Yackboy, where to start
Until the rings bed in up to a litre per 5,000kms is acceptable. Use this as a rough guide. That being said any more than that there is still the chance that the rings will take up, but more than likely there is a fault that has presented itself.
There are a number of questoins that need to be asked.
Given that the engine is "breathing heavy" I think you mean that the engine has blowby or is fumey. were the rings checked in the bore to ensure that the correct end gap was present, were the pistons checked in the bore to ensure that the piston/bore gap was correct. Was the bore checked for out of round, and to ensure that there was no taper present.
When the engine was assembled were any pistons difficult to get in, that required extra force. If so then some of the rings may have been broken when the engine was assembled.
When the oil rings were installed did you ensure that the ends butted together on the middle spacer ring and that that the upper and lower scraper ring end gaps were opposed.
When the two compresssion rings were installed did you ensure that the rings were not lined up and were opposed.
Other things that can cause oil usage is the cylinder head valve stem seals or the valves loose in the guides. This will not however cause blowby.
Essentially if you can answer that the above has been checked when the enginewas assembled, then there is a chance that it can take up.
HTH
Keith
