Cam timing on asymetrical cam lobes - one for the real experts

[Sci85]

Ok so I'm working on putting this '90 ZX-10 engine back together and read on the dynojet set that they recommend 102/105 cam timing for this motor. The factory service manual does not list the OEM centerline numbers only opening and closing timing. And, they do not list at what lift those readings are made from so I have no idea how to check what I have for a baseline. Anyway, I've used the centerline method on the last GS I did to figure out the timing at .050" lift but this cam is really different. The lobes are not symmetrical and one side has an extremely steep ramp with the other side very gradual. This time, I measured the timing on the degree wheel at 1mm or approx .040" of lift on the open and close sides, added 180, divided by two then subtracted the lowest number. Here's what I got:

Exhaust - measured at 1mm from closed
Open @ 34 degrees BBDC
Closes @ 19 degrees ATDC

So 34+19+180/2-19 = 97.5 degrees(!?). This seems very odd to me.

Intake - measured at 1mm from closed
Open @ 8 degrees BTDC
Close @ 45 degrees ABDC

45+8+180/2-8 - 108.5 degrees. Hmm.

So my question is am I doing this correctly for this type of cam? Do those numbers sound right for this type of engine? Is 102/105 reasonable as suggested by dynojet?

I'm certainly no expert so any input is appreciated.

[Nessism]

What about finding the point of max lift and calling that the centerline?

[Sci85]

I'm not sure the .050" on either side of max lift and divide by 2 works on a cam that doesn't have symmetrical lobes. I did that method and came up with 111 degrees for intake and exhaust which seems once again very odd. I set my old 550/650 conversion to 102/106 I think using that method and it worked beautifully. But this cam is funky and I just don't know how to deal with it.

[blowerbike]

why not use the lobe center method?
16 valve GS's have kinda square lobes...the above is what i use.

[Sci85]

Ok, after a LOT of reading, I have learned that the old lobe center method (ICL) is not accurate enough for these new asymmetrical cams. There is a better method. I don't know if there's an actual name, but it's referred to the .050" lift method which is basically to say that you have to measure the lobes at opening and closing @ .050" of lift. Not that hard really but just different. That's why my numbers were all so odd looking compared to the old symmetrical cams and the intake center line method.

Here's one of the better write ups I found for reference:

http://forums.corral.net/forums/5-0-5-8-engine-tech/1372375-trying-degree-cam.html

Unfortunately, the Kawi service manual doesn't tell me $hit as far as numbers I can use since it doesn't list what lift they used for the timing numbers they state. They just give Intake and Exhaust opening and closing degree's but no mention of at what lift they took those numbers. Anyone have clue?

[blowerbike]

i set my bandit at 100/101......worked great and fast in the middle and top.
lobe center method........

[GregT]

Usually the factory figures are at 1mm lift - call it .040in.
What you don't say is what clearance you're measuring things at. I usually set assymetric cams at zero if they have screw adjusters. The ZX will have shims though so running clearance will do.
As far as what lift to measure at, enough so that you're past the ramping...I use .040 for everything, others prefer .050in. No real difference.
With assymetric cams you must do it as you have in your first attempt. Measure at a given lift, opening and closing. You seem to have done the math right and what you came up with is a normal sort of set of figures to start from. From here it's adjust via slotted sprockets till you have the LC you want.
102/105 is fine - as is 104/106 in these motors. AFAIK std is around 106/108. At least on the ones I've seen here....

[Sci85]

Thanks for the reply GregT. I don't know the prior history of this motor, but the cams appear stock to me. When I opened up the motor, the cam sprockets did not line up with the factory marks in the service manual. Like a bonehead, I didn't take any measurements prior to stripping it down. So, I put the cams back in how they were when I opened it up but the readings were bizarre. Not even sure how it was running as the exhaust sprocket was two teeth off the marks!

Anyway, so if my calculations are correct in my first post, then I can be reasonably certain that the lobe centers I calculated are accurate right? So now I just slot the cam, make the adjustment, then remeasure as before.

Oh, and I put my dial indicator on the valve spring retainer to take measurements. I've read some saying you degree the cam not the valve and to measure at the lifter (car guys). For these types of cams, should the dial be on the cam lobe or is measuring off the spring retainer ok as well?

Thanks again for the clarity. It really helps.

[GregT]

Thanks for the reply GregT. I don't know the prior history of this motor, but the cams appear stock to me. When I opened up the motor, the cam sprockets did not line up with the factory marks in the service manual. Like a bonehead, I didn't take any measurements prior to stripping it down. So, I put the cams back in how they were when I opened it up but the readings were bizarre. Not even sure how it was running as the exhaust sprocket was two teeth off the marks!

Anyway, so if my calculations are correct in my first post, then I can be reasonably certain that the lobe centers I calculated are accurate right? So now I just slot the cam, make the adjustment, then remeasure as before.

Oh, and I put my dial indicator on the valve spring retainer to take measurements. I've read some saying you degree the cam not the valve and to measure at the lifter (car guys). For these types of cams, should the dial be on the cam lobe or is measuring off the spring retainer ok as well?

Thanks again for the clarity. It really helps.

Sounds like you're doing fine. As long as the readings off the spring retainer are repeatable that's fine too. Try and get the dial gauge in line with the valve angle as it's less likely to move off the retainer.

Rereading some of the answers above can i clarify lobe centers....The figure you want is the geometrical centerpoint of the valve opening period. Stated as so much either before or after TDC.
NOT the point of maximum lift. Cams can be ground assymetrical in the lift/fall curves as well as assymetrical to compensate for leading/trailing followers. It's often a minefield but as long as you know what it is you're looking for - and why - it's pretty easy.

Oh, reminds me of a motor I did for a speedway sidecar too. It was sold out of town and the new owner opened it up for a look. Rang a very good tuner local to him, "the cam timing marks don't line up ! Help..." The tuner (who I knew well) asked him how it went, B..... well ! was the answer. Who built it ? greg T was the answer...."don't move anything, mark it and keep it like that " was the sensible answer from my friend....i ran into him a couple of months later and he told me the story, we had a good laugh over that one.

[Sci85]

Thanks Greg.

Well, my factory service manual states the valve timing as below but mentions no lift reading:

Intake: 38 BTDC open, 68 ABDC close, duration 286
Exhaust: 60 BBDC open, 40 ATDC close, duration 280

My GS was so much easier...WTH!
My numbers above are not even close to those and I cannot for the life of me figure out why they are not. I took my measurements at .040" opening and .040" before closed. I have the cams set at the factory marks and 30 pins between the marks as called for in the manual. So, I don't know how the heck Kawi came up with those numbers but I can't figure it. That's what really has me discombobulated. At this point I don't even think I'm gonna fool with changing the lobe centers since I can't get it to agree with the manual. I'll probably just leave it at the factory marks and be done with it. But, there's just something in me that wants to figure out what the heck is going on. Argh...

[Sci85]

I wonder if someone swapped in a different set of cams from another Kawi like from a ZX-1100 or something maybe? The sprockets are defintely stock and the cams have factory markings but is it plausible someone stuck a different set of cams on this thing? I did notice in my pre-breakdown pics that the cams sprockets were not set too the factory markings. The exhaust side was two teeth different. Hmm...

[GregT]

Doesn't matter what lift the factory figures are taken at - using their figures the standard lobe centers are 105 inlet and 100 exhaust.

Just work as you have been toward the centers the cam grinders recommend.

[Sci85]

Ok. Thanks again GregT. You've been a big help.

[Sci85]

Ok after searching for weeks I lucked out and came across a blog by a guy that rebuilt his early model ZX-11 (same cams and timing as the ZX-10) and he also came up with the same cam timings as I have. Not sure why the service manual doesn't jibe with reality but at least I feel certain now that I did everything right.

So now I want to advance the int came 6.5 degrees and the ex 6 degrees. To advance the cam timing, I need to move the cam forward in the direction of engine travel in relation to the sprocket correct?

[rphillips]

I'm having trouble figuring why the shape of the lobe, or how steep the ramps were on either side, would have any affect on the lobe center.