BGF RB80, larger intake port?

[maurtis]

I am looking into various HT kits, and noticed BGF is posting a different kit on eBay now. I had been looking at the Z80S kit, but I am seeing him posting up RB80, which looked identical.

I sent him a question about what the difference is, here is the response:

"RB80 is bigger intake port. 3 L tank, better parts. and runs smooth"

Maybe this is a 2012 change for all of the HT kits coming out of China? Any ideas?

 

[biknut]

I have a Z80S kit and there's nothing impressive about it, except the price was low. It has a small width front motor mount. The crank had more than 0.003 runout.

I hope the kits are better. Sounds like they might have 40mm intake width on the studs. The Z80 is 30mm. i hope these new kits are better quality. I like buying from BGF.

 

[biknut]

After looking over the eBay listing, the only difference I can tell is, it comes with bigger intake, which means none of the regular intake manidolds will fit. It has the bigger gas tank. It seems to have a short 4 bolt chain tensioner. Probably has a center head spark plug hole, but it's hard to tell. In some of the pictures it's slant. Can't tell about the size of the front motor mount, but I guess it's the small one.

 

[maurtis]

I finally ordered my china girl yesterday (heehee), I did end up going with the BGF RB80 kit. There is not a single marking in the box or engine itself, so no idea what factory it came from, assumed it was a "Red Bat" because of the "RB" in the name?

Overall I was pleased with the "quality" of the engine. The castings are reasonably good compared to some of the others I have see on this site. There is still some cleanup to do, but overall not bad. I have not opened her up yet, though.

I did notice a good amount of metal shavings near the sprocket, though. Definitely going to have to give her a through going-through. Hopefully those shavings are not indicative of something trying to die before I even get started.

About the intake, the studs are 40mm apart. I noticed though that the intake manifold is aluminum, I think the others I have seen are steel? And it is also tapered, the inside diameter goes from 18mm round at the carb side to 20mm x 15mm rectangle on the motor side. And from the looks of the indentions on the gasket, the intake manifold pretty closely matches the intake port, woohoo. The port itself looks pretty clean, too.

I still have to pull the spark plug and move the piston to TDC to see how much of the intake port is covered by the piston skirt, that is a project for tonight.

On the exhaust side, there is a little slag where the port meets the piston, but not much. The exhaust itself needs a lot of help, though, to get port matched.

 

[biknut]

Can you please measure the width of the front motor mount studs. Are they 40 or 50 mm?

 

[maurtis]

The front mounting studs are 40mm apart center to center.

 

[biknut]

The front mounting studs are 40mm apart center to center.

Thanks, good to know. I wish they were 50 mm, but it's only an issue on a small frame.

 

[biknut]

That metal dust is probably from when they drilled the rear motor mount holes.

 

[maurtis]

That metal dust is probably from when they drilled the rear motor mount holes.

I really hope so. I will feel better this weekend when I can dig farther in and see if things stay fairly clean or get uglier, lol.

 

[biknut]

I can't wait to hear how it runs.

 

[biknut]

I finally ordered my china girl yesterday (heehee), I did end up going with the BGF RB80 kit. There is not a single marking in the box or engine itself, so no idea what factory it came from, assumed it was a "Red Bat" because of the "RB" in the name?

I think your assumption is reasonable, considering BGF has been known to sell Red Bat motors in the past.

 

[maurtis]

The manual from BGF mentioned these motors were test run at the factory. I was thinking the oil residue I was seeing on the piston may have just been from assembly, but pulling the plug I can see it has definitely been run already. So either I got someone's refurb, or they really were test fired at the factory...

Looks like I need to do a little trimming on the piston skirt. I was hoping this would magically not be the case, lol.

 

[Mannhouse51]

Keep us informed on how it runs please. Thanx

 

[maurtis]

Keep us informed on how it runs please. Thanx

Will do!

This weekend I took off the head and was glad I did, there were a couple small nicks on the squish band and one sizeable gash. I ended up sanding down almost half of the thickness of the squish band to get it out. After putting the head back on and manually turning over the motor by hand I did not hear the spark plug hitting the piston, so hopefully it was not too much.

Then when I tried to separate the cylinder from the crankcase, I could not get it to budge. After a few minutes, I chickened out and took it as a sign that I was not meant to be in there, lol. So the piston skirt will remain untrimmed until something goes boom and I have to rebuild, or I get to the point where I want to tune the crap out of this motor

Both the exhaust and intake ports look really clean as is, so now just waiting on my miscellaneous bits to arrive from SBP, trim the exhaust gasket and pipe a bit to more closely match the port, then install.

 

[Al.Fisherman]

Did you loosen these two bolts...It could cause the case to pinch the jug?????

 

[biknut]

Sometimes I have to whack the cylinder with a rubber hammer because they used gasket sealer on the base gasket.

 

[Mike B]

If it's been fired, that's a good thing.

 

[biknut]

I don't really see much difference in the size of the intake ports other than wider spacing for the manifold studs. I'm guessing those cylinders will probably interchange with the more common ones. I guess the big improvment is that the intake gasket has more area for a better seal.

 

[maurtis]

Did you loosen these two bolts...It could cause the case to pinch the jug?????

I did not loosen those, that might have helped, lol.

As far as the "larger" intake port, I think you are right biknut, looks like the difference is in the stud spacing. I do like that I do not have to modify the intake manifold to match the port, though.

 

[mapbike]

I like the extra sealing surface around that intake port as well, I never have issues with the old style because I use Permatex High Tack Gasket Dope on everything but the exhaust gasket, but there is a much less chance of having a leak with the stock junk gaskets these engines come with if the surface area is larger, that may be the main reason for the change, less warranty issues from burned up engines do to being run to lean from an air leak...Shrug....???

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