Comment on this please: Big Problem with Chain Tensioner Installation
 

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

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 :confused:

What do you mean by seen?

-Wayne

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.

"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.

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

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?

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

Hmmm.. this sounds familiar. Check this post.
http://forums.pelicanparts.com/showthread.php?s=&threadid=70518&highlight=bb80sc+ and+chain

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.

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.

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%.

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.

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.

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

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.

Was I just lucky?
 

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.

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

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!

<b>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!</b>

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

That should read: "Spin the engine clockwise by hand......"

the fact is you CAN let a portion of the chain go slack. that would be the section that the idler sprocket normally holds tight. as long as the engine and the cams remain in the #1 TDC position, nothing will change when the tensioner is removed and the idler assembly is removed. i've done 100s of them that way with no problems. the beginner could tie the chains up with a zip tie to lessen the chance of a mistake, but shops generally don't do that.

enlightenment please
 

I just ordered my tensioner upgrade parts from Wayne and will be doing the job in a few weeks.

One thing puzzles me. I have rebuilt a couple dozen engines of all kinds except 911 (timing chains, timing belts, timing gears, OHV, SOHC, DOHC, etc) and I don't understand why you would need a dial gauge to set cam timing. All those other engines had timing marks on the crank and cams. Set the marks and make sure the slack in the belt/chain is where it should be and you're home. Is there some fine adjustment that allows you to dial the cams in more accurately than that? What am I missing? Not that I would dismiss the opportunity to acquire another tool of course.

Re: enlightenment please
 

On a "normal" car like a 944, the cam and crank gear have marks that you line up when you set the cam timing.

On a 911 there is a TDC mark on the crank pulley but nothing for the cams sprocket. The cam sprocket is adjustable and the cam is timed such that a valve (#1 or #4 intake) is open a specified amount when the crank is at TDC. You use the dial indicator to read the valve lift.

-Chris

Wayne, in my opinion, you shouldn't recommend that people take this on without a dial gauge. Cam timing should always be checked before putting the covers back on. Furthermore, I think you should really emphasise turning the engine over by hand after the tensioners are installed. This should be a mandatory part of the procedure, not just check if you want at the end.

-Doug Clauder

just turning the engine over by hand to feel for interference isnt a "check" for properly timed cams. What could you do at best turning the engine over by hand? 4 RPM, then of course there are the thermal issues and acceleration of all these parts trying to work in unison. cam timing should be checked, then re-checked, with vise grips, clamps, blocks or whatever to take all slack out of the chain. When you can repeat the reading a few times in a row your ok.

Unfortunately this is a DIY'er like alot of us, and he had something go awry. And Wayne was his beacon to this upgrade

Hell I did a tensioner upgrade on my 2.0T, That upgrade morphed into a 9.8:1 full "S/906" improvement to my engine!!!. I followed the factory procedure to the letter.

When I started the engine after the tensioner upgrade, it sounded like a million bucks. I let the engine idle at about 1800 rpm for about 20 mins while I cleaned my tools and neatened up my garage.

So I take my car out for its first ride (post upgrade) and at 5800RPM I broke all the rockers on the passenger side of the motor!!!!!

I have no Idea why this happened ( well I do now because the cams in my engine were not stock)

I drove home on 3 cylinders, then started the $mucho dinero 2001 2.2S Porsche engine

One thing I think Wayne should stress is that the engine you are working on may not have the cams you think!!!!!!!!!! You have to know what kind of cam is in your engine before you time them!!


I knowBTDT

I guess I got lucky. This was the first project I performed on my SC, and it seemed very easy and straight foward.

Now adjusting the valves the first time was a whole different story!:eek: I bet I'm the only person to get them too tight, and not too loose the first time.:mad:

All,
Ah, been there, in my 77 911S, a tensioner failed , an awful noise. Living quite dangerously, I drove it home jacked the back end high and removed muffler, tin etc to have a look. Thought there was one chain but discovered a second , one on each side.
I had the rear end high as I had not drained the oil. Neither had I set the engine at TDC. I removed the right side tensioner and ordered the Carrera upgrade.
The following day, Val didn't like the threat posed to the kiddies by the high rear end so she lowered the car.
We had a large oil spill out the back but worse, as the rear wheels touched the gound, they must have rolled forward an this was enough to rotate the engine and the sudden tug on the chain rotated the cam and the chain jammed on the inner sprocket. I was not able to get the chain loose without removing the cam sprocket.
Got it all back together but not before learning how to time the cams.
Were I to do it again, along with all the good suggestions on this thread, I would mark the sprocket and chain before disassembly to be quite certain thay went back together in the same relative position as they came apart.
Ned Monaghan

Most Do it yourselfers dont even know what a dial indicator is never mind own one. I feel this would open doors to a more risky situation(they may read it incorrectely and start changing things that were allready correct). Also some dial indicators(like mine) are not metric which could lead to further confusion and a disassembled engine on its way to the trusty mechanic on a flat bed. When I changed my chains (see my tech arcticle) http://www.pelicanparts.com/techarticles/911_carrera_chain_tensioners/911_chain_replacement.htm
I had to read the timing procedure 3-4 times before I fully understood the procedure and I have owned and operated my own repair shop(no porsches) for over 12 years.


Kurt Williams

Please excuse me Wayne, I don't have your book yet.

I have done a lot of these. I mean a lot!

Yes, a dial indicator should be used. Get the holder too!
It doesn't have to be metric. If you can't do the math, there are a lot of conversion tables.

You should rotate the engine by hand at least 4-5 times between each camshaft timing adjustment. This is just to get accurate valve lift measurements. This is a must to get all of the slack out of the motor.

You can get to all of the cam chain ramps. It takes a little patience. You may even drop a ramp into the motor. No big deal, just take the sump plate off and push it out with your finger.

For an earlier poster:
The driving gear mechanism of a 911 camshaft allows for minute changes in camshaft timing in relation to crankshaft rotation. You can read the benefits of this from some of the Hot Rodding publications. Especially beneficial if you are a serious autocrossor.

The cam chain slip will always retard the camshaft. This allows the exhaust valves to hit the piston tops. Obviously, the expensive valves.

After looking a JW's post, I realize that I've never been able to R&R chain tensioners with out messing them up. I believe that it can be done without retiming the cams, however my level of expertise doesn't let me. JW is right in that the upper run of the chain if not disturbed, will keep the motor in time.

My guess is that if there is still compression, a light grind of the exhaust valve face will correct the problem and buttoning the motor back together would fix it. BTW, you will be using the dial indicator this time. The important thing is to get the measurements for both sides of the motor within the specified valve lift range and that they both be even!

Good luck,
David Duffield

I'm with old_porsche when he writes "The driving gear mechanism of a 911 camshaft allows for minute changes in camshaft timing in relation to crankshaft rotation. You can read the benefits of this from some of the Hot Rodding publications. Especially beneficial if you are a serious autocrossor. "... I found this out when I rotated the crank to recheck my cam timing, and found the cam timing had moved a hair.. this bothered me..I could not figure out why this happened, so I walked away from adjusting for the day..anyway, finally it hit me [not an expert] that the drive gears off the crank doesn't come back to the same chain link every revolution..I believe it took 9 or 11 revolutions of the crank to return the drive gear to the exact spot on the chain..then my timing matched up..good trivia................Ron

Ok, now you guys have got me worried. Didn't think it would happend, but it did. I'm about to do this procedure, what's the bottom line from the experts? Need a consensus, time cams or not. I don't have a Z-block, and I don't have the dial guage (although may be able to use one at the auto hobby shop...but I really don't want to do the job there), if the cam has to be turned, doesn't that also require another tool?

I can keep chains tight (I think), I can rotate the engine (clockwise) by hand. Is this enough? Also, if you do feel it bind, what do you do? You're no longer TDC, can't go forward, can't go back.

Bottom Line: Do I buy the Z-block and borrow the guage?

thanks

Rob...not a pro, but I would have a dial indicator and Z-block around to recheck cam timing [neurotically writing].. in spec twords retard/advance is another story, but I like to know that BOTH cams are the same spec..........Ron

This whole matter is silly, and you're all losing your heads. If you took 1 minute to think about how the 911 timing chain works you would understand that letting the chain go slack is not a problem and that cam timing has nothing to do with it.

Again, for those who care about how it works:

If the tension side of the chain does not skip a tooth then the timing is not affected one iota by changing the tensioners, or anything else on the "slack" side of the chain for that matter. If you want to be sure mark the sprocket position at TDC when you begin the job and check it before buttoning up. If the chain skipped a tooth on the tension side just get it back to the proper tooth and the cams will be perfectly back to the same timing they started at. Fine cam timing is only critical when you reassemble the engine and the distance or tolerance between the layshaft centerline and the cam centerline has changed or a new chain is used.

Umm, you *definately* should speak for yourself on that one!

Lots of us are not professionals, but do things a LOT more major than chain tensioners. And, I dare say, a lot of us do a better job than a lot of "professionals," many of who don't really care about your car and are not really very skilled.

These are pretty basic mechanical devices, not nuclear reactors.

Just a couple of notes to add here,

Several years ago I loaded up a cylinder with gasoline on my Ford racecar by accident, not realizing this I turned the motor over and blew the head gasket into the adjacent cylinder. Upon teardown I notice signs of the valves having touched the gasket but I didn't think much of it until I put it back together and it ran terrible. The compression test showed weak compression in that cylinder, I removed the head and discovered a very slightly bent exhaust valve. So in fact slightly bent valves can produce some compression. Second, if the cam jumped one tooth on the crankshaft sprocket that is the same as 1/2 tooth on the cam sprocket (cams turn 1/2 crank speed) I would have to believe that on a 9:1(approx) production motor that the valve pockets in the cylinder would be large enough to not hit a valve that's 1/2 tooth off but I could be wrong given the fact that while I'm an old hand at engines I'm new to Porsche engines. However a cam that is "out of phase" like this might allow compression losses because (assuming the valves did not hit) one of the valves would be partially open during the compression stroke, much like the lower compression shown on a full race cam. My advice would be to remove the timing covers and check the valve timing then perform a leakdown, or barring that perform a leakdown with the cam properly positioned via looking at the cam and not the engine timing marks (i.e. remove the valve covers and make sure both valves are closed for the leakdown) if the leakdown turns out OK I'd definately look into the cam timing. A perfect example of my experience with this is installing a timing belt on econobox 4cyl engines, they will crank over and sometimes barely run with the belt off by one tooth on the cam yet never bend the valves. Perhaps this individual can have another mechanic look at it for him or even perform these tests himself? The fact that all three cylinders exhibit close to the same low compression leads me to believe that the cam timing is in fact out by one tooth.

And as others have pointed out it is very important to gently rotate the engine by hand whenever the cam drive is serviced.

I made a "Z block" from a flat piece of steel with two holes drilled to bolt into the valve cover holes then used a magnetic base and dial indicator when I checked my 2.0E cam timing. Worked like a charm.

RoninLB is correct. Due to the length of the chan and the number of teeth on the cam sprocket, you must rotate the motor 9-10 revolutions before the same link will line up on the same tooth on the sprocket.

If the chain doesn't slip while installing new tensioners and or ramps, there is no problem. The question is probably, "How do I know if the chain has slipped?" After you have installed the tensioner and you rotate the motor thorugh by hand, if you feel any binding or that the pistons are hitting anything, you need to time the motor. Remember I said, rotate by hand with the spark plugs removed! Do it very slowly. Everything shoud feel very smooth. If It doesn't then its cam timing time.

This will not work on the 72T motor. I think this is the only motor that Porsche built which is a "free spin" motor. That is, you can rotate the crank without hitting the valves. I found this out when the son of a close friend called me. He was in tears. His father hand loaned him the 72T. The cam chain had broken and he had driven it home not telling his father. He was really worried about the damage he had done to the motor. The only thing hurt in the motor was the chain!

Good luck,
David Duffield