Great stuff.
Could it be me? Possibly. Oldjohnno, I’ve made heaps of junk through my own ignorance, stupidity, stubbornness (why else would I be playing with a 202!?), and sometimes bad luck. Why do I have the issue? Dunno for 110% sure, but I know for fact I am not the only one, and plenty of smarter blokes than me.
I wasn’t particularly trying to bring up a solid lifter / cam / break in / failure discussion. I had already decided to groove the lifter bores and use a soft stock type spring for the next run in as opposed to removal of the inner spring only, but I like some of your thinking, in particular probably the suggestion to use three diferent springs (soft -> intermediate -> final springs). It’s not really that much more work, say most of day by the time you get the springs changed and drive for 3 to 4 hours. I could also borrow some 1.5 ratio rockers and that would give over 0.050” less lift and subsequently less lbs.
FWIW - I’m currently assembling a modest engine. It’s only going to be a short term thing, but if it goes and hangs together ok might end up as a spare. I’ve got a couple of cam options, one nicely broken in (but relatively less intensity) cam that has about 12 hours on it, and two agrresive comp cams (one of which is a little out there in terms of design). I haven’t decided yet, but I think I’ll run the broken in cam and new/refaced EDM lifters. There is a deadline for this so time will dictate exactly how I run the cam in. Most likely on stock type springs for a few hours (on the road), change springs, another run and then onto dyno for a very quick check/tune of high rpm. I will groove the lifter bore, and I’m thinking about modding some side plates to watch lifter bore rotation on initial start up / first 30 mins stationary run.
…I’ve got another block out for machining that will be getting built to a better level. It’s getting 7/8” lifters which will run in the correct alignment to the cam. It was harder to find someone to do this than I thought it would be. The comp cams will be tried in this on the dyno. Will be a pain in the arse to break them in before dyno but there no way around it.
…back to the original topic. the roller cam engine will most likely follow, but in reality that is one to three years away depending on how the above motor goes, and if my wife finds out how much I’ve been spending. I have started messing around with it. I’ve got a couple of different types of roller lifter here. All looks possible depending on final base circle. High lift may need bushings, and cause tie bar hassles, but I need to get a bigger lift cam into my dummy up block and have a proper look. Tighe will make the blank to the common bored out roller bearing cam tunnel size, but I’m not sure it’s worth the mod. As per the last line of your first post in this thread - “Only thing I can tell you for sure is that it will be expensive”
Bomber makes a good point; if I'd had a series of cam failures after doing much the same things that work for everybody else, I'd be taking a very close look at the common denominator (ie. me) in the failures. I don't mean to sound like a smart-arse saying this either; I've certainly contributed to enough of my own failures.
This bit's going to be long winded, so I'll apologize up front. Nearly everything involved in racing engines has been oversimplified to the point where it can be covered in a magazine article or a pub discussion. But I think in reality nearly everything is much more complex. In the case of cams, I don't think it's as simple as saying "if you do X,Y and Z everything will be fine". If we look at cam survival rates, I think that the risk of failure rises pretty dramatically once you go past the typical street and strip profiles. In other words pretty much anyone can take a street and strip cam and provided they don't do anything too stupid it'll survive the break-in and last a reasonable time.
But as soon as you start using lobes with higher acceleration rates and spring rates, then the risk of failure rises steeply and I dont believe the usual "20 minutes at 2500" is enough to give a good chance of survival. And even if you do get through the break in phase you won't necessarily get a good life from the cam. Bear in mind that most of the 0.842" lobes that we'd be using would be developed on a gen 1 SBC, and that our Holden six cams are even skinnier than the little Chev camshafts. So a profile that's a bit "iffy" with a smallblock is even more so when it's used in a Holden with a necessarily smaller base circle. If you try to use a profile that's right on the bleeding edge with a smallblock it'll probably fail in a six, so don't get too greedy unless you're prepared to bore out the cam tunnel and use a custom core.
The next thing to consider is the break-in process. What we want here is to develop a thin, work-hardened layer on the lobes and lifter faces. With a street and strip or an old-style race cam 20 or 30 minutes seems to be enough but with more agressive profiles I think you need to go to a bit more trouble. The hard skin is going to have to be thicker to survive long-term, and it takes a lot longer to develop it. It might take a couple of spring changes, and the initial run should be on very weak springs. With all of the break-in runs the longer the running time the better. As for rpms you need to be spinning fast enough to ensure lifter rotation but not so fast that you're on the verge of floating the very light springs - you need weight over the nose to bed in the entire lobe, not just the flanks. Around 2000 to 3000 should be ok, and the longer this process lasts the better - with a street car I like to drive it for at least a couple of hours on the soft springs (being careful not to float the valves) and 3 or 4 hours would be even better. Run low ratio rockers if you can.
Depending on the cam profile and the springs required for maximum rpms you might need to run it again with intermediate springs before putting the final springs in. Run the revs higher this time to keep the pressure over the nose down (say 4000 or so) and again the longer you can run it the better the sliding surfaces will end up - if you can do this for a couple of hours then that would be good. After this you could fit the final springs and rockers and run it to maximum rpms. Bottom line is that the longer and more gradual the process is then the greater your chances of success are.
Everything else (oils, lifter alignment etc) has been done to death. There's no need for a special break-in oil but it wouldn't hurt either if it makes you feel better. Thousands of people have used EDM'd lifters successfully, and if the engine is going to have to run at low rpms I'd use them. But I'd definitely try to limit the low rpms as much as possible, that's what gives the high pressure over the nose.
