Grubee GT5B - A Pursuit of Reliablility

Put the bottom end together with the new SKS bearings and seals.

The seals I ordered from Amazon for like 10$ a set were not very good quality at all. I ended up ordering some OEM seals from (where I got my engine kits) and they are the same ones that came on the engine, but they look a lot better than the originals, and we're like $1 or $2 a piece. I will take pictures of both and post tomorrow. Regardless I used the "OEM" replacement ones instead of the random ones I ordered off amazon (they looked terrible).

Still looking for a better replacement for stock seals, I've got a few leads to a few sites and I think I may try them in the future, although they aren't the 100% oem sizes (if they can be trusted).

Lubed EVERYTHING up with slurry mix of 2 stroke and vaseline because I don't know how long this engine is going to sit before I end up installing it.

Ended up having issues with the clutch bearings / clutch shaft seating properly so I removed it from one side for the time being. Sanding down surfaces (15.02 to 14.98) (haven't measured outer bearing surfaces yet) After mating both case surfaces one of the clutch bearings got pushed slightly out on one side which was causing binding. Not playing around with that. Once I get the tolerances a little better it'll go back together (probabably this weekend).

The paper towel is just to stop the rod from clanking around.


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I'll upload pictures tomorrow (nothing special or revealing) but the engine is 100% put together at this point. All the bearings and actions feel great. I have the 2nd rebuilt clutch ready to put on the new engine but haven't installed it yet. Everything else is put together.

One thing I want to do before I use the engine is fix the squish gap. I haven't seen very many comments, if any, regarding the Grubee GT5B squish gap on a stock motor, but both of mine are around 2.6~mm which is a bit much for me. I'll be re-decking the jug at some point before I install it. Low and mid end torque aren't the greatest from my experience, and this may be partially why.

I ended up using the replacement seals I ordered from which are basically the same as stock but they looked a lot better than the crappy ones I found on amazon. There are still some alternatives mentioned previously in this thread that I have not tried (It was something like $10 a seal vs $0.99). The "stock" seals have worked fine for me on the 'throw it on the bike and go' motor, so hopefully these hold up the same way. Regardless I bought 5 each of the thick vs thin seals vs 1 aftermarket/other brand seal so I'm ok with it.

I used the 2-stroke and vaseline mix on all the parts of the engine liberally because I'm not entirely sure when I'm going to install it. The engine I have currently is around 600+ miles and is making strange noises (like piston slap) above 7000rpm so I have no idea how long it will last. Have no idea what's making the noise.

When I install the new engine on the bike I'm going to pull apart and rebuild the original. I already have a spare head and piston / bearings / seals ready to go.

One thing I will say. I've noticed on the engine on my bike that the bearings with the metal covers that come stock with these leak out their own bearing grease slowly over time (specifically the ones on the clutch shaft of course). This means that small particulates can also get into the bearings, which I have no doubt is happening.

I should be getting my driver's license back in a few weeks so I think once that happens I'm going to pull the "old" engine and put this one on the bike and see what happens. The only thing stopping me from doing that at the moment is I use my current motor/bike for essential purposes (I live 10ish minutes from town and cannot afford a Taxi every time I need to buy something) and it's proved itself reliable to me at this point.

Basically the only thing I didn't do to this engine is balance the crank, which I'm considering pulling it back apart to do. But I think I may just do it on the 'old' engine once I rebuilt it. I haven't quite figured out how I want to properly balance it. I've watched a lot of videos on that and have read a few threads but still haven't quite figured out how I want to go about it. I'm kind of anal with that kind of thing.
Pics or it didn't happen ...
I balanced mine with the half inch 15mm method, and it made a world of difference. Not perfect, but 80% better. I like the way the guy from Build Brake Fix did his. Seems like it was about as balanced as one could get it without a computer. I was impressed. Gonna try that next time. Any way you do it is going to be an improvement.
Here's a simple method I used. Bike revs up high, and fast really smoothly. Vibration is nil compared to stock, and actually feels like it runs better.

This here is the best way I've seen so far. Longer video, but absolutely worth it. Trying this myself next round.

Here he goes more in depth on the different crank and rod types/weights. Breaks down the weights of everything like a good cheat sheet.
Yeah I think I'm going to pull the crank back out and do this. I'm going to wait until I get my actual driver's license back, just in case. My current engine has been making a strange noise lately that I don't like and want a backup available.