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Old 06-14-2008, 06:05 PM
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HoughMade HoughMade is offline
Motorized Bicycle Elite Member
Join Date: Apr 2008
Location: Valparaiso, IN
Posts: 624
Default Grubee Gearbox- run it with lube!

I have always used grease only in my Grubee Skyhawk II attached to my Honda. Grease worked OK and I was satisfied. There was some noise, but it did not really annoy me. However, one of the “problems” with the 4 stroke is that it is so quiet, every other noise besides the engine seems loud. At speed, I did not really even hear the engine, only the gearbox.

Also, the clutch chattered if I revved up at a relatively low speed (48 tooth sprocket). I just figured I needed to pedal up faster. Doing that, no problem.

However, it's never done, so I am always looking for improvements.

I ran into a friend of mine this week, I had not seen him in a little while. He is a gearhead, so I mentioned my motorized bike project- guess what, not only does he have one, he uses the exact engine and gearbox that I do

He suggested I try what is suggested on the bicycle-engines website- a 50-50 mix of gear lube (85-140) and stop leak/smoke. I decided, why not?

I had thought that something thicker than gear lube, but thinner than grease so it would flow may work because it would cling to gears. The key is the “stop leak”. I’m not talking about some substance just designed to swell seals, but to stuff you would add to engine oil (in the old days) to thicken it so it was too thick to leak much around worn guides. There is a product called “motor honey” that was as thick (or thicker) as honey. Sometimes it might be called “stop smoke” or something. The brand does not matter, but you want that thicker than thick stuff that says it keeps an engine from smoking.

Well, I got it- the gear lube pours great, the stop leak pours....eventually. I mixed in a container 50%-50%. I never expected this, but the real challenge was pouring it in- not hard, just took forever (heating it may help, but I have not tried it). You pour it in where the engager arm goes into the gearbox. It pours very, very slowly and it will make a mess if you try to go too fast. Also, add no more than 5 ounces, 4 is probably better. You just want enough for the gears to dip down into. You do not want to come anywhere close to filling the thing. If you put too much in (which I did, by maybe ˝-1 ounce) the excess will back up out of the fill hole when the gearbox is engaged and running, but when enough is out, it will not come out anymore.

You may need to seal the gearbox. I used the original gasket, but I also used form-a-gasket as well. There was a little weeping at first at the seams, but it stopped.

The results? The clutch chatter is gone. A good thing. This means the clutch is engaging more smoothly because it slips in, rather than grabbing all at once. However, I have not been able to detect any slippage once the clutch is at a speed where it should be fully engaged. I can actually leave from a standing stop without pedaling- I do not suggest making it a habit, but I wanted to try it. Rather than just bucking and the engine wanting to die (it never had died, but it lugged very low before), it just takes off smoothly, if a little slow. The website says that the clutch may slip when you first try it, but slippage will stop after some use. I did not notice that (other than the gradual slippage on engagement). The website also says to add a little more when the clutch starts to chatter.

I now have about 30 miles running "wet"....I ain't going back to dry. It got better as time went on- less slippage at startup, but still smooth.

I still hear the gearbox, but much, much less and the engine much, much more. Before, at speed, I never heard the engine, just the gearbox. It was not annoying the other way, but this is better. Now the engine is the dominant sound, and it is not any louder than it was.

I just got back from a 17.5 mile ride and it all just gets better and better! My engine is now well broken in. It just pulls and pulls and with the gearbox lube, it runs smooth. I will not make a habit of it, but I met and possibly exceeded the 40 mph speed limit on one road, at least according to my speedo.
29/10ths cubic inches of raw power.
HoughMade at
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