engine and drivetrain Km Steel Rocker Arms

[alexfl82]

Hi, 

my engine broke a rocker arm last weekend, I use my car for tarmac rally.

Engine has Schrick 316º and Schrick valve springs. Power band actually with weber 48 is around 6000-7500rpm, very close to the redline of the original M10 rocker arms.

 I have read a bit about KM Cams steel rocker arms, but not much.

The price is good (185€ shipped), but I’m not sure about use them.

I don’t want use any other aluminum rocker arm (I.E., etc….) all friends that used them had problems with them. 

Anybody using the KM rockers?

Positive feedback?

My biggest dude is about the pad, and if it can ruin the camshaft. The extra weight is not a problem for me.

I know that Lester Owen rockers are a good option, but costs 650GBP + VAT.

Thanks in advance for your help. 

Alex.  

[FB73tii]

I bought KM Cams rockers after reading recommendations here (John Forte and others) and also having a set of new aluminum rockers from another supplier damage my Schrick 316 cam on break-in. I had the cam ground to repair the damage (fortunately caught it early) and re-broke in with KM Cams rockers and no problem. I used moly-graphite lube on the cam lobes and Joe Gibbs high ZDDP BR30 break-in oil for the cam break-in. Then due to a mis-specification error on my engine (valve-piston clearance too tight and valve springs a bit light for the steel rockers), I had a valve hit a piston and bend and cause havoc. The intake valve head broke off and the piston pushed it into the exhaust valve head and bent the exhaust rocker shaft. After all this the KM Cams rocker is fine--those suckers are strong. I had my other motor (M10 with 336 Schrick cam) built using KM rockers but have not fired that one up yet.

 

See here for engine failure carnage:

http://www.bmw2002faq.com/topic/144536-valve-guide-major-failure-why/#entry942450

 

Fred '69 & '74tii (both with KM Cams rockers)

Edited October 9, 2013 by FB73tii

[kbmb02]

Data point: I and several other racers here in Southern California run Ireland Engineering's HD rocker arms, with cams including the Schrick 304 and Schrick 316 at RPM's up through 7,800 and higher. Absent piston to valve contact, binding valve springs or other install issues, I haven't seen or heard of an HD rocker breaking (I once had an issue with wear on a Schrick, which I traced to using an inadequate oil (Mobil 1)).

 

Some install them right out of the box, others (okay, that's me) race prep and shot peen them once more for piece of mind.

 

Again, that's just a data point on the IE HD rocker arms. I have a sample of the KM rocker arm in my box, but have not run them. -KB

[alexfl82]

Do you think Schrick double spring valve will be fine for the KM rockers?

[alexfl82]

Fortunately this wasthe only part broken.

[FB73tii]

NOTE: UPDATED 10/27/13

I realized my graph had the wrong open pressure, I forgot to add in the base closed pressure. I have replaced the graphic below with a full data set and updated graphic.

 

NOTE #2: All spring heights and pressures quoted are for the BARE SPRING only, no spring cup or retainer.

-------------------------------------------------------------------------------------------

Alex--obviously critical to get this right--it would be great to hear from race engine builders the actual measured spring pressure they are using and what their valve train configurations are.

While I am not qualified to tell you which springs to run or how much seat (closed) and nose (open) pressure is required for your application, I can share my thoughts and research. I have been told that valve springs do not always measure out at what the spec says, and this weekend I found that to be true with the new VAC dual springs I ordered. I'll have to call them to find out why this is. Often times the spring supplier does not specify how the springs were measured. I.e., with or without retainer, height of inner retainer spring shelf, with or without spring cup.

Below is a graphic giving my calculations (from published or verbal specifications) for five dual springs used with high-lift M10 race motors, as well as my actual measurements on a RIMAC spring tester for two of the five. I have been told that Schrick springs do not measure out as stiff as published, but I have no personal measurement to back up that assertion.

 

UPDATE: Table of open and closed spec and spring rate in lb/inch for all these below. Nose pressures are calculated at max lift for a Schrick 316° cam with 0.010" valve lash.

 

 

 

You also want to consider a number of variables regarding the weight of the drivetrain. Steel rocker arms likely have a greater polar moment of inertia than aluminum rocker arms, but this is hard to measure and cannot be deduced simply by comparing the overall mass of steel and aluminum rockers. Dual valve springs have more mass to control than single, on my 336 cam engine we are using single-wound Comp Cams beehive springs (Bill Watson at Road Rockets, a BMW M10 and M12 engine specialist, has used these on similar builds).

Titanium retainers are lighter than stock, and beehive spring TI retainers are lighter than dual spring retainers. My first +1mm valve set came from SI valves and the intakes averaged 92.3 grams each. My new set of Manley +1mm valves are 7.5 grams lighter each! Similarly, SI exhaust valves averaged 82.0 grams each, and the Manley exhaust valves are over 5 grams lighter each. You can always use shims to increase spring pressure if needed. Finally, I believe Schrick used to make steel M10 rocker arms. I can't find them in the current catalog, but I have the info at home. If this is correct, one can imagine the Schrick springs and rockers were designed to work together with Schrick high-lift cams.

Another thing to consider is that dyno pulls do not simulate valve train accelerations seen on track. When I first dynoed my engine (before the V/P contact), there was no sign of valve float up to the 8,000 RPM redline we used. However, this is a long flat out pull, constant conditions if you will. On track the valve train sees higher rates of change in acceleration (slew rate) than on the dyno under downshifts. I am not talking about mechanical overrev due to shifting into the wrong gear, but mechanically increased rates of valve train acceleration that the valve spring have to cope with. My valve dropped right after a downshift from 4th to 3rd. I did not exceed 7500 RPM, but the rate of change was rapid enough to float the valve. And, my V/P was too small to begin with (0.055" intake, 0.056" exhaust with cam straight up). On the next build I am using 0.091" intake and 0.110" exhaust just to be *very* safe.

I look forward to a continued discussion and input from folks more knowledgeable and experienced than I.

Thanks, Fred '69 & /74tii

Edited October 28, 2013 by FB73tii

[Tommy]

Well Fred, there's very few more knowledgeable than you in this area. Definitely not me, but I can confirm that Schrick rockers were available couple of years ago at least. Not sure about today. They don't look at all like KM rockers. I would estimate them weigh about half of KM's.

 

I would have expected them to be state of the art but after hearing about recent experiences I'm not so sure. A friend was putting together engine with Schrick everything - 316 (or 328?) cam, springs, retainers, rockers, maybe even valves(?) but didn't manage because retainers were binding with rockers. Another friend just broke couple of the Schrick steel rockers in his turbo racecar. Very carefully put together, about an hour track time.

 

  Tommy

[TobyB]

 

 

 the actual measured spring pressure

What Fred said, but especially, THIS.

(Fred, that's an awesome write- up!)

 If you're building a motor to rev over 6500, you have to measure the pressures.

Yep, on every spring.  Every time the head comes off.  Sometimes, you're smart to take the head off just to measure, even.

 

I keep getting taught that, over and over....  I had some BMP springs that didn't do what I though they would, and

broke rockers 

because-

yes, some springs need shims to obtain proper pressure- but you have to be paranoid about coil stacking, too-

if the coils are uneven, pressure will go up before it stacks solid, and that can be almost as bad as stacking solid.

OR it can be a useful feature.

 

And my experience mirrors Fred's- if you have a weak spot in the valve train, you find it when you downshift,

especially after a nice, long, redline- type straight.  When you get that tailwind and another 200 revs...

It's the throttle- closed vacuum added to all the other forces, and it ALWAYS takes out the intake first-

IF you're running equal intake and exhaust spec stuff, and there's not a problem with your exhaust side.

 

The KM rockers were on my list if the Ireland HD's had problems, but so far, they have been just fine for my 

(7500- rpm limited) use.

 

t

[FB73tii]

Tommy, is the photo below a Schrick rocker arm? I found my info, prices range from $1780-$2600 USD per set (if still available). Sorry that your friends are seeing them break. Toby, interesting to hear that it is the intake that takes the hit on downshift.

 

------------------------------------------------
Schrick Steel Rocker Arms

Motor Nord
Björneborgsgatan 49
851 21 Sundsvall
Sweden

Telefon: 060-15 74 00
Fax: 060-15 74 05
car.special@motornord.se

http://www.motornord.se/system/webshop_showdetail.asp?HID=256&FID=313&HSID=3054&Kid=3240_5032&PID=115633

Stål vipparm Dr Schrick

Det här är det  värsta vipparm du kan hitta till dessa motorer. Tillverkad av Schrick i Tyskland i stål med längre klack och bronsbussning. Klarar garanterat dom värsta kamaxlarna och vilket varvtal som helst. Vipparmarna säljs styckevis

Art nr: 000213063

1.950,00 kr
$325.26/each ($2602/set as of October 2013)
------------------------------------------------
Schrick metal roller drag levers for extreme performance for M10+M30 engines
Product number: CP000213063

Schmiedmann
Sandvadvej 9,
Korup
5210 Odense NV
VAT: 29634602
Denmark
Phone: +45-65941545
Fax: +45-65940098
odense@schmiedmann.com

http://www.schmiedmann.com/en/product/1942992-new?product=CP000213063

$222.59/each ($1780/set as of October 2013)
------------------------------------------------

--Fred

[flybmw02]

I have run the km rockers and they are great you will not be disappointed its a true race rocker longer and wider pad. They are  heavy and I would definitely run a double spring the Shrick  springs are kind of short and not that strong. I have run most aftermarket rockers and had many expensive failures. KM also has a really nice fully adjustable cam gear.  

John

[kbmb02]

I've got this spring measurement tool in the shop, and spend more time measuring than I probably should (though, not as much as Toby would recommend...). -KB

[Tommy]

Tommy, is the photo below a Schrick rocker arm?

 

I can't say for sure because I haven't seen them that closely. But yes the style is same, totally different compared to KM.

 

  Tommy

[FB73tii]

I've got this spring measurement tool in the shop, and spend more time measuring than I probably should (though, not as much as Toby would recommend...). -KB

 

Oh, I want one of those! Website says readout to 0.2 lbs. I bought one of those bench vice spring testers for $70 and it was a POS. Not even accurate to 5 lb in practice, which is certainly not good enough for checking race valve springs. At least my local machine shop lets me use their RIMAC, but graduations are only in 2lb increments, --FB

[TobyB]

I use a cheaper one, I'll admit.  They're not great, but better than nothing.  I also have a load- cell version that works

better, but is a royal pain to set up, since it's not really meant for valve springs.

I tried making an on- the- car version, but that got silly...

 

And if John says the KM rockers are good, buy them.  Full stop. 

 

t

[alexfl82]

Thanks a lot for your advises.

Finally I ordered the KM rockers.

Regards.

A.