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3-Series (E21, E30) Chat relating to the BMW 3-Series from 1975-1983 and 1984-1991 line. Specific models: BMW 315, BMW 316, BMW 318, BMW 318i, BMW 320/4, BMW 320i, BMW 320/6, BMW 323i, BMW 320i. E30 Family models include: BMW 325e, BMW 325i, BMW 325is, BMW 325ix.

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Old 02-14-2010, 05:05 PM   #1 (permalink)
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Cam Question

I'll try to make this short and sweet,.........

I'm currently working on an 87 325ic that I've received as a basket case. The PO was convinced that there was a blown head gasket. Long story short I've found no evidence to support that conclusion.(no warping, cracking, etc)

The PO changed the oil and filter and added something to the cooling system to stop the (supposed) leak well before I started working on it. I flushed the cooling system and performed a leak down test with good results.

Anyway I pulled the head and had it pressure tested and checked for warping,cracks and or other flaws in the casting (all past with flying colors) From this point, for all intents and purposes the head has been rebuilt, machine work is done and parts have been acquired. I'm now in the process of reassembling all the components, and I have a couple of questions.

What is the spec (in lbs.)for the spring pressure (stock dual springs) on the seat and over the nose and what is the installed height spec. for a stock cam and springs.

Now for the BIG question, one that I have yet to see asked on this (or any other board). What is the proper cam shaft break in for an m-20, or is there one. The reason I ask is most of my prior engine building is centered around domestic (U.S.) cam in block push rod V-6's, and V-8's.

With a vast majority of the above mentioned the cam shafts are splash lubed so the RPM's need to be kept elevated for an extended period of time so as NOT to wipe out a lobe or lifter before they establish the proper wearing (breaking) in relationship with each other.

So the question is this, how is the cam and rocker assembly of the m-20 (the rocker arm to cam lobe contact point) oiled? Is it pressurized or splash lubed? The last thing I want to do is wipe out a brand new valve train due to an improper break in.

Sorry for the short story being so long, and thanks in advance.


Tim
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Old 02-14-2010, 11:57 PM   #2 (permalink)
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BMW specs show a nominal free spring height of 46mm(1.811 inches), and requires on inspection that the springs be of the SAME COLOR CODE, and that the springs are ALL the same height, stand straight, and are square/perpendicular. If one or more is of a different height, you replace them as a set, and not individually.

* the rationale is that valve springs in bimmers are supplied by different manufacturer's and each might differ slightly in height if only to achieve the required spring resistance when the cam lobes push on the valves.

There is no break-in procedure provided for camshaft/rocker arms/lifters/valves, but as in any good shop practice procedure, it is incumbent upon yourself to check that all oil holes and passages are properly cleaned and free of sludge, deposits , or obstruction that might restrict oil flow.

As well, on assembly, a good oiling of all moving parts before installing the valve covers will ensure sufficient lubrication until the crankcase oil circulates through.

** make sure the new head gasket is EXACTLY the same hole-for-hole. I have encountered cases where, in aftermarket gaskets there was a hole missing on a new gasket, and the missing hole just happened to be the oil passage hole

Cheers
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