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Broken Timing Belt Tensioner

Posted by sdp 
sdp
January 25, 2012 11:18PM
I heard a screech from my sons car and I pretty much decided the water pump was going. I told him to avoid driving it since the pump could go at any time.

I ordered the pump and he was going to make a short drive somewhere. He came back in the house and said the car died not more than 20 feet from where he was parked. He didn't tell me until later that the car just suddenly stopped/stalled.

I thought it odd that the water pump would seize enough to stall the car without throwing a belt. When we disassembled the front end I was shocked to see that the belt was wearing through the housing and the tensioner was at an angle. Enough of a slip that the piston and valve hit.

I just received the replacement tensioner tonight, but I do not want to remove the head to investigate. I was planning on realigning the timing and putting the belt back on in order to do a compression test. Of course I will confirm that I can fully rotate the engine before any cranking is done.

My question is:

  1. What do I need to disconnect electrically so that I can crank the engine without damaging anything upstream from the distributor?
  2. I would imagine a bent valve would show zero compression.
  3. What compressions should I see given that it is a 200k+ mile engine?

Peter
January 26, 2012 09:27AM
Quote
sdp
I heard a screech from my sons car and I pretty much decided the water pump was going. I told him to avoid driving it since the pump could go at any time.

I ordered the pump and he was going to make a short drive somewhere. He came back in the house and said the car died not more than 20 feet from where he was parked. He didn't tell me until later that the car just suddenly stopped/stalled.

I thought it odd that the water pump would seize enough to stall the car without throwing a belt. When we disassembled the front end I was shocked to see that the belt was wearing through the housing and the tensioner was at an angle. Enough of a slip that the piston and valve hit.

I just received the replacement tensioner tonight, but I do not want to remove the head to investigate. I was planning on realigning the timing and putting the belt back on in order to do a compression test. Of course I will confirm that I can fully rotate the engine before any cranking is done.

My question is:

  1. What do I need to disconnect electrically so that I can crank the engine without damaging anything upstream from the distributor?
  2. I would imagine a bent valve would show zero compression.
  3. What compressions should I see given that it is a 200k+ mile engine?

Peter

Sorry to hear that sad smiley

1. You don't need to disconnect anything. You can use the diagnostic connector and a push botton switch to make the engine turn over. I made this tool for the purpose...

Depending on the year of your E30, there will be a different pair of pins to jumper. I no longer have my Bentley so someone else will have to give you the diagnostic pin numbers to use.

2. A bent valve will definitely show zero or very low compression.

3. It doesn't matter how old the engine is, it will need to have at least 120psi in all cylinders to operate properly. When new, I believe it was 145psi.

Sadly, there is little to no chance that you won't have a bent valve...even at idle 700rpm); the engine will have hit one or more valves. The head wil have to come off for a rebuild at the very least.
sdp
January 26, 2012 11:34AM
Bummer... We just put in this rebuilt head a little over 1 year ago. In hindsight, we should have replaced that tensioner.

Having the bearing go out is one thing but I didn't realize that the pulley is a pressed in fitting and not a weld or bolted down. Seems like a weak point for something so critical.
January 26, 2012 07:56PM
Turning the crank with the starter is not a good idea until the cam and crank are in correct timing with a new belt. Very unlikely that you can find a position for the cam that would not put at least one valve in conflict with a piston. At or near top dead center, the pistons will have tremendous leverage to bend a valve stem even if you are turning the crank by hand.

After you put the new belt and tensioner in place, remove the spark plugs and use the compression tester. Pull the fuel pump relay before cranking it over.

I would expect over 160 psi, might go to 180.

My guess is that the head will need rework. Might check the rocker arm clearances and see one or more with a whole lot more than 0.12 clearance to verify bent valves that will not close.

Bob in Everett
sdp
January 26, 2012 10:55PM
Yeah... I knew I had to get the timing right before any cranking was done. The belt was not completely loose since the housing kept the tensioner pulley relatively in place. Provided the belt did not skip I would think that the crank/piston advanced without advancing the cam at the point the engine seized. That would mean that I should be able to reverse the crank a bit before putting the new belt and tensioner in place. Then I can slowly rotate the crank and verify the timing mark. I hope. Last time I messed up putting on the belt and the timing was off by 1 maybe 2 teeth and I had a clapping sound when the car started. I just really don't want to remove the head AGAIN. Probably all a mute point but it's worth a try.



Edited 1 time(s). Last edit at 01/26/2012 10:56PM by sdp.
sdp
January 28, 2012 04:54PM
Well.. turning the crank with the new tensioner and belt didn't help.. It was pretty much stuck in both directions so I started with removing the valve cover.

Major disappointment. 5 broken rockers and that wouldn't have been the worst thing... 1 broken bracket between 5-6 and cracked bracket at the end of the rocker shaft.
Pulled the head and all 6 exhaust valves created indentations on the piston. Naturally all 6 valves are bent to some extent.
I'm really surprised that the pistons on the intake side have a milled indentation but not on the exhaust side. I don't see that the intake side valve hit, but of course the brackets are broken on the intake side so they must have hit. Maybe one can't tell because of the piston indentations. Come to think of it, because of the indentations, the valve hits flatter on the piston and probably because of that, the valve can't bend as easily and the force is transferred up to the rocker and rocker shaft.. that's why the bracket broke.

Based on the impact marks on the piston, I'll bet as the timing started to slip, there must have been some sign of clacking from the engine. Some difference at least in sound and performance! I noticed a lot of deposits on the spark plugs and inside on the piston head. My son claims he didn't notice.
I'm so disappointed because this head was really nice and I spent an extra 200-300 to have the bottom resurfaced and all the valve stem bushings/gaskets(?) replaced at the end of 2010.

IDK... We're really hurting financially right now due to some unexpected issues. I'm thinking maybe have the bracket welded down and the valves replaced. I know welds are pretty weak and may not hold for an extended period. Maybe if it's not expensive... give it some more life and then scrap the car. Oh well.

To anyone new to working on these cars... They always recommend replacing the belt.. Replace that belt tensioner too!!! it's not expensive and if your car has high miles... as you can see... does major damage if it goes.



Edited 2 time(s). Last edit at 01/28/2012 04:58PM by sdp.
January 28, 2012 06:45PM
Complete replacement engines from parted out wrecks are not very expensive. I have seen offers for sale of running engines for about $200.

You can convert to an engine from an E36 for a little more. Those engines need the oil pan from an E-34. If the car is in good shape, it is worth keeping as they do not make them any more. There are about 60 of them converted to racing in the Pro3 circuit in Washington and Oregon. The E-30 makes a very good track car.

Bob in Everett



Edited 1 time(s). Last edit at 01/28/2012 06:48PM by Bob in Everett.
January 28, 2012 06:45PM
Quote
sdp
Well.. turning the crank with the new tensioner and belt didn't help.. It was pretty much stuck in both directions so I started with removing the valve cover.

Major disappointment. 5 broken rockers and that wouldn't have been the worst thing... 1 broken bracket between 5-6 and cracked bracket at the end of the rocker shaft.
Pulled the head and all 6 exhaust valves created indentations on the piston. Naturally all 6 valves are bent to some extent.
I'm really surprised that the pistons on the intake side have a milled indentation but not on the exhaust side. I don't see that the intake side valve hit, but of course the brackets are broken on the intake side so they must have hit. Maybe one can't tell because of the piston indentations. Come to think of it, because of the indentations, the valve hits flatter on the piston and probably because of that, the valve can't bend as easily and the force is transferred up to the rocker and rocker shaft.. that's why the bracket broke.

Based on the impact marks on the piston, I'll bet as the timing started to slip, there must have been some sign of clacking from the engine. Some difference at least in sound and performance! I noticed a lot of deposits on the spark plugs and inside on the piston head. My son claims he didn't notice.
I'm so disappointed because this head was really nice and I spent an extra 200-300 to have the bottom resurfaced and all the valve stem bushings/gaskets(?) replaced at the end of 2010.

IDK... We're really hurting financially right now due to some unexpected issues. I'm thinking maybe have the bracket welded down and the valves replaced. I know welds are pretty weak and may not hold for an extended period. Maybe if it's not expensive... give it some more life and then scrap the car. Oh well.

To anyone new to working on these cars... They always recommend replacing the belt.. Replace that belt tensioner too!!! it's not expensive and if your car has high miles... as you can see... does major damage if it goes.

Good writeup on why the tensioner should be always replaced together with the new belt.
Please keep us posted on the next thing you go from here.
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