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Cam and follower breaking

Engine Building Fundamentals

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Discussion and questions related to the course Engine Building Fundamentals

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Camshaft manufacturers usually recommend around 2500 rpm steady for 20 minutes or so for break in. How do you take this into account as it seems to contradict the cycling methodology you discuss?

Whether or not this presents a problem for you will depend on your engine type. The requirement for a specific cam break-in procedure is really critical for the a flat tappet style of lifter. If you're running a roller cam then the sliding friction between the cam and tappet is eliminated and hence the break-in procedure is not so critical. The recommended break-in procedure is designed to ensure the rpm is high enough to maintain adequate lubrication of the cam to tappet interface thanks to oil splash from the crank.

I spend most of my time assembling double overhead cam engines with roller rocker or finger follower valve actuation where this really isn't a consideration. That aside, the procedure for break-in that I discuss in the course is still applicable. Note that I recommend applying load as soon as possible and using a modest amount of rpm initially. The cam doesn't really care about the load but it's the rpm that's important from a lubrication perspective. By using a modest amount of load and 2000-3000 rpm for the first 15-20 minutes, this will aid your engine and cam break-in simultaneously. Make sure that during this time you vary both the rpm and the engine load.

While I'm always incredibly careful with my engine break-in and have used the same techniques religiously for the last 15 years, the reality is that with modern rings and modern honing techniques it's getting pretty difficult to end up with your rings not bedding. It's certainly less critical than it was a few decades back.

Hello,

Follow up question for clarification. Regarding the statement "applying load as soon as possible and using a modest amount of rpm initially. "

Referring to the use of the word "initially", does this mean apply load immediately upon first start or apply load after the engine has reached operating temperature? If the recommendation is to apply load once the engine has reached operating temperature, then the next question is: how do I reach operating temperature? With a normal idle or a fast idle or a fast varying idle? In my particular case, my engine has a flat tappet cam profile.

Thanks in advance.

I would do it as soon as practically possible. 1 or 2 minutes of idling won't hurt, but as soon as I knew it was stable and running, I would put the load on the dyno and get it up to 2000+ RPM.

For the pushrod*, flat tappet/follower, the single most important part is the splash lubrication, and making sure there is a very liberal coating of the manufacturer's cam' lube or some other anti-scuff lubricant on it - not forgetting the cam' gear* that drives the distributor and oil pump, if used.

If need be, just run the engine at 2k+ no-load for the 20 minutes, while running through the basic checks for oil pressure, leaks, strange noises, etc. After that there's plenty of time to start loading the engine as part of the ring break in and tuning.

Remember, the engine load makes NO difference to the camshaft loadings

[edit] Forgot, for (D)OHC engines it isn't that significant a concern as most will use some form of pressurised feed directly to the lobe-follower interface. Some don't, though, and if they use splash the same practice would be expected to be used.

It's not uncommon to just run the inner spring(s) for the initial cam' break in when heavy springs are to be used (damn good practice, actually) and then the lift is checked for possible lobe failure before the actual springs being used are fitted.

*Don't forget to double check compatibility of the gear with the camshaft - get it wrong and the gear and/or cam' will wear rapidly - seen it happen when the aquaintance ignored my query.

I built a DOHC engine recently, that required this type of cam break-in. I did a lot of reading up on it first, to make sure I knew what i was doing. I like to understand the theory and the mechanics behind what I'm doing, as opposed to just blindly following instructions.

The cam buckets are just splash lubricated, no direct oil feed. The theory behind the 2000 to 3000rpm for 20-minute break-in is three-fold:

Firstly, the oil pump isn't spinning fast enough at idle to get adequate oil flow up to the head to help the cams that are only splash lubricated. So 2000+rpm solves that.

and Secondly, when the engine is moving slowly at idle, there is lots of time for the slow moving cams to displace the oil and break through the oil film between the cam lobe and the bucket. Which would result in direct metal on metal contact and can ruin a set of new cams and buckets very quickly. But at the higher rpm, the oil doesn't have enough time to get pushed out of the way, so it is able to act more like a fluid bearing. Think kind of like a non-Newtonian fluid at higher rpm.

Third, the extra speed helps the cam lobes to mate to their cam buckets as quickly as possible. Once they're mated properly, the cam lobe will "push" the bucket to spin in its bore.

When the cams/buckets are broken in properly, you should see a nice clean and obvious circular pattern on the top of the cam buckets. If there is no clear circular pattern on the bucket, it'll probably look like the lobe is just pushing straight against it, that means the bucket is not spinning. Which means the bucket and the lobe are just grinding against each other, and will completely fail at some point soon.

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