Perhaps an update for additional information might be in order?

I can attest that folks still DO have valve spring issues. =)

When the spring in my .91 gave up the ghost, I purchased this spring. https://www.towerhobbies.com/cgi-bin/wti0001p?&I=LXWY25

Also worked in my Thunder Tiger .91, and yes, I bought two and did intake and exhaust at the same time. Main reason being, if one spring is compromised, how long until the other spring shows the same issue? I will say that the O.S. .91 runs like a sewing machine!

Here is a thread I did highlighting the spring swap.
https://www.rcgroups.com/forums/show...iners%21%21%21

Hope it helps!