Saabscene Saab Forum - Saab Technical Information Resource banner
1 - 18 of 18 Posts

·
Registered
Joined
·
135 Posts
Discussion Starter · #1 ·
As I have my engine in bits to get the head skimed, thought I'd inspect the timing and balance chains. Problem is I can't decide whether to replace nothing, the chains or the chains, sprockets & guides.

Bearing in mind my chains have not been noisy, the car ('97 2.3 LPT) has only done 92K miles with FSH, and the sprockets look OK is it worth replacing the chains and leaving the sprockets alone? If the sprockets will last another 40K miles I'd much rather wait until then. Has anyone else put new chains on old sprockets, if so how long did they last?
 

·
Registered
Joined
·
194 Posts
I don't think putting new chain on old sprockets is ever a good idea. Lets face it, you currently have your engine in bits. Are you planning on keeping the car? If so, just do the chain and sprockets while you have the chance. Do you really want to take it all apart again in a couple of years time?
 

·
Registered
Joined
·
1,749 Posts
On my '97 with about the same mileage as yours, I had a nasty chain rattle so bought the entire kit for balance and timing gear - chains, sprockets, tensioners, guides, etc. My car also had a FSSH.

Having bought all the bits, I changed them all. However, in the same situation again, I'd just do the guides and chains. This is because I honestly could not see any difference at all between the old and new sprockets. The old ones showed no signs of wear.

At some point ('92 maybe?) a couple of weak sprockets were hardened. Since then, unless the car has done starship mileage, and if it's had regular oil changes with good oil, the sprockets don't seem to wear much.

In fact, the chain guides on mine were fine too after 98,000 miles. However, they are cheap and easy to replace.

It's really down to you, but doing the sprockets adds a lot of cost, compared to chains and guides which are cheap. If the sprockets look fine - and they did on mine - I'd be tempted to leave them until you do the chains again at 250,000 miles

The other dilemma would be the balance chain tensioner. You can't really check its condition and you can't get to it easily, so you could do that as preventative maintenance.

While you're there though, you may as well do the crank oil seal, since that's another cheap item.
 

·
Registered
Joined
·
545 Posts
You are at the sort of mileage where chain wear becomes an issue and the tensioners are unable to take up any more and the noise will start. I would save yourself a weekends work later and replace the chains now unless cost/time are an issue or you plan on getting rid of the car in the next year. Removal of the timing cover is easier with the head off and the coolant is already drained.
On the 2 cars I have replaced the timing chain, one had done 110k miles and only the chain was replaced to keep the cost down although the sprockets were fine. The other had done 140k and I replaced the guides also since they were cheap. Once in bits I found some wear on the crank sprocket but I could not get one easily at the time so had to leave it. The worn guides did not look much different to the new guides. Neither engine had a balance chain so I can not comment on that.
 

·
Registered
Joined
·
135 Posts
Discussion Starter · #6 ·
Thanks all for your thoughts.
I do understand the reasons for not putting a new chain on badly worn sprockets but to me my sprockets do not look very worn at all. I understand the length of the timing chain tensioner can give some indication of wear, it was 10.5mm for me, think this is pretty low?

Paul, of the two cars you fitted new chains to without replacing the sprockets, how many miles have they done since and have there been any chain related problems since?
 

·
Registered
Joined
·
8,216 Posts
Definitely worth changing the chains while you have the head off as they're cheap and it's a pig to get the timing cover off with the head and sump in place (actually, getting it back on is the bigger problem).

I have done this twice myself and didn't change any sprockets that looked OK. That left only one very worn balance shaft sprocket to change on one of the cars. The other sprockets looked like new on both cars. Have a really good look at the balance shaft sprockets, especially the one on the exhaust-side shaft.
I did one car at about 140K miles and the other at 160K. I've only done about 10K miles in total on the two cars since, though. Both were balance shaft engines (a B204 and a B234).
 

·
Registered
Joined
·
545 Posts
James, the 110k mile car was a friends and he sold it within a year - the chain was that worn it was catching on part of the timing cover and was that noisy he dare not sell it before the repair. The other was mine and that I sold 2 years later at 154k miles. Both were ok when sold. In both cases the tensioner was at its limit.
 

·
Registered
Joined
·
1,908 Posts
When retorquing my head bolts last week, I noticed my top two cam sprockets showed no wear at all - car 140k miles on 1998 2L Eco.

Chained looked 'OK' but then it was hard to see/tell how much it was worn. The car runs as smooth as a babies bottom!

Based on the above, sounds like I should get a 'cut and shut' chain only replacement soon. This is done by splitting old chain at top (with only cam cover removed) and connecting a new chain with split link onto old chain, feeding it around sprockets, then removing old and reconnecting the new chain. Quick and cheepest option. Then I only have to wait until balance chains start to rattle.
 

·
Registered
Joined
·
2,242 Posts
Well this is one of my sprockets. All of them had the same type of pitting but didn't look particularly worn to me but then i'm not a judge of worn sprockets! For me, the expense of 3 sprockets, guides, chain and tensioner for just £130 or so seems like a small price to know that it's all done once and for all.
 

·
Registered
Joined
·
8,216 Posts
Originally posted by Paul D:
[qb]Then I only have to wait until balance chains start to rattle. [/qb][/b]
I had the balance chain jump on a worn sprocket an dthere was no rattle. I did notice an increase in engine vibration but who knows how long it had been out of place before it was mis-timed enough to cause noticeable vibration?

Not sure I've ever heard of the balance chain rattling, come to think of it...

David, I wouldn't have put a new chain on those sprockets. I'm no expert either but they look worn to me.
 

·
Registered
Joined
·
1,908 Posts
Dave,
That looks like a drive sprocket. Can anyone advise if Drive sprockets wear faster than the two driven (cam end) sprockets, and if so (as I suspect - being smaller) typically by how much?


Thanks for the feedback Bill.

It does surprise me that Balance chain/sprockets evidently wear/fail with a similar lifespan to that of the cam chain and sprockets. I'd have thought it should last around 1.5 to 2x as long!

Not having seen a balance shaft, I am surprised it carries as much load (relative to it's strength/size, etc) as that placed on the cam chain/sprockets.

Anyway, here's hoping that my complete abscence of any sign of wear on my cam sprockets (at 140k) is also indicative of my balance chain sprocket condition!
 

·
Registered
Joined
·
8,216 Posts
The balance shafts turn at twice engine speed, which is four times the speed of the camshafts. The balance chain is narrower and the sprocket teeth smaller than on the timing gear since, as you rightly point out, there is less load on the balance gear.

Fingers crossed, though, and if you have a sudden onset of engine vibration and all the engine mounts are OK (as they were on mine), then it would be worth doing the chains as a precaution and checking the sprockets. Apparently there are other possible causes (although rare). Mark E had one of the spring fingers from the clutch pressure plate break off, causing imbalance. I can only assume it also made a loud noise when it happened
 

·
Registered
Joined
·
2,242 Posts
Bill, I didn't

This is my point, if they were left with oil on and a reasonably good inspection, they looked ok, no real obvious hooking and only when degreased and looked at under an 8x lupe could you really see this level of pitting.

For me, when the timing cover and head is already off, the cost of a £130 kit for the lot seems silly to scrimp on.

David.
 

·
Registered
Joined
·
1,908 Posts
Dave,

Did your 'driven' (cam end) sprockets look same, better/worst than the 'drive' sprocket (pictured?)?

Fully agree extra £130 worth doing if head off, etc. If I can acertain that driven/drive sprockets wear at similar rates, as my cam sprockets are fine (i.e. no wear/pitting), then I should be able to save £300+ with a new cam chain only mod, applied by the cut/shut method.

I have heard of sprockets much worst than that pictured above, with hooking, etc - so mine have a long way to go yet at 140k miles.
 

·
Registered
Joined
·
2,242 Posts
Paul, cam sprokets were just about the same. Like I said, when oily (and even wiped) they looked "ok" but there's ok and proper.

I just remembered putting a new chain on and old pushbike and it would jump and snatch and in the end I put the old chain back and it was sweet as anything.

Without the ability to test against blueprints, I chose the only sensible route to me.

David.
 

·
Registered
Joined
·
1,908 Posts
Thanks for the info Dave,

Agree absolutely.
Every case needs to be assessed on it's merits.

Plus, it's a balance on what is cost effective, relative to how long one plans to keep the car and cost of work against value of vehicle, etc.
 
1 - 18 of 18 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top