m20b25 valve springs; should they be replaced?

[wakeboardr42393]

Rebuilding my engine to race in a production class (engine must remain Pretty much stock oem) and i want to know if i should buy new valve springs.

Has anyone had their m20b25 valve springs tested for spring force when rebuilding their engine? If so, what shop have you used? And what is the spec they should measure to? Or is it worth it to get all new springs? I was having issues with breaking rocker arms while at the r3vlimiter before teardown.

I plan on Ordering all new springs and rockers and cam from BMW but I want to get your opinion on the springs before I confirm the order.

[digger]

according to metric mechanic

[ELVA164]

My opinion is to play it safe and replace them.

[redlightpete]

Has anyone here ever broken an OE valve spring? How about valve float issues, presumably from springs that have lost force? I've never heard of either issue with an m20.

[TobyB]

But you hear of people breaking rockers all the time, at redline, or under...

I use an inexpensive Summit valve spring pressure tester.

I found all the springs I had for the i head were fine, so I reused them.

The same has not been true for M10 aftermarket 'race' springs.

t

[wakeboardr42393]

Thanks for the responses everyone! I think i will go to summit today and buy one of those valve spring testers, and use the specs from metric mechanic! Now, is there a difference between seat pressure and nose pressure (as written in the specifications) when i'm testing?

and yeah, i was wondering if valve float at the upper end revs could have been causing valve float in small amounts, maybe making the case worse for the rockers, along with the worn cam, valve guides, and rocker pads.

[digger]

Thanks for the responses everyone! I think i will go to summit today and buy one of those valve spring testers, and use the specs from metric mechanic! Now, is there a difference between seat pressure and nose pressure (as written in the specifications) when i'm testing?

and yeah, i was wondering if valve float at the upper end revs could have been causing valve float in small amounts, maybe making the case worse for the rockers, along with the worn cam, valve guides, and rocker pads.

seat pressure is the force in the spring at zero valve lift. so its how much force the spring is exerting on the seat. this is equivalent compressing the two springs to a length of 1.465" note that the inner spring gets compressed a little more due to the step in the retainer of a couple mm or so.

then as the valve opens the force in the spring increases. you compress it to a length of 1.04" which approximates the spring force over the nose (max lift).

so 1.465-1.04= 0.425 which is approx what stock cam lift is

most likely cause of wear is wrong oil with not enough antiwear and extreme pressure additives

[TobyB]

Yes, weak springs ARE hard on cam and rockers- it can cause pocketing and galling
(says Delta Cams)

A slightly too- stiff spring is always better than a slightly too- weak one. That said,
the factory springs seem to be pretty darned good, in the (limited) number I've tested.

t

[ForcedFirebird]

You were not getting valve float, or you would likely have bent valves. I have found over the years that the rocker is stronger than the valve by a good margin. Had a head come in last year after an intermediate gear failure. Every single valve was bent, five rockers broke and both rocker shafts bent.

I have raised the rev limiter in my tired m20 (head rebuilt about 8yrs ago) to 7100 (had a 4.27 and 4.10 back then), and banged it off the limiter here and there on the track for 2yrs, never broke a rocker. BUT - the valve guides are tight and I hold a tighter-than-spec lash. I believe the rockers break when the lash is too loose and guides are worn.

With a fresh head, I tend to adjust the rockers to .008" (should say fresh guides). It will lope a little more at idle, if a customer complains, I loosen them up a bit. Unknown or high mileage, they go to .010".

[nando]

spring steel doesn't really wear either. unless it gets damaged somehow, it doesn't really break or change over time - you'd have to bend it past the yield point. if they were aluminum, then they would fail after X number of cycles, but steel doesn't work that way.

personally, I doubt they actually need replaced unless something damaged them. the rockers and valve guides are the wear items.

[ForcedFirebird]

Spring steel still breaks. Not on an m20, but I have had stock valve springs break in the past.

[TobyB]

My experience has been that BMW- sourced springs are very good. They are not perfect,
however, and have a little variation, in both height and rate. If they overheat drastically, all bets are off,
but it's really really hard to overheat a BMW spring in an older engine. Higher lift
and higher revs don't seem to bother them too much, so I suspect they're way over-
engineered for the application.

Aftermarket- read, racer- springs are a lot more variable. Especially from 'tuners'
rather than manufacturers. Isky springs were as good as BMW's. Schrick, likewise.
Things from other 'race' shops were more variable, with heights varying after time,
to the point where pressures dropped and rockers broke.

Springs DO age- the usual symptom is that they lose height, but they can break, too.
The rate should never change- much. Even in cheap springs.

That's what I've found, over the years...

John, my experience with floating the valves in an M10 was that I could get away with
mild float for some time, and it tended to eat the lash pads and hammer the valve
faces. When it got worse, the throttle closing at the end of the rev- limited straight
was always where the rocker broke- that extra vacuum held the intake open a little
longer, and when it snapped back, it took the rocker with it.
Predictably, if that happened with a tailwind on an engine that had been together
with marginal springs for some time, the intake lash pads
would show noticeable galling and 'pick out' erosion. If it was something dumb
(a less- gentle overrev, a void in the rocker, etc) on an engine with stiffer springs,
there wouldn't usually be any galling.
This was with an effectively stock rate spring running at about 1k over factory redline...

But that's just what I found...
t