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Old 12-18-2010, 11:18 PM   #1 (permalink)
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v-thunder cam marked wrong!

I pulled the the V Thunder 3030 (530 lift) cam out of my 93 FXR today to put in the S&S 585. When I was looking at the 2 cams, I noticed they looked alot alike. I checked the end of the v thunder cam & it had 3030 on the end. After alot of measureing of the 2 cams, I found out the 3030 had .585 lift! I checked it against the lift of the S&S 585 & the numbers were the same. That's a difference of .055! Good thing I had the valve springs to handle the lift. The S&S comes on later & harder. V Thunder makes 3 cams with .585 lift & I'm not sure which 1 this 1 is. What I am sure of is this is not the 530 lift 3030. Makes me wonder about some of thier other quality control on the rest of thier parts. Has any one else ever has some thing like this happen to them?
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Old 12-19-2010, 07:56 AM   #2 (permalink)
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how are checking the lift?
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Old 12-19-2010, 08:35 AM   #3 (permalink)
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I have run the 3030 and 3040. Both with no problems. In my 107, I am running an S&S 600. Great cam. Love the motor.
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Old 12-19-2010, 09:12 AM   #4 (permalink)
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Originally Posted by prodrag1320 View Post
how are checking the lift?
Measured up from the bass circle to top of lobe with calipers, multiplied by rocker arm ratio for valve lift. I have no way of measuring the duration but both cams came out to 585 lift. In hillbilly measurements, you can take the rear lobes of both cams & place 1 on top of the other & they touch.With .055 difference, you could see the gap with just your eyes. No gap. I had a buddy whose a machinest take a look at both cams because I thought I was doing something wrong. He says both cams have the same lift. Going to take the 3030 to work & put a mic on it & see how close I got with just the calipers.
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Old 12-19-2010, 09:14 AM   #5 (permalink)
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I have run the 3030 and 3040. Both with no problems. In my 107, I am running an S&S 600. Great cam. Love the motor.
What comp. pistons did you have with the 3030?
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Old 12-19-2010, 09:36 AM   #6 (permalink)
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So out of curiosity, what were the measurements you got? from the sides of the lobe to the height of the lobe. You could accept .005 but .055 is a big difference, would be a big stuff up on there behalf
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Old 12-19-2010, 09:53 AM   #7 (permalink)
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So out of curiosity, what were the measurements you got? from the sides of the lobe to the height of the lobe. You could accept .005 but .055 is a big difference, would be a big stuff up on there behalf
From the base cicle of the cam to the top of the lobe on both cams is .360 X the rocker arm ratio(1.625) gives the advertised valve lift = .585. I've been a shade tree motor head since I was 12 years old & spent 5 years wrenching on Japaneese bikes. This is the first time I've ever seen a cam marked wrong. Leave it to me!
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Old 12-19-2010, 10:02 AM   #8 (permalink)
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To be that far out on the specs doesn't say a lot for comp's quality control
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Old 12-19-2010, 11:04 AM   #9 (permalink)
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To be that far out on the specs doesn't say a lot for comp's quality control
That's what I thought. I've been using thier push rods for a while & I think they're some of the best & easiest I've used. This motor has a set of thier liffters(in it when I bought the bike). They seem to be ok, they're very quite, quiter than the S&S in my Dyna. I know that when things are mass produced, things slip by. It just really blew my mind when I took this thing out. Comp cam is right next door to Jonesboro, over in Memphis. They have a loyal following in the street rod/hot rod crowd here & I believe they make a very good product. If you knew me, you would understand that I would be the one that found the wacky cam!LOL! Think I'll drop them an e-mail & see what they say. I also think I'll hang on to the cam just for shites & giggles.
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Old 12-20-2010, 09:46 AM   #10 (permalink)
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You have to measure the BASE CIRCLE first then measure the LOBE then subtract the base circle from the lobe , that will give you the gross cam lift then mutiply by your rocker arm ratio , or send your cam to somebody that has a cam doctor and they will give you ALL the spec's of your cam.
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Old 12-20-2010, 06:34 PM   #11 (permalink)
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You have to measure the BASE CIRCLE first then measure the LOBE then subtract the base circle from the lobe , that will give you the gross cam lift then mutiply by your rocker arm ratio , or send your cam to somebody that has a cam doctor and they will give you ALL the spec's of your cam.
I did, .408- .048 x1.625, both cams......
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Old 12-20-2010, 08:50 PM   #12 (permalink)
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OK, I've been reading this stuff and I DON'T GET IT!! Why does a cams lift have to be so involved as to have a formula?? If the cams lobe pushes the lifter up 1/2 inch, then why isn't the cam designated as a .500 lift cam?? Why do you have to measure the base, measure the lobe, then subtract the base and then multiply by the rocker arm ratio?? (whatever that is)?? Somebody help me out here!!
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Old 12-20-2010, 09:27 PM   #13 (permalink)
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OK, I've been reading this stuff and I DON'T GET IT!! Why does a cams lift have to be so involved as to have a formula?? If the cams lobe pushes the lifter up 1/2 inch, then why isn't the cam designated as a .500 lift cam?? Why do you have to measure the base, measure the lobe, then subtract the base and then multiply by the rocker arm ratio?? (whatever that is)?? Somebody help me out here!!
Cams are advertised in valve lift, not lobe hieght. The actual lobe height on these 2 cams was .408. That was from the tip of the lobe to the bottom of the lobe. On the other side of the lobe is the heel of the cam(or base) This was .048. So when the lifter follows the cam to it's lowest point, it's ridding on this machined low point & not on the actual core of the cam that rides in the bearing & bushing. If you look at the end of the cam, it looks like the shaft runs through the lobe. The rocker arm ratio on an evo is 1.625:1, not 1:1. So if the cam lifts the lifter 1/2 inch, the valve will move 1 5/8 inches. That's 1 hell of a big cam! This is how it was explained to me a long time ago. If I'm off base here, some one please chime in as I don't want to spread the wrong explanation. I hope this helps, I'm not very good at trying to explain things.
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Old 12-20-2010, 11:05 PM   #14 (permalink)
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Thanks for trying to explain it. I'm still having a rough time understanding the formula concept. For one thing, if the cam lifts 1/2 inch, the valve wouldn't open 1 5/8 inches, because you are starting with 1/2", not 1". I think it would only open 13/16". I adjusted my pushrods the other day and I could clearly see that the lifters were moving approx. 1/2". I didn't measure them, because I wasn't interested in how much they moved at that time. But I guess I'm interested now. I agree with you, 1 5/8" is not conceivable that the valve would move that much. Even 13/16" seems way, way too much travel for the valves to open. I wish I had a cam in front of me so I could visually study it and while I'm at it, I'd like a cut-away version of the evo engine so I could study it too. I think I'll go get a giant metal band saw and put my engine in it so I can really tell what's happening!! Naw, forget that. Seriously, I still need some help here understanding cam lift and valve travel. Thanks
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Old 12-21-2010, 04:53 PM   #15 (permalink)
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Thanks for trying to explain it. I'm still having a rough time understanding the formula concept. For one thing, if the cam lifts 1/2 inch, the valve wouldn't open 1 5/8 inches, because you are starting with 1/2", not 1". I think it would only open 13/16". I adjusted my pushrods the other day and I could clearly see that the lifters were moving approx. 1/2". I didn't measure them, because I wasn't interested in how much they moved at that time. But I guess I'm interested now. I agree with you, 1 5/8" is not conceivable that the valve would move that much. Even 13/16" seems way, way too much travel for the valves to open. I wish I had a cam in front of me so I could visually study it and while I'm at it, I'd like a cut-away version of the evo engine so I could study it too. I think I'll go get a giant metal band saw and put my engine in it so I can really tell what's happening!! Naw, forget that. Seriously, I still need some help here understanding cam lift and valve travel. Thanks
you're right. I get lost in the numbers too! That's why I make notes as I go. If the lifter moves a 1/2 inch then the valve will move 1 & 5/8 times the 1/2 inch is what I meant to say. So, if the lifter moves .500, then the valve moves .8125. Where the rocker arm extends out from the shaft to the valve is 1.625 longer than where the push rod meets the rocker. This way it can use leverage to move the valve with less stress on the cam & lifters. I really wish some one that's better at explaining this than me would chime in here. Since the part of the rocker arm that opens the valve is longer than the part that the push rod meets, you have to multiply to get the actual valve lift.
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