spring pressures for cam break in?

[rfoll]

We needed a cam for a budget 406 build, and ran into this deal from Competition Products...https://www.competitionproducts.com/How ... mwmyI1YZdk I have heard that it's a good idea to remove the inner spring when breaking in the cam, but since we will be removing valve springs anyway, why not use lighter springs? This makes me wonder if there are minimum open and closed pressures required to make the event successful. I have many sets available and the means to pre-determine open and close pressures.

[rebelrouser]

Lot of the other guys may have better advice, but from my perspective the deal of using a weak spring to break in a cam just is not practical, unless you have a dyno to break in the cam, and then swap to the heavy spring. A couple times I did the weak spring, run the cam in, then switched to heavy springs and then it went flat. Then that turns into a, you did not break the cam in right, I sell good stuff, you just don't know what you are doing, argument. One time I got an aggressive flat tappet cam looked at the specs, and called the guy, I told him there is no way this cam will live with these spring pressures. he told me it will be fine. Did the break-in, changed springs, cam was flat in 4 passes at the strip. I sent him the cam and all the good lobes had good break-in marks. So my engine is full of metal from the cam failure, so the guy says will sell you a replacement cam at racers net, which was the same price I bought the first one. On a flat tappet hydraulic or flat tappet if the cam needs more than 130lbs on the seat and 300lbs open, I just buy a roller, if you want a good race engine just buy a roller. Just call Howards and ask. Seems most of the cam companies do not want to give spring specs any more. The spring specs should be on the cam card in my opinion, If I need to use an aggressive flat tappet cam, I run EDM lifters, which you can not do with a hydraulic. just my 2 cents.

[Walter R. Malik]

If I need to use an aggressive flat tappet cam, I run EDM lifters, which you can not do with a hydraulic. just my 2 cents.

There are hydraulic "oiling" lifters. They use a small flat ground down the side just short of the lifter face.

[tenxal]

We needed a cam for a budget 406 build, and ran into this deal from Competition Products...https://www.competitionproducts.com/How ... mwmyI1YZdk I have heard that it's a good idea to remove the inner spring when breaking in the cam, but since we will be removing valve springs anyway, why not use lighter springs? This makes me wonder if there are minimum open and closed pressures required to make the event successful. I have many sets available and the means to pre-determine open and close pressures.

We use the light spring method for breaking in our cast cams. On a SBC, my break-in springs are Iskys that set up with 110 on the seat and about 225 open. A quality lifter is mandatory and use a good break-in oil (BR30, Lucas, etc.). We just did two over the past couple weeks on the dyno. After break-in, the PAC 1409X's went on (225 seat/415 open).

On the link you provided...the cam is listed as a mechanical cam. But the lifter adjustment is shown as if they are hydraulic. I have no experience with the Scorpion branded lifters in a race set up.

[dannobee]

Obviously a roller cam is out of the question, probably banned by rule. And if it's a lift rule race engine, it's likely got pretty aggressive lobes.

Years ago when I started building circle track engines, I had a race cam go flat on break-in. Since I "just" built it but didn't perform the break-in, I started asking questions that might be relevant here. Stock type springs are used during cam break-in, then changed to race springs after break-in and rechecking that the lift is still there.

When you first lit off the engine, was EVERYTHING set and ready to go? Was the engine cranked over excessively, perhaps to time the distributor? Was the engine allowed to idle at any point in time for the first 15 minutes? Was the engine stopped, for any reason, in the first 15 minutes?

EVERYTHING needs to be ready before you light it off for the first time. Distributor in correctly, timing close to base setting. Coolant/water needs to be full. Carb needs fuel in the bowls and in sufficient supply to support running for half an hour. Idle screw on carb turned in a few turns so that engine can't idle below 2K RPM. Sufficient oil and any oil lines double and triple checked. Only then can you light it off. If you screw up any of these things, or shut it off for any reason, you'll probably lose a lobe on a race cam. Even excessive cranking to fill up the carb bowls or timing the distributor can cause a cam to go flat. It's THAT critical.

[CamKing]

For any flat tappet cam, that will be running over 300# of pressure at max lift, we recommend you reduce the spring pressure for break-in, This can be done by pulling out the inner springs, running lighter springs, or reducing the rocker ratio by running break-in rockers.

[rfoll]

I guess I should have mentioned we have a test stand. The link provided is in error, https://www.summitracing.com/parts/hrs- ... /chevrolet The heads are not on the engine, making it easy to do the first round of spring change. I have a spring tester and I will check the springs on the head to see where we are. I set up these heads over 6 moths ago and don't remember what the pressures are. The previous cam had more lift. Staying under 300lbs. over the nose is good info, but does the seat pressure matter at all? Sorry about the confusion about the specs. Thanks for the replies, Rick. Another note here, Howards suggests starting out with the lash .005 tighter spec, and shutting the engine down to cool off half way through the run in. I have never heard of such things.

[engineguyBill]

When you first lit off the engine, was EVERYTHING set and ready to go? Was the engine cranked over excessively, perhaps to time the distributor? Was the engine allowed to idle at any point in time for the first 15 minutes? Was the engine stopped, for any reason, in the first 15 minutes?

EVERYTHING needs to be ready before you light it off for the first time. Distributor in correctly, timing close to base setting. Coolant/water needs to be full. Carb needs fuel in the bowls and in sufficient supply to support running for half an hour. Idle screw on carb turned in a few turns so that engine can't idle below 2K RPM. Sufficient oil and any oil lines double and triple checked. Only then can you light it off. If you screw up any of these things, or shut it off for any reason, you'll probably lose a lobe on a race cam. Even excessive cranking to fill up the carb bowls or timing the distributor can cause a cam to go flat. It's THAT critical.

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ THIS ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Even when using lighter springs or low-ratio rocker arms for camshaft break-in, ALL of the points listed above must be followed exactly.

[CamKing]

I guess I should have mentioned we have a test stand. The link provided is in error, https://www.summitracing.com/parts/hrs- ... /chevrolet The heads are not on the engine, making it easy to do the first round of spring change. I have a spring tester and I will check the springs on the head to see where we are. I set up these heads over 6 moths ago and don't remember what the pressures are. The previous cam had more lift. Staying under 300lbs. over the nose is good info, but does the seat pressure matter at all? Sorry about the confusion about the specs. Thanks for the replies, Rick. Another note here, Howards suggests starting out with the lash .005 tighter spec, and shutting the engine down to cool off half way through the run in. I have never heard of such things.

I've never heard of shutting an engine off, in the middle of break-in, We break the cams in for 20 minutes at 2,000rpm.
Setting the lash tighter is a good idea. It makes sure the lifter is on the gentle lash ramp, when it starts to open the valve, and when it seats the valve.

[rfoll]

I just broke in a cam on the test stand 3 days ago. Finally had a 60 degree day that would allow an instant start up. It snowed this morning, season opener at PIR. Cam break in is the only part of engine building and always makes me nervous. It's the easiest way I know of to toss hundreds of dollars in the scrap pile. I have never lost one on the test stand, but doing it in the car is really iffy since the car many other things to attend to.

[swampbuggy]

One thing i did not see mentioned ( i could have missed it ) is never assume the "new" lifters will be ok clearance wise in your block. As we know there must be enough lifter to lifter bore clearance at running temperature to permit the lifters to rotate. This may be step 1 on the list to prevent failure Mark H.

[rfoll]

It's been in the back of my mind of late. I rebuilt a 283 for a friend last year and the new lifters had stuck plungers, wouldn't run correctly at 1/4 turn adjustment. I set the clearance at near 0 and they eventually freed up. Just when you think you have seen it all.

[Walter R. Malik]

One thing i did not see mentioned ( i could have missed it ) is never assume the "new" lifters will be ok clearance wise in your block. As we know there must be enough lifter to lifter bore clearance at running temperature to permit the lifters to rotate. This may be step 1 on the list to prevent failure Mark H.

The lifter to bore clearance must be "correct", to much is just as bad, (sometimes worse), than not enough), ... to much clearance and the lifter can sit flatter on the lobe and lobe taper means less for lifter rotation.

[rebelrouser]

Obviously a roller cam is out of the question, probably banned by rule. And if it's a lift rule race engine, it's likely got pretty aggressive lobes.

Years ago when I started building circle track engines, I had a race cam go flat on break-in. Since I "just" built it but didn't perform the break-in, I started asking questions that might be relevant here. Stock type springs are used during cam break-in, then changed to race springs after break-in and rechecking that the lift is still there.

When you first lit off the engine, was EVERYTHING set and ready to go? Was the engine cranked over excessively, perhaps to time the distributor? Was the engine allowed to idle at any point in time for the first 15 minutes? Was the engine stopped, for any reason, in the first 15 minutes?

EVERYTHING needs to be ready before you light it off for the first time. Distributor in correctly, timing close to base setting. Coolant/water needs to be full. Carb needs fuel in the bowls and in sufficient supply to support running for half an hour. Idle screw on carb turned in a few turns so that engine can't idle below 2K RPM. Sufficient oil and any oil lines double and triple checked. Only then can you light it off. If you screw up any of these things, or shut it off for any reason, you'll probably lose a lobe on a race cam. Even excessive cranking to fill up the carb bowls or timing the distributor can cause a cam to go flat. It's THAT critical.

I have to agree with you 100% and it is one of the hardest things to get people to understand, that is why in my post if you do not have access to a dyno or run stand I never trust a customer to do it right. I don't know how many times they call me to come over and help them swap out the springs, and I see a can of gas with a hose, jumper wires for the ignition system, etc. And I am like what did I tell you, the car needs to be right and ready to run, but all they wanted to do was hear the engine, then they admit well we had a fuel leak, and a water leak, then the battery went dead etc. Most of the time they get lucky, but not always.

[Caprimaniac]

What have been said on triple check everything.

Was given the following advice after a catastrophic attempt to run in a cast flat tapppet:

Run cold water from a garden hose into the radiator/ cooling hoses. Or have it on hand, if it gets too hot during run-in.

If it’s a new build, a bit of uncertainiy around like too small a rad, a worn old waterpump, may blocked water lines....

In my case I did a very stupid thing... head gasket wrong way and no water circulation made headers glow, engine boiling.... $ drain.
Made me switchbto solid roller & stayed on that route since.