RESTful API Design: Operation that involves more than one resource

Question

I have following model:

class Bikes:
   id: int                 # primary key
   group_id: int           # for split/merge (see below)
   quantity: int           # number of items 
   is_broken: bool         # true if all are broken
   repair_request_id: int  # reference to some RepairReqest (if broken).

repair_request_id is set to some RepairRequest object that describes a request for repair quantity of Bikes. is_broken must be true if repair_request_id is set.

My RESTful API for it:

GET /bikes        # returns list
GET /bikes/:id    # returns single instance
PUT /bikes/:id    # updates existing or adds new instance on list, returns instance data

With PUT I can mark Bikes as broken by setting is_broken=true and repair_request_id=R.

Now I need to add an operation that allow to add RepairRequest for part of bikes with group_id=X by splitting a single instance in two.

Assuming that I want to add a repair request for quantity=Q bikes from group_id=X I need to do following steps, in single transaction:

1. Find A, where A is: Bikes with group_id==X and is_broken==false
2. Create B, set quantity=Q, is_broken=true
3. in A, Set A.quantity = A.quantity - Q
4. Save all

This creates new instance and modifies original one. There is a requirement that I can have only one instance with group_id=X and is_broken=false, so when Bikes B are repaired they are merged back with following steps, in single transaction:

1. Find A, where A is: Bikes with group_id==X and is_broken==false
2. If not found, update B (is_broken=false, repair_request_id=null)
3. If found:
   1. Set A.quantity = A.quantity+B.quantity
   2. Delete B

Merge can be done with PUT /bikes/:id. This could return a different instance that was sent, but this is fine for me.

Problem is with split operation. My requirements are:

• Backend should decide if it needs to do split or just call the same handler that was created for HTTP PUT.
• I do not want to expose transactions in REST API - one HTTP request is a single transaction.

My current idea:

  POST /bikes/1/operations/set_broken

  payload:
  {
     "quantity": Q
  }

  response (after split):
  [
    {
      "id": 1,
      [...]
      "is_broken": false
    },
    {
      "id": 2,
      [...]
      "is_broken": true
    }
  ]  

Do you think it is clear? Or do you know a better design pattern for this scenario?