Car wouldn't start. I found the chain skipped several teeth and was quite loose see pictures. I also found exhaust side guide rail was broken. I know this is an issue, mainly due to a faulty tensioner design. The tensioner has been replaced 3 times in my car already. I've compared my old tensioner with the new one I got from the dealer and they are exactly the same. Same length and same pressure to compress the piston in the bolt. Thus I have concluded my old tensioner is still good. Here's the problem though. If the tensioner is good how the heck could there be so much slack in the chain? I did measure the old chain up to the new one and there is a small difference, so the old chain was stretched a small amount, maybe 1/4 inch longer at most. I don't suspect that small amount of stretch in the chain caused all that slack. What's going on here? Any suggestions or comments are greatly appreciated.

 

When you say you have replaced the tensioner 3 times are you also referring to the timing chain? I had all my timing chain components replace 2 years ago at 47,000miles, the newer tensioner only lasted 13,000 miles. My SA told me that they do a ton of timing chain replacements a week, they just keep coming back again and again.

Tomorrow I'll know if my timing chain is still within specs, if it is then I must replace the tensioner since it's already slacking. If it's not my SA will go ahead and replace all timing chain components under the 2 year unlimited warranty. Since my components were replaced almost two years ago Mini has updated the tensioner and the timing chain with a stronger one.

 

I replaced my tensioner with the one from ECS Tuning. It was the 83mm, longer than the stock one. $26 shipped. Took an hour to install myself. Worked like a charm.

 

Did you lock the crankshaft and install the cam locking tools?

 

Keep in mind the amount of stretch in the old chains is an issue....always replace the entire set including chain and guides. We see this far more common in those that run a synthetic blend instead of a premium full synthetic.

 

Just the tensioner was done. It was done at dealer along with other work. I'm doing it myself this time and I'm replacing the entire assembly with chain, guides, tensioner, and bolts.

 

I always used castrol full synthetic. I planned on replacing the entire assembly. Just trying to figure out how or why chain was so loose considering the tensioner was still good and chain stretched only a very small amount. I guess it's just a horrible design and tensioner isn't providing enough tension. I'm so fed up with this car can't wait to get rid of it when it's running again because it's just a short matter of time before something else goes wrong.

 

After replacing my tensioner I notice I had less hesitation on acceleration with Sport Mode off, more responsiveness. Does anyone know what the chain slack would be on a brand new timing chain? I wouldn't expect every new chain to be the same, just curious how far my chain has stretched if at all.

 

Not sure how much slack a new chain should have. I think it's supposed to be pretty tight, virtually no slack.. I could be wrong, it's a good question. Hopefully someone else can respond.

 

I noticed something different about the newer 5th gen tensioner, the piston moved so much smoother in and out than even a new 4th gen tensioner that I had side by side for comparison. If your tensioners piston isn't pushing inwards smoothly when cold than why expect it to open smoothly when it's hot.(?) Another thing I notice is that the 5th gen tensioner didn't have a super strong spring in it, my thinking is that with all springs there is always a point where spring tension is higher on the bottom off the spring.

This point on the spring could cause a tensioner to push harder on one side causing the piston to get stuck causing the piston to be crooked. This is when things start to go wrong with the tensioner, I think that the newer designed tensioner is relying on oil presure because of the springs always pushing with uneven presure. Nothing else could explain why there's a weaker spring in the newest tensioner.

 

I think you are right that the tensioner relies on oil pressure you can see the inlet hole for oil near the base of the bolt and an even smaller hole at the head of the piston. My problem is my old tensioner, which by the way is the so-called updated or improved version, is the same length and pressure as the new one and yet my exhaust guide broke and chain was way loose and skipped a couple teeth after coming to a screeching halt because of bad tranny. The only thing I can think is that the small amount of stretch in my chain was the cause and that it doesn't take very much stretching to cause such failure.

 

Sounds like you got a 4th gen tensioner, 5th gen longer version is the final version. When was your timing chain components installed? The 5th gen hasn't been out long, timing chain has also been updated since 2013.

 

By "cam bolts" I assume you refer to the sprocket bolts, which would be correct, not the cam cap bolts holding the cam to the head. When using the actual tensioner, you may or may not be applying the correct amount of tension. Depending on chain slack / wear, the tensioner would probably bottom out (or tighten to the block) before the correct tension is applied. Also, this tensioner is hydraulic --- not a solid mechanical connection to the mounting bolt head. The pretensioner tool uses a solid bolt, from chain guide to torque screw head. Correct pretension is set with a torque wrench with the tool. Torque is spec'd in the Bentley manual.

You might get lucky and remove enough slack, but that's not a gamble I'm willing to take --- engine timing is too critical to get it wrong.

The above quote and my response is from a different thread --- https://www.northamericanmotoring.co...n-install.html

Shanksamillion, if it's a Mini tech giving you this advice, you should consider finding a different source for the work you can't / won't do. Using a pretensioner is a little more work, but at least it's done right!

My experience was re-using the same guides, tensioner, and chain that were in use when I tore it down, with maybe 20K miles on them. As for chain stretch / slack, I'm clueless about how much is allowed, or how to measure it. But, think about it --- when the Vanos system is functioning, there is a significant amount of timing change that can't happen without chain slack. The tensioner just keeps the chain tight so it doesn't jump sprocket teeth.

 

Thanks for the info. Yes, I was referring to the sprocket bolts. So the slack in the chain was already there before I disassembled everything. The tensioner that was in the car, with slackened chain, is the latest iteration tensioner. It is exactly the same as the new one I bought from a dealer. I'm guessing the slack in the chain, before I took it apart, was due to a steched chain and not the tensioner. I guess I will just order the pretensioner. I can get it for $30. My cam locking tool didn't come with one. How tight, or how much slack, should be in the brand new chain?

 

Use tool # 11 9 340 to tighten the chain to 0.4 Nm or 3.5 inch-pounds.

You really should get the Bentley manual for all the torque info. It can always be sold to the next owner if you sell the car.

 

Your timing chain is BUST if it's 68mm of slack.

 

Would you share with us how this slack is measured?

 

There's a tensioner tool that ECS Tuning sells, sorry on my GS and can't provide link till I get home.

 

I have the tool listed in Bentley's manual. If this is the same tool, how is it used to accurately measure slack?

 

Insert the housing and turn the shaft against the chain, then measure the shaft that's sticking out of the housing.

 

So, since the housing must first butt up against the chain guide, the guide has to be monitored for movement when installing the housing --- to ensure minimal contact. Then the shaft is tightened (from being flush with the housing) 'til the proper torque is achieved. Then the housing is removed and exposed shaft is measured.

This is how I interpret your description. Since 68mm is just shy of 3 inches, it can't be a legitimate limit for slack, unless the guide has been removed and / or a different tool is used.

Please go into a lot more detail with the measurement process, including accept / reject limits.

 

See page 3, it should make perfect sense.

 

I don't think that is correct. The VANOS system effectively lives in between the cam sprocket and the camshaft itself. It varies the position of the camshaft relative to the position of the sprocket, so no slack in the timing chain is needed.

 

Yes, it does. Thanx for posting this. My tensioner tool didn't come with any instructions. When I re-assembled my engine, the chain was quiet when torn down so I didn't think to check it for slack.

You're probably correct --- I've never really thought about the system, just accepted that it's a great feature.

 

I took my chances without the pretensioner, .6nm is the torque on the pretenioner which is less than 1/2 foot pound, .44 ft/lbs actually. Is it possible to have the chain too tight? I haven't turned the crank yet, so I'm not sure what the result is but it does look pretty darn tight. Also, if I do see any slack, what is the max the chain can slack between the cam sprockets?