Cam lift specs for 750SF2?

TeddyG said:
Does anyone know this?- according to the Green Book it should be Profile 7/1 but I don't see it stamped on the cam, thank you
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Every SF2 cam i've ever seern has 7/1 stamped on it. My SF1 cam (supposedly 5/1) had no stamping and I have another cam that looks like a 5/1 cam (but very similar to an SFC 5/C profile) that also has no stamping. You will definitely need to know what cam is in it if you plan to check cam timing. This is done at max lift, which is halfway between the opening and closing figures. Your chances of getting an accurate picture of cam timing by observing when valves actually open and close are as close to nil as to be meaningless. The slightest change to valve clearance (ie tappet to valve clearance) and your figures will change.

Is there a reason you want to know? Unless you plan to slot your cam wheel and do some tricky adjustment work I wouldn't advise going there.
 
If you're looking for cam lobe centers they are not neccessarily at the point of max lift.
The correct way to find lobe centers is to note the opening point at usually .040in lift
and the closing again at .040in before hitting the seat.
Then simple arithmetic will give you the geometric lobe center.

The single OHC motors should be measured at running clearances. As PB2 points out
Any change here changes everything.
 
GregT said:
If you're looking for cam lobe centers they are not neccessarily at the point of max lift.
The correct way to find lobe centers is to note the opening point at usually .040in lift
and the closing again at .040in before hitting the seat.
Then simple arithmetic will give you the geometric lobe center.

The single OHC motors should be measured at running clearances. As PB2 points out
Any change here changes everything.
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Good info, Greg. My bad for assuming max lift = centre open/close. I got that advice from Brook Henry (V-2) who said the vast majority of cams followed that rule. Simple process you describe, as per max lift or piston stop methodology.
 
piranha-bro2 said:
Good info, Greg. My bad for assuming max lift = centre open/close. I got that advice from Brook Henry (V-2) who said the vast majority of cams followed that rule. Simple process you describe, as per max lift or piston stop methodology.
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Depends too on cam follower geometry. Most SOHC motors with leading and trailing followers won't have max lift at the geometric lobecenter.
Bucket and shim most often will.
 
Well, a friend took measurements by eye of the lobe bottom and then top edges, subtracted that amount, and claims the lobes are worn well beyond the limits -even when compared to the GT lift specs.
Which is odd, since the lobes are smooth across the width of the lobe- wouldn't the followers leave sort of a divet since they don't appear to be as wide and don't contact the extreme edges of the lobe, leaving a slightly raised edge?
There is a "7" stamped on the cam end.

The followers all have wear on them but I can't judge what's acceptable, and the attached has a groove from riding against a lobe.

The lobes all have a "flattened" wear pattern on the top portion of each lobe.
Before I spend $600 on reconditioned cams and followers, I want to be sure it's needed, thanks guys
 

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Hard to glean from the pics, but is that dark area on the rocker the only portion that has been making contact with the cam lobe?? If so, it's definitely not right and indicates a lack of parallel between cam and rocker. The cam lobe contact area looks fine to me eyes.

Not sure if rocker ratio is one-to-one but the easiest way to measure lift other than actual valve movement using a dial gauge is to measure across the base circle (the narrowest portion) and compare with the measurement across the widest portion - diff between the two = lift.
 
my SF1 has sufferred that cam flattening syndrome, probably because it spent a lot of time ticking over in heavy traffic when it was under 2 years old, I need to renew the cam and dont realy want the SF1 profile as was told that a) it did this and b) its not a very good design anyway,

..........so all you 750 nuts out there, tell me what I should put into my stock SF1 (except for ported head and SFC 2 into 1) to gain good running and reliable power??
CLEM
 
That definitly is no wear to worry about, worn/knackered cams look very, very different. Rocker pad actually looks terrific. Before faffing around checking cam lifts and timing, which will most probably be close to spot-on, I'd be looking for correct phasing left to right, a common cause for horrendous vibration. I've found cam pairs out as much as 13°, that's 26° at the crank!

Clem, see if you can unearth a 7/1, imho the best all-round cam for road work, at the sedate speeds us old buggers should be adhering to. Works excellently in small-valve heads as well, I've upgraded a couple of GTs with them!

piet
 
I discovered that the previous lift measurements were done wrong and I'm having them re-measured- if they're in spec I'll leave them be
 
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Ted, which part of that rocker face in the pic you posted is the actual contact patch? Your photos could be a little more informative :) You mention that "the attached has a groove from riding against a lobe" ... I'm not sure what you mean by that.

Never had an issue with my SF1 cam (which was unstamped). Had plenty of top and and no noticeable hollows in the low or mid. It was an early SF1 so I did actually wonder if it was an unstamped 4S. Visual comparison with a 5/C and a 7/1 made it look a lot like the SFC cam.
 
Sorry- it's hard to get a good pic showing the wear, but the wear is over the entire curved face that contacts the cam, and the shiny chromium plate is worn away and shows a duller surface. My friend just re-measured the lobe lift w/ a dial indicator and finds that the wear is @ 25% from spec. I'll order refurbished cams from either Wolfgang or DAM Classic Racing, and either have the followers resurfaced or replaced. This bike has a questionable past so there's no way of knowing if the cams had been reground before as a quickie fix before selling it to me. This would explain the poor performance of the motor that I've been unable to remedy after checking everything else, and posting endless questions on this Forum.
 
Don't be too hasty, Ted. If that pic is what your rocker surfaces look like then no way would I be replacing them. Also, unless you measure actual lift (dial gauge on valve tip from closed to fully open) I don't think you can get an accurate measurement from base circle dia minus max width of lobe.

I just measured the unmarked cam in my spares which I THINK is a 5/1 from an SF1 (and which may or may not have been ground) and the base circle measures between 25.6-26mm. The diff b/w base circle and max dia is 8.1mm Inlet and 7.6mm Exhaust. Unless there's something very wrong with these cams (which I doubt), it points to a rocker ratio of greater than 1:1 because lift on either SF1 or SF2 cams as shown in the Laverdamania table is well over 10mm Inlet and 9.7mm exhaust.

What I'm saying is that you can't assume your cams have been ground to buggery and are unserviceable. Before going all out and spending big $$$ on stuff, do the cheap work such as Piet's suggestion of checking L-R cam sync and cam timing in general. Personally, i'd also be splitting the cases and having a closer look at the crank.

Out of interest, have you checked for good fuel flow from both taps? It was mentioned by someone elsewhere that they had a similar power dearth with a Beemer and it was due to blocked tank tap filters. Not sure if anyone had suggested this previously over the many many pages of trying to trace your fault.
 
If your cams ARE worn, I'd be making bloody sure the oil flow to the head is unimpeded when you put the motor back together. Simple way to do this has been mentioned several times on this forum.
 
TeddyG said:
My friend just re-measured the lobe lift w/ a dial indicator and finds that the wear is @ 25% from spec.
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Teddy, I have the head etc from my SF2 apart on the bench and took these measurements.
I believe that the quoted lift numbers are at the valve not on the cam so we must allow for the rocker arm ratio which measures roughly 45:35 or 1.29 so that based on my measurements of the lightly worn 7/1 cams as below I get lift at the valves of 9.9mm and 10.2 mm.
Hope this helps.

7/1 from left (tach drive) to rightbase circle mmlobe mmvalve lift
1​
26.1​
33.8​
9.9​
2​
26.2​
34.2​
10.3​
3​
25.7​
33.4​
9.9​
4​
25.7​
33.6​
10.2​
rocker ratio
35​
45​
1.29​
 
1.3 : 1 is a common rocker ratio. Plenty of aftermarket profiles designed around that ratio.

! : 1 as a rocker ratio I've only ever seen in Benellis. The singles have it on both inlet and exhaust.
The twins use 1.3 : 1 on the inlets and 1 : 1 on the exhausts.
Makes putting better cams in them rather difficult.
 
Your experience to the fore again, Greg. I've never had reason to even think about rocker ratio; I check and adjust cam timing, but have never had reason to check such things as rocker ratio. Phil Todd has told me he uses a 6/C cam (the SFC Elettronica option) with rockers that have been re-radiused to tame the open/close ramping a little.
 
Thank you Arancia- this might explain why I'm seeing such low numbers, and it's interesting you're showing similar measurements to mine for the entire lobe.

Since the cam lobes have even wear across them without any divets from the followers, I'm skeptical of this much wear at 15K miles. When I mic the very base lobe I see 26.15 and I see 33.55 for the entire lobe height, and subtracting the 2 equals 7.40. Multiplying your 1.29 equals 9.54. My friend used a dial indicator to locate the true center and measured it again, but still arrived at a low number. So either your method is correct, or my cams are under spec. Attached is info from Megacycle. I'm having a machinist/engine builder measure it again later today.
 

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