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Quick Fill

Quick Fill Caps are Here!

New from Buku: Quick Fill Crank Case Caps!

Now you can purge dirty grease and refill your Quick Fill Crank Case Cap with new, clean grease without removing anything from your car or motor!

Simply slide the retaining O-ring from the groove at the edge of the cap and use the syringe and tapered needle (included with caps) to refill the grease.

The new grease purges old grease and dirt through a second purge port on the opposite side of the cap. When you're done simply wipe off any excess grease and slide the O-ring back into position. Takes less than a minute!

Can be refilled as often as necessary to maintain peak sealing performance.

The new cap is thicker and more durable and also has a special grease reservoir inside to provide superior seal protection. Requires the use of 3 brass shims (.03” total thickness) for installation.

Quick Fill Caps are the easiest and fastest way to insure stable and consistent performance, eliminate ghost flame-outs, 2-stage idles, and tuning irregularities and most importantly, completely protects your engine and bearing from dirt and contamination!

All New!

Buku Crank Case Caps (Patent Pending)

This amazing new product is sure to become a mandatory accessory for all nitro motors.

  • Increase overall engine life.
  • Substantial increase in front bearing life.
  • Reduce front bearing and engine maintenance.
  • Remarkably increase tuning window.
  • Eliminate random flame outs.
  • Stabilize idle and tune.


You're probably already asking yourself how this simple plastic cap can deliver all these benefits... What exactly does it do and how can it solve so many problems?

The simple answer is, when used with the special grease included with the caps, it completely stops air leaks through the front bearing.

Although not widely known, air leaks through the front bearing cause an almost unbelievable number of problems...

Initially we designed the Cap to increase bearing life by preventing dirt from passing the front bearing seal, a problem that is becoming increasingly common with today's high output motors. When we began testing, the progressive effects of even minor air leaks started to become evident.

How to Test for Air Leaks

It turns out that front bearing seals begin leaking air in as little as two tanks of fuel. Of course at this point the leak is minor and probably wouldn't be noticed by most drivers. It's not just air that is leaking through a seal; it's also microscopic dust particles. These dust particles are gradually pulled down the crank and into the motor where they abrasively wear the engine components. The dust is so fine that it typically doesn't cause the type of highly visible scoring that occurs from large particles entering the motor though a detached or poorly maintained air filter.

Although our testing is ongoing, assuming proper air filter maintenance has been performed, it now appears that much of what is typically associated with “Normal” wear to the crank pin and connecting rod is substantially increased if not CAUSED by front bearing leaks!

The same is true for the piston and sleeve as well as the wrist pin and rear bearing!

It's not just premature wear that a front bearing leak causes...

When a bearing leak is extremely bad it will make a motor un-tunable. That's when most people first notice they have a problem. Unfortunately, at this advanced stage it's too late and your motor has already suffered premature wear.

The reality is that even small leaks cause tuning inconsistencies that are many times associated with nitro motors being “finicky” or “hard to tune”. Maybe nitro motors aren't so hard to tune after all!

As a motor is being broken in after a number of tanks it's very common to require jetting adjustments to compensate for the break-in process. This seems perfectly reasonable but ongoing testing is revealing that a substantial portion of the jetting sensitivity that is exhibited as a person is moving towards a race tune may be caused by a minor bearing leak that is getting progressively worse with every tank of fuel.

That's because of the highly inconsistent nature of an air leak through the bearing seal. This inconsistency means it's impossible to tune accurately. The best that can be hoped for is a balance of the variability: rich enough that you don't run too lean or flame out when air leaks, but lean enough to run properly when there is little or no leak.

What makes this balancing act even more difficult is that bearings tend to leak more when the motor is under high load. So, you are leaking the most air when under full throttle, meaning you have to compensate by running a rich setting on your High Speed Needle (HSN), but...

The leak will be less apparent at low speeds or idle. This means that your idle mixture could be set more accurately, except for the fact that you will probably have to set it somewhat lean to account for the rich HSN setting. This is going to affect your idle and the idle drop time off full throttle, among other operating characteristics.

One more detail: bearing air leaks become progressively worse as an air filter becomes clogged. So now the longer you run, especially in dusty conditions, the more severe the air leak and its impact on jetting, idle and the overall stability of the tune.

It's pretty easy to see that an air leak makes accurate tuning pretty much impossible, a fact we quickly noticed during field tests.

What we are seeing:

The most stable and easy to tune motors ever! The worst and most un-tunable motors are becoming the easiest to tune and most reliable. No flame-outs. Increasing the stable running window from as little as one hour (1/12th of a turn on the HSN) to six hours (half a turn)! Highly consistent jetting even in changing weather and temperature conditions…

And of course, dramatically reduced engine wear from the front bearing all the way to the piston and sleeve!

How it really works...

The dust cap is only one component of the system. The second critical component is the special grease which is held in place by the cap. The grease being present on the front bearing seal stops the initial air leak from ever beginning.

Bearing seals are effective initially at stopping air from leaking through. Once the leaks starts however it doesn't stop. So stopping the leak in the first place is critical.

The problem begins when the motor exposes the intake to a substantial vacuum pressure to draw in the fresh mixture through the carburetor and air filter (the reason air leaks gets worse as an air filter gradually clogs). As a bearing seal wears it reaches a point where the vacuum can just begin to pull air through the seal. And because the first draws of air will contain at least a little microscopic dirt the leak will compound.

The grease stops the air from getting through the bearing seal in the first place. How? Think how easy it is to breathe air through a drinking straw. Now try drinking peanut butter through a straw!

The higher viscosity of the grease is enough to prevent the vacuum from overcoming the very small voids in the seal. No initial leak, no problem!

The Buku Crank Case Cap is so effective at preventing bearing and engine wear and so dramatically improves tune-ability and stability that our prototype testers wouldn't even THINK about breaking-in or running a motor without a seal!

How long does a seal last? As long as a seal is not damaged by an impact, if it's properly installed it can last for several gallons or longer. Of course you should be periodically removing your flywheel to inspect the seal for damage and repack with grease if necessary.

How much space does it take up on the crankshaft? The seal and 2 brass shims (included) takes up only ½ mm (.020”)


The seal cannot be run with flywheels that have a recess on the back, engine facing side. If your flywheel has a recess we recommend upgrading to a Buku clutch system for full compatibility with Buku Crank Case Caps.

#3000Q $6.95
Buku Grease Refill.

Pre-Filled Syringe and Fill Tip for Quick Fill Crank Case Caps
#3010Q $3.95
Buku Crank Case Cap O-Rings.

4 Replacement O-Rings for Quick Fill Caps
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