How many Kms is too many (engine swaps)

So after some thought over the past couple of days ive decided to get a m15a for my gen 3. And i was wondering how many kms is too many for a second hand engine? whats the ideal kms for a engine swap?

The issue is not how many Km it has completed, it's how the previous owner(s) has looked after and maintained the vehicle.
As Lambert said, low km reduces the opportunity for neglect, but if you can inspect the engine before you purchase its always the best option.
Look for:
Clean engine oil - not black gunk. 
Clean / new spark plugs that are the correct operating colour.
No sludge or black gunk under the cam cover.
Any signs of overheating, melted sensors etc.
Covered in silicon RTV in place of proper gaskets, its been apart - why? (Run away!)
If you can do a compression test on each cylinder, better still hear it running.
General condition of the engine - Clean (good) - mud dipped oily mess.(look closer, its had a hard life)

If you can tick all these boxes then it should be in good order and should run for many more km. But nothing in life is a certainty.
Good luck.

Mike
 

^^^this^^^ and look for a sign that tells you if the cambelt has been replaced.

My 2001 car has done a little over 100k miles. All was in good condition according to the list above. But I couldn't find a sticker or sign if and when the c/belt had been replaced. So, we (a mate and myself) took the cover off and discovered that it was probably the original belt. Worn. As was the tensioner. Despite the fact that the car had its (last 5yrs in a row) maintenance at a Suzuki specialist. The fact that it has a maintenance history was one of the reasons I took the risk of buying a high-miler.

A replacement set is next to nothing. And 2.5 hrs later, all was reinstalled and the car ran again.

Menno

M series engines has no cam belt.

But service record would be great if you can not meet the donor. Best is if you can see and hear it running. Anything below 80000km should be ok.
M series engines has very little problems. Only overheating but very rare and the few times i heard of this it has been 140000km ish.
Low milage, low wear on the pedals, shifter, steering wheel, looking tidy overall should be fine.

My donor I know nothing about other than low milage and a freak rear accident so the front was fine.

Rare things a clean VVT, but hunt them out. If tis a scrapper you cant run, take the rocker cover off (you will need to for the swap anyway) and have a good look for gooey bunged up oil in the passages, that indicates a lot about the condition of the engine.

as an example of what to look at here are two engines with the rocker cover off (both M series VVT, old one an M13 with at least 100k miles and the new one a M18 but literally brand new)...

New:

 

Old:

 


The old one has a lot of oil sludge build up indicating its not had as many oil changes as it should of had, therefore the one to avoid. No engine with miles on will be as clean as a brand new one, but should be better than the old one pictured. 

Hope that helps 

what about getting a motor that is abit higher like 140 000kms and giving it a rebuild?