which rockers to buy and where?

[guibo09]

application: future 3.0L stroker with an aggressive streetable cam, and upped springs if necessary

use: (auto-x, lapping, daily summer driver)

goal: reliable 7000rpm rev limit


i'll be replacing all 12. what rockers do you guys recommend, OEM, IE HD, or other? i definitely dont have the budget for billet rockers and do not think they are necessary.

[Knockenwelle]

There are a lot of bullshit theories surrounding rocker arms for the M20. First, know this: unlike steel, aluminum does NOT have an infinite fatigue life. Supplanting the materials science explanation, just know that means that under repetitive loading, it ages and gets weaker over time. Steel gets to a point in its cycle life where it stops getting any weaker. So the top three concerns for rocker arms in the M20 are, in order of importance: age, average RPM, and spring load. At reasonable spring loads, and without revving the piss out of these motors, the rockers will last quite a long time. However, when a high-mile motor is subjected to a new owner's probing of the rev limiter, they WILL break in short order.
Also, material quality plays a big part in their longevity. Though there are many different vendors of rocker arms and vehement proponents of each, unless there is a blatant manufacturing defect such as porosity or core shift, or a lack of engineering in making the product robust enough, it's hard to go wrong with any of them. 7kRPM is not an unusual goal for the rev potential of an M20. I spin mine reliably to 7400, and I'm just using Febi stock replacements (though I inspected them thoroughly). My motor has about 2k miles on an all-new set installed with the total rebuild (as well as a Schrick 288).
Another point to consider, as I mentioned, is the spring load. There is absolutely no need for huge valvesprings on the M20. I used a set of the Metric Mechanic beehive springs and retainers. Though only a single spring, which actually has less nose pressure than a stock i double, the improved dynamic response and savings of 2/3 lb of total weight is a big help and will extend rocker and cam life quite a lot. Whatever you do, stay under 200 lbs of open spring force.
HTH.

[guibo09]

thanks for the advice.

so to summarise, you suggest i used stock OEM rockers, with some upgraded springs for when i will run a more aggressive cam?

how necessary are the springs to run an agressive cam to 7000rpm? im assuming my current old oem dual springs wont cut it, are there other alternatives besides MM?

[Knockenwelle]

Yes, stock rockers will work fine. Just look for a set with the shallowest adjuster notch and inspect them (all) thoroughly for any signs of casting defects. In a (track?) car driven enthusiastically with a big cam, remember that they will not last forever, and consider them a consumable.
As far as valvesprings, do some research about beehive springs before you look elsewhere. There is no downside to them; they just work. It's the advancement of technology at work. MM sells the only ones I found, and theirs come with spring seats and retainers, both specialized to fit the M20 properly in terms of locating the spring and install height. IIRC, the stock i springs will bind before the bigger cams reach full lift. Also, Jim at MM recommended that spring pressures be kept under 185lbs max to avoid cam wear and rocker breakage. The stock i cam produces enough lift with the stock i springs to create 165 lbs of open pressure: you don't have a lot of room for more lift if you want to stay under 185.

[guibo09]

some more great advice thanks!

i will probably go with the MM spring kit, i just checked and it's actually very reasonably priced, 20$ per valve.

tell me more about your setup. you are running a straight 288 schrick with MM springs, oem rockers, oem valves, and a 7400rpm redline without issues?

[Justin B]

Stock rockers are not steel. They are cast aluminum or aluminum alloy, which is why people use billet rockers. It removes any doubt that there are casting imperfections, especially microscopic voids/air pockets however small of a chance that is. That said, OEM valves probably are fine if they're brand new but some are still better than others. If its a high performance build where rockers may be a concern I would at the least buy MM's inspected, prepped and shot-peened rockers. FWIW, I am building a stroker motor too and am using the MM Rally cam, springs, etc. However I have to still chose rockers myself. I like the billets, but theyre SO expensive. VAC wants 1900 bucks for their set with the Porsche style elephant-foot adjusters.

[StereoInstaller1]

I would feel a whole lot better if those bitchin' $2000 rockers were at least roller on the cam side.

Overpriced? Maybe, just a bit. If there were enough guys doing these, Crane or someone would have stepped in 20 years ago...

[StereoInstaller1]

Oh yeah...anyone ever do cryo treating of stock rockers?

[Justin B]

I would feel a whole lot better if those bitchin' $2000 rockers were at least roller on the cam side.

Overpriced? Maybe, just a bit. If there were enough guys doing these, Crane or someone would have stepped in 20 years ago...

Seriously, its all too often that I wish I had a small table top lathe and CNC mill.

Oh yeah...anyone ever do cryo treating of stock rockers?

Not that I know of...might be worth trying though.

[Knockenwelle]

Ooohhh, that's a good idea. I dunno why I didn't think of that for my rockers. I've had valvesprings for SB Chevy race motors done, and it tripled spring life on a road-race motor with .662/.672. I considered some of the inspected rockers, but other than shot-peening, they really don't do anything I didn't. There's only 12, and I just couldn't justify the cost. Besides, worst-case for a broken rocker is a dead cylinder. Billets ARE tempting. As far as roller rockers, the geometry is already pretty good. You could gain a few friction HP, and a bit of low-lift duration, but the factory rocker actually allows a lot of ramp rate. They're a matter of course in all my pushrod motors, but I wonder it if would really be worth all the custom parts to convert an M20. I wish Jesel made a set.