Why do some new cams require a 'break-in?'

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2,187
Location
Arizona
I've been wondering that since seeing it posted here on the board a fair amount. This makes no sense to me. The valve springs exert the same amount of pressure regardless of how fast the motor is turning or whether it's turning at all. What's the thinking behind this? Is there any actual thinking behind it at all? BTW, the aftermarket cams I've installed in the past have not had such a stipulation.
 
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43,652
Location
'Stralia
Everything requires break-in, to maximise the contact area netween new componentes. Most things break without issue or special treatment. Some manufacturers stipulate additional procedures to be sure to prevent problems.
 
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516
Location
Massachusetts
quote:
Originally posted by bulwnkl: I've been wondering that since seeing it posted here on the board a fair amount. This makes no sense to me. The valve springs exert the same amount of pressure regardless of how fast the motor is turning or whether it's turning at all. What's the thinking behind this? Is there any actual thinking behind it at all? BTW, the aftermarket cams I've installed in the past have not had such a stipulation.
The lobes of a flat tappet cam in any V8 Chev, Ford or Mopar are splash lubricated. Lubrication at idle is minimal and not enough to lubricate the cam/lifters until they are worn in or seated to each other. Unlike your experience, any flat tappet cam I have installed required about 1/2 hr run time at 2,000 to 2,500 rpm to break it in. This does not apply to later roller lifter applications. [Cheers!]
 

bulwnkl

Thread starter
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2,187
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Arizona
I can accept that, Russ. What I'm asking is more to do with why 2-2.5k rpm is magic. There doesn't seem to me to be more stress on a cam at higher rpm, and there certainly isn't <i>less</i> oil at higher rpms. I also have never installed any roller-lifter cams; only finger-follower. Still curious...
 
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1,967
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Kitsap, WA
Over simplified but: You need parts to be moving to build hydrodynamic oil film, think of it as surfing or a boat getting up on plane. The faster the cam spins the more chance it has of building an film of oil preventing metal to metal contact. Now consider the camshaft spins at one half crank speed. So your engine at the recommended 2000 rpm intiial start-up only has the cam spinning 1000rpm, barely enough to build good oil film. Good quality assembly lube is paramount. In some builds using lighter valve springs during breakin, or removing 1 of the dual springs is the only way to keep from wiping the cam.
 
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2,387
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Chicago area
Like Shannow said, all cams [and all parts] require break in. Doesn't it seem right that parts should mate together? You have to break your shoes in, before they wear out.
 
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1,855
Location
Australia
what you are actually trying to achieve is correct lifter rotation on the cam lobe. The lifter has a convex radius grond on it's contact face, IIRC it's around 1-1.5*. The cam lobe has a taper aqcross it's face, eg, one side is higher than the other looking across the lobe. This combined radius and taper ensure that the lifter constantly rotates relative to the lobe, if it didn't, the lifter and lobe would chew out in no time flat. By running in the cam and lifter, ie. i/2 hour at 2-2500RPM, you are ensuring lifter rotation actually happens and that they actually 'bed' in to each other to continue rotating.
 

bulwnkl

Thread starter
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2,187
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Arizona
Well, tdi-rick's post would explain why I haven't seen this recommendation myself. The rest of the general wear-in explanations are still escaping me, I'm afraid. The reason is that I don't immediately see how the load on the cam or lifter is any different under various operating conditions the way that load varies, for example, on the rings, pistons, bearings, and cylinders. I can see how too low an operating rpm could possibly maybe give insufficient lubrication if the oiling system was designed such that it shorts the cam of oil at idle, though that seems like an utterly stupid design flaw to me. Anyway, let's keep trying...
 
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2,364
Location
sebring, florida
it is a stupid design flaw. why have a splash lubed cam in an engine with an oil pump? i am pretty sure that only these old fashoned splash lube cams require any special breakin. anything ohc, it gets force fed all the oil it can handle. my ohc motor at nearing 100,000 still shows the original factory machine marks on the lobes. there is literally no wearing down of the lobe or follower.
 
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1,855
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Australia
sheesh, in a pushrod engine with conventional (non roller) lifters, the reason is as I said above. Every conventional lifter push-rod race engine I've ever had anything to do with had the cam run in. A mate even made a cam running in rig for Formula Ford 1600's, it was that critical.
 
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267
Location
Idaho
quote:
Originally posted by Master ACiD: it is a stupid design flaw. why have a splash lubed cam in an engine with an oil pump?...
Because it was "adequate" for stock use with relatively low spring pressure at moderate speeds. Many millions of this type engine have driven billions of miles with no significant problems due to this inherent design flaw. Put higher pressure springs in to allow high rpm use in a high speed operation and now there is a significant need for better lubrication to allow a favorable break-in, as was explained above (some engine builders will install lighter springs for break-in). The only way to get this improved lubrication is to keep the engine revved up enough to allow plenty of 'splash oiling'. Ignore this advice at your own risk. Joe
 
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3,442
Location
Austin, TX MSA
quote:
it is a stupid design flaw. why have a splash lubed cam in an engine with an oil pump?
Gee, only about 1 billion small block V8 chevy/ford/mopar engines were built this way before the advent of roller cams... As Lazy notes, it's fine for stock cam grinds and lower springs pressure. Breaking in more radical cam grinds and higher spring pressures requires more care. The lifter bottoms and cam lobes are not micropolished and thus have different friction patterns on them. You have to run the engine faster to increase oil volume and avoid wear on the lobe ramps. Also, I highly recommend NOT using white lithum grease for this as someone above recommended. Use the cam grease recommended by your cam manufacturers. All that aside, if I was building a hi-po small block, I'd probably use one of CompCams kits to put a roller cam in an engine that was originally non-roller. Yes, it's more expensive, but it enables much more steep lobe profiles and better performance without giving up so much in the way of a radical idle and poor vacuum. IMHO.
 
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2,364
Location
sebring, florida
quote:
Originally posted by Brons2:
quote:
it is a stupid design flaw. why have a splash lubed cam in an engine with an oil pump?
Gee, only about 1 billion small block V8 chevy/ford/mopar engines were built this way before the advent of roller cams...

you could make the same arguement about flat heads, or worm gear steering. just because alot of splash lube engines were made doesnt make it right, or even good. it is what it is. dont get me wrong im not bashing american car makers. vw pancake motors also had splash lube cams even though they had oil pumps. if an engine already has an oil pump, why not force feed the cam some oil? doesnt make sence not to. i wonder if there is any modern engine made today with a splash lube cam? anyone know? id be curious as to this.
 
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3,593
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Outside smalltown, IL
A better question would be, what engines have direct oil feed to the cam lobes? None I'm aware of. They all feed the cam bearings and the lobes get what escapes between the cam journals and bearings.
 
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260
Location
Newtown, PA
quote:
Originally posted by jsharp: A better question would be, what engines have direct oil feed to the cam lobes? None I'm aware of. They all feed the cam bearings and the lobes get what escapes between the cam journals and bearings.
*Nods*, my DOHC saab has splash lubed cam lobes. The cam journal is only a few millimeters away, but it's still splash lubing. Do you have to use a special kind of oil for cam break in?
 
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267
Location
Idaho
I chose Delo 400 15w-40 to break-in my fresh 300 Ford this spring. I also added an extra quart. And I slobbered plenty of Clevite cam lube goop all over the cam lobes and lifters when I assembled the engine. Plus I pre-lubed the engine by spinning the oil pump with a drill before startup. Then did the 2000rpm thing for 20 minutes. All this for a near-stock engine, but I am running a high-rate, short overlap cam with all new components so I was careful to ensure proper break-in. I believe the significance of the 2000-2500 rpm spec is that we want enough revs to thoroughly lube the cam but we aren't quite ready for max rpm just yet. Joe
 
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1,910
Location
Vista, CA
The 2.5k speed, besides washing the cam in more oil than idle speed also carries away a tiny bit more heat which could be generated while the parts meet each other for the first time. This could include a few particles, too. This faster speed could also help in say a turbo motor when you finish a long run on the freeway and pull off to get gas. Running a little above idle for a few minutes can lube the cams better and carry away some extra heat from the cams and the turbo. Going to idle just means that the cooling slows down quicker than the production of heat.
 
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