Knocking Sound under Acceleration

Post by **dalebrignall** » Mon Dec 07, 2009 4:33 pm

my mothers saab 9000timing snapped when she started the car ,it had only done 79000,the car is 20 years old and seviced every year this was the first one that a saab garage had seen,so it can happen.

Post by **bmcecosse** » Mon Dec 07, 2009 4:37 pm

Chain - or belt ? The SAAB chain can jump off - I've had that happen!

Post by **dalebrignall** » Mon Dec 07, 2009 5:36 pm

the chain snapped roy the aa man dug it out with a screw driver the head had to be skimmed and 4 new valves,its a 2.3 lump so no spare cylinder heads about so it cost her

Post by **dalebrignall** » Mon Dec 07, 2009 6:50 pm

sorry for hijacking the thread back on track now

linearaudio · Post by **linearaudio** » Mon Dec 07, 2009 7:06 pm

What was the question now?

It worries me that with all this stripping of the engine, nothing has yet been found to cause the knocking! I still have a nagging feeling that this may just be something daft like the exhaust drumming on the chassis, and all this expensive work won't prove anything

Diffficult to judge, but the head gasket does look a bit black between 1&2, anyone else looked and thought that?

Post by **PSL184** » Mon Dec 07, 2009 7:14 pm

My initial thoughts were that the HG looked OK....

linearaudio · Post by **linearaudio** » Mon Dec 07, 2009 7:40 pm

PSL184 wrote:My initial thoughts were that the HG looked OK....

Hmm yes, clutching at straws a bit with the blackish bit- just not many more things to look for, are there?

Post by **bmcecosse** » Mon Dec 07, 2009 7:59 pm

Head gasket is fine - unless there is a damaged piston (and that can be checked without popping the engine) I tend to agree - I've been thinking the same thing. But then again - looks like Dad is enjoying himself taking it to bits - I reckon he wanted a wee project!

linearaudio · Post by **linearaudio** » Mon Dec 07, 2009 8:37 pm

Looks like thats your Christmas present-in-kind from Dad then, Stephen!

Post by **stephenpolhill** » Sat Dec 12, 2009 12:33 pm

Hi there. Quite alot has gone on recently, I just haven't had chance to update. I have uploaded more pictures on Facebook to see what you think.
So far we have taken the engine out using a homemade wooden frame and some rope. The frame is two good bits of wood in an 'H' shape just with 2 bits of wood across. A friend and I lifted while Dad guided it out and lifted across.
We have found that Piston 4 (see pictures on FB) has quite a few grooves/scratches in it which according to another MM friend could have been caused by the carbon deposit which was on the pistons. It could have also caused the white/blue smoke and poor oil consumption I had a few months ago (now gone).
The middle crackshaft bearing looks a bit worn and when you run your finger over feels a bit grooved. We are changing these bearings anyway but could it be the cause of the knocking?
Like BMC said, Dad is enjoying taking it apart and I am learning quite a bit. If anything it is a 'good' check for anything else..
Any thoughts on anything would be fantastic. Thanks again for all of your help

Facebook pictures link - http://www.facebook.com/album.php?aid=1 ... bc64c7805b

linearaudio · Post by **linearaudio** » Sat Dec 12, 2009 1:03 pm

Ah-ha! I reckon your opening statement about the flickering oil light/ putting 1LITRE of oil in, combined with the state of no 4 piston may be your noise. Looks like no 4 has tried to seize through lack of oil/ temperature. I may be imagining it, but is that a little fracture line from the slot under the rings, leading into the bottom ring gap? I believe it is not unknown for those pistons to fail there- that would certainly cause a rattling! Alternatively the noise may just have been horrendous piston slap! Is no 4 particularly more loose in the bore than the others? What is the state of no 4 bore? It could well be rebore time! I don't think I would classify the state of the piston as "very scratched-but should be OK"!

Post by **bmcecosse** » Sat Dec 12, 2009 2:51 pm

I agree - the bearings don't look too bad - new shells may do the trick - for a while. But these pistons are horribly scored - that's not just down to 'a bit of carbon' . However - you may be able to keep it going by cleaning it all off (and yes - inspect carefully to see if that's a crack LA has spotted) and are the rings all in one piece - and are they free in the grooves ? Also clean off the bores very carefully - and if not too badly marked - it should be ok. If you do decid to go for a rebore - then may as well have the crank reground too, and if doing all that - don't forget to fit a new oil pump!

Post by **stephenpolhill** » Sat Dec 12, 2009 3:07 pm

There is a slight 'shadow' of scratches in the liner of cylinder 4 but not deep enough to feel. The piston rings were all in one piece and could be turned. They have been removed and seem OK. Some of the marks in piston 4 are deep but no sharp edges.
The journals of the crankshaft generally feel smooth although a couple of them look 'scored' (see pictures), particularly middle-main.

Post by **PSL184** » Sat Dec 12, 2009 3:11 pm

The centre main bearing is always the first to go. If it is only slight then you have probably git away with it. As long as you don't have any deep grooves or scratches anywhere you are best to clean everything up and rebuld with new bearings etc and make sure everything is correctly torqued up. Otherwise, the option is to go for a full rebore and crank regrind whilst you have everything apart......

Post by **bmcecosse** » Sat Dec 12, 2009 6:17 pm

Don't really see anything there that would have been 'knocking'!

linearaudio · Post by **linearaudio** » Sat Dec 12, 2009 6:32 pm

bmcecosse wrote:Don't really see anything there that would have been 'knocking'!

Bet it was the exhaust pipe knocking on the chassis!

Post by **bmcecosse** » Sat Dec 12, 2009 7:38 pm

Most likely something like that!

Post by **bmcecosse** » Sat Dec 12, 2009 7:39 pm

Most likely something like that! Certainly don't see anything too serious in the engine.

Post by **stephenpolhill** » Sun Dec 13, 2009 5:22 pm

I wouldn't be too annoyed if it was because there has been quite a big oil leak we needed to sort anyway. Its a good excercise for Dad and I to take it apart and find any other issues. From what you can see, are there any other things we should look out for?
We are going to get the crankshaft reground (is that the word?) by an engine place then buy some oversized bearings to match.

Post by **bmcecosse** » Sun Dec 13, 2009 6:00 pm

I didn't think the crank was that bad - suggest you fit a new oil pump if doing the regrind.. And - inspect the oil filter carefully - are the plate and spring present and correct ? New timing chain a good idea too. While the head is off - you should be cleaning it all up and grinding in the valves!