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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: DuncK1100 on November 24, 2023, 06:47:48 AM

Title: 4 Valve A or B
Post by: DuncK1100 on November 24, 2023, 06:47:48 AM

Hi,
Can anyone explain the terms 4V A and 4V B to me.
I have a '94 K1100LT.
Thanks in advance.

Title: Re: 4 Valve A or B
Post by: Laitch on November 24, 2023, 07:39:15 AM

Welcome to the forum, Dunc!
In what context did you find those terms?

Title: Re: 4 Valve A or B
Post by: Duckbubbles on November 24, 2023, 11:19:30 AM

Haven't heard those terms, but could it refer to the 1000cc (4 valve A) and 1100cc (4 valve B)?

Frank

Title: Re: 4 Valve A or B
Post by: jbt on November 24, 2023, 11:20:39 AM

Maybe it's because there was a slight modification of the connecting rods lenght  in august 1992, passing from 125 to 131mm.
So the pistons are different also, the stroke did not change.

Title: Re: 4 Valve A or B
Post by: Laitch on November 24, 2023, 03:20:06 PM

Quote from: jbt on November 24, 2023, 11:20:39 AM

Maybe it's because there was a slight modification of the connecting rods lenght  in august 1992, passing from 125 to 131mm.
So the pistons are different also, the stroke did not change.

The lists below are from MaxBMW's K1100LT parts list.

Title: Re: 4 Valve A or B
Post by: Duckbubbles on November 24, 2023, 10:03:07 PM

If I remember correctly, those ratings are used at the factory to match sizing and weight of reciprocating parts.  Ran into this rebuilding a K100 engine probably 30 years ago.  I think a similar system is used for piston rings and bearings, and probably more.

Frank

Title: Re: 4 Valve A or B
Post by: jbt on November 25, 2023, 12:59:22 AM

For Airheads, A, B and C were markings used to match pistons precise size to the different bore sizes of the cylinder, according to the manufacturing variations within 3 classes of tolerance.
K1100 pistons have the same kind of classification, with 2 classes only. They are rated A and B.