Timing Chain Rail Break
 

I'm wondering if anyone out there could give me an educated guess or opinion. My mom's '87 420SEL (w/135,000 miles) just broke its timing chain rail & this is how it happened...

The car was backing out of the garage & it begins to make some kind of loud, weird, metal chain like noise, then the engine was shut off, then restarted but the noise are now louder, so it's shut off again, now the car will not start at all. There are no visible sign of valve cover damage. When my cousin took the valve cover off, pieces of the plastic rail fell out!! but the chain is still on the gear & it turns fine. The engine was on for maybe no more than 30 secs at a time.

Without looking at it & listening the description above, my dealer's service adviser thinks there is a "very good" possibility (sounded like better than 90% to me) that there was NO valve damage. He also said that you can't visually inspect for valve damage by only removing the valve cover in this case. You would have to repair the TC, then do a compression test... but he believes the engine speed was low enough to not cause any damage to the valves. Does this sound possible??? or does always involve valve damage no matter what.

If I should take his word for it & sunk $1,000 for the TC repair, pray really long & hard that there will be no valve damage, or otherwise I would have to shell out another $4,500. Or I simply just call it quits now because $5,500 is just not worth it.

Thanks!

Here are some thoughts:

How do you know the timing chain rail broke? Did you take it apart already or did the shop?

You (or the shop) can determine whether the valves were bent by doing a leak-down test one cylinder at a time. The engine can be rotated by hand (assuming that the chain didn't break) until the valves are closed. Then the cylinder is pumped full of compressed air. The air can only escape past the rings or one of the two valves. Your mechanic will know immediately if there are bent valves.

So, you shouldn't have to spend $1000 to find out the extent of the damage.

No. The $1,000 is for the replacement of timing chain, tensioner, the cheapo plastic rail guides....etc. He is saying that he couldn't tell me whether or not there is any valve damage until after the timing chain is repaired.

$1000 to change a timing chain and tensioner is more than twice what I would pay. What dealer/shop is this?

That's Competition Imports in Smithtown. Through the help of another member I found a mechanic at Competition who does some work on the side, but his price is about the same to do the TC. However, he only charges around $2k to rebuild the heads/valves instead of Comprtition's $4,200.