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YOUR RESEARCHWhat would cause timing chain guide excessive wear?
Reported or suspected cause
just error in timing the engine
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Reported cause
I can tell you for sure that the deviation being at -4.50* after new pads was due to just error in timing the engine...
What would cause timing chain guide excessive wear?
Frequently discussed work
Adjust cam timing almost continuously and this may be contributing
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Suggestion
If you normally dive it at approximately 2500-3000 rpm the engine is adjusting the cam timing almost continuously and this may be contributing to premature chain guide wear.
What would cause timing chain guide excessive wear?
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Leading evidence: 'just error in timing the engine' (1 discussions report identifying this cause; no attributable repair resolution). Across 1 matching discussions, the most frequently mentioned possible cause is 'just error in timing the engine' (1 discussions; 1 report identifying it and 0 suggest it). The most frequently discussed action is 'Adjust cam timing almost continuously and this may be contributing' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
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Performed · outcome unconfirmed
Make sure the shop makes note of whether they were installed correctly or backwards.
What would cause timing chain guide excessive wear?
Install pads backwards
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Performed · outcome unconfirmed
Another possibility - the previous shop installed the pads backwards.
What would cause timing chain guide excessive wear?
Replace chain while in there
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Performed · outcome unconfirmed · Original poster
The work order noted deviation was -10.00, so I'm thinking that they just changed the chain while in there for the guide work.
What would cause timing chain guide excessive wear?
Replace timing chain
Performed · outcome unconfirmed
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Performed · outcome unconfirmed · Original poster
When he had that work done they replaced the timing chain, but I'm not sure why exactly.
What would cause timing chain guide excessive wear?
Frequently discussed actions (10)
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Adjust cam timing almost continuously and this may be contributing
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Suggestion
If you normally dive it at approximately 2500-3000 rpm the engine is adjusting the cam timing almost continuously and this may be contributing to premature chain guide wear.
What would cause timing chain guide excessive wear?
Replace expansion tank they remove fuel filter
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Suggestion · Original poster
Two bonus repairs once engine was back in and running; expansion tank broke, and while replacing expansion tank they remove fuel filter that well over due for changing.
What would cause timing chain guide excessive wear?
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37 eligible posts · 0 unverified posts · 1 discussions match the subject in their title or opening post.
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There are many guides, so adding
link
to be specific on the guides I'm referring to. The variocam guides on my 996 were changed at 48k miles(new chain), I'm at 72k miles, and car is under repair to get new guides--again. If the guides are wearing that quickly would it be safe to assume that the actuator \ solenoid is bad? I am moving forward with replacing both variocam's(timing chain tensioners)--
ouch
. But, I am curious if the issue of excessive wear of the timing chain guides can be attributed to a faulty actuator.
No CEL, but found some bits in the oil and wanted to make it right. Deviation went up by .-75 to -5.25 within 1000 miles, so something was definitely up.
While getting this done I'm throwing in new LN IMS bearing, AOS, chain guides, water pump.....I'm a bit at my ends with this car, and probably going to be selling after I get a few months of driving on the repairs. The old saying of "get the best car you can afford" held true for me, but after these repairs and previous, I'm at the all in cost of buying a 997 or 996 TT.
Appreciate any feedback! This repair has been a bit of a mystery for two indy shops, as well as contacting LN to give them the scoop in vitals of the car. I'm all in on making it right, but extremely frustrating at times.
A couple of questions for clarification:
1. Were you the owner at 48K when the prior work was done?
2. If so, what happened at that time to cause a timing chain replacement?
3. What is the service history? Engine oil drain intervals? Oil weight/spec used?
The previous owner had the work done. When he had that work done they replaced the timing chain, but I'm not sure why exactly. The work order noted deviation was -10.00, so I'm thinking that they just changed the chain while in there for the guide work.
Previous owner did their own oil changes, which is what was hiding the guide debris findings from being in any paper work I got. There's no doubt he was seeing guide pieces in each oil change, based on what I'm seeing over the course of very short interval changes.
He was using Driven 5-40 for oil changes.
The car is currently at the shop that he had work done at previously, so I feel good that they've got some history with it, and have all the notes from work done.
How do you drive the car?
If you normally dive it at approximately 2500-3000 rpm the engine is adjusting the cam timing almost continuously and this may be contributing to premature chain guide wear.
It is better to keep rpm above 3000 to keep the cam timing out Don the switching range, it id also better for thre IMS bearing to be running at the higher rpm. Remember the IMS bearing runs at one half of the engine rpm.
The IMS RPM is a new fun fact for me, I didn't realize the gearing was that different, and did wonder how a bearing like that could take such abuse at high RPM's. Thank you.
As far as driving habits go, I don't abuse the car, but every time I drive it is with intent. I do a slow warm up, let temp get to 18|0, and then drive it like it should be driven. I don't lug the motor, as it's painful to listen to, and during that warm up time still go up to 3k before shifting.
I wasn't sure if perhaps the engine being out of time could somehow cause more guide wear if the variocam was off a bit, but also don't know all the in's and out's of how the system works as a whole. Lots of education going on with the finer details, but I do know the guide rails should last longer than 20k miles.
Unless you are doing the work yourself how could you justify putting that much money in a car that�s running reasonably well and then turn around and sell it?
5.75 is high but still in spec.
I�m not sure there�s a right answer for that, other than what is the obvious one for me. I can�t sell a car to someone knowing there are underlying issues. Aside from selling, I don�t want to drive a car that I know is chunking guide rails, and already had a clogged scavenge pump.
I know that the deviation value isn�t high, but it�s not based on that data alone. There are chunks of plastic in the oil, and they got there in a very short amount of time. Deviation on bank 1 was moving quick, and as soon as I saw bank 2 creeping up I figured it was time to operate.
I had already budgeted to do this work, minus the guides, so it�s not really an issue from that aspect. I wanted an LN IMS bearing installed, and come to find out that was the least of my worries. I did find out today that I have a dual row, so that�s an interesting piece of info, I figured it did since it was built early �00.
Not sure if that answers your question, but we all have are own perspective with these cars. For me personally, I want to keep it running, and when I sell I want to have good records for a buyer that is excited for what could be their first Porsche.
I guess I look at it differently. The issue is that these start to wear the moment you start the car.
There is a rebuild kit for the variocam units from Hartech if they are determined to have gone bad.
That would usually throw a CEL though.
For reference.
My original chain rails with 27k on them.
Interesting, can you clarify on this? Porsche documentation indicates 5 chain variocam activation between 1300-5120rpm. I�ve seen other references to natural resonance for the M96 engines between 2500 and 3000 but nothing to back that up.
Anyway, as others have said the OPs cam deviation is still in spec. Cam deviation is pretty heavily influenced by engine temp, enough that I�ve seen my numbers vary 0.5 degrees or more cold->hot. There can be other causes for cam deviation beyond the guide pads. These pads would be wearing very prematurely, and that could indicate another possible cause. �Pad material� in the filter could also be the main chain guides which are also plastic and a source of wear. Replacement pad material would be light yellow and main chain pad material much darker, that might help differentiate. (Granted, 20k miles might make that more challenging).
Can I ask about whether you�ve installed new timing chain tensioners? (The 3 cylindrical oil-fed ones, not the variocam tensioner). New tensioners could in theory contribute to increased wear on the main chain guides, or even rotate the scavenge pump sprocket and impact timing.
Doubt the variocam actuators could cause premature wear. The position of the pads is held static relative to each other. The actuator just uses oil pressure to move the tension on the cam chain from one side to another. It�s all-or-nothing and the limit is mechanically set.
Another possibility - the previous shop installed the pads backwards. One pad has an oil feed hole. If they�re installed backwards the lack of oil could cause wear and the numbers you�re seeing.
Will be interested to see what you find out.
The original material when I removed sump 1000 miles ago was a mixed bag of black and orange / yellow�ish. The most recent oil change revealed what I considered to be newer pad, and it was orange, so figured that was for sure from the variocam side of things.
Step 1 was to replace the 3 tensioners you mentioned, and that had no impact on deviation on either bank, so that was a bummer.
Lots of deductive reasoning on this one. Ultimately, after talking to LN, and others, we came to the conclusion that it has to be the variocam itself. I thought about just swapping out the solenoid, but figured I�d get two new actuators to remove that variable altogether.
So, current situation is replacing the main large guides, as well as the variocam guides. It is wild that the pads would be chunking at 20k miles. I should know all the details by end of the week. Added new coils to the list today, they are the older type, and a few had some cracking�
Huh, yeah that material does sound like the new pads.
Make sure the shop makes note of whether they were installed correctly or backwards. One of the more popular YouTube videos on pad replacement shows an install where they make this exact mistake.
The **** thing is I don�t think I�ll get an honest report on root cause, due to this being the shop that did that work under previous owner. I have seen where the pads with the oil feed are put on the wrong side, etc�
Good call, I will be sure to ask about the old pads, I did ask for them to save all parts as part of the job. They said they won�t save IMS bearing, because it gets sent back to LN, but I can get photos.
Whichever way you go: keep or sell, I appreciate your sincerity and honesty for making it right and not another problem for next person if you do decide to part ways.
Kind of the cost of doing business I think. The buy-in cost isn't where it ends, or even close. For my 997 I'm at the point where I could be in a higher mileage turbo, but then I'd imagine it would be the turbo cost plus whatever to get it sorted.
A word of caution. The old bearing has to go back to LN as part of the registration of the new bearing. If the shop is going to return it, make sure they do. If they are handling the registration of the new bearing, make sure you check on the LN website that the registration was completed. I've seen the ball (bearing) get dropped before and then when you go to sell the car, there isn't a registration to back up your effort.
Good question. They were the OEM Porsche part number according to the invoice I had, but you never know for sure, which sucks. The deviation even after they were replaced only went down to -4.50, so I really do think that there was something up with the variocam that might be causing the grinding of the guides.
Thank you for this! I just sent the shop an email asking for assurance that the bearing was going to be sent to LN, and timeline on when I'd see the LN bearing assigned to my VIN. I also asked for photos to have documentation of the new \ old bearing.
I did get a small victory in overall cost, I've got the dual row, so that saves a bit on labor versus the single row.
Like hbdunn said the vario-cam units can now be rebuilt using an O-ring kit from Hartech ( finally available after 25 years..lol)..
The O-rings deteriorate after 20-25 years of synthetic oil and heat and crumble apart and cause the vario-cam units to be slow to move or to return to rest, it wouldn't surprise me for it to cause the deviations to be shewed also...The o-ring kit cost $175usd compared to $3k usd for both vario-cam units....
I guess we will get a good look at your new guide wear when they are out.....
Skip,
Can you please confirm the activation point of the vario cam on the 996.1 engine. I had been told it was between 2400-2800 rpm but one of the bulletins says on at 1300 and off somewhere near 5900 rpm. Is that for a 996.1 or a 968. I just want to be sure.
Thanks
Mark
Sure Mark, the vario-cam for 996.1 turns ON at 1200 rpm and stays ON untill 5120 rpm, then turns OFF for increased top end power/rpm ..( unless the oil temp exceeds 265F , then it waits untill 1400 rpm to turn ON )
The resonance that has been mentioned in the timing chains is very high at low RPM, ( under 3k rpm) due to the 3 cylinders on dual cams causing the cams to spring forward then resist turning as the spring pressure resists advancing...You can feel this by turning a cam by hand, it will get increasingly hard to turn as the valve opens, then as it closes it will jump forward.....This action is much pronounced in dual cams, and even more so when you have basically two 3 cylinder engines ...That's why our engines are so much happier above 3k RPM's...
Thank you for your knowledge on this. Based on your comment regarding activation of the variocam at specific RPM�s, would it be possible that due to the wear of the o-rings it never fully disengages at the lower RPMs, causing excess guide wear?
I am really hoping the replacement of both units fixes the issue, and I�m home free on future issues when it comes to guides!
I had to replace my pads at 55k. I do know that the tensioners are towards the end of the oiling system, and my car knocks and rattles if I do a cold start and just let it idle. Ever since I startup and drive off immediately, I get zero knock/rattle, and zero plastic bits in the oil filter. I�m not saying that�s the cause of the premature wear, but I suspect cold starts cause the most wear on the pads. I would think that keeping revs up should splash more oil on the chain than idle.
Agree, for sure. My routine isn�t as drawn out as I made it sound with the arm up. I start it up, get my phone sorted, pop the sunroof and other checklist items like oil pressure, then off I go. It�s less than a minute.
I try not to be too delicate with the car and drive it, but the one thing I am cautious on is getting on it too hard too early. The transmission also doesn�t feel the greatest when cold, so it kind helps regulate�
Well, lets wait to see how much actual wear there is on the newish vario-cam pads.......It is very possible that the deteriorated o-ring is holding the tensioner from full seating at the rest point , at that is skewing the deviation valve...( because a 5* wear in 1k miles doesn't seem plausible)
He said a couple posts back that cam dev after pad replacement was still -4.50. So it's actually only a 1.25 degree change in 24,000 miles. He reported 0.75 deg change in the past 1000 miles.
Shoot me an email at
[email removed]
if you�d like to order a set of seal kits. Our first shipment of them is supposed leave out from the UK next week.
Ahh !! So that why it didn't seem plausible, I totally read that too fast....thanks ...lol
I can tell you for sure that the deviation being at -4.50* after new pads was due to just error in timing the engine... I have seen it many times. If not using the timing tool and the "Porsche special tensioner" it is very easy to be off by 3-5*...( a Pro can quickly pop the scavenge pump out and go back in a nudge the exhaust cam a little and get the deviations on point)...
Remember, the timing is done on the exhaust cam, but the deviations are read on the intake cam .. ( a lot of things in between that have to be perfect)
As far as performance goes, being off - by 3-5* will just move the power band up a little toward the top of the RPM range. I have moved cam timing - and + as much as 10* just to change the power band before...But when using 0* as a basis for wear monitoring ,it will matter a lot more....
I suspect you newish cam pads are not worn much at all...
I have a feeling you may be right about the timing piece. The engine was mechanically in time, so no issue there, but I did wonder if maybe the deviation was high due to some other variable in timing?
I don't have old guides(pads) in hand yet to, but they for sure were warn, because I was seeing the newish yellow color in my oil.
I just got call back and the results are exactly what I was hoping for:
Bank 1: -1.25 (Previously -5.50+)
Bank 2: -.75 (Previously -1.25)
Two bonus repairs once engine was back in and running; expansion tank broke, and while replacing expansion tank they remove fuel filter that well over due for changing.
I get the car back tomorrow! Current readings at the shop(warm) are:
bank 1: -1.1
bank 2: -.60
That's pretty amazing. All new guides and new variacams + pads, I think those deviation numbers beat the factory! We weren't sure what the root cause of the deviation was, and it definitely came down to the varioncam(cam tensioners) being faulting in some way that wasn't throwing a code. They must have been engaged throughout the entire RPM, which was causing excessive wear on the pads.
I did end up doing my complete wish list while the car was in, so also completed:
LN IMS Bearing
AOS
Water Pump
Coolant Reservoir
Fuel Pump
Coils Packs
This will now free me up to do some suspension refresh and some new wheels. Getting the extra items replaced was a tough pill to swallow, I generally won't do work unless there's a reason, but since the engine was out I didn't want to regret not having the work done. The crap part is that none of this is really going to make the car drive that much different, perhaps the power will come on a little earlier with the deviation being dialed in, and the fresh fuel filter helping the petrol flow!
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