oscarfromla

iTrader: (9)

I'm building my first SBC and have run across a problem. I installed a camshaft I purchased from Mike Jones that says the intake valve should open at 0.050" at 2* ATDC. Mine is actually at 7* ATDC. I know turning the cam gear one tooth will change over 8*.

I pulled the crank gear off, changed the install from the "0" keyway to the "A" keyway (it has 3 keys). Now the intake valve is opening at 2* before TDC. Is this a significant discrepancy?

Should I consider using a degree bushing kit?

Lastly, I noticed that my degree wheel has 2-4* of slack due to slack between the crank and crank socket. Is this normal? How do you accurately degree a camshaft with this problem?

Any help is appreciated.

AlkyIROC

First of all I think your cam secs are a little out of whack. My cam at .050" open on the intake is 31* BTDC which is in the more normal range.

First of all, get a degree wheel that doesn't have "slack" or fix whatever is causing the slack. Verify the piston TDC and reposition the pointer on the degree wheel to TDC as a new reference before you start rotating the crank to get .050" lift on the intake. Only rotate the crank in the normal direction of rotation. If you have to back it up, go back even more then rotate back in the proper direction of rotation to get to where you wanted to be.

sofakingdom

iTrader: (1)

Your amount of timing chain slack is pretty normal.

Now imagine what's it's going to be like in a couple thousand miles.

ONLY pay any attention to the cam timing specs when rotating the motor in the "forward" direction. It never rotates the other way. And, there is no force or tendency on the part of the cam, to rotate the other way.

Basically, after the motor has run enough to break in, the cam timing will be some arbitrary unknown unkowable random amount RETARDED from wherever you install it; and after 10 times that much run-in, it will probably change by THAT MUCH MORE AGAIN.

"measure with micrometer, mark with chalk, cut with axe"

There comes a point in this sort of thing, where the random unknowables that you CAN'T control, become greater than that which you CAN control. Once you reach that point, the best you can do is, "bias" your errors in the opposite direction from wherever the random stuff like wear and "chain stretch" (wear), will send them.

IOW leave the cam a few degrees "advanced" from wherever it's "supposed" to be; and from there, over the course of its lifetime, it'll kinda drift through "correct" and continue onwards. Might be 5 minutes, 5 weeks, or 5 years after you first fire it up; but you can be 100% CERTAIN that it's never going to drift the opposite way.

oscarfromla

iTrader: (9)

The slack in my degree wheel is coming from the crank socket, it does not hug the crank as good as I would have thought. I only found this problem when looking for TDC with since I have no choice but to go CCW after hitting the piston stop going CW.

I may have been putting too much emphasis on being "dead on." I can get within 4* on the advance side. If that's going to become insignificant once the motor is up and running, then less work for me.

Thnx

Atilla the Fun

You're running a 25:1 1000-cube big-block, not a mild-cam 350. For any cam that'll be streetable, a normal intake opening at 0.050" tappet ride is within no more than 8 degrees of top dead center. Everyone swears by advanced cams, but once you try replacing a 100,000-mile timing set, and suddenly have no top-end and no gain in low-end, you'll forget all about advancing cams.

AlkyIROC

First of all, if the crank gear is loose on the crank snout then there's a serious issue. It shouldn't move at all. It needs to be driven on and a puller takes it off. Even if the key was worn, the gear should still be tight on the snout.

It doesn't matter on the size of the engine. Opening and closing angles for all cams fall into a specific range. A low performance cam will probably not give a .050" open and close degree. Comp Cams lists their lower performance cams at .006" and even still, those cams start opening the intake around 20* BTDC. It's unlikely they be ATDC by .050" lift.

If you look at a solid degree wheel like the small one that Comp sells, you can see exactly the range that the majority of all performance cams (not stock replacement) will open and close the valves. If measured at the standard .050" lift, all cams will open the valves in the same range. Yes a basically stock grind hydraulic roller will open the intake .050 very close to TDC but one that opens it after TDC isn't normal. Since he's installing a camshaft that's probably better than stock, the intake open will probably be a lot f4rther away from TDC

He's saying his grind is supposed to be 2* ATDC at .050" lift. I have no idea what kind of special purpose that camshaft is ground for but it's not a normal grind. Even blower and turbo cams work in the normal ranges. If the cam is a basic stock replacement grind then you're probably not going to see a big difference by not degreeing in the cam. Line up the dots like a manual says and slap it together. All you're doing is checking to see that the cam grinder did a good enough job. Once you put some miles on the engine, parts start to wear and change tolerances anyway.

oscarfromla

iTrader: (9)

My crank sprocket to crank fitment is fine, it's nice and tight. I have to press it on, and had to use a puller to pull it off. Its the crank socket tool to turn the crankshaft that has some play. That's what the degree wheel is mounted too. I bought a ProForm one, so maybe I need a better quality one to give me a tight clearance.

The picture above is the cam degree wheel I have, I wondered why my intake valve opening fell outside the displayed range. Would the 10.9:1 compression I plan on running have anything to do with it? Here's my cam card by the way:

AlkyIROC

OK, cam card confirms the setting which I still find really odd especially for a SBC cam with mid .5xx lift. Looks like it's going to be a real torque cam.

Degree wheel needs to be solidly attached to the crank. If it doesn't bolt directly to the crank, it should bolt to a balancer that's pressed onto the crank. Since it's sloppy in relation to the crank, how were you able to determine TDC?

oscarfromla

iTrader: (9)

I used my best judgement to pull the slack out of the crank socket and take the readings. Using the degree wheel attached to the balancer is a good idea. I have a couple of old stock balancers that I don't plan to re-use. I could press those on just to check the timing to ensure a solid reading, and just make sure my readings are close enough to the cam card specs.

AlkyIROC

The main reason to check the cam degreeing is to make sure the cam grind is the same as is on the cam card. With timing chain stretch over time, it will never stay the same. The majority of people won't play with cam timing to see if advancing or retarding it will help what they generally use the cam for. Depending on the cam grind and the valve reliefs on the piston, there may not be enough leeway. Installing it straight up is always recommended.

I've given up on timing chains for my engine. I tried a dual idler gear system quite a few years ago. After one day I yanked it out and put a chain back on. This year with my new engine, I'm taking a different route. Best choice was to go with a belt drive system like Jesel, Comp Cams or a couple of other high end brands but I decided to go with a Milodon single fixed idler gear system. Once the cam is degreed in, the cam timing will never change. There will be no timing fluctuation from a sloppy chain etc. Nothing will wear out or stretch. The downside is the cost. A good chain system with billet gears is around $100. A good belt system, not the cheap Procomp stuff, is around $1000-$1200. My gear drive including shipping and taxes was $800.

86LG4Bird

iTrader: (1)

Strange specs indeed. I assume its a turbo/blower cam ??

From my experience, I really think you should leave it at that "2* before TDC" point that you have it at now.
Nearly any SBC will run better with a 106 ICL than a 110 ICL.

oscarfromla

iTrader: (9)

It's not for a turbo/blower cam. This is meant for a street rod that will hopefully pass California smog. Maybe that, coupled with the fact that it's a little under 11:1 static compression has something to do with the 2* ATDC.

oscarfromla

iTrader: (9)

I just ran how going from 110 to 106 CL would affect my dynamic compression ratio. It would go from 8.8 to 9:1, slight difference, but still an increase. I will only have access to 91 octane and I'm worried 8.8:1 is too much already.