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Discussion Starter · #1 ·
I have just been told from my garage that my car is not going to full boost because of balance shaft bearing sprocket/chain wear and/or incorrect refitting. This causes noise picked up by the knock sensor.Note that there is no chain noise coming from the engine. I haven't picked up the car yet,I will post more later. I do not know how the garage concluded that,I'll let you know.

What do you think? Anyone else had this problem?

Are the sprockets/chain expensive?
Do I need to remove the engine? (I wouldn't think so, but in the Haynes manual the procedure is in the engine removal section!).

In idle, every 3-4 seconds,there is a slight "knock" that can be felt inside the car. However, I think this has been reported by many of you in the past. Is it normal, or is this more evidence?

How hard is it to replace the sprockets and chain? Could it be done in a day?

Sorry for the long questions...

Harry
1991 CS Carlsson auto with 100k
 

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Just last week, I replaced all the balance and timing chains & sprockets, however, wear is evident on removal of the timing cover. My exhaust balance shaft sprocket had worn down to the ring (no teeth!) and the chain had resultant flat spots, although the car's performance did not appear to be compromised. However, ask your garage if they removed the timing cover to confirm their findings....is it a SAAB dealer? Also, these parts will be expensive from the dealer but you will get the original parts from Europarts.com at a discounted cost. If you are replacing just the chains, sprockets, etc., you do not need to lift the cylinder head....just the rocker cover on the top of the engine and the timing cover on the side (behind front tyre) needs to be removed. If your car has done high mileage, might as well remove the head and change the gaskets, etc.
It is fairly easy to replace the chains, sprockets, etc. provided you have the right tools and facility (torx keys, torque wrench, bench vice and the HAYNES mamual!), trying to achieve this work in a day is not advisable! Keep us posted on the developments....post your email and I will send you a few images of the engine opened up.
 

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Discussion Starter · #3 ·
Thanks for all the info. No, the garage (who is a Saab specialist) did not open the cover. His evidence was a resonance of the engine (and car) at high revs (in neutral). There is no noise coming from the engine, but, as you 've seen, these things tend to fail, so I think I'll take a look. The thing I'm sceptical about is the problem affecting max boost. Of course, I'll sort it out anyway, but I really want to sort out the boost problem as well...

Would a bleed valve help in this situation? I read in a post that Abbots recommended this as the best approach to getting full boost (Of course, as long as you know that the engine is in good condition and is not limiting the boost because there actually IS a problem)

Opinions, please!

Harry
1991 CS Carlsson,100k
 

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Whao! This mechanic must also be a magician! Can tell chain/sprocket wear by ear! Be very skeptical! Anyway, if no noise, then no problem! Your boost problem could be something minor related to turbo, etc. However, some further replies to your post may yield some solutions. Will send you engine images later.
 

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Sounds very strange to me for noises other than knock to be assumed by knock sensor.
Correct me if I'm wrong anybody but I thought a knock sensor worked by comparing noises during knock to noises without and hence removing all other noises to leave only knock.
A loose bolt securing the knock sensor might give false readings.
Come to think of it my car with DI and Trionic has no knock sensor the spark plugs are able to tell when combustion is taking place.
 

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Are all balance shaft engines fitted with DI and hence have no Knock sensor?
Do DI cars with and without Trionic have no Knock sensor?
If this is true then it makes the garage's assessment a little less believable!!
 

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I think all Trionic cars have no knock sensors but will have balanced shafts. Trionic from 93 onwards? All Trionics have DI. Early balance shaft engines (pre 93) will have DI/APC engine control which has a knock sensor.

Townsend has a list of engine control systems (be careful though this is for the US market)
 

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Come to think of it my car with DI and Trionic has no knock sensor the spark plugs are able to tell when combustion is taking place.  [/b]
The DI Pack measures resistance across plug gap only prior to firing , in order to determine which cylinder is on 'compression' stroke. Never heard that DI Pack measures 'when combustion is taking place' though - and even if it did, how would this detect 'knock'?
 

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I thought Trionic / DI measured conditions before, during and after combustion and this is one of the reasons it was so advanced when it first came out being the only system that did this.
The system must measure knock somehow as there is no knock sensor, not sure how though.
 

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I am pretty sure that the 'knock' that the knock sensor is intended to sense is not mechanical 'knock' or noise but 'detonation knock'which is probably akin to 'pinking' (uk)or 'pinging'(usa).

Loose sloppy or worn timing chains could presumably cause such a 'knock' by causing the inlet / exhaust valves not to be operating at exactly the right timings. Well, that's what I think if you can make sense of it......
 

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Quote: >> I thought Trionic / DI measured conditions before, during and after combustion

Curious! Anyone other 'experts' out there who can clarify how 'DI/Trionic' system detects/controls 'knock'????

Quote: >>I am pretty sure that the 'knock' that the knock sensor is intended to sense is not mechanical 'knock' or noise but 'detonation knock'which is probably akin to 'pinking' (uk)or 'pinging'(usa).

Agreed. 'Knock' = 'Pinking' = pre-ignition.
This relates to spark plug timing (not valve timing) though. Low octane fuels 'pink' earlier than higher octane fuels, which is detected by the 'knock detector' and the ECU backs of the spark plug timing until knock/pinking is no longer detected. Hence the Saab system can use different octane rated fules (e.g. 95RON and higher) fuels and adjust the spark plug timing accordingly for best performance.
 

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Discussion Starter · #14 ·
So, as I see it, it is highly unlikely that my boost problem is related to the balance shafts. Excessive noise may trigger the knock sensor, but my engine runs quietly so it's highly unlikely...

Right?

Harry
 

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Harry,

IMHO I am inclined to agree with Saabpilot, quarryeff, etc.

Engine noises take a tuned ear to distinguish, but I would definately get an independant opinion from another 'expert' and don't mention the verdict of the first 'expert' until afterwards!
 
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