quite a lot of headaches when trying to degree the cam until I found out. If the cam does toruch the rockers simply grind away some material from them.

Cheers
TG 

just lay it in the head and cam cover and spin the cam, marking where it contacts. grind away a little at a time until it no longer contacts.

[turboguzzi]

I know this is an old topic but, I think I might be running into this problem. exactly where should I be grinding off material? pics would be helpful if anyone has some.
Thanks

Kevin
On top of the cam to casting clearance issue, make sure you also drop the cam on the rocker cover and check that the lobes arent rubbing against the underside ot the rockers.

Happened to me with a megacycle and caused quite a lot of headaches when trying to degree the cam until I found out. If the cam does toruch the rockers simply grind away some material from them.

Cheers
TG 

my motor is apart now, so will try to take a shot. if the problems exists, you'll see it right away when you drop the cam in the top cover and turn it.