How much damage can a timing chain cause to the engine when it goes out? I have a Pontiac with a 389 that has tossed the timing chain and I am worried on how much damage it could of caused. On top of that. Would it cost more to rebuild the engine if it is damaged or just replace it? Thanks, Brandyn
Normally it won't do any damage. Depending on whether the valves interfere with the piston travel, how fast the engine was turning when it grenaded... on timing belt / multi valve cars it usually always causes damage. If it does, it's usually just a bent valve. Put a new chain on it, spin the motor by hand with no plugs in and see if it feels fine and doesn't bind, put a new chain on, compression test. If you have a bad compression reading on a cylinder, a valve is bent more than likely.
I've seen them break and if it stops dead not do too much damage and other times pretty much grenade the engine. Gotta look into it and see how far the cam timing went off - then check for bent valves and contacted pistons.
Pull the front cover, put in a new timing set, and before you close it up, start the engine. That will tell you right away what you have. Something else to think about is if the cam gear was nylon tooth all that plastic is in the pan waiting to get sucked into the oil pump. If thats the case, consider dropping the pan and clean it out. Re engine damage, unless you were running the snot out of it when it went, its probably ok. I started out in a garage back in the day and I'm tellin' ya I did alot of those, don't recall a Poncho ever bending valves when the chain went, unless someone was winding the piss out of it.
I've had it happen a couple times on Pontiacs but never had any valve damage - I just had to put in a new chain and gears, and everything was fine afterwards.
Yep. And as thunderroad312 said. Fire it up as soon as you get the new chain on. You'll know right away if its good or not. Posted from the TJJ App for iPhone & iPad
It really depends .. Could be nothing , but could be valves or pistons. I once had a valve break off and bounce around in the cylinder ... But you would know if that happen
Over 60,000 on a stock Pontiac plastic timing gear loosing the timing gear is called normal. I had one in a customer's car go out when I fired the car (a 63 Catalina) up on the front end rack after I aligned the front end. Do yourself one hell of a big favor and drop the pan and dig the plastic out of the oil pickup screen. I've seen too many of them that had the screen plugged up with plastic gear pieces to where the oil didn't flow. If it ran good and had good compression I'd think about changing the rod and main bearings and rear seal while I had the pan off or at least checking them closely. To me those engines are easier to work on than a sbc so you shouldn't have any problems.
A stock Pontiac usually won't hit any valves. If it has a higher lift cam, it might hit a valve. I concur with the advice to clean out the nylon teeth in the pan. The pieces can get into the oil pump bypass valve either causing low oil pressure or high oil pressure on a cold start. I've seen oil filters blow off on a cold start and oil galley plugs blow out if a better oil filter is used.
I worked at a Pontiac dealer in the 70'S. Did many timing chains, never had one that bent a valve, but they all were stock. I did see some that had plastic teeth in the oil pump screen.
A second on dropping the pan and cleaning out the remains of the stock nylon gear as it ends up stuck in the oil pick up. I also have changed many over the years with out finding any bent valves... Id say your probably OK.
I dropped a timing chain on a 69 Pontiac 428 360 horse engine at the top end of second gear and ended up with bent push rods and valves, plus filled the oil pump screen with bits of plastic timing gear.
lost the chain in my 69 Gran Prix, replaced the chain but it never ran right again. pretty sure I bent some valves, but I was like 20 and could very well have put someting back together wrong since I had not yet become the all star mechanic that I am now.
If you don't want to put it all back together a quick check would be a compression test after the new chain is on. Anything major would show up than.
What 55 chieftain said x2. Put a new chain on & ck compression before you button it up. If comp. is ok then drop the pan & cleanout the broken bits & you'll be ok.
The Jalopy Journal
