Topic: 550-650 Cam Swap Mod

[88BuckMeister]

Question to all you brilliant motorheads...

I haven't gotten my project thread up and running yet, but in my 74 CB550 build, along with 61mm bore and Dynoman 61cc high compression piston set, I found on your forum many saying put a SOHC CB650 camshaft in the bike due to its higher lift and longer duration. But while you can see that every aftermarket racing cam says "performance springs required", nobody mentions this with the 650 cams. Not required? I don't think the OAL of any lobe exceeds 2.0...but these lobes seem huge compared to the stock 550 cam.

I'm also attaching pictures of the material I had to take off of the head for the lobes to clear (was told this may have to be done depending on the casting). I have to post the pics in more than one post due to size limitations. If you all could take a look at the machining job, the lobe clearance that resulted from the material removal, and the condition of both the cam bearing surfaces on both the cam and the head and let me know if you see any issues, I'd greatly appreciate it. I'm new to this and am still flabbergasted there's not supposed to be any insertsble cam bearings in this head, but again, I'm new to all this. Best wishes

Buck

[88BuckMeister]

More pics

[calj737]

If you had to remove that much from the valve pocket, then you will Oakley have to also remove just a bit from the underside of the rocker arm.

I needed to do both of these using an aftermarket cam.

[88BuckMeister]

But how would I determine whether that's necessary? For instance, you can rotate the camshaft and view where clearances are either non-existent, or unacceptably low. But to measure lobe movement with reference to the head cover or the rocker arms would require the head cover to be installed. I guess you could use Prussian blue...but are you referring to where the lobes contact the rocker arms, or how high the rocker arms are moved upward as to contact the head cover? I did look at your picture  but wasn't 100% sure what I was looking for specifically. Like I said I'm an aircraft mechanic so this bike stuff is fairly new to me... thanks

Buck

[88BuckMeister]

If you had to remove that much from the valve pocket, then you will Oakley have to also remove just a bit from the underside of the rocker arm.
 
I needed to do both of these using an aftermarket cam.

My question still stands about how I would be able to tell whether or not I need to do this, but I see where you're talking about. Like the lobe surpassing the rocker arm contact surface and hitting the arm itself. Yeez. How on earth would I determine that in terms of whether or not it needs to be done, and furthermore, how much? 😶

[88BuckMeister]

These are my rockers

[calj737]

Valve cover upside down on a table, drop the cam in. Move the arm to a fully open and fully closed position. Rotate the cam while the arm is in these positions and check for any contact.

The material removed was VERY slight, but necessary. Dykem or Prussian Blue works.

[88BuckMeister]

That's brilliant. You're brilliant. Thank you like I said I'm pretty new to this so I'm not the smartest yet lol. But that I will do! Also, are performance springs required for this? Like I said I don't think the difference is that crazy. I've seen specs floating around the forum but I don't know how reliable they are...but if stock springs will work for what's essentially a stock cam just for a different bike, I'll take it. Plus everyone who posts or writes about this specific mod mentions nothing about performance springs being required

[Mark1976]

Valve cover upside down on a table, drop the cam in. Move the arm to a fully open and fully closed position. Rotate the cam while the arm is in these positions and check for any contact.

The material removed was VERY slight, but necessary. Dykem or Prussian Blue works.

+1 to the above.
   Different springs aren't a requirement. When I did the swap, I didn't find any interference issues, but that was my experience, yours could be different, that's why you check. Your gaining a little more lift, that's about it. It'll pull a little more lively once your above 7k. Every little bit helps. One thing at a time...

[calj737]

I have not installed a 650 cam in a 550 motor, but many others have. If you are dead certain you have one, then stock springs should be fine (provided obviously they are in good condition).

I read you’re using an MLS gasket and larger pistons. It is my strongest advice that you dry assemble the motor and check the valve/piston clearance by rotating the crank/cam by hand. In stock form, most pistons are about .050 short of the deck. The stock gasket is another +/- 0.050. Depending upon your piston-deck height and gasket thickness, you could run into a small conflict. Best to check before full assembly.

Machinist’s clay is the best method. Also, if you can use a micrometer to check the deck height above the piston at full TDC, this should aide you in determine safe operation. But your cam can affect the interference measurements (hence the clay).

In my HiPo 500 build, I had my pistons sitting 0.032 deep, but the cam lift (MegaCycle 125-20) caused me to clearance the piston domes (see below). It took the clay method to confirm all this.

Hope this helps-

[newday777]

Also, are performance springs required for this? Like I said I don't think the difference is that crazy. I've seen specs floating around the forum but I don't know how reliable they are...but if stock springs will work for what's essentially a stock cam just for a different bike, I'll take it. Plus everyone who posts or writes about this specific mod mentions nothing about performance springs being required

Necessary? Not really.
I couldn't find the post or articles in my search
But....I think that I've read that even stock cams get gains in using performance springs, especially in high rpms(the 500/550/650 love being in high rpms), less oscillation bounce harmonics? I might be wrong?

Here's a video on valve spring bounce ie slinky effect

Here's a good read on valve springs and lift

http://forums.sohc4.net/index.php/topic,188783.0.html

[88BuckMeister]

I have not installed a 650 cam in a 550 motor, but many others have. If you are dead certain you have one, then stock springs should be fine (provided obviously they are in good condition).

I read you’re using an MLS gasket and larger pistons. It is my strongest advice that you dry assemble the motor and check the valve/piston clearance by rotating the crank/cam by hand. In stock form, most pistons are about .050 short of the deck. The stock gasket is another +/- 0.050. Depending upon your piston-deck height and gasket thickness, you could run into a small conflict. Best to check before full assembly.

Machinist’s clay is the best method. Also, if you can use a micrometer to check the deck height above the piston at full TDC, this should aide you in determine safe operation. But your cam can affect the interference measurements (hence the clay).

In my HiPo 500 build, I had my pistons sitting 0.032 deep, but the cam lift (MegaCycle 125-20) caused me to clearance the piston domes (see below). It took the clay method to confirm all this.

Hope this helps-

Once I so the clay trick, what should the valve/piston clearance be?

[88BuckMeister]

UGH ITS NOT A MLS HEAD GASKET ITS .043 CFM MY BAD!

[calj737]

There’s a lot of options for clearance in people’s opinion. There is no “magic number” either. That 0.032 for a squish is often targeted, but that would likely require some decking and milling of the block, head and dowel pins to get that. And there’s a base gasket to factor in for clearance (just as a reminder).

As long as you don’t have interference, let it be whatever stock is. Unless you’re willing to embark on several hundreds of dollars of machining to chase some performance? Then you’d want to be shipping the head to Mike Rieck for porting and polishing, new springs, retainers, and send along your intake ports for the same plus matching. (It’s a deep rabbit hole to extract every ounce of performance from these little beasts…)

[Mark1976]

   Install the (a) stock 550 cam, get a measurement and that's your baseline (regardless of stated historical values), it is what it is. Your not using an MLS head gasket so you should be getting a pretty generous clearances on the intake and the exhaust. The pistons are your unknown, but I'm willing to bet that if you contact the piston supplier they will be able to give you a little bit of direction here. What have you got to lose. Without good verifiable numbers, yer just guessing...

[88BuckMeister]

I guess my question is if I do a mock head assembly and check the valve clearances using the clay trick, ehata acceptable? I found one build thread here like this where somebody said they had .1 across the board and wondering if that's okay...I can't seem to find the stock clearance in the manual

Haha then again that guy blew up his engine 🤔

[Mark1976]

   .100 is a good number, as a rule. If you look up basic valve/piston clearance's, it's .1 for exhausts. 080 for intakes, exhausts run hotter thus the extra .020 for clearance. Install either cam and see what you have. Personally, install a stock cam, see what you get, go from there. At this point, just to see where you are with the pistons you have. Everything to gain, nothing to lose...

[88BuckMeister]

   .100 is a good number, as a rule. If you look up basic valve/piston clearance's, it's .1 for exhausts. 080 for intakes, exhausts run hotter thus the extra .020 for clearance. Install either cam and see what you have. Personally, install a stock cam, see what you get, go from there. At this point, just to see where you are with the pistons you have. Everything to gain, nothing to lose...

Thank you so very much. I think I'll do that and see what I've got.