TB breaks/then...?

[Bear]

I hate mentioning it its like tempting fate. But, it does happen. I am wondering what the first response to it might be. First, it would seem that the first step would be to rotate the crank and cam by hand in sync and then check compression (or leakdown) to see if the head and valves are OK. If they are, then the motor would be good to go? That way, you could avoid taking the head off. Or is this too much wishful thinking and should you just count on, at least, a few bent valves. Moving on, if the valves are bent, then can the head be re-used if the valve seats are visually OK?

 

[mailman]

The extent of damage will vary case by case, but suffice it to say the damage will be major. If the engine is running when the TB breaks (how else could it break /images/graemlins/confused.gif) the recriprocating pistons will slam repeatedly against the open valves and bend/break the valves and damage/break the aluminum pistons (and/or aluminum head), and potentially score the piston bores. This will, of course, be more severe should the TB break at high engine speeds. As for the valve guides and seats, sure they could be damaged in the process as well. I'm not sure the damage could progress any further to such areas as the connecting rods/crank or the camshaft, but anything's possible I suppose.

Bottom line ... don't be a dummy ... just change the TB as recommended in order to minize the risk of this potential damage all together. Of course, other things that lead to TB failure are waterpump leakage and cam seal leakage ... so inspecting these areas should be made a routine part of maintenance.

Of course, botching a TB job is just as bad. You should do a search on the site ... there is a plethora of info out there. Happy reading ... /images/graemlins/grin.gif

 

[Bear]

Ouch! So it looks like the head comes off.

I asked the question thinking that the one thing that is in our favor is that the injection pump shuts down thus the force of combustion is not there, but of course there is still inertia, engine and car. So, maybe on an automatic car the damage would be minimal. Not so on a clutch car, unless you had a really fast foot.

I am not too concerned with TB changes - thx. for the reminder though. I am bit worried about the tensioner going up though as has been reported. How do you prevent that? I don't know.

OK back to the topic. TB goes, then you take the head off, right? If the pistons and cyl. walls look OK do you stop there or keep taking it apart to look at the bottom end?

If valves are bent, which seems like a certainty, then if the seats are OK then what? I.e., is there a technique like magnafluxing for aluminum?

It would be nice if there was a "crush" piece (think collapsible steering column)designed in the valve train to take up the force. Or a spring arrangement. Blowing a motor seems like unfair punishment for not doing the maintenance or being unlucky one day.

 

[Growler]

[ QUOTE ]
Blowing a motor seems like unfair punishment for not doing the maintenance or being unlucky one day.

[/ QUOTE ]

that is why it is called Maintenance...it maintains...

Being unlucky does suck tho. it happened to my bug about 10000 miles ago (roughly 32kon the ticker the belt snapped, before I owned him. now I have a 42kmile body with a 10k mile engine under the hood. and another 12k miles (or until 2/05)of CPO warranty to make sure all is still good.

 

[Drivbiwire]

When a belt breaks the pistons almost always survive proivided that a valve did not break off and drop into the cylinder if thats the case read on otherwise start sourcing a long block or complete engine...

Busted belt parts needed:

4 intake valves
4 exhaust valves
8 guides
8 lifters
8 sets of spring retainer clips
8 valve oil seals
1 head gasket of appropriate thickness (There are 3 thicknesses available)
1 complete timing belt kit
1 water pump kit
1 gallon of coolant
1 gallon of oil
1 set of head bolts

That pretty much describes everything you need. Usually a small brake hone is all thats required to smooth out the lifter bores. You dont want to take away too much metal, just enough to rid the bore of any gouge marks from the shattered lifter bodies. Obviously you need to make sure you got all the metal out so a good cleaning with stoddard solvent is a good idea.

DB

 

[jjvincent]

[ QUOTE ]
I am wondering what the first response to it might be.

[/ QUOTE ]
My wallet just got lighter!

 

[saabguru]

Consider, in a manual trans car, the car is pushing the engine long after the cam stops. Perhaps, at idle, the engine could survive.

10K miles belt inspections are specified in the manual. Among other defects, if there is any oil on the belt, any fraying, if there is more than 2mm space between the belt and the edge of the tensioner roller- the book says:"Replace the belt before driving the car further" The belt must be replaced at 60K mile intervals regardless on manual transmission cars, and at 40K on automatics.

My belt at 61K had worn teeth, but it's so easy on an A3, there's no reason to wait.

My first time, I did the belt, tensioner, and water pump in a long afternoon. The dealer bills four hours for it. He wanted a $500 dollar bill. I made GOOD money that afternoon.

 

[Bear]

jjv, LOL!

Thanks for the comments guys!
So, generally speaking, its not THAT bad. Note too that the ALH block is cast iron, a good thing, beefy. Even a cracked piston could be replaced as mentioned around here somewhere.

DB, do you recommend taking the head to a shop for putting the new guides in and lapping the valves?