super rat bottom end on boygoesfast?

Whats the crankshaft size on the bottom end?

newer ones have the balanced crank & take the H2 top end nicely

I just ordered 2 from BGF today. Looked like he had a limited amount, and for $75 I thought they were well worth a try. I've been looking for a new bottom end to play around with, perhaps doing a puch hybrid experiment or two, and the internal CDI was an added bonus. That really cleans up the look. I plan on removing the stock spark plug wire and adding an 8.8. Hopefully my plans work out. More to follow this summer...

I saw those bottom ends in his ebay stores as well but didn't buy because I didn't know which stroke crank it had, but the internal CDI definitely makes for a nice clean looking install. Keep us posted on how it works...

I messaged BGF right after I purchased and asked if these were actual Super Rat bottom ends, or just replicas. I also asked about the stroke length. The reply back that I got was "same as Super Rat". We shall see. I'm not buying any top end goods until I know what it is I will actually have next week. Even if its just a regular stroke, the internal CDI was what I was after. Anything more is just China Girl gravy!

I never owned a "Super Rat" china girl, but I remember reading somewhere that the CDI was one of the biggest problems with that design because it would get to hot and fail, hopefully you'll have a good go with those lowers.

I'll following along to see what you get and what you do with it.

Map

I've never heard anything beyond what I heard for the china girls in general, but You maaayyyy run into issues running a normal cylinder with it. See the normal HT's run a 36mm stroke (yes, even the GT5a, measured and detailed by myself), the Super Rat has a 40mm stroke. You could run a bunch of base gaskets to make up the difference but your ports are going to be wacky, and you may even have issues with the piston dropping below your intake port. The SR has numerous different measurements from the Standard HT. The cranks are different, the Super rat has larger bearings, you CAN throw a superrat crank into a standard HT case using 6002 bearings, but the same can be said of most moped cranks in that case, the issue is your gears (if the SR match, great!) and your magneto (you'll need to drill it out and make the mounting hole larger to accomodate the larger crank).

It'll be a pain, and probably net you piss-poor performance (due to the porting anyway), but it should run. If you can, grab a GT5-a cylinder. It's just a shortened SR cylinder. The intake is larger, but the port timing themselves may be off as well.

RGZWS6 said:

I messaged BGF right after I purchased and asked if these were actual Super Rat bottom ends, or just replicas.

Click to expand...

I doubt anyone would make a replica of a cheap china engine. These engines are actually replicas of some old russian motorcycle engines & Whizzer engines.

No doubt the SR has multiple different parts, and they are all but impossible to find for sale. However, and interesting discovery is that BGF is now selling the internal CDI as a part, all by itself, for $18.99. Seems he may now be the guy to go to for the SR projects. Perhaps he has those other SR-specific parts too. I pinged him on one of his top-end kit about the specifics, so soon I will have my answer.

UPDATE: BGF has the wide mouth 40mm intake jugs for $15 (not listed), but when I asked for the matching top end kit as a whole, he referenced me to the regular PK-80 stuff for $45 shipped. Not sure all of that would work well together with his SR bottom end. Gunna keep looking. King's needs to re-stock their dern shelves!!