[ss3966]

I have a last chance to change my cam degreeing before installing the engine and the degree of difficulty will be greatly increased. The cam is Comp Cams 11-250-3, or XE284H in a BBC 496, using a Cloyes double-roller with 3 choices of straight up, 4 degrees retarded or advanced. A Comp Cams rep said it has 4 degrees of advance built in, as does their catalog.

The cam card says the cam card lift/duration specs are given for a 106 degree intake center line. When I use the Comp Cams degree kit, when installed in the "straight up" keyway, I get 114 degrees. I asked the rep about this, and he said to ADVANCE it 4 degrees. Then I got an intake center line of 118 degrees. So went back and installed the crank sproket 4 degrees retarded and got 108.5 degrees. I have left it there for now.

The lobe separation is 110 degrees, but don't entirely understand the relationship of this spec. I know I cant change that with a crank sprocket as its how the cam is ground, and don't want to confuse the issue. My undertanding is that Comp Cams builds in 4 degrees to allow for timing chain stretch. I just couldn't get anywhere near the 106 degrees cited on the cam card with either the "straight up" keyway or with the advanced keyway.

Should I tear it back down and go with 114 degrees or intake center line or stay at 108.5 degrees?

 

[trmnatr]

You would like to try to get it @ 106icl

Double check finding TDC- when you have the degree wheel all set up go to max lobe lift then back the engine up .100", turn engine .050" in normal direction and write that number on degree wheel down, then turn it to max lift then the dial indictir will start going backwards, go .050" in normal direction yet indictaor will be going backwards from max lift and write that number down, add that with your last number and divide by two = ICL

Check it a couple times {finding TDC}

 

[ss3966]

When double-checking TDC, I did find it moves by 1-2 degrees on the second time, presumably being more accurate. Also ran through the dial-indicator sequence a couple of times to double check the ICL.

Having to use the "retarded" keyway to get closer to the 106 ICL is concerning, but 108.5 degrees is much closer than the 114 or 118 degrees I got with the other keyways. Maybe this means I'll have a shorter service life as the chain stretches. The cam help reps haven't been so hot the advice, especially telling me to advance the cam, which just took me to 118 degrees, even further off.

Don't know what else to do, and will keep it at 108.5 degrees unless I receive further recommendations - which are appreciated.

 

[trmnatr]

is it possible your checking the exhaust lobe? If thats the case it woud be 114° when straight up and 118° when advanced 4° just like your coming up with, maybe your checking the exhaust lobe?

With a 110° lobe center with 4° advance your ICL is 106° and ECL is 114° - This could be a possible mistake - everybody has done is a time or two - even engine builders

Make sure your on the intake lobe and double check, start over, find TDC and recheck ICL from there

 

[Wolfplace]

Bart,
It sounds exactly like Butch stated as you are showing the cam going the wrong direction for the intake lobe
If you advance it 4° the intake number should get less not more, the exhaust is the opposite, it gets larger.

 

[ss3966]

Yes, yes - I had another big bowl of dumbass soup for lunch today. I was checking the exhaust valve. The mind immediately knows that Number 1 cylinder is at the front on BBC, so the intake must be the front valve. Just have to look at the porcupine valves to see the difference.

At least knew to ask, and got excellent-keister saving before having to do the job in the car with fluids installed etc. Why don't I feel so good though? Thanks again - I'm off to go do it right . Could have been much more painful.

 

[3V Performance]

is it possible your checking the exhaust lobe? If thats the case it woud be 114° when straight up and 118° when advanced 4° just like your coming up with, maybe your checking the exhaust lobe?

With a 110° lobe center with 4° advance your ICL is 106° and ECL is 114° - This could be a possible mistake - everybody has done is a time or two - even engine builders

Make sure your on the intake lobe and double check, start over, find TDC and recheck ICL from there

Great job Butch, good catch.

Also check your intake open @ .050. You can never go wrong that way.

Tom

 

[trmnatr]

Yes, yes - I had another big bowl of dumbass soup for lunch today. I was checking the exhaust valve. The mind immediately knows that Number 1 cylinder is at the front on BBC, so the intake must be the front valve. Just have to look at the porcupine valves to see the difference.

At least knew to ask, and got excellent-keister saving before having to do the job in the car with fluids installed etc. Why don't I feel so good though? Thanks again - I'm off to go do it right . Could have been much more painful.

Dont worry i have done it one time that i recall, im sure Mike has and others, when your in the middle of it then ordering parts and all it strange happens

I put a rod in and went to put the bearing in - answer the phone i couldnt find the bearing, looked for for 10-15min, I put it in the rod before i took the phone call

 

[real reddog]

Excellent thread

 

[trmnatr]

I have a last chance to change my cam degreeing before installing the engine and the degree of difficulty will be greatly increased. The cam is Comp Cams 11-250-3, or XE284H in a BBC 496, using a Cloyes double-roller with 3 choices of straight up, 4 degrees retarded or advanced. A Comp Cams rep said it has 4 degrees of advance built in, as does their catalog.

The cam card says the cam card lift/duration specs are given for a 106 degree intake center line. When I use the Comp Cams degree kit, when installed in the "straight up" keyway, I get 114 degrees. I asked the rep about this, and he said to ADVANCE it 4 degrees. Then I got an intake center line of 118 degrees. So went back and installed the crank sproket 4 degrees retarded and got 108.5 degrees. I have left it there for now.

The lobe separation is 110 degrees, but don't entirely understand the relationship of this spec. I know I cant change that with a crank sprocket as its how the cam is ground, and don't want to confuse the issue. My undertanding is that Comp Cams builds in 4 degrees to allow for timing chain stretch. I just couldn't get anywhere near the 106 degrees cited on the cam card with either the "straight up" keyway or with the advanced keyway.

Should I tear it back down and go with 114 degrees or intake center line or stay at 108.5 degrees?

Bart,

Did you get her all squared away ?