Now that I have my '86 740T back on the road, I probably need to put to rest one of the reasons I got the car ultra cheap, back in 2001... a persistent tapping sound, that techs either diagnose as a bad valve or a piston problem (wrist pin?).

Here is the kicker: the car has 550k kilometres (about 340k miles). Was owned by two salesmen with large, dispersed territories, then by a lady who had a 70-or-so miles a day commute.

However, the engine is really, really strong. In fact, it's the strongest 740T I have ever driven, and the two Volvo techs who have worked on it report much the same. I have NO idea when/if it was rebuilt, though I am certain the turbo was changed as this one is perfect.

I could believe that its performance might be due to a shaved head as a result of previous work (as an example), except that despite its oommph it seems perfectly happy to run on regular unleaded (my last 700T had to have mid-grade or premium after we shaved the head).

The dilemma is that I have access to a very inexpensive, used B230ft from a rusty wagon. I am loathe to pull the head off a high-mileage car like mine and start some sort of adventure in a shop (the daily "Um, we found something else wrong with your car" calls, BDDTNTS), but I also hate the idea of giving up this stormer for some mediocre engine that only got used on grocery runs in an automatic wagon.

I've put some 15-20k kms on the car with this noise there, and it never seems to get better or worse (except it's more audible in cold weather, of course). I looked at the FAQ and this sound isn't the one covered there... it's present from startup and is there when the engine is hot, but it is only present below 2000 rpms or so. It is LOUD... in winter people think it's a diesel.

Thoughts, wisdom, suggestions are welcome. I have a limited time frame in which go either grab this used engine, or let it pass.

Many thanks,

Steve
'70 142s
'75 164e
'86 740T
Two dead Mercedes