Comment on this please: Big Problem with Chain Tensioner Installation

[Wayne 962]

A customer recently sent me this email:

I purchase all of my parts through your company and do most of the work on my 1982 SC targa myself. I bought the car with 110k miles and have put roughly 10k on it in the 2 years I have had it. I am an engineering student at Michigan State University and my Porsche is my only form of transportation, so I am meticulous with my maintenance on it. Well, after my car's 30k mile tune-up, my mechanic suggested I change my tensioners. I read up on the job on your website and bought your "101 Projects for Your Porsche" book. It is an very good book. I studied up on this procedure of replacing the chain tensioners and made sure I had everything I needed. I bought your kit and some chain ramps and went to work. I did everything that your book said to do. I tied the chain together near the cam sprocket to make sure it didn't move whatsoever. I then replaced 4 of the chain ramps. I couldn't get to two of them, but since I had to get to work the next day and the other 4 old ones weren't bad at all, I left two of the old ones in. Afterwards, I retimed my car, again, following your book, just to be on the safe side. When I started it to set the timing, however, I noticed a funny faint knocking. I didn't know what it was, but thought it could be the new tensioners. I didn't drive it to work the next day, fearing something was off. I had it flat-bedded to my mechanic (Euro Autowerks in Belding, MI: about an hour away from my house), who did a compression test. My whole right bank of cylinders had compression at or around 70, with number 2 being 65, compared to 140, 140 150 on the left bank. He explained that when I changed the tensioners and the ramps, there was another sprocket inside the engine, which the chain must have skipped off of. He said that simply keeping tension near the cam sprocket and making sure it didn't fall off wasn't enough. The funny noise was my valves crashing into my pistons. It could have been worse, if I had decided to drive it. So, I now have to find a way to come up with $3500 bucks for a valve job. Afterward, I will be forced to sell my car. I just can't afford to have another repair bill that high, and it kinda takes the fun out of driving it. Please make it clear to your current (and prospective customers) that they need to take precautionary steps above and beyond what your book and technical articles have laid out. I will, unfortunately, not be buying any more parts from you, as I will no longer have any use for them, not being a Porsche owner anymore. I think this is very important and should be brought to anyone's attention who may be doing this without the intention of turning their $500 bill and 5 hours of work into a $3500 (or more) bill and 2 weeks worth of work. Thanks.

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Obviously, I feel extremely bad for the guy. I went back over my text for both 101 and the tech article. What I don't understand is if he re-checked the camshaft timing, then he should have had no problems whatsoever. This doesn't make any sense.

The faint knocking is not symptomatic of a failed chain tensioner - ghosts walking through the hallways dragging chains is that sound.

Also if he had bent valves, wouldn't the compression check reveal much less compression? I told him to do a leak down test, thinking that if the valves weren't closing, then he would have near 100% leakage.

Is the mechanic taking him for a ride? I'm not completely sure. I know that mechanics often secretly laugh at the owners who do their own work, and some wouldn't hesitate to take advantage of them to clean up 'messes.'

Please comment on this, I would hate for this fellow to have to sell his car...

-Wayne

[layzee]

As you say Wayne, his story is most disheartening, but it doesn't really all add up. I agree with you about the compression - mysterious. Has he seen any of this valve damage

[Wayne 962]

What do you mean by seen?

-Wayne

[john_colasante]

What I find odd is that the guy says he "started it" to set the timing. This is a lapse in procedure if there ever was one. Further it is highly unlikey that the chain skips a tooth especially on the big sproket. Something doesn't seem right. I wouldn't be surprised if your hunch is correct there Wayne.

[Phoenix-MN]

"When I started it to set the timing, however, I noticed a funny faint knocking. "

I think here is talking about ignition timing here. Can't have the engine running and adjust the cam timing Been there myself many years ago, thought everything was tied down secure but the chain still jumped and when I turned the engine over by hand I had major (stop dead in it's tracks) interfeance.

[Joeaksa]

Wayne,

Something is screwy here. I agree with you that if the valves have hit the pistons they probably will be bent but bending them is normally not going to cause them to lose part of the compression, it will lose all compression in that cylinder.

I guess that it could mean that all three valves have very slightly touched the pistons and are just slightly out of alignment and could be still seating slightly against the valve seat thus allowing for partial compression, but there is a lot of theory here and have never seen this happen in the real world.

If he timed the valve timing on the motor correctly after doing the swap and then checked the timing, then the valves should have been in correct reference to the pistons and no conflict should have happened.

I wonder if he did time the cams wrong and ended up with one bank off so far that the intake valves are not opening up at the right time and thus not allowing the air to enter to allow for a correct reading on the compression test. If he is getting 60 or 70 pounds compression then I just do not feel that the valves have kissed the pistons.

JA

[Targa77]

I would have him get a second opinion just in case his mechanic is taking him for a ride. I know that won't be easy or cheap. Do any of you guys know and trust anyone in that area?

[dhaines]

I agree with Phoenix, I think he was refering to ignition timing, not cam timing. Still seems odd to have skipped a cog on the gear if in fact the chain was kept tight. too bad it spoiled his Porsche experience

[T Bird]

Hmmm.. this sounds familiar. Check this post.
Costly engine timing mistake.....

[TigerTrash]

There are somethings you just leave to a professional. I will do most maintenance items on my car. But major items (tranny rebuild, tensioners) are just best left to a pro. I have had both items done in the last year. Did I spend another 1200 or so bucks on the extra labor? Hell yes, but I now have a warranty from my mechanic, a car that purrs, and no additional worries. If I do have a problem I call my wrench, he sends out a flatbed and calls me when the car is finished. No charge. Now I am fortunate in the fact that this is a second car for me. It is not a daily driver. If in fact someone is looking for a reliable mode of daily transportation perhaps a better choice would be a Honda or something.

[GIBSON]

Please correct me if I'm wrong here, but isn't it standard procedure to spin the motor by hand several rotations before even putting the chain box covers back on? I can't imagine a scenario where one could not detect even the slightest valve to piston interferance if the engine was rotated carefully by hand after the tensioners were installed. I have many times installed these tensionsers, rotated the engine and found to my dismay that I had to go back and reset cam timing. No problem, takes a few minutes to re-set, then spin the motor again to varify that it spins freely and no problems.... Maybe I'm missing something here but I can see no reason for piston/valve damage as a result of a tensioner upgrade if you follow that simple procedure.
Just my opinion.

[john walker's workshop]

if the engine is set to #1 cylinder TDC, the tensioners can be removed without any tying up of the chains. the cams just sit there, unless you try to turn them, then they pop over one way or the other, which of course messes up their original timing position, requiring the cams to be repositioned back to their approximate correct position, and then retimed with the dial gauge. during the course of swapping the ramps, you also have to be careful not to move the cams. the ramps also can be swapped without creating some slack in the chains. if the chains are moved to create slack, you effectively have moved the cams, which can result in the aforementioned problem. an inexperienced person may not even notice that this has happened. if the cam timing was checked prior to running the engine, the problem would have been obvious, and corrective measures could have been taken to prevent the disaster. inexperience played a role here. 70# compression could be possible with slightly bent valves. the leakdown would probably be real high, like 90%.

[BK911]

While this isn't a difficult procedure, one small error can result in disastrous results. I agree with GIBSON 100%. ALWAYS check/adjust cam timing before buttoning everything up. Even if you are positive nothing shifted, it may have been out before. For a little more time and one additional tool you may gain some HP back.

You state something like, "If the chain skips a tooth you will need to adjust cam timing." Maybe if you put out another Edition of your Projects book you can recommend checking/adjusting cam timing regardless if you think the chain moved. Unfortunately one person learned the hard way.

[Doug Zielke]

I think the cam timing slipped, marginally, but enough to have the valves hit the pistons. If this guy can find a trust-worthy person with a boroscope, he can look for himself.

[Vipergrün]

Been there done that While replacing my ramps I took slack in the chain from one side of the case to the other. The cams did not move, but I evidently skipped a tooth on the intermediate shaft sprocket. My symptom was a LOUD knocking noise, followed by not being able to turn the motor over by hand. The #6 sparkplug also had a nice gash in it from the valve...

Would it be worth while for this guy to have the cam timing done to see if that fixes things? If the timing were off just a bit, wouldn't that not let the valves seat all the way without actually hitting a piston?

The unfortunate thing is that the bill could go higher, they probably won't know til they start taking it apart.

cheers
-Brad
80SC

[john_colasante]

If the cam timing was fine before you change the tensioners, then the timing need not be checked. This is because the fine cam timing is governed by the "tension" side of the chain. Even if you were to skip a whole tooth as long as you got it back on the right tooth you would not need to retime the cams. The only thing that might change the cam timing is if you install a new chain because it will not be identical to the old chain's dimensions because of wear or tolerances. So all you really need is a gross check that a tooth hasn't slipped. I don't think this would require the use of a dial gauge as this is a visual inspection of the cogs.

[Kurt B]

When I changed my tensioners, I tied the chain to the sprockets in two places each, and I got a black pen and marked a line on the chain and the sprocket in a couple of places on each side, so there was no way it could skip a tooth without breaking the line...and it was fine.
Was there a risk with what I did? Was I just lucky I got it back on right? Because it seemed to me that there was no way either sprocket could spin without moving the other and staying lined up with the chain as it was with the old tensioners in there.

[Wayne 962]

John, you're glossing over the topic. Simply putting the chain back on *might* work, but it's certainly not a good way of going about this.

The fellow here checked his igntion timing, not his camshaft timing, as he told me this morning.

I would think that if the camshaft timing is one tooth off, that might be enough to show low-compression on the compression test? Hmm, wait a sec, no it wouldn't. The valves are still opening and closing all the way - they are just doing it some amount of degrees off...

-Wayne

[Early_S_Man]

Wayne,

Mistakes do get made sometimes and the details get left out of the 'irate' aftermath account! As JW says ... if the crank and cams aren't moved, I don't see how one side could get out of time. And, yes, it seems that turning over the engine afterwards by hand and checking for noises or resistance would have caught the problem early, when correction was still possible without damage!

But, the bottom line here is that YES, the mechanic is taking advantage of fear, inexperience, and an assumption that big pockets from the parents will come up with a windfall $3500 that he wouln't have gotten otherwise! This story reminds me of the 'quick and dirty' $2400 repair by a very shady and opportunistic mechanic on one cylinder after a missed shift and mechanical overrev. Sadly, some mechanics can take advantage of the unwary!

[Wayne 962]

Okay, the first time I heard this, I thought that it was a fluke. This is the second time that I have heard this, so I have added the following additional warning to our website and the 101 website as well. The procedures are correct on all accounts, I just want to emphasize the part about keeping the chain as tight as possible...

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WARNING: Carrera Chain Tensioner Upgrade - This is a relatively straight-forward upgrade. However, there have been reports of some people who seem to have made mistakes during this upgrade. As a result, the camshaft timing became lost, and when the engine was started, the valves hit the pistons and became bent. The result was a $4000 top-end rebuild.
Don't let this stop you from performing this upgrade though - it is very useful, and very worthwhile for ensuring the longevity of your engine. The key to remember here is to make sure that you do not let tension off of the chain at any time. Keep the tension on the chain by making sure that the idler sprockets are tight against the chain. If you are replacing your idler sprockets, then keep tension on the chain by tying it tight. DO NOT LET THE CHAIN GO SLACK AT ANY TIME. Following this simple rule should make this upgrade uneventful.
If the chain does happen to slacken up, then you need to check your camshaft timing (documented in 101 Projects). A good check too before you close up your chain tensioner housings is to make sure that when your engine is at TDC (Top Dead Center), the dot or '930' mark on the two camshafts are facing upwards. Spin the engine clockwise with the chain covers off just to make sure that there are no problems with the chain. This is a good last-minute check to make sure that everything is okay.

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-Wayne