what happens during crankwalk?

[The_Baldman]

What actually happens during crankwalk? What makes the 6 bolt better? Is there any machining that can be done to a 7 bolt to avaid crankwalk? Thanks in advance.

 

[DGajre777]

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What is 'crank walk'?
What is a 'walking' crankshaft?
Is there a recall or TSB regarding the crank walk problem?
How can I tell if my car has a walking crankshaft?
Search for this topic now!

A 'walking' crankshaft is a crankshaft that moves too much inside the engine. This is also known as excessive thrust bearing play. The movement is usually due to the crankshaft not fitting inside its bearings correctly. While not bad for the crankshaft, the movement can place excessive or uneven loads on the bearings, causing premature failures.

Many 2G owners have suffered from walking crankshafts. It appears that Mitsubishi built many 2G engines using defective crankshafts, which were machined out of specification and are thus capable of moving around too much inside the block. All 2G model years appear to be affected to some degree.

To fix this problem, Mitsubishi has designed several versions of matching crankshaft bearings. This allows the defective motor to retain the crankshaft, yet matches the bearings correctly so as to eliminate the excessive crankshaft movement. Matching the bearings in this manner is tricky and requires exact information about when the crankshaft was manufactured, which may be determined by color markings on the crankshaft itself. The 2G factory manual includes information on how to match crankshafts to bearings.

1G owners do not generally need to worry, as there are no chronic problems with crankwalk in per-1995 cars. However, it is possible for any engine to experience crankwalk if there is a problem with the crankshaft bearings. It has been reported that 'small rod' / 7-bolt flywheel motors (manufactured from later 1992 through 1994 on 1Gs) are more prone to crankwalk than 'big rod' / 6-bolt flywheel engines (manufactured from 1989 to early 1992). However, there can be no guarantees, since big block V8s and all other engines can also suffer from crankwalk.

It can be difficult to tell if a particular car is experiencing crankwalk. Symptoms are usually indirect and difficult to diagnose until major damage occurs.

Since the clutch places pressure on the crankshaft, many owners have reported clutch or shifting problems associated with the walking crank. Having the clutch 'stick' down on left-hand turns is often a telltale sign of crankwalk. Other symptoms include inconsistent engagement height, poor or rough engagement, difficulty shifting, ticking noises and varying pedal height or pressure. Another possibility is having the engine RPM decrease significantly when the clutch pedal is down.

Another problem with crankwalk is that the crankshaft may move so much as to literally tear up and destroy the 2G crankshaft angle sensor. This problem usually manifests itself as a ticking noise coming from the timing belt area, as the sensor is literally and slowly ground away by the crankshaft. Any such noise should be investigated right away to prevent serious problems.

Unfortunately, cranshaft angle sensor failure usually leads to a replacement sensor, rather than a replacement crankshaft, as mechanics fail to diagnose the underlying problem. 2G owners who have experienced premature failure of the crankshaft angle sensor should investigate the possibility of a walking crankshaft immediately.

For more information, read this post by Paul Estavez, which describes the crank walk problem in detail. Also read Road Race Engineering's archive of posts that contains all of the Talon Digest posts about the walking crankshaft problem. Those who appreciate that a picture is worth a thousand words will appreciate the Crank Walk Photo Archive.

Although 2G DSM owners have been anxiously awaiting a recall or TSB on the crankwalk problem, there is none as yet. According to Paul's second post on the subject, there may never be a TSB, although some members of DSM Canada are pushing for one in this thread on their discussion board. As a result, it is doubly important that affected 2G owners get their bearings (or blocks, if necessary) replaced before their warranty expires. This might be difficult for owners of aftermarket clutches, as dealerships often claim the aftermarket pressure plates are the cause of the problem.

And other one from Magnus Motorsports:
http://www.magnusmotorsports.com/crankwalktheory.htm

FYI - There are a million threads on here about crankwalk, well maybe not a million but a LOT. And why is this in the Advanced Tech forum??

 

[Defiant]

What actually happens during crankwalk?

The thrust bearing fails.

What makes the 6 bolt better?

The bearings are larger, and the thrust bearing's saddle isn't held tight to the rest of the block by the girdle.

Is there any machining that can be done to a 7 bolt to avaid crankwalk?

Some machine shops claim so, but of course their answers are all big effing secrets. The actual incidence of crankwalk is lower than the number of threads about it on this site.

Thanks in advance.

Yeh. Search.