BMW M10 rocker arms

[tzei]

Hi

Has anyone any information where to get strong rocker arms for BMW M10 engine? and/or material requirements for making them. Orginal r.arms tends to broke now that i have startet to enjoy living over 7000 rpm for longer durations.

Ireland and Skidmarks are having difficulties to have them made.

[graham bahr]

Originally Posted by tzei

Hi

Has anyone any information where to get strong rocker arms for BMW M10 engine? and/or material requirements for making them. Orginal r.arms tends to broke now that i have startet to enjoy living over 7000 rpm for longer durations.

Ireland and Skidmarks are having difficulties to have them made.

Lester Owen is your man anything he doesn't either know or make for these engines isn't worth knowing. i have used many race parts from lester including steel rocker arms, in my engines, he isn't cheap, but then were talking about low volme quality stuff here its its not gonna be

from the uk his number is 01952 616846.

p.s once you reach about 7500 your find clutches start to explode also, so best order a steel fly wheel for a race clutch at the same time

[tzei]

Steel r.arms... aren't they a bit on the heavy side? How stiff valvespring are you using? Have weighted them and how much did they cost?

Running a steel 2002 flywheel, Sasch race sintered plate & pressure plate(?) (assembly) - i think you know what i mean. I think they hold (have done so far). But i'll upgrade in the future - torgue figures are bit too small even now.

Does mr Owen an e-mail adress or are there any other means to get in contact with him besides phoning?

[graham bahr]

tzei i'll send you a pm rather than boring everyone on here with tales of tuning m10's

[daj]

graham, Its far from boring !!! Please share with us? I am trying to put something together myself at the moment

[graham bahr]

you want m10 then ok you got it.!these are my own findings after lots of years and many many many dyno sessions tuning one for race use.

every thing here is stuff i've learnt the hardway, without any doubt the best worlds best builder of these engines is lester owen, but i couldn't afford lester money for a race engine. so i just bought the stuff i couldn't do without from him.

the only real weak point in these engines is the rocker arms, BMW origonals are better than pattern ones but even then will break is regulary asked to exede 7,000 rpm.
using revs upto 7500 i found using a lightened 316 flywheel and std 215mm clutches were just fine even with 190bhp, this gives a much lighter assembly than the seriously heavy 230mm type flywheel as fitted to Tii's.
once i'd tuned to the point when i was shifting at 7700 i found clutch covers started
exploding with a worrying regularity, even using uprated sachs competition std type covers. at that point a bought a steel flywheel and 7.25 race clutch.
once you get to 8,000 rpm the oil ways in the block are getting a bit marginal, particulary the drillings to and from the oil filter housing, the oilways meet up but there is a 50% miss match between them where they do with is bad news as they also make 90 degree turns at the same time, the cure is to drill the oilways out by quite a few mm, this massively will improve oil flow, finally drill a couple of extra supply holes in the centre main bearing shell, this will improve oil flow to no's 2+4 big end, it sound a little odd but thats infact what bmw did when they stretched the E30m3 to 2.5litres

crankshafts are indestructable, conrods will stand 8800 all day long, infact they will go to 9200 but only once, the second time at those revs they break! std rod bolts are fine, infact i've never even used a new set!

topend now, as long as you have got the later tii 46mm inlet and 38m exhaust valves std valves are plenty big enough, you can buy bigger inlets but its a waste of time and money, i have usfully increased the exhaust valve size but the gains aren't huge and only worth looking at for over 200bhp.
all the heads are quite good, ports only requiring a bit of blending to remove any sharp edges, valve guides can be ground flush with the ports without overly shortening there life.

to get real power these engines need real compression lots of cam and a nice tight squish to make them burn properly.
squish is easy, run the pistons 0.023 inch out of the top of the block, this gives 0.030 squish, any less and it wont burn properly and your loosing out on compression, this is a tighter clearance than most engines will stand but its fine on an M10 because the rods are so strong and dont stretch much.

now comes the tricky bit, almost any sort of real cam in these engines will give valve to piston clearance problems, made worse by the need for high compression.
if you use the 121 type head and skim it down to the point you have almost hit the inlet valve seats and your using 121 tii pistons you can get 12.1 CR, but you will need some massive cutouts machined in the pistons to clear the valves. it can be done i got 12.1 despite the 6-8mm deep valve pockets we put in the pistons.
you can only do this with the 121 head, due to its smaller chamber, inital higher cr and the fact that the pistons have very thick crowns. try this with an e12 head and you have no compression as the pistons will end up with holes in them!
having skimmed all this metal off the head, the timing chain tensioner needs modifying to keep the chain tight and the cam sprocket will need redrilling to get the cam timing right, its also a good idea to drill and tap the cap for the tensioner to make it manually adjustable as the tensioner can back off when you lift from high revs.

lester gets high cr by using a domed forged piston and machining the combustion chamber to accept it, its arguably better, but costs ££ to get the head machined and about £1000 in pistons, i used std off the shelf Mahle £200 pistons which coped with 8200rpm just fine.

cams for all round competition schrick 316 is best, and is just about within the scope of std rockers, if you get the rest of the engine right its good for around 195bhp.
336 is next, but much more peaky and you really do need those steel rocker arms to make use of it, not to mention a close ratio gearbox

carbs, twin 45's with 38 chokes will get you 180+bhp, 48's with 42 chokes 215bhp
engine management and throttle bodies is better though, i once cut up a weber inlet manifold and welded it back together without the bend and gained 10bhp! speaking to lester he confirmed he found the same by using a chevron inlet manifold which has only a slight bend not 30 degrees like std, unfortunatly this only works with throttle bodies as it would tip the carbs up too much. whilst on engine management double injecting was found to be worth 12bhp in the midrange!

there you go, i could write much more, including stuff about 2.2, 2.3, 2.4,2.5 engines but everyones already asleep i guess

[pmoloney]

Anything on M20's by any chance!! :-)

[TEAM78]

You sure know your stuff Graham

[graham bahr]

Originally Posted by pmoloney

Anything on M20's by any chance!! :-)

i've worked on loads and long time ago played with them for fast road use, but i've not done any race tuning on them. my favorite was 2.6, using 325 bore with a 323 crank, unlike doing a 2.7 conversion with an ETA crank you can rev the 2.6 hard.

[graham bahr]

heres a tip, i've only used it on m10 but it would work on m20 as they are so similar in the valve train infact the m20 has a bigger rocker ratio so it would work better, if you looking for every fraction of valve lift, face some extra material of the inlet valve seats, it will sit the valve deeper in the head, thus pushing the stem through the head further, this will move the contact point of the valve adjuster and increase lift, go too far and the adjuster will walk off the edge of the valve, but on an m10 you can gain 0.020 + valve lift depending on where every thing started, more possibly on an m20

[drjim]

Apologies for reviving such an old thread, but I am intrigued by Graham mentioning "2.3 2.4 and 2.5 engines" I had a brief PM discussion with Graham about a sensible approach to a budget M10, but I thought you couldn't get much above 92mm bore, which with an S14 crank gives 2.3L - how can 2.5 be possible???

There's not enough information on M10's on the web, so I implore Graham to tell us more!

Jim

[tzei]

I've seen old blocks bored to 93.4mm so with evo3 crank you're close to 2.5ish.