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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: alabrew on April 08, 2019, 04:50:47 PM

Title: Check my shim maths
Post by: alabrew on April 08, 2019, 04:50:47 PM

Before I hit the Buy button, thought I would ask for a check of my shim replacement calculations, s'il vous plait

#1 intake is tight at .127 + 2.65 shim = 2.777 - .20 = 2.577 or 2.60

#2, 3, 4 exhaust are tight at .203 + 2.45 shim (all) = 2.653 - .30 = 2.353

Hit the button?

Title: Re: Check my shim maths
Post by: Scott_ on April 08, 2019, 06:23:18 PM

Depends on what bike you are working on.........

Title: Re: Check my shim maths
Post by: alabrew on April 09, 2019, 01:00:00 PM

Sorry I didn’t specify, it is for the ’85 2v.

Title: Re: Check my shim maths
Post by: Scott_ on April 09, 2019, 06:50:24 PM

In that case, yes, your numbers look good.

Title: Re: Check my shim maths
Post by: alexg on April 11, 2019, 12:22:31 PM

#1 intake is tight at .127 + 2.65 shim = 2.777 - .20 = 2.577 or 2.60.
I would use a 2.55 mm shim. I realized the rounding rules, etc, but I prefer to have a little more gap than tighter. If any, the gap will be on spec in a few thousand miles, as the seat/valve wears faster than the cam/shim.

Title: Re: Check my shim maths
Post by: Laitch on April 11, 2019, 02:01:35 PM

Quote from: alexg on April 11, 2019, 12:22:31 PM

#1 intake is tight at .127 + 2.65 shim = 2.777 - .20 = 2.577 or 2.60.

You mean it's too tight for you then, because his calculation seems to place it within spec.

The spec is 0.15mm to 0.20mm. As measured, the gap is currently 0.023 out of spec using a 2.65mm shim—0.150 - 0.127 = 0.023. He is increasing the clearance by 0.050mm  using a 2.60 shim—0.127 + 0.050 = 0.177 That puts it in the center of the spec. It looked good to Scott and it looks good to me, too.

Title: Re: Check my shim maths
Post by: alexg on April 11, 2019, 03:32:25 PM

You are right.

Title: Re: Check my shim maths
Post by: stokester on April 11, 2019, 06:06:53 PM

Don't know where you plan on buying them but some Japanese bikes use the 29mm size and may be available locally for less than what BMW charges.  Mine were swapped without charge at the local Yamaha/Kawasaki/Suzuki dealer.

http://www.motobrick.com/index.php/topic,12283.0.html (http://www.motobrick.com/index.php/topic,12283.0.html)

Title: Re: Check my shim maths
Post by: alabrew on April 12, 2019, 03:34:58 PM

Thanks for the confirmation of my numbers.

I ordered from newmotorcyceparts.net as I had seen it mentioned here.
I figured the local dealer wouldn’t have any in-stock and they would have to order them too.
I don’t have a enough of a relationship with any dealers to ask about swapping.