Measuring Cam Duration

[Guest]

I am trying to degree my cams(112, 110) and while doing so noticed something strange.

The cams are Web 70-252
Grind 212
Lift .370/.370
Duration 284/284.
Duration at 0.050 lift 256/256.

Lash is set to zero.

The exhaust is fine and I get 256 at 50 thou lift measured at the retainer. But on the intake though, I get 284 at 50 thou when i should get 256.

Am I doing something wrong or is something messed up with the intake cam even though they were brand new in the box? I also noticed that my head has GSXR rockers with a ratio of 1.5 so I am only getting 0.348" of lift instead of the GS rocker arms with a ratio of 1.6 to give the advertised lift of 0.370"

I will go through again tomorrow and post opening and closing degrees.

 

[4cyl h2]

I am trying to degree my cams(112, 110) and while doing so noticed something strange.

The cams are Web 70-252
Grind 212
Lift .370/.370
Duration 284/284.
Duration at 0.050 lift 256/256.

Lash is set to zero.

The exhaust is fine and I get 256 at 50 thou lift measured at the retainer. But on the intake though, I get 284 at 50 thou when i should get 256.

Am I doing something wrong or is something messed up with the intake cam even though they were brand new in the box? I also noticed that my head has GSXR rockers with a ratio of 1.5 so I am only getting 0.348" of lift instead of the GS rocker arms with a ratio of 1.6 to give the advertised lift of 0.370"

I will go through again tomorrow and post opening and closing degrees.

I went thru the same thing on the lift ( mine were the 370 lift #190 grind has lower 350 lift I think katman mentioned it too for me part the problem was I checked at 5 thou valve clearance but lift was still less than advertised. You might set to 0 and retry. On the duration dbl CK your dial and wheel setup and prob will come up close to correct. Those are good cams if you have enough engine for them. What you got??

 

[Guest]

it is a 1400 with a massaged 1150 head. 11:1

 

[GregT]

If the followers have a different radius on the face contacting the cam, you'll get a different duration. Larger radius, longer duration, smaller radius, shorter duration. Total lift won't chage but the area under the curve does.
If they've been refaced, that could answer your question.

 

[RichDesmond]

I am trying to degree my cams(112, 110) and while doing so noticed something strange.

The cams are Web 70-252
Grind 212
Lift .370/.370
Duration 284/284.
Duration at 0.050 lift 256/256.

Lash is set to zero.

The exhaust is fine and I get 256 at 50 thou lift measured at the retainer. But on the intake though, I get 284 at 50 thou when i should get 256...

LOL, you're assuming that the spec is what they are?? Silly boy...

I had one of my superbike SV motors built by Carl Ahlfeldt (a legendary drag bike builder). I handed him a box with the cams and then pulled out of my pocket the sheet with the specs from Mega-Cycle. He took the sheet and without as much as a glance wadded it up and tossed it in the trash. When I looked at him he just grunted, "we measure". I felt a little dumb.

 

[GregT]

Very true Rich...But I've had a longstanding agreement with my local cam grinders - If it's more than 2 degrees off the card specs, it's coming back and it's gonna get painful...
That's worked through four different owners of the business so far.

Actually, as more are done on CNC grinders, the repeatability is getting better. My local bought a CNC grinder from Comp Cams in Nashville a few years back.
It was interesting talking to the guy who came out to install it. Comp Cams simply don't do small run work.

 

[RichDesmond]

Very true Rich...But I've had a longstanding agreement with my local cam grinders - If it's more than 2 degrees off the card specs, it's coming back and it's gonna get painful...
That's worked through four different owners of the business so far.

Cool that you have local guys you can work with like that, makes life a lot easier. If you're buying off the shelf stuff though it's a little different. Sometimes things are spot on, sometimes off by a little, sometimes by a lot. If Carl had called them directly for the cams they would have made sure they were right, but I'd bought them before I knew to drop his name.

 

[RichDesmond]

...I also noticed that my head has GSXR rockers with a ratio of 1.5 so I am only getting 0.348" of lift instead of the GS rocker arms with a ratio of 1.6 to give the advertised lift of 0.370"

I will go through again tomorrow and post opening and closing degrees.

Just noticed this part. That rocker ratio difference is also affecting your duration numbers, since it takes more rotation to get to 50 thou.

 

[4cyl h2]

Any new results yet. If this is a street bike it's gonna be a blast. What lobe centers u planning to set to. And what carbs u using

 

[Guest]

It is a street bike running some RS 40 mikunis. I am setting them at 110 in, 112 exhaust. Once my minions, I mean children, are to bed then I am headed to the shop for more checking and will post the results

 

[Guest]

There appears to be a lot of knowledgeable people in on this thread, so here goes. I recently put some Cam Motion cams into a 1980 GS1100. They're either G3 or G4...I won't know for sure until I go back in. The problem is the head. It's been shaved 0.030. I took these same parts to Scott at S & K in Dayton a few years back to put into a different bike and when he was done the bike was scary. He degreed IN and EX at 110 deg. But here's the part driving me crazy. Before he started with the cams he marked a different TDC or F1-4 on the electronic timing plate than where the stock mark was. About a month ago I took the bike to someone I thought could get everything straight. He changed the cam timing on the IN cam and the bike won't run after 5000 rpm. I just bought a Web Cam degree kit and believe I can get them both back to 110 deg, but don't understand the electronic timing mark. I am certain the ignition and cam timing are both wrong. Anybody on where to start?

 

[Guest]

Problem: Solved!

Solution: Some dumb arse (me) didn't double check pin count between cams after removal and install. Actual count...22, not 20...lol

Anyways, here are my numbers now.

Intake:

18 BTDC
+ 58 ABDC
+180
-------
256 DURATION @ 0.050"

256 / 2 = 128

128 - 18 = 110 deg Lobe Center



Exhaust:

60 BBDC
+ 16 ATDC
+180
-------
256 DURATION @ 0.050"

256 / 2 = 128

128 - 16 = 112 deg Lobe Center

 

[Guest]

There appears to be a lot of knowledgeable people in on this thread, so here goes. I recently put some Cam Motion cams into a 1980 GS1100. They're either G3 or G4...I won't know for sure until I go back in. The problem is the head. It's been shaved 0.030. I took these same parts to Scott at S & K in Dayton a few years back to put into a different bike and when he was done the bike was scary. He degreed IN and EX at 110 deg. But here's the part driving me crazy. Before he started with the cams he marked a different TDC or F1-4 on the electronic timing plate than where the stock mark was. About a month ago I took the bike to someone I thought could get everything straight. He changed the cam timing on the IN cam and the bike won't run after 5000 rpm. I just bought a Web Cam degree kit and believe I can get them both back to 110 deg, but don't understand the electronic timing mark. I am certain the ignition and cam timing are both wrong. Anybody on where to start?

Print this off and follow it:

http://www.faliconcranks.com/pdf/degreeing_In_your_camshaft.pdf

With a degree Wheel and a piston stop you can find your actual TDC. If you don't have a piston stop I have seen them fabricated from an old spark plug or use a dial indicator through the spark plug hole.

 

[Guest]

There appears to be a lot of knowledgeable people in on this thread, so here goes. I recently put some Cam Motion cams into a 1980 GS1100. They're either G3 or G4...I won't know for sure until I go back in. The problem is the head. It's been shaved 0.030. I took these same parts to Scott at S & K in Dayton a few years back to put into a different bike and when he was done the bike was scary. He degreed IN and EX at 110 deg. But here's the part driving me crazy. Before he started with the cams he marked a different TDC or F1-4 on the electronic timing plate than where the stock mark was. About a month ago I took the bike to someone I thought could get everything straight. He changed the cam timing on the IN cam and the bike won't run after 5000 rpm. I just bought a Web Cam degree kit and believe I can get them both back to 110 deg, but don't understand the electronic timing mark. I am certain the ignition and cam timing are both wrong. Anybody on where to start?

I don't think Ray has seen this thread ......

 

[Guest]

It is a street bike running some RS 40 mikunis. I am setting them at 110 in, 112 exhaust. Once my minions, I mean children, are to bed then I am headed to the shop for more checking and will post the results

"1400 streetbike"..."massaged 1150 head" Let me see if I can get Rapidray in here....

 

[Guest]

"1400 streetbike"..."massaged 1150 head" Let me see if I can get Rapidray in here....

Funny you say that. The head and pistons came from Ray.