I keep breaking rockers. Bad luck? Or something sinister.

[MidnightSpeeder]

I need some M20 expert opinion here because I'm stumped. Here's a bit of backstory: I blew a head gasket at 250,000 miles. I pulled the head, had it machined and cleaned and put her all back together. It lasted for 3,000 miles then snapped the tip off of a rocker arm. So I pulled the head again and took it to the machine shop and had them replace ALL of the rockers, figuring if one broke another might break soon due to high mileage. With 12 new rockers on the head, I put her all back together again. 300 more miles and I broke another rocker. I've been digging for info as to why this might happen and i'm coming up dry. I've also never seen this happen. Am I just having a terrible-ass run of bad luck and one of the rockers in the new batch was defective? Or is there something mechanical that could be causing these things to snap off right before the valve eccentric? For those 300 miles it ran damn good, so I don't think I have anything going on, and i'm religious with my valve adjustment and timing, I don't accept less than perfect.

[e30davie]

Were the 1000miles and further 300miles sunday drives or thrashing on a race track?

What do you set your valve clearances too? can you still hear some ticking even with them adjusted to spec?

[digger]

- the cam is worn?
- valve springs are shot ?
- clearances done poorly ?

The above can create bad dynamics.

- crap cheap Chinese rockers perhaps ?

[MidnightSpeeder]

Were the 1000miles and further 300miles sunday drives or thrashing on a race track?

What do you set your valve clearances too? can you still hear some ticking even with them adjusted to spec?

Just backroad drives to work. After I put it back together I don't Rev past 5k for a few days then I maybe redline it once per day. I set them to .25mm per the Bentley manual spec and yeah I get the sewing machine tick even when adjusted to spec.

[jeffnhiscars]

you do mean 25mm not .25 right ?

[vpilarrt]

you do mean 25mm not .25 right ?

Umm, you do realize 25mm = 1" and .25mm = .010", right?

[MidnightSpeeder]

Was confused for a second lol.

[LateFan]

"Set your cold valve clearance to 1". Listen for clatter, watch for flying metal. Repeat."

[jeffnhiscars]

The metric side of my brain was on hiatus

[e30sh]

Inspect the next batch you get. Pull the eccentric pin and look for air pockets in the casting where it was machined. Even genuine BMW ones have the air pockets ever now and then.

Genuine is $$ now. Febi was OK for a while, not sure where they are made now. Don't know what other brands to recommend if you are on a budget.

Good luck.

[MidnightSpeeder]

I'm starting to lean towards the side of bad luck. The first rocker that broke was intake cylinder 2. This one's intake cyl. 3. And my camshaft looks clean and pointy.

[e30sh]

Did they replace the rockershafts with some off brand? Maybe the oiling holes are off a bit or full of crud.

[e30davie]

Pretty bad luck to have two go on you.

I you hear some ticking with the clearances set then i think that its fair to say they are about right and are not the cause of your issue.

Dodgy valve springs is a good suggestion, as i suppose if the springs were not springy enough then perhaps it could cause some issues, but that would essentally be valve bounce/float, which I'm sure you would hear if it was happening below 5000rpm.

But that is really clutching at straws.

[TobyB]

Intakes do tend to break first with weak valve springs.
You DO have inner and outer, right?
The float's not audible, nor is it very severe- all the rocker has
to do is slightly lose touch with the cam when you lift off, and 'pop',
you're down a cylinder when you get back on the gas...

If you had a SBC, there's an on- engine checker you could buy.
Sadly, for an M20, I think you have to take it apart and measure them.

And I dunno what's going on with M20 rockers currently, but for M10's the OEM rocker
was a Febi, voids and all, with a 250% markup. I eventually gave up, and bought
the IE 'Heavy Duty' Fabrique au Chine rockers for not much more than Febi,
and never had a problem after that. That said, the Febis, voids and all, held up
to about 7500 with good springs.

MS, you're a prime candidate for sticking a little camera down the plug hole and
making sure there are no shiny moon smiles on the tops of your pistons....


t

[Garage30]

I once had a customer car who also kept breaking rockers. When the engine overheated I pulled the head for parts and found a couple ever so slightly bent valves. Probably from a money shift or something.