Please advise…Timing belt tensioner go bang. (15 Viewers)

[nissanh]

I think whoever tighten those two bolts at the tensioner torqued too hard and was in severe strain and eventually both snapped. I don't think the belt can put that much pressure on the adjuster bearing arm to push the tensioner out of it place by snapping the two bolts. Your tensioner is still in one piece. Only broken parts are the two bolts. Do you see any markings on the tensioner?

 

[JungleMunkee]

I think whoever tighten those two bolts at the tensioner torqued too hard and was in severe strain and eventually both snapped. I don't think the belt can put that much pressure on the adjuster bearing arm to push the tensioner out of it place by snapping the two bolts. Your tensioner is still in one piece. Only broken parts are the two bolts. Do you see any markings on the tensioner?

 

[Moparsncruisers]

It snapped the bolts, something forced it out from where it was.

Which is why my guess is they weren't tight when installed. If those bolts were torqued down i highly doubt they both would just shear like that. Even if the tensioner pulley failed. Thats the "loose" side of the belt.

 

[JungleMunkee]

Well right/passenger (even cylinders) bank is out of time. Coincides with the codes I got. Belt is perfect. I bought a bore scope and leak down tester to check cylinder health after this but everything looks fine. That was my first big job so maybe I did forget to tighten or over tightened. Lasted 68k miles at whatever rate.

 

[Nardulli]

Is it in time? Put it Tdc and see if the marks line up.
What’s all that buildup on the old tensioner?
The amount of force it took to jettison that tensioner is your biggest problem.
As you take it apart the culprit will become obvious.
Borescope the cylinders to look for evidence of piston / valve contact.
Don’t try running the engine before you discern the root cause.

 

[JungleMunkee]

Is it in time? Put it Tdc and see if the marks line up.
What’s all that buildup on the old tensioner?
The amount of force it took to jettison that tensioner is your biggest problem.
As you take it apart the culprit will become obvious.
Borescope the cylinders to look for evidence of piston / valve contact.
Don’t try running the engine before you discern the root cause.

No the passenger cam is off time significantly. I have it at 50 degrees atdc and the drivers side is perfectly on in the pic I attached. Might be hard to see. Borescope is happening tomorrow. It was dirty all around the lower area. I’m not sure what it is yet.

 

[vipergrhd]

Were you able to extract the broken bolts? Are they cross threaded? The bolts must have had stress cracks to just snap clean, it doesn't look twisted due to over tightening. Could you compress the tensioner easily? Who did your last T/B job?

 

[JungleMunkee]

Were you able to extract the broken bolts? Are they cross threaded? The bolts must have had stress cracks to just snap clean, it doesn't look twisted due to over tightening. Could you compress the tensioner easily? Who did your last T/B job?

Yes they spun right out with lock grips after soaking them in penetrating oil. Couldn’t compress it on the floor. I did the last timing belt change 68k miles ago.

 

[JungleMunkee]

I scoped the right side cylinders and there was no contact made. It’s chunky in there though. They were all similar except no.6 spark plug was loose so I’m sure that’s part of it. It didn’t rip out threads though, luckily.

 

[JungleMunkee]

I have more but this is the general state of my 2001 with 287,500 miles. Indeed, does indicate it’s not an interference engine.

 

[JungleMunkee]

Is this too much oil and build up inside? It looks like a lot. Worn rings? Do I need a head gasket considering this and all the rest of the gunk on the engine lower?

 

[Trunk Monkey]

Have you done a compression and/or leak down test?

 

[JungleMunkee]

Have you done a compression and/or leak down test?

No sir I’m working in that after lunch. The timing belt is off but it’s already out of time, so I guess it’s no big deal to move the crank. The left cam is in time right now though.

 

[JungleMunkee]

Here is cylinder 3 on left for comparison. Valve seals bad?

 

[nissanh]

Don't do a head gasket. Valve seals can leak with the age and there are ways to install valve stem seals without removing the head from the engine. It will burn oil at the first startup and that's it. this is another good thread to prove non-VVTi are non interference.

Add Gumout to your fuel tank to clean up the injectors and potentially the buildup inside the cylinders. It is about $3.60 at Walmart and the best cleaner I have seen in the market for less than $4.

That continental belt looks fine for 68K miles!

 

[ndg]

Were you able to extract the broken bolts? Are they cross threaded? The bolts must have had stress cracks to just snap clean, it doesn't look twisted due to over tightening. Could you compress the tensioner easily? Who did your last T/B job?

Regarding bolt failure modes, there are a few!

• The obvious one is that something put too much force on a bolt in tension and in failed, that is a massive amount of force.
• Next (and not relevant to this failure as the tensioner body would react any shear in the bore) is that it saw too much force in shear, but the clamp forces in a joint are normally designed to take the load, the bolt just holds them together, so if it sheared it was under torqued.
• The bolt could be over torqued leading to partial yield of the thread, typically at the root which could then fail later.
• There is also under torque which leaves the bolt vulnerable to fatigue failure, particularly at stress concentrations like the thread root.
• This part has an unusual design with both fixings on one side, so if the bolts became loose the tensioner body could lever the bolt heads with every speed change in the belt (crank torsional vibration caused by each cylinder firing). This would put significantly more stress on the bolt than if they were either side of the tensioner.

I'd guess that it's the last one in this case. But without someone who really understands failure analysis looking at the actual parts it's just a guess.

Inside the cylinders you have a bit of carbon build up, but I wouldn't pull the heads for it. The cross hatching on the bores looks really nice - hopefully mine are in the same condition! The amount of oil (?) floating about seems strange, but I'd be suprised if it was coming from a head gasket unless you had major smoke issue before failure. As nissanh said, it could be valve stem seals. It could be excess fuel from failed starts, but looks a bit viscous for that.

The belt may look fine, but if it's skipped teeth it will have been damaged.

In your position I'd install a new belt, tensioner and any other bits that have taken a beating on the timing system - with a flapping belt, that could be everything. Then crank four full turns of the crank by hand with the plugs out to make sure everything feels smooth before spinning it on the starter (again plugs out, be aware that some of that oil may be blown out in the process). If all sounds good, rebuild and fire it up. Is the exhaust smoke short lived or persistent?

If you want to minimise cost risk you could do just the tensioner to start. If all is well when you run the engine, you then go back in and replace the belt, pulleys, waterpump etc. More labour, but lower spend risk.

 

[3_puppies]

IIRC you stated the tensioner will not move/compress?

 

[JungleMunkee]

Regarding bolt failure modes, there are a few!

• The obvious one is that something put too much force on a bolt in tension and in failed, that is a massive amount of force.
• Next (and not relevant to this failure as the tensioner body would react any shear in the bore) is that it saw too much force in shear, but the clamp forces in a joint are normally designed to take the load, the bolt just holds them together, so if it sheared it was under torqued.
• The bolt could be over torqued leading to partial yield of the thread, typically at the root which could then fail later.
• There is also under torque which leaves the bolt vulnerable to fatigue failure, particularly at stress concentrations like the thread root.
• This part has an unusual design with both fixings on one side, so if the bolts became loose the tensioner body could lever the bolt heads with every speed change in the belt (crank torsional vibration caused by each cylinder firing). This would put significantly more stress on the bolt than if they were either side of the tensioner.

I'd guess that it's the last one in this case. But without someone who really understands failure analysis looking at the actual parts it's just a guess.

Inside the cylinders you have a bit of carbon build up, but I wouldn't pull the heads for it. The cross hatching on the bores looks really nice - hopefully mine are in the same condition! The amount of oil (?) floating about seems strange, but I'd be suprised if it was coming from a head gasket unless you had major smoke issue before failure. As nissanh said, it could be valve stem seals. It could be excess fuel from failed starts, but looks a bit viscous for that.

The belt may look fine, but if it's skipped teeth it will have been damaged.

In your position I'd install a new belt, tensioner and any other bits that have taken a beating on the timing system - with a flapping belt, that could be everything. Then crank four full turns of the crank by hand with the plugs out to make sure everything feels smooth before spinning it on the starter (again plugs out, be aware that some of that oil may be blown out in the process). If all sounds good, rebuild and fire it up. Is the exhaust smoke short lived or persistent?

If you want to minimise cost risk you could do just the tensioner to start. If all is well when you run the engine, you then go back in and replace the belt, pulleys, waterpump etc. More labour, but lower spend risk.

It does seem like I might have been a too gingerly in the bills so they fatigued over time like in your last example. I’ll be sure to torque to speed this time. I bought a new aisin timing belt kit including water pump. Finishing up the last 3 cylinders leak down test today. So far high 80s to high 90s for the 5 I’ve done so I think the rings are fine. Might replace valve seals but unsure. Then I’ll focus on the feel of the engine while hand turning. I didn’t notice any exhaust smoke before. Thank you.

 

[JungleMunkee]

IIRC you stated the tensioner will not move/compress?

Yeah I pressed firmly on the concrete and it didn’t budge. I’ll see how much force it takes today. I think the kit said 100 lbs or so but I don’t have it in front of me, right now.

 

[JungleMunkee]

When I went to do the scope on cylinder 6 the spark plug was completely loose!