New Stroke 82. mm
Original Stroke - 69. mm
Multiply By (formula) x 0.0197
= The Spacer Size 0.256"
As you can see the amount of spacer to get back to the original deck height is 0.256 inches.
Note 1: If you change the rod length and/or cut the case deck down to get a full seating surface, such as with a hole cut for 92mm or 94mm size pistons, you must add and/or subtract the full amount of these changes. Shorter rod subtract, longer rod or case cut down add.
Note 2: The above measurement will be mathematically correct, but not necessarily physically correct when you put the engine together. This is due to many unknown variances. This will only get you close to the stock deck height. If you are going to lower the CR as you must for today's pump gas you must calculate how much more spacer you will need in addition to the above amount.
If you don't know how to achieve this, the calculation formulas are listed in our GB 770 instructions and/or in GB 801-CR on compression ratio vs. today's fuel and how to make your engine live and provide better cooling with more power.
Note 3: The recommended procedure is to pre-assemble the engine to achieve actual measurements with our GB 751 deck tool, then order the proper spacers and shims. If you are unable to pre-assemble the engine and must order the spacers with your parts I suggest you purchase extra shims of 0.007", 0.010" or what you feel may be needed so deck may be added if necessary.
Steel spacers and shims are stackable. I, personally, do not recommend more than 2 shims together under one cylinder. With the availability of spacers in about every 0.020" thickness you have no need to stack more than 1 spacer and 2 sets of shims to achieve any deck required. If not, it may require that you have custom spacers made.