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Race Motor Rocker Arms


kuroneko

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Does anyone have any real world, longer-term experience with both KM steel (see below)?  VAC Billet Rocker arms?  

 

My race motor build is coming together.  The bottom end is all but done, awaiting custom pistons for final fitting.  

 

The top end is also ready to go and I have a 316 cam arriving next week.  The only decision I haven't made is what to do about rocker arms.  I had initially decided to try the KM steel rockers (mostly based on what I read here).  Not ideal but the M10 race motor world is a small universe of information to sample from.  At least for me getting my feet wet in the 2002/M10 world just recently.    I've seen Fred's (?) commentary about the his engine failure and how the KM rockers held up.  However, this decision has been "chilled" quite bit based on some recent direct commentary in speaking to a very respected vendor.  Not necessarily strength but poor results from cam wear from rocker pads. 

 

I've read or heard nothing about the VAC rocker arms. 

 

Lester Owen rockers are tried/true, safe decision (and a costly one as well)  but I also like the idea of trying something different.   As long as it isn't penny-wise and pound foolish.   

 

So if anyone has any real world experience to share on either KM or VAC rockers, for an extended period of time, particularly in race motor, one that has actually been raced...it'd be greatly appreciated.  

 

Edited by kuroneko
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What is your rev limit?

 

This will probably not help with your decision, but it's a data point.

I ran stock rockers for a long time, and they only failed when I had

valve spring problems, or overrevs.  I ran a 7500 limit, and various cam profiles and spring combinations.

I then went to IE's rockers (they were version 2, I think)

and had no problems with cam wear or breakage, with springs from earlier experience, and an 8000 limit.

 

John Forte (flytii?) has done a lot of work with the KM rockers.  Many others have had

experiences with Vac's stuff.  I know the VAC parts have gone through several iterations.

 

There are a LOT of variables with rockers and cams- geometry, valve pressures, oil chemistry,

how you break it in, how well the pads seat, seat metallurgy, and so on.  And some luck!  By the time you

get to the bottom of it, there will be no one 'right' answer, and what has apparently failed for others may

work for you, or vice versa.  Good luck!

 

t

 

"I learn best through painful, expensive experience, so I feel like I've gotten my money's worth." MattL

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1 hour ago, TobyB said:

There are a LOT of variables with rockers and cams- geometry, valve pressures, oil chemistry,

how you break it in, how well the pads seat, seat metallurgy, and so on.  And some luck!  By the time you

get to the bottom of it, there will be no one 'right' answer, and what has apparently failed for others may

work for you, or vice versa.  Good luck!

 

t

 

What he said (and some luck, indeed). My luck improved when I chose oils with higher zinc content. -KB

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I had the skid mark racing rockers. Initially early on they had a pad issue and many cams were ruined. I started using them after that and I never had any issues across 3 motors and 3 sets of rockers. The key is running as much spring pressure that is required and not more. 

 

Not sure if the SkidMark rockers are now the VAC ones?

 

AK

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Thanks, yeah, I get all that.  Oil, zinc, break in, luck, no right answer, etc etc........  

 

Toby.  On the rev limit, 7,500 (self imposed) all day, but certainly will want to be able to run it higher when "necessary."  Hah!  I don't have one now but may put an MSD in to set a 8,500 hard rev limit.  Maybe.  But if you need a box to tell you it's time to shift at 8,500...probably need to work on some awareness skills in "traffic."    I've been told by that stock style M10 aluminum rockers --- whether they are "hd", shoot peened, polished, radiused, massaged, coddled, sung to before hand...whatever...will not last in that range (7500-8500) for any period of time.     I've broken my share of aluminum M20 BMW rockers and certainly know that is case in that context.  They''ll be ok 7500 but anything above that and all bets off as to what can happen and how long they'll last.  Certainly if I ran M20 aluminum rockers in that range, I'd be replacing them regularly, broken or not.   And there's not a ton of difference between the two.  

 

I guess mostly fishing for real world experiences good, bad or indifferent on the KM and VAC specifically.   To be a bit more direct, I was painted a pretty dour picture of the KM rockers and cam wear.

 

I'm leaning towards Lester Owen but I'd really like to know more about VAC before going that route. Getting myself over the fact the VAC are aluminum is tough in my simple, small mind.  

 

 

 

 

Edited by kuroneko
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3 hours ago, Anthony said:

I had the skid mark racing rockers. Initially early on they had a pad issue and many cams were ruined. I started using them after that and I never had any issues across 3 motors and 3 sets of rockers. The key is running as much spring pressure that is required and not more. 

 

Not sure if the SkidMark rockers are now the VAC ones?

 

AK

Thanks Anthony.  Not sure, I'll ask VAC.  The look very similiar to the Schrick ones in design...but they are aluminum billet.

 

I happen to own one of Skid Marks first cars, pre 2002 years.  An E21  Twice removed from them and it was fitted with a stroked M20.  I no longer own it, sold this fall as I  didn't drive it much as my attention has been elsewhere in racing last few years. Then I picked up my first 2002 for vintage purposes going forward...and it was game over for the poor E21. BUT  It was a great race car, I really loved driving that thing, was quite a handful but a blast.  Both fun to drive but also fun knowing you could flog it at will as another M20 can be picked up anytime anywhere and dropped right back in without much ado.  E21 is under appreciated and a great car if have the right powerplant. I wish I could have kept it to flog around at occasional track days.  I digress....

Edited by kuroneko
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9 hours ago, kuroneko said:

Thanks, yeah, I get all that.  Oil, zinc, break in, luck, no right answer, etc etc........  

I'm leaning towards Lester Owen but I'd really like to know more about VAC before going that route. Getting myself over the fact the VAC are aluminum is tough in my simple, small mind.  

 

I understand you're asking about Lester Owen's rocker arms vs the VAC units, I'm leaving this data point here for those searching in the future...

 

I've got over a half-dozen M10 race engine builds which use Ireland Engineering's cast aluminum HD rocker arms combined with a Schrick 304, not-too-heavy valve springs and all engines rev easily to 7,600 (we're well-beyond peak power at that point). I once hit 8,500 (don't ask). No breakage, cam wear (once) due to engine oil. I recommend them.

 

And yeah - with more RPM's plus a cam with more lift, your results may vary.

 

On a separate issue, I'm curious to know whether your Schrick 316 is made of a genuine Schrick blank? That's a 'big journal' cam, correct? -KB

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6 hours ago, kbmb02 said:

 

I understand you're asking about Lester Owen's rocker arms vs the VAC units, I'm leaving this data point here for those searching in the future...

 

I've got over a half-dozen M10 race engine builds which use Ireland Engineering's cast aluminum HD rocker arms combined with a Schrick 304, not-too-heavy valve springs and all engines rev easily to 7,600 (we're well-beyond peak power at that point). I once hit 8,500 (don't ask). No breakage, cam wear (once) due to engine oil. I recommend them.

 

And yeah - with more RPM's plus a cam with more lift, your results may vary.

 

On a separate issue, I'm curious to know whether your Schrick 316 is made of a genuine Schrick blank? That's a 'big journal' cam, correct? -KB

 

Thanks KB, appreciate the insight, it very good to know.   On the Schrick, yes, it's a big journal cam.  As to the material, I sure hope so!  I won't have it in my hands until next week and I bought it as a new genuine Schrick.  Not from Ebay...from Korman to be precise.  

 

Edited by kuroneko
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4 minutes ago, kuroneko said:

 

Thanks KB, appreciate the insight.   On the Schrick, yes, it's a big journal cam.  As to the material, I sure hope so!  I won't have it in my hands until next week and I bought it as a new genuine Schrick.  Not from Ebay...from Korman to be precise.  

 

 

Here's why I asked:

We've seen this alternate-blank version from VAC, and Walloth / Nesch, it'll be interesting to hear what Korman sends. (note that thus far, I've only heard of this issue on 'normal' journal Schrick cams). -KB

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7 minutes ago, kbmb02 said:

 

We've seen this alternate-blank version from VAC, and Walloth / Nesch, it'll be interesting to hear what Korman sends. (note that thus far, I've only heard of this issue on 'normal' journal Schrick cams). -KB

 

Weeeell...that's interesting.  I should have cam next week.   I'll take a look and certainly report what I find in that thread when I do.    Sounds like you initial skepticism has turned to belief that your 304 cam IS a genuine Schrick?  Or is that still an open question?

 

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I have been racing since 1988.  I have always used stock rockers.  I have never had one break on me.  I shift  at 7500 RPM. 

Now that I have jinks myself--

I am using a 316/328 cam running in Amsoil.  Good oil and proper valve clearance has worked for me.  Going to Indy this year.  G

 

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17 hours ago, kuroneko said:

 

Weeeell...that's interesting.  I should have cam next week.   I'll take a look and certainly report what I find in that thread when I do.    Sounds like you initial skepticism has turned to belief that your 304 cam IS a genuine Schrick?  Or is that still an open question?

 

 

If genuine = made or contracted by Schrick' = then yes, Schrick says it is.

 

    However...

 

The blank is not what Schrick has used previously (no Schrick stamped into the casting); one can get the 'new' blanks and put a 304 grind on it for less money.

The grind on the recent cam is 'different' (overall lobe is smaller), though lift and duration are quite close according to my cam guy.

Finally: Though possibly a coincidence, when I had the 'new Schrick' and 2 test cams shipped back to me, the new Schrick broke in half during shipping.

 

-KB

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errr....   well, which half do you think you'll use?

 

As to a rev limiter, yes, use one 

 

As to M20 vs M10 rocker geometry, it's more different than it looks.  Same design, but the dimensions

and angles are different.  The M20 head is much smaller per cylinder than the M10.  I was surprised...

 

t

"I learn best through painful, expensive experience, so I feel like I've gotten my money's worth." MattL

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I have an M20 powered E-Production car that has VAC "Unbreakable" rockers. The car's previous owner helped VAC through multiple iterations before breakage became less of a problem. I've had the car 18 months and haven't broken a rocker although I have a new set of KM steel rockers in hand based on John Forte's positive experiences with them. Just haven't needed them yet. The M20 in the E-P car is 12/1 CR, Shrick 304, Ferrara valves, aftermarket injection, Electromotive ignition and dynos 236 torque and 225 h/p at the wheels.  

eprod2016JTI.jpg

73 2002 Tii Sold

71 2002 Ti Vintage racecar

84 BMW 325 E-Prod racecar Sold

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