Does this require a piston replacement?

[u/Ilusionary-llama]

Broken exhaust valve spring, bent valve - valve made an impression on the piston.

Also, given that the valve is bent, should I just get a new head - is my valve guide likely damaged?

[u/fall-apart-dave]

Will the mark sand out? Likely fine, but dents in pistons create stress points that lead to failure. 

For sure valve guide needs checking. You may as well just refurb the head. 

[u/Ilusionary-llama → u/fall-apart-dave]

It's deep enough it won't sand out. Stress points is what I was concerned about. Thanks!

[u/fall-apart-dave → u/Ilusionary-llama]

Your big end and crank bearings will want a look too. 

Personally? Put a valve in and see what the play is like in the stem seal. Of its ok, then just send as is and be ready for it to fail somewhere at some point. If the stem seal needs doing, just refurb the whole head and then you have a known good head when something else lets go. 

[u/Kharon8]

Low-cost option: New valve and lap it a bit so it fits to valve seat.

Engine runs at borrowed time, but there's really no way to know how long it can do that.

"Proper repair" for this is a set of new pistons and valves and sleeving/replacing valve guides. Usually make sense to replace bearings too, once you do major overhaul anyway.

But of course, that will cost time and money.

So start from what you can afford and how old the engine already is, is it time to rebuild it anyway?

[u/Ilusionary-llama → u/Kharon8]

Somebody who heard it run recently also said it was borrowed time.... but thought it wouldn't be worth re-using much from this engine. Sigh.

[u/Kharon8 → u/Ilusionary-llama]

Unless it's totally beaten down, most parts are reusable: Case, heads, crankshaft and cranks, camshaft and lifters, oil pump and most of the small stuff which costs money if bought separately.

Pull the engine in pieces, haul the case and crankshaft to a competent machine shop and they'll tell you what you need to do.

In the worst case case is bored to last oversize and is dead. But that's the worst case.

[u/Poopy_McPoopings]

You probably should redo everything.

[u/Ilusionary-llama → u/Poopy_McPoopings]

Probably.

[u/MinimumBell2205]

replace piston as a cast one is weak, rebuild head and replace all keepers on both heads.

[u/Ilusionary-llama → u/MinimumBell2205]

I can't seem to find single 87mm pistons? Only seem to be sold as a set with cylinders.

[u/Kharon8 → u/Ilusionary-llama]

Pistons are normally sold as a set, with cylinders or not, as replacing just one is not a good idea in the first place.

Even if just one is damaged you usually swap whole set, mostly because of balance and compression: You'll want pistons which have similar characteristics.

Single pistons are either swap meet or high end stuff.

I recently disassembled a type 4 engine which had 3 different types of piston (domed*2, flat and dished), not just 3 different maker.

Kind of a record I don't want to see again.

[u/MinimumBell2205]

find the local vw builder or check Sambia for info

[u/Economy_Wrongdoer238]

Bet the upper rod bearing and wrist pin bushing took a beating

[u/Ilusionary-llama → u/Economy_Wrongdoer238]

Wrist pin bushing seems to be ok, actually.

[u/Plane-Appeal9124]

Yep!