Can a valve spring be replaced w/engine in car?
 

I have seen a video of someone replacing the chain tensioners in car and am wondering if anyone has experience changing a broken spring in car?

Any helpful links also appreciated....

Thanks!

The answer is yes. You can use compressed air in the cylinder to hold the valve closed as you are removing the spring and keeper, however one inadvertent bump to the valve stem will result in losing air pressure and a dropped valve. Another method is to stuff the cylinder with rope then roll the piston up to hold the valve closed.

given that these are flat engines, less worry about dropped valves. You can put rope in the cylinder too also.

Thanks so much for the replies. I have changed springs out in other applications and am familiar with options on how to do the job.
I am just wondering if there are any interference issues or special concerns that would make this operation not doable in-car with the Boxster...
Thanks again!

Read up on what is involved to R&R hydraulic valve tappets. This is a tedious job to do in car but needs to be done before you can get to the retainers. Hopefully it is a broken exhaust valve spring.