Snapped Valve-stems in Pistons: Okay to leave Pistons in ?

OK, you what happens when timing-belts snap, but this took a couple twists:


- Snapped while cranking: Starter turned over less than 2 seconds - engine NEVER started.

- Foolish me, attempted to remove timing belt (before realizing internal carnage) by taking breaker-bar & socket to force crankshaft pulley to turn. Forced it pretty hard (barely moved) before removing cyl.head to discover grisly result.

- A couple pistons have deeply gouged "hole-dimples" where valve-stems were "planted" (center of pistons, but no scoring of cyl. walls)

- Machine shop re-worked entire head: guides/valves/etc + outsourced to TiG-Welding aluminum specialist (there were cracks somewhere, maybe due to my forcing crankshaft to turn?)



Finally ready to re-assemble, but wondering: Is it necessary to replace pistons ? (Hope not, as can't spend $$ paying shop to do it)
Not sure it's a factor, but car's been stored in this condition for years since my brilliant move.


ENGINE:
- Only 70k (orig. owner)
- E30 2.0 six (yep, Euro engine)

Honestly, they probably wouldn't hurt anything, but just knowing those divots are in the piston tops would keep me up nights worrying about just how much more damage was done that you can't see, like a broken ring or bent rod. You're several hundred into it already. It's your choice to either put it together as-is, or tear it down and make sure there's nothing worse than just dinged piston tops going on.

As stated above just the thought of knowing the pistons are in there and in not so great shape. Considering you were turning it over by hand, i doubt a rod was bent and positive a ring didn't break. You should be okay to button it back up. However do so at your own risk.

Considering the belt snapped while cranking I doubt any real damage to the piston, rod or crank.

im not a fan of damaged pistons. i would change them and bore and hone the walls

I will admit to putting a few back together with dings in the pistons without a problem but I'll also say it wasn't my car and the owners really couldn't afford the extra work so they were done with a very limited warranty .I wish you the best of luck but the decision is yours. Do you feel lucky today?

Originally Posted by toybuilder

I will admit to putting a few back together with dings in the pistons without a problem but I'll also say it wasn't my car and the owners really couldn't afford the extra work so they were done with a very limited warranty .I wish you the best of luck but the decision is yours. Do you feel lucky today?

IMO, the bottom end takes more abuse at idle that what happened to his engine during the cranking process...

Mark7 is right but your half way to rebuilding your engine completely so if money or skill isn't an issue then it seems like a good time to refresh your baby.You said your the original owner so I would guess you definitely plan on keeping this car.

You'd be surprised how much torque a good starter puts on a motor !
I have seen a starter bend rods on a hydraulic-lock'd motor

But then again, I have often done heads on these M20 motors as a result of the belt snapping
Nearly always whilst cranking or idling, which makes sense.
Never heard of any further damage, apart from dimpled pistos from the valves, as long as the valve did not snap & score the sleeve etc.

I'd take a small ball-peen hammer & then a die-grinder to the marks on your pistons to make sure they do not cause "hot spots" later on.