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| Preparation |
| Before assembly, we inspect the head for cracks. Then it
is cleaned and, to remove stubborn carbon, we glass bead (an aviation
approved method for carbon removal on aluminum). Then the head is surfaced
with the front cover attached to the head. It is important that you send
your front cover with your head when any kind of work is done to it. |
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| Parts Replaced |
- Inspected new rocker arms and shafts.
Before installing a new rocker arm we first inspect them. The two
major areas we are concerned with are: (1) The correct hole position
for the eccentric cam. If it's too high or too low, it's hell to get
the eccentric in the right position for proper valve adjustment (see
illustration). (2) The rocker pad making square contact with the cam.
You cannot assume that a "new" rocker arm is just fine because
there are a lot of junk rocker arms being sold and we found they all
need to be inspected. We also replace rocker shafts.
- Valve Guides and Seals
We replace all valve guides with aluminum silicon bronze (very wear
resistant/low expansion alloy) valve guides. These guides can be fit
tighter and often extend life. To cap off the valve guide, we use
Teflon valve guide seals. Teflon seals last almost forever and oil
consumption through the valve guide stays about the same over the
life of the engine. More conventional rubber seals seal too good initially
and the guides tend to wear from lack of lubrication. With age, the
rubber seal gets hard and that, combined with a prematurely worn guide,
causes the smokies to occur out of the tail pipe during deceleration.
We have used Teflon valve guide seals exclusively for 15 years now
and have found them to be a proven performer. They are also original
equipment seals on Mercedes Benz, Porsche 911's, Peugeot, and other
European car manufacturers.
Over the years we used Teflon valve guide seals with great success.
They can be a little tricky to install if you don't have the right
tool. The tool we use is a "plastic tee" fitting commonly
found in a hardware store for less than a dollar.
- Worn Valves
Intake valves are very durable. Exhaust valves in their old age tend
to wear at the bottom of the valve stem. If the valve stem tapers
more then .001", we replace the valve.
- Using the Single Roller Cam Chain
The engines we've built since Nov. '86 use a single roller cam chain.
From '79 on all BMW Engines (to our knowledge) have used this chain
except the M3 which uses a double roller. It seems odd that the M3
would use a double roller chain because the M6 and the new V-12 both
use the single. We've observed that the older BMW Engines using a
double roller would tend to be worn out (the cam chain tensioner would
be bottomed out) at about 100,000 to 120,000 miles. In comparison,
we've seen many post '79 engines using single roller chains that had
over 150,000 miles (even as high as 230,000) and the chain still had
a fair amount of service life left. We feel that the shear mass of
the double roller chain causes it to beat the life out of itself.
When it comes to strength we have never seen any single roller cam
chain break and BMW seems comfortable using it to move 24 valves.
Also, we find that the single roller reduces unwanted chain mass that
has to be rotated and is also quieter than a double roller chain.
In essence, we consider the single roller chain a nice upgrade for
a BMW engine which once had a double roller chain.
- Modified Oil Sprayer Bar (6 Cylinder)
Big six engines have a nasty habit of knocking out the #1 cam lobes.
We enlarge the sprayer bar hole to .075" at the front to deliver
more oil to these lobes. This modification is done with a punch instead
of a drill to avoid putting metal shavings in the sprayer bar.
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| Story Time |
| Some years back we did offer porting only on our heads.
The customer would install his old rocker arms and shafts. Our cylinder
head porter would do a trial assembly taking .002" undersize rocker
shafts that slide easily into the head to do a mock up on the valve train.
We had a standardized set of rocker arms that we used to set up the correct
eccentric position. We would set up the valve train to where the eccentric
hole (for valve adjustment) would sit in the 1:30 to 2:00 o'clock position.
We did about 15 heads before we discontinued this service. It ended when
two heads were returned to us because the customers couldn't get all the
valves to adjust when assembling the heads. The problem was they had bought
junk rocker arms where the eccentric holes were incorrectly located. We
replaced their rocker arms, assembled their heads, and sent them back.
Now, we don't sell a head unless we assemble it. |
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| More Story
Time |
| Years ago we had a new "Eta" head brought to
us with all new rocker arms and shafts. The guy just wanted us to assemble
the head. After we assembled the head we couldn't get any valves in the
head to adjust - not one! Again these were junk rocker arms. |
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