Topic: 126-00 cam cards

[AlekStooge]

I have a Megacycle 126-00 cam. I'm installing it using the lobe centerline method.
http://forums.sohc4.net/index.php/topic,140833.msg1890649.html#msg1890649

My original centerline numbers were intake=100.75 and exhaust=109.875. No matter what I did I would be off on my centerlines. I did this several times. I proceeded to call Megacycle and after asking me a bunch of questions they told me I would not match up my centerline numbers by measuring at the valve spring, despite me having seen it done before. They mentioned the cam card was revised a while back. I decided to settle for somewhere in the middle 104-105.

Here are the numbers I got.


Here is my cam card. Revised 2000.


and here is what I found on the forum. The old cam card numbers.

Original post. http://forums.sohc4.net/index.php?topic=142000.0

Well, my numbers almost match the old cam card.

First, why? I'm guessing the cam card was revised because the cam profile was changed.

Second, what do I do with the numbers I'm at? Should I increase (retard) my exhaust so I can be 1 degree apart on my centerlines like on MY cam card or should I reset valve lash (were using running clearance here remember) and aim to have the lobe centerlines even like on the old cam card?

Here is my project thread if you're interested. http://forums.sohc4.net/index.php/topic,158001.0.html 

[Sam Green Racing]

Alek, I'm not sure why the numbers never match the numbers on the card but from what I've heard, this is not only Megacycle cams that it happens with.
I see from reading your build thread that Mike ported your head. Have a word with Mike but I think you might have it right finding the mid way point between them.

[calj737]

With an adjustable sprocket, and a degree wheel that's large enough in diameter, you should be able to match your lobe centerlines to within 1/2* or better. You're pretty close, and probably close enough. How large in diameter is your wheel, Kyle? Dave made one that was like 18" in diameter and found he could get his C/Ls within 1/4*.

[flatlander]

yes, line them up so that the lobe centres on in and ex are the same - or as close as you can get. sounds like you're almost there and as cal says, it's probably good enough if (!) you are certain your measuring setup is good and accurate. so you might want to repeat your setup and re-check, see if you get roughly the same numbers.

cam card specs are measured with zero lash, not running clearance as you are doing. also, they are not 100% the same for all copies of the same cam model. so you can have a bit of deviation. common practice with these single cams is to set lobe centres to the same value (within a small tolerance) and call it a day.

[DaveBarbier]

My understanding was that you only try to match lobe centerlines if the cam card has them matched. The cam card that Alek has has them 1° off of each other. 109.5° vs 110.5°. But it IS weird that he's matching the OLD specs.

Can he measure the profile of his cam to determine which cam grind he has?

I was able to get very close. Ultimately a <1/8° difference. I've heard of others getting as close if not perfect to the cam.

The large wheel helps tremendously, I think Alek is using a smaller wheel, but that shouldn't throw off his numbers that much, I don't think. Right?

To me the simplest explanation is that he has a cam grind that matches the old card. Of course there's user error, but user error that gets you almost perfectly matched to the old specs? Seems unlikely to me.

[flatlander]

the old card spec has them matched up. i suppose that's the "theoretical" design. the new card spec is taken from re-measuring an actual production cam. i've discussed this extensively with megacycle when i had trouble hitting their numbers with my copy of the same cam.
i went back and forth on the degreeing process and numbers with megacycle and mike for ages, re-doing it all over. what it all boiled down to is the process summary in dave's thread and the above advice of getting the lobe centres even.

apart from user error or measuring tolerance that should sort it out. i really wish this will save everyone some time as i don't wish anyone else to go through all the discussions and multiple degreeing attempts that i went through

[AlekStooge]

"My understanding was that you only try to match lobe centerlines if the cam card has them matched. The cam card that Alek has has them 1° off of each other. 109.5° vs 110.5°. But it IS weird that he's matching the OLD specs."

This in essence was my question.

Flatlander:
"cam card specs are measured with zero lash, not running clearance as you are doing."

Apparently it's better to do it this way. See step 6.

"what it all boiled down to is the process summary in dave's thread and the above advice of getting the lobe centres even."

I think I'll match them up at 105. I couldn't find it again, but I remember reading something about measuring cam base circle to check the grind but that sounds like it's more work than it's worth. Should I use running lash from the old cam card specs .004 and .005?

[flatlander]

Should I use running lash from the old cam card specs .004 and .005?

no idea to be honest. the new spec is a wider (actually, wider than many more extreme grinds!) and i don't understand why. i asked this in the high-po forum. no answer. dave asked in his build thread also the question why these megacycle spec for lash are relatively wide. no answer.
seems like nobody knows. i set mine initially to the wider, newer spec. i think in future i'll go for the old one as you suggest.

[DaveBarbier]

Mike was saying that the larger valve lash helps the aggressive ramping go easier on the components.

I personally wouldn't run tighter lash because you think it's either a mistake or they don't know what they're talking about. Chances are, Megacycle knows it's wide and they like that. I would start veering from recommended specs only when you have vast amount of experience, testing and knowledge on the subject.

That being said, I have no idea why the lash is wider than the more aggressive 126-20 cam. Perhaps if one were to get a 126-20 cam now, it would have the wider .005"/.006" spec? (Meaning they recently changed since I got my cam)

[flatlander]

That being said, I have no idea why the lash is wider than the more aggressive 126-20 cam. Perhaps if one were to get a 126-20 cam now, it would have the wider .005"/.006" spec? (Meaning they recently changed since I got my cam)

exactly, that's what puzzles me. would be interesting to see a newer cam card for the 126-20. when is yours from? or could be that they did not re-measure the -20, only the -00 and therefore don't have updated spec for it.

[AlekStooge]

I understand what your saying about keeping it safe. However my numbers come out to what is on the old cam card. Which means....it must be the old grind. Why that was done, is part of the reason I'm posting here. It would makes sense to use the valve lash that is recommended with that grind. Makes sense to do so. Numbers don't lie, right?

[DaveBarbier]

I got my cam back in the winter. They could have changed clearances, but everything I'm saying is just speculation. I have very little experience with this sort of thing so I can't be much help. I'll leave it to the people who have degreed more than once, haha.


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[flatlander]

alek, they did not change grind. they just re-measured a sample of the cam in 2000. in that year they used digital instruments which were not available at the time when the numbers in the printed catalogue were given. so both old and new numbers are for the same cam profile, but taken from different copies oft the cam and with different instruments. i confirmed this on the phone, with jim and barbara at megacycle.
which ones are the "real" numbers? it's a toss-up, if you ask me. as long as you get lobe centres to match up, and measure correctly, you're golden.

dave, your cam card would  mention if the numbers came from a re-measured cam. and chances are that it would have been done well before this winter. makes no sense that they would measure some cam profiles in 2000 and others, 16 years later.
if you cam card doesn't say anything then i would assume that the -20 may not have been re-measured which would explain why they still give the "old" valve lash spec for it.

[AlekStooge]

Thanks for doing that you didn't have to.

"if you ask me. as long as you get lobe centres to match up, and measure correctly, you're golden."

Except on one card they match up on the new one the exhaust is one degree higher.

I readjusted my sprocket last night with .004 and .005 valve lash on the old card. My numbers ended up being even. Intake=105.05 Exhaust=105.125.
Then I rechecked TDC.I tried to check valve to piston clearance but realized I don't have the soft springs. I should be good though.

[flatlander]

sounds perfect.
i think the old values is what they designed for initially, and the new ones are what they measured on an actual sample and there it was one degree difference for some reason.
you don't 'need' the soft springs for checking valve-piston clearance, it just makes it easier to push them down. i also don't bother with soft springs coz i'm no whimp

oh and i called megacycle when i was in doubt about my own cam, a while ago. i'm just passing on the info, no need to give me too much credit!

[AlekStooge]

So when checking valve clearance I'm just not using enough man power?

[MRieck]

Thanks for doing that you didn't have to.

"if you ask me. as long as you get lobe centres to match up, and measure correctly, you're golden."

Except on one card they match up on the new one the exhaust is one degree higher.

I readjusted my sprocket last night with .004 and .005 valve lash on the old card. My numbers ended up being even. Intake=105.05 Exhaust=105.125.
Then I rechecked TDC.I tried to check valve to piston clearance but realized I don't have the soft springs. I should be good though.

That is good.

[AlekStooge]

Now would be a good time to install my ignition. I have a C5 from GV1390. It seems like it's intended to be straight forward but I'm still a little confused on a couple things.

http://www.c5ignitions.com/installation-manuals.html




What do they mean in step 2 by original coil power wire can be reused?

Step 5. The instructions describes a yellow wire that goes from the coil to the module trigger leads. I only see a black ground wire coming from the coil. Also they say to connect the red to the coil I thought that would go to the battery post.

[MRieck]

Blue/yellow is from the ignition (points) plate. Black/white is the power wire to both coils. The black/white (or maybe just black on the 550) powers the coils.....the blue/yellow wires tell the coils what to do.

[DaveBarbier]

There are different manuals for the different C5 ignitions. If you're having trouble finding the right manual then you can give Paul at C5 a call or email and ask. He's super nice and ready to answer whatever questions you ask.

That being said, they're pretty straight forward as Mike alluded to. Coils need power and ground plus the signal wires from the ignition plate. Ignition plate itself needs power and ground too. That's about it. There might be other colored leads that you ground or unground to tell what timing curve you want the system to use. Mine, and I believe all, have 4 factory curves to choose from.


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