Well they can be if treated wrong. Don't let them sit, even in perfect storage conditions.
I dropped into my old mate Gary Parkers place yesterday. Gary is a mechanic with a shop in Beaudesert, south east Queensland. A long time stalwart of the Triumph club here in Queensland with about 6 Triumphs, I watched him rebuild the engine & gearbox of his supposedly restored Dolly Spring over a couple of years a while back. He is meticulous.
He was working on a rather nice TR7. It was evidently restored by one of us old bloke type owners about 10 years ago, then driven rarely, before sitting for 5 years.
The new owner is from Murwillumbah almost 1000 kilometres from Sydney on the Queensland boarder. After some testing around Sydney he headed for home. Along the way it started to use water & get a bit hot. It was still drivable, so he kept going, but should not have. At home he took the thing to a good, [but not classic car experienced], mechanic who found a water passage in the head face very corroded.
A replacement head was sourced, & the thing reassembled. Now it had a light but worrying knock. He looked for a "triumph" mechanic & found Garry. Compression was down on No2, & with the head off again, Gary found
light scoring in that bore.
With the piston out he found No2 piston ring broken, & the ring groove was damaged. A honing cleaned up the bore, but the head required valve guides & seats to be good. After new pistons & a head rebuild the owner will have really nice car, for about twice the original purchase price.
Yes it is partly his own fault, not stopping when it started using water, but I hope this has not soured his desire for a 7, or any old car in the future. It sure can get expensive making mistakes when you first get involved with Triumphs, or any old machine.