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The 6 bolt cranks were the norm in M10 motors during most of the 60s. I believe BMW introduced the 8 bolt cranks during the latter part of 69.

 

So, going back to your idea, the 6 bolt crank uses a 6 bolt flywheel. And, a very specific pressure plate with three prongs and coil springs and corresponding throw out bearing must be used with this flywheel unless you have a machine shop modify the flywheel to accommodate the newer style diagphram pressure plate. I believe the modification entails drilling new mounting holes and / or pins for the newer style clutch. Why do this ? Well those old pressure plates cost an arm and a leg compared to the newer ones. They are not readily available. And, they look pretty funky.

 

There are guys here who have done this.

 

 

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24 minutes ago, Slavs said:

The 6 bolt cranks were the norm in M10 motors during most of the 60s. I believe BMW introduced the 8 bolt cranks during the latter part of 69.

 

So, going back to your idea, the 6 bolt crank uses a 6 bolt flywheel. And, a very specific pressure plate with three prongs and coil springs and corresponding throw out bearing must be used with this flywheel unless you have a machine shop modify the flywheel to accommodate the newer style diagphram pressure plate. I believe the modification entails drilling new mounting holes and / or pins for the newer style clutch. Why do this ? Well those old pressure plates cost an arm and a leg compared to the newer ones. They are not readily available. And, they look pretty funky.

 

There are guys here who have done this.

 

 

So what would be causing my clearance problem?  The throw out bearing?

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2 hours ago, Hans said:

My 67 2000CS came with 6 bolt. I switched to 8 to get bigger clutch. Seems happy. So I expect you could do the reverse. With smaller clutch. 

The 6 bolt 2000CS crank uses the large clutch (225mm-228mm). The old clutch used with the 2 liter engines is a large clutch. When they switched to 8 bolt crank, they continued using the large 228mm clutch disk, but with a different pressure plate and throw out bearing. At some point at about 1974 they adopted the smaller 215mm clutch disk from the 1802 for the 2002 as well, excluding the tii, which I believe continued using the 228mm clutch. I'm not a tii expert. There are others here who know the tii well.

 

 

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1 hour ago, djminkin said:

So what would be causing my clearance problem?  The throw out bearing?

Your issue is at the front of the engine, not the clutch. And, I don't know what plastic timing cover you're referring to. As far as I know all 2002 cranks are the same, except that the early cranks are 6 bolt. I'm not aware of any other differences between them. What may be different is the front pulley on the tii. But, I'm not sure. Somebody here can provide the answer. I've explained the clutch.

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US 2002s switched from 6 to 8 bolt crankshafts (and from coil spring to diaphragm spring pressure plates--and their appropriate throwout bearings) at VIN 1665200, sometime in late Feb/early Mar 1969.  My 4 Feb assembly date car is 399 from the changeover.    With the 6 bolt crank/flywheel, you must use the coil spring pressure plate, as the bolt pattern for mounting is different from the later pressure plate.  

 

mike

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8 hours ago, Mike Self said:

With the 6 bolt crank/flywheel, you must use the coil spring pressure plate, as the bolt pattern for mounting is different from the later pressure plate. 

 

There is - I believe - an option: JB Racing makes an aluminum 6 bolt flywheel, machined to work with later 228mm clutch pressure plate. (FYI: the early 6 bolt 2 liter crank is lighter than the 8 bolt version). -KB

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We've gone off a tangent with the 6 bolt vs. 8 bolt 2L 80mm stroke cranks. Both cranks fit in the block identically. It's just the aft portion of the crank, where the flywheels mounts, which is larger and different to accommodate the two extra bolts. Otherwise, I believe the cranks are identical. The 6 bolt 2 liter bolt crank may be only marginally lighter due to this only difference. It is a fully counterweighted crank unlike the 71mm stroke cranks of the 1600, 1802 and later 320i 1.8L and E30 1.8L cranks, which are noticeably lighter since they only have half the counterweights as the 2 liter crank.

 

There is one 6 bolt 80mm stroke crank, however, which is noticeably lighter. It also lacks half the counterweights, like the 71mm stroke crank. This crank was used on the early NK1800 motors from 63-68. At some point during production BMW redesigned the 80mm crank to a fully counterweighted crank. This was done to make the 80mm stroke motors smoother. The shorter 71mm stroke motors don't need the fully counterweighted crank. BMW first  incorporated the fully counterweighted 80mm stroke crank most probably during 1800TISA production. This was their flagship race car and test bed as it was a race car. As far as I know, the new 2L motors which made their debut in 1966 used the fully counterweighted crank.

 

During 1968, BMW redesigned their 1.8L motor to a short 71mm stroke configuration, resulting in a smoother running motor. It was the better option vs. installing a heavier fully counterweighted crank to their earlier 80mm stroke 1800

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19 hours ago, djminkin said:

Can an early 6 bolt crank with a 6 bolt flywheel go into a tii car from 71?  I’m having some clearance issues with the front crank pulley rubbing on the plastic timing cover.  

There is no difference in the snout between the 6 bolt and 8 bolt cranks.  If it is touching it is more likely because the plastic cover is distorted because of heat and time (this is very common on Tii's)  

 

There is no reason not to use a 6 bolt crank if you can deal with the flywheel/pressure plate issues.  Just make sure you use NEW flywheel bolts, Loctite and the proper torque on the bolts.  

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