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Discussion Starter #1
I've got a pair of cams that are stamped 'Alfa Ricambi' AR111.272S. Is anyone familiar with these. Are they Colombo Bariani cams? I looked at their website but didn't see this particular part designation.

These cams are on my '74 Spider. The engine is a 2L, 10.4:1 compression pistons, 40DCOE32 Webers, electronic ignition, w/oversize exhaust valves, stock exhaust manifold.

Does anyone know what the lobe center specs are?

I've got a low rpm stumble that's driven me half nuts and now I'm wondering if the cams aren't set correctly. I've done everything possible to sort out the carburetors & fuel supply (boiled out rebuilt fuel tank, new low pressure fuel pump/fuel filter, cleaned and rebuilt Webers, played with jetting so much I now have more jets than I know what to do with).

As always, thanks for your help.

Mike
 

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Don't know how much this helps, I have a list of Alfa Ricambi cam specs (us) with part numbers, all of them start with AL and then four digits, but that doesn't mean that the part is what was stamped on the cam. Playing detective, do you know what the recommend clearences are for your cams? Anyway all the cams on this list (other than the 12.5mm lift, which I doubt are streetable) are either 100 or 102 degrees.
 

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Discussion Starter #3
Thanks for the detective work. I've got a Alfa Ricambi catalog too and I see that there's a 11.1 / 0.437 cam lift listed (it's part number AL5418A) and as you indicate the lobe centers are listed as 100°. Maybe that's what I've got.

I wrote to Columbo Bariani thinking that maybe it's one of their cams. I don't know if they stamped their cams with 'ALFA RICAMBI' or not. I'll share what I learn if they write me back and confirm that it's an older model of theirs.

I guess I should just adjust the cam timing to 100° and see if that finally improves drivability and removes the stumble - wouldn't that be nice.

Thanks for pointing me to the Ricambi catalog.

Mike
 

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Discussion Starter #4
Mr. Mauro Bosio, of Acar Milano (he was referred to me by Colombo Bariani) was kind enough to give me the following information regarding my cams:

###
Dear Mr. Gallagher,

We refer to your e-mail message of 24th September to confirm you that the set of cams AR111.272S you have are COLOMBO & BARIANI cams. They are old profiles for your car.

Would you please note the data :

Lift : 11,1 - 11,1
Phase : 26° - 66° / 66° - 26°
Valve opening : 272° / 272°
Cam Lobe center : 110°

We have only one question : where did you buy these cams ??

We await your kind reply and best regards.

ACAR RAM SRL
M.BOSIO°
####

I bought the cams some 17 years ago and can't remember if I bought them from Rex Chalmers (former owner of Omega Motorsports) or Alfa Ricambi in Glendale.

I wonder if the lobe centers are supposed to be set at 110° and I've had them set at 102° all along would that contribute to the low rpm flat spot or stumble that I've been experiencing. I know, I know, "Mike, set the cams at 110° and see for yourself!" But I was just wondering, you know, theoretically. ;)

Or are the profiles of these cams good or bad? I really need to read a little more about performance engine tuning to get a better understanding of this whole, for me, esoteric cam theory stuff. I'm a visual guy. I remember seeing a 3D animation of an Alfa engine. Does anybody have a link to that?

Thanks again to everyone on this remarkable forum.

Mike
 

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Sorry for the thread necromancy, but i have a pair of these cams (AR111.272S) in my '73 Berlina. I am searching for the valve lash specs, which I cannot seem to locate anywhere...would anyone out there have them?

TIA
-Andy
 

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AR Ricambi, successor to Shankle. 11.1 mm lift, 272 duration. At least I'd think.
Barring anything else, Norman Racing recommends 102/102 as a good starting point if you don't know what you have or what you want, as long as you check your piston/valve clearance. I would think stumble is in the ignition first, fuel delivery second.
Andrew
 

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Agreed.
What is the initial timing? Has anyone ever set the timing at the "Massimo" mark at 4000 RPM?
 

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In my experience ignition timing, even if wrong but reasonably in the ballpark, doesn't cause stumbles, at least on non-high-strung engines. Too much advance gives good power but pinging when you ask too much. And can make hard starting as the engine fights itself. Too little advance is nice and smooth but the engine feels like it doesn't want to go rev up, no pep. But I haven't experienced stumbles from wrong ignition timing.
Andrew
 

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I have experimented with cam timing with my car on a dyno. Different cams but what worked best for me was as much advance as possible without piston valve interference on the intake. In my case 98 but with my previous pistons 101. The exhaust timing has less effect than intake and 108 worked best. I suggest those as a starting point but be sure to check the piston to valve clearance whenever you adjust the cam timing.

Port size and intake length can influence the optimum Intake timing and exhaust design can influence the exhaust timing.
 

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Sorry for the thread necromancy, but i have a pair of these cams (AR111.272S) in my '73 Berlina. I am searching for the valve lash specs, which I cannot seem to locate anywhere...would anyone out there have them?

TIA
-Andy
Regarding lash specs, your best bet is Richard Jemison will weigh in.
 

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We are talking to different things here, cam timing and ignition timing.
Andrew
Yes, I know. I'm just wondering if that's even been checked. It appears jets have been thrown at this problem and now the cam timing is in question.
I guess I'm a back to basics guy. What if the dizzy isn't advancing? Frozen weights etc.
Cam timing is easy to check. I guess get that out of the way.
 

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Richard Jemison
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First, C&B recommends wide LSAs to avoid issues of bent valves from installation issues from novice owners. Forget 110 LCs.
These cams are old design slow ramp rate cams. The intake cam needs to open as early as possible to get an earlier closing (critical valve event on the intake cam, which reduces reversion) Thet should be set at the LC that is most advanced and still provide .040" P to V clearance. (See the copy of my PDF file on checking P to V clearances below.) Target 100-to 102 LC on the intake if there`s room. Valve float on the intake side will never result in a contact situation.

On the exhaust side P to V clearance is critical as the piston will push a floating valve if clearance is inadequate. Commonly achieving the needed minimum clearance (.080" ) is generally contrary to maximizing the valve events for best power production, but with slow ramp rate cams there`s nothing to do but find the most retarded LC that gives you adequate clearance..
You want the opening of the exhaust valve as late as possible (cam retarded) to maximize the length of the power stroke. BUT... the same lobe will be controlling it`s closing which has to result in adequate clearance as the piston comes up...
read the info below re: P to V clearance.

As to lash, Try .015" intake and .016' exhaust.

CAM SET UP NOTES
Piston to Valve Clearance Check


This is very important since when cams are advanced the piston clearance reduces dramatically, and Lobe design can effectively advance the valve opening.

Set Intake and exhaust cams at initial LCs as indicated by provider`s set up instructions, and lash
settings.

By running the .040 plastic wire-tie between the Intake valve & piston, and .075 - .080 on
the Exhaust side you can check if there is any interference and see that you have adequate
clearance between piston & valve. If by turning motor over by hand you feel some interference
using a .050 thick wire-tie, (or .075 on the Exhaust) but the motor continues to roll through, you are
at the limit! YOU MUST ROLL THE MOTOR OVER (by hand)BOTH FORWARDS &
BACKWARDS TO BE SURE THERE IS CLEARANCE AT THE LIMITS!! REMEMBER,
WHEN OFF THROTTLE THE CHAIN TENSION REVERSES!!
If it locks up, retard the cam on the intake side, (or advance on the exhaust side) to get more clearance. and try again until the clearance is found. Each hole on the vernier sprocket changes the cam timing 1.5 degrees at the cam (3 degrees at the crank).

I suggest as a test to find this limit, you advance the intake cam until you do find the minimum needed clearance, and permanently mark that point on the cam cap. That will be the point where the cam must NOT be advanced past. Then do the same with the exhaust only retarding it until the limit is found.
Timing initially is dependant on design of cam lobe. Older designed, and aggressive large duration cams will be more retarded.(intake) and advanced (exhaust) because of ramp & valve lift in order to fit in a engine that is already assembled and valve relief's not designed for large cams.
Tighten and install lock nut on intake and bolt through sprocket and cam nut. Inspect carefully.
Roll the crank over by hand to verify timing.
When the intake cam is at the limit, or LC setting whichever is more advanced. You are there!
When the exhaust cam is retarded as much as clearance allows you are there.
 

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What if true TDC were never determined and the timing pointer is in the wrong spot?
Shouldn't that be done as a foundational step?
Nothing will ever be correct if that is no set correctly. talk about bad cam timing!!!
 

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I wouldnt even use that when setting up valve timing...I use a TDC indicator with a dial gauge on the end of it. it threads into the spark plug hole on the other end.


Do this, then check P to V clearance (carefully!) as Richard talks about above.
 

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I wouldnt even use that when setting up valve timing...I use a TDC indicator with a dial gauge on the end of it. it threads into the spark plug hole on the other end.


Do this, then check P to V clearance (carefully!) as Richard talks about above.

CORRECT!!

You never know where the pointer is set unless you check it with a TDC indicator.
 

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Think about it guys. Sure you should know where TDC is but if you are advancing the intake cam as far as it will go without piston/valve interference then it is not that important for it to exactly accurate. Same goes for retarding the exhaust cam.

Jim Steck once told me that when he sets up cams on a motor on his dyno he only marks the cam caps after he has found the best position for them. Establishing exact TDC could be done at the same time. He does not always know what the timing is in degrees, It is the same principle.
 

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Think about it guys. Sure you should know where TDC is but if you are advancing the intake cam as far as it will go without piston/valve interference then it is not that important for it to exactly accurate. Same goes for retarding the exhaust cam.
I get that. But what if the issue all along has been that TDC was never determined, and all subsequent adjustment were made to cam and ignition timing?
 

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If you know for sure where they should be set then accurate TDC is important but how often is that the case? In my case the reason that 101 intake LC worked best with Venolia pistons and RJ575 cams was that there was insufficient clearance to advance it any further.

Also consider the accuracy of setting the LC or the ignition timing. Maybe you can set the TDC pointer to +/- 0.5 degrees. You cannot get close to that accuracy when you mark the cam cap with a Shankle/Centerlie template but that is OK since the smallest change that you can make to the cam timing is 3 degrees. And this assumes that the LC mark on the camshaft is very accurate, which it probably is most of the time but how do you know for sure? Similarly you set the ignition timing with a strobe when the marker on the pulley is dancing around a little. I suggest that there is usually an uncertainty of a degree or two in that measurement which is not a big deal since 1 or 2 degrees change has little effect on engine power unless you are at the threshold of detonation.
 

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Some people don`t seem to read, or have insufficient mechanical aptitude to comprehend that setting cam LCs at optimum position to get best valve events has nothing to do with TDC. You are setting the cam position at the optimum point where P to V issues are at the limit clearance wise.
The earlier (advanced) you can set the intake cam then the earlier it will close reducing reversion and improve the power stroke. Set with adequate clearance the piston will never touch the valve.
Valve float from inadequate spring pressure and too high RPM only acts as a rev limiter on the intake side..

The later the exhaust valve opens the longer the power stroke, BUT critical is having adequate P to V clearance as the piston can & will hit a "floating" exhaust valve. Then you can kiss the head, piston, liner good by...
 
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