Anybody recognize this cam?

jay760

XS650 Guru
Messages
1,131
Reaction score
520
Points
113
Location
Somerset
as the title says, does anybody recognize this cam, I thought it was a megacycle 250 40 until I bought one, it's nothing like it the lobes look to be much larger, only identification is an 8 78 which I assume is the date it was made and a c on the outer lobe.
 

Attachments

  • 006.jpg
    006.jpg
    95.7 KB · Views: 310
  • 007.jpg
    007.jpg
    83.6 KB · Views: 264
Just for comparison a picture of the lobe on the 250 40 cam I received this one has 250 40 stamped on the cam.
 

Attachments

  • 001.jpg
    001.jpg
    86.5 KB · Views: 310
  • 003.jpg
    003.jpg
    83.6 KB · Views: 278
Yes, that's an interesting lobe profile, weld-up/regrind. Long duration, looks to have wider lobe centers. Why the woodruff key notch?

In the '70s, you could get cams built-up/reground to custom profiles. Mine was done by a local hobbyist type, using a profile-follower cam grinder, and I selected the profiles. But, mine's unmarked. Yours, being marked, might signify a more prominent grinding business, like Crane, or something else identifiable as 'C'.

I'd do a test install, minus pistons, use just inner springs, degree wheel and dialgauge to get valve timing specs. Might find something interesting there. Could require special setups to run it, or it could be just a failed experiment. Since you're UK, could check suppliers to Tony Hall...
 
I was running it in the bike last year, bought it from the US, it was on ebay they had the hole engine on there, I bought the complete top end, didn't fancy the postage for the whole engine, head was ported with 750 barrels and pistons, when you looked at the pictures of the bottom end the studs were notched so you could remove the top end, the other interesting thing about the engine was it had 256 rods on a 447 crank.

It ran well, best time of 12.2, highest speed recorded was 115 in 4th, that was without being set up properly, just put in to where the marks were before, now I'm rebuilding the engine would have liked to get it set up properly.
 
Last edited:
The only thing I can find with reference to C is either as twomany says Crane, or Andrews made a C grind camshaft but can't find either with xs650's
 
256 rods on a 447 crank, might have been a 306 or 366 crank, since they have the starter gearteeth, unless the sprocket has the 447 toothcount.

Have you thought about the degreewheel/dialgauge reverse-engineer thing to get its timing specs?
 
Just measured this cam inlet is approx .435 exhaust .395 this is using the rocker ratio given on xs650.org.au
 
Just managed to measure the cam


Inlet 22 btdc 64 abdc 0.430 lift
Exhaust 60 Bbdc 45 atdc 0.400 lift

Any clues on this cam?
 
Last edited:
Strange timings on that cam, offset lobe centers.
Dunno what lift you're measuring at, 0.000", 0.012", 0.040", or 0.050"?
Intake duration 266°, lobe center at 111° atdc.
Exhaust duration 285°, lobe center at 98° btdc.
Intake opening sure looks late.
Would need to shorten the intake guide.

Suppose you were to advance its timing by 11°, even up the overlap.
That would give:

Inlet 33° btdc, 53° abdc, 0.430" lift.
Exhaust 71° bbdc, 34° atdc, 0.400" lift.

Suppose you were to advance its timing by 6°, equalize the lobe centers to about 105°.
That would give:

Inlet 28° btdc, 58° abdc, 0.430" lift.
Exhaust 66° bbdc, 39° atdc, 0.400" lift.

Strange grind, indeed.

You could try to get a copy of Signal's "cam lobe centers" spreadsheet.
http://www.xs650.com/threads/attaching-an-excel-spread-sheet.35200/

Grind thru this.
http://www.xs650.com/threads/what-do-i-need-to-degree-a-cam.34965/

Play around with various advance/retard timings until you get something sensical...
 
Measured at .040 lift with 0 clearance for the opening
Lift I measured from 0
Thought I'd measure it the same as with the megacycle cam, when I hot it there were no valve seals as when they went on it hit them so changed the guides, the cam does work quite well.
 
That long duration exhaust is somewhat backwards from traditional cam timings. May have been trying to solve the exhausting problems on the 750cc engine.

For reference, the 256 cam and 447 cam.
Note the 256 longer duration intake.
Note the 447 symmetry...

70-73-CamTiming.jpg


74-83-CamTiming.jpg
 
Ok, can also look at it from TDC.

Inlet 72 Bbdc = 108° ATDC
Ex 84 abdc = 96° BTDC

The thing with cam timing is that it's a part of the total package, the goal being to maximize induction and scavenge super-charging. Cam profiles, port design, valve design, inlet and exhaust geometries all have to work together to get this. There's some general principles to apply, and established setups for a particular engine, but without exotic test equipment and experimentation, it's like throwing darts in a darkened room...
 
Thought I’d use this old thread to post this up to see if anyone can tell me if this is a legit shell cam. The the lift numbers aren’t adding up to me. Height is 1.52” and base is 1.20” for a lift of .320”.
61B84140-2C86-4151-8629-19DCE4020384.jpeg
3B4D51BB-6D92-4F97-B107-7DD37BE02CFB.jpeg
22A93E3F-BEDC-4514-A45F-B9320D5EA986.jpeg
467A306D-B495-497C-B058-CB0D4B9F24BD.jpeg
 
in this image you need to measure from top of cam base to top of lobe and multiply by rocker ratio of 1.21 or 1.24 for cam lift
shell cam.jpeg
 
37B82F0F-0FAB-44C5-B6E6-B23261B5E56F.jpeg
Thanks @Jack but It wasn’t me measuring it and I believe that is the second lobe in not the first. This picture should be more accurate. The seller was saying the PO said it was a shell #2. I can’t seem to find any specs on shell #2 but what I am calculating it might be a shell #1. The height of the lobe is 1.52” the base is 1.20” subtract the base from the lobe height and you get 0.032”. Multiple 0.032” x 1.21 the lift ratio and you get .03872 or approximately .039” of valve lift. The valve lift of the shell is 0.403” so I would say that with a more accurate measurement it would be closer to the shell #1 cam.
 
Back
Top