I have an ovalized bb on my schwinn BMX cruiser. Is this fixable of is the frame trashed? Other than the cranks coming loose a lot and having to ride with an allen key to tighten them all the time, the bike rides fine (for now I suspect)

The bb shell could be replaced by a frame builder but the cost would probably be prohibitive for the quality of the bike.

As a stop-gap fix I suppose you could epoxy the cups in place or use one of the Locktite gap filling cylindrical fit bearing and sleeve locking compounds.

Thanks man, I knew there had to be something to keep it alive longer. I appreciate it.

How have you determined that the BB has gone oval? and what is it exactly that you are referring to? The BB shell? Something about the axle

Cranks coming off is usually a sign of the crank arms having been poorly assembled initially, and the fit between the surfaces having been mashed up. This leaves the BB + BB shell unaffected but the crank arms are usually beyond repair.

I had the local bike shop look at it. I has a set of profile race cranks, spindle, bearing, etc.. and are all fine. The LBS mechanic said the bottom bracket is ovalized, I trust him with that. I just get the feeling that they may be telling me I need a new frame to make a sale. I'd rather repaiir anyway e if possiblsince these mid 90 schwinn cruiser frames are no longer available.

Back in the late 80's my son bought a high end Schwinn frame. The bottom bracket would come loose no matter how tight you tried to make it. The LBS mech kept trying to make it tight but it would still come loose. I think he really busted a gut trying to tighten it, as he would not let us watch. Finally I discovered the BB was ovalized. The Schwinn rep came in and agreed with me and was amazed that it was me and not the LBS mech that discovered the problem. Schwinn replaced the frame no questions asked. They paid the LBS to rebuild all the parts onto the new frame. So if I were you I would check if the frame has a lifetime warrenty with the manuf. You too may get a new free frame.

A loose BB due to the BB shell being ovalized isn't something you can tighten with an allen wrench. Which part are you tightening with the allen wrench to make it useable for a bit longer each time? I suspect that we're all talking about different things here. The only thing that an allen wrench would be used for would be a wobbly crank arm mounted on a square taper or spline BB.

Can you give us a picture of what you have now and draw a nice colored arrow on the part that keeps coming loose that you're tightening? Because as it sits now the only thing I see in this thread is confusion.

I sense there is an atapter in the OPC BB shell to use a 3 piece crank with a normal threaded 1.3 ish inch BB.
Have you considered using threadlock on the bolts that hold your adapter rings together , if that in fact is what you have?

If it is a shell ovalization, going back to a common one piece crank
and banging in the strong stamped cups would probably do a job of forcing it back into shape somewhat.

Ashtabula cranks are pretty forgiving, of abuse and low maintainence , though heavy.

What BCRider said.

I agree with BC too. when the OP said BNX Cruise I assumed an Ashtabula crank, but just what is the OP tightening?

No amount of torque or thread loc will fix this problem. The frame is shot.

OK, I can see how a busted up BB shell could cause the BB itself to loosen, but according to the OP it's the cranks that are coming loose. Can't really get the symptoms and the diagnosis to match here.

Pics required.