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Adjusting Adjustable Pushrods
You may skip this section on pushrod adjustment in either of the following situations:
- If you have fixed length pushrods
- If you are reusing adjustables, but all the following apply:
- You have not loosened the adjustment nuts.
- You have not had your valves out.
- You are reusing your cams.
- You are reusing your lifters.
- You are happy with their current length.
First, be certain you have rotated the crankshaft to TDC (beginning the compression stroke) for the cylinder you're working on. See the previous section if you are uncertain how to do this.
Begin by using a 10mm open-end wrench to hold the lowest nut on the upper end of the pushrod.
Use another 10mm, open-end wrench--or just use your fingers--to begin raising the ball on top of the pushrod. Continue lengthening the rod this way until the ball seats into its rocker arm, yet has not begun pushing its lifter-spring down. You can feel it, if you work carefully.
Now, while still using one 10mm open end wrench to hold the lowest nut, screw the adjuster nut (the top one) up (counterclockwise). As you do this, count the wrench turns (nut faces).
Continue doing this until you bottom out the lifter spring. (Mine were about 37-38 turns. Yours may differ. I have Speedstar roller lifters.) You'll know when you've reached bottom, as it suddenly gets stiffer to turn the wrench.
Screw the adjuster nut (the top one) back in (clockwise) a certain number of turns, to set your lifter 'preload.' The proper amount of lifter preload is highly debatable, but the following section covers the theory and reasoning, as I understand it.
Calculating Your Adjustable Pushrod Preload
Stock, fixed length, pushrods push down into the lifter-spring a little (Yamaha is sometimes overly conservative since they don't want to be sued no matter how poorly consumers might maintain their bikes). As your aluminum engine warms up it expands (gets taller) by a greater amount than the pushrods will expand. Therefore, it is vital that the pushrods are long enough to maintain zero valve lash regardless of engine tempurature.
Some engine builders feel that the expansion can be enough to exceed the lifter spring preload if not set sufficiently deep. The result, according to these builders, is excess chatter in the engine's top end. This noise (and the associated potential wear) can be reduced by adjusting pushrods to be slightly longer that account for two things:
- They aren't so long that they would bottom-out the lifter springs, no matter how cold (read: shortened) the engine gets.
- They're long enough that even when the engine gets to its highest operating temperature (read: gets tall) the lifters springs are still pressing up against the pushrods so as to maintain zero valve lash, and everything stays quiet and proper.
Now, with all that being said, you must decide what pushrod length you believe will accomplish this happy coexistence of parts. Actually, it's a little easier than that. You just need to decide who to believe, based on a lifter spring percentage of preload:
- Yamaha says to screw your adjuster nuts back in by 14 'flats' -- which is approximately 50%, but that is for their Speedstar roller lifters, which they no longer sell. Yamaha does not print a opinion an adjustable pushrods for flat tappet lifters, as they do not offer them.
- David (Bulldog1602) Tise, (BulldogsCustomCycle.com owner, and one of the top R* engine builders on the US East coast) screws his adjuster nuts back in by 33%. This provides a two-thirds preload.
- Greg Wicks, (Nemesis Racing founder) recommended a preload of 50%, but said that any preload between 50% and 70% is good.
- DK Montgomery, (Nemesis Racing US distributor and DK Powdercoating owner) recommends screwing the adjuster nuts back in by 30% to 50%. This creates a 70% to 50% preload.
- Patrick Racing recommends screwing the adjuster nuts back in by 1/4 turn (roughly 0.005"). Note: PR appears to use a Shubeck (or similar) lifter, which has very limited hydraulic travel, so using the 'percent preload' method of adjustment is not applicable or necessary.
- Skip Dowling (Orient Express Owner) recommends screwing the adjuster nuts back in by 1/2 turn (roughly 0.010"). Note: OE appears to use a Shubeck (or similar) lifter, which has very limited hydraulic travel, so using the 'percent preload' method of adjustment is not applicable or necessary.
Note: I used 50% for mine. In my opinion, since the hydraulic lifters will automatically pump up to eliminate any slack in the valve train (which is why they were invented), any top-end chatter/noise you hear when your engine is warm can not be eliminated by increasing the lifter preload.
Adjusting the Adjustable Pushrod Preload
Decide on your preload amount and calculate the number of wrench-turns you’ll need. See the calculation tip below. Then while still using one 10mm open end wrench to hold lowest nut, screw the adjuster nut (the top one) back down (clockwise). As you do this, count the wrench turns (nut faces).
Calculation Tip: In other words, multiply the total wrench-turns times the percentage you want, to get the number of wrench-turns to lower the pushrod.) For example: 37 'total-turns' X 0.33 'if using 33-percent' = 12 'turns-back'.
Once the pushrod length is set to your satisfaction, lock the pushrod adjuster-nut by jamming the middle nut to the lower nut.
Nut Locking Tip: Be VERY sure you tighten the locking nut securely and firmly down onto the lower nut, while holding the lower nut with another wrench. I thought I had, but one came loose after only seven miles. Jam the nuts securely together, but not so hard as to damage the threads. Since my 10mm wrenches are short--and therefore torque loads are small--I used most of my hand strength.
Also be cautious that one of your wrenches doesn't catch the other nut by mistake. It will falsely create a feeling of 'locked.'
Repeat this process for the other pushrod. Then rotate the crank to TDC for the other cylinder, as described above, and repeat this process for both pushrods of the other cylinder.