Valve noise & Saab 8391450 tool

[Rog13]

Browsing Stag YouTube videos I found this one https://youtu.be/zAfyi75_zFQ?si=oC5CR9ZJj_78A9wi (and several more in a series) documenting attempts to locate the source of knocking/ticking in a stag engine. The conclusion is cam chain but this eventually proves incorrect.

A contributor In the comments section believes the noise is due to valves and recommends a special Saab tool (Nr 8391450) for measuring valve clearance and fixing the problem. This is said to be superior to the factory procedure.

I know Triumph and Saab engines share engine mechanicals. Curious to know what the Saab tool is and why it would be used. Also curious about the engine knock demonstrated in the video and said in comments to be caused by a valve. Can anyone elaborate?

[ramjam2005]

Sticky valve or bucket shim / cam-follower gap incorrect ? But it is quite pronounced. I've always found the Stag engine to be a bit tick-ety tick-ety even when in fine fettle, not the quietest/smoothest of engines.

No knowledge on the Saab tool. Sorry.

[jbuckl]

Can be little end wear.
Can be tappet bucket / bore wear.
Rarely can be bucket touching a short bore (machining error)
If it’s none of those, cam chain / guide / tensioner wear or incorrect settings.

what was Marshman’s findings?

[mole42]

Or it could be the valve touching the piston.

[Rog13]

Marhsman suspected cam chain/tensioners and undertook repairs. However the noise persisted and there was no final conclusion The comments contributor hias7568 seems emphatic that valve clearance adjustment (with Saab tool) will fix it.

[jbuckl]

Took a look at the Saab tool.
It looks like a grip for removing the bucket.
Cant see how it can help with adjusting really.

[DJT]

My thoughts exactly.

https://www.worthpoint.com/worthopedia/saab-90-99-900-valve-engine-tappet-513419997

Feeler gauges, ROM, micrometer and patience. Luckily they rarely go out of adjustment between rebuilds.

[marshman]

Marhsman suspected cam chain/tensioners and undertook repairs. However the noise persisted and there was no final conclusion The comments contributor hias7568 seems emphatic that valve clearance adjustment (with Saab tool) will fix it.

I am pleased to report that I did eventually find the cause and effect a cure!

A brief history. The noise started a long, long time ago, think it was in 2010, after I had returned from trip to Reading, (around 250 miles at motorway (ish) speeds). At this point the engine had only done a few thousand miles since the previous owner had a full engine rebuild at a renowned Stag specialist. Over the intervening years I replaced timing chains, tensioners, oil pumps, relief valve springs, jack shafts, water pump , heads (two different sets) etc. Nothing made any difference. Earlier this year, after 13 years of being embarrassed by the loud knocking, I decided to sort it once and for all. Tried process of elimination, shimmed the jackshaft "C" plate as I thought it could be end float of the jackshaft, removed oilpump drive temporarily to remove strain on the jackshaft, checked cam buckets for "slop" etc. all made no difference. So removed the heads, no evidence of valves contacting pistons. Then I noticed No. 2 piston was sitting proud of the block on one side. Further investigation revealed that I could rock the piston side to side. None of the other pistons did this. So pulled the block and stripped it all down. I found No.2 piston skirt badly scored and worn. Fortunately the bore was not too badly damaged and a light honing cleaned it up nicely. So I rebuilt it with new pistons, fitted new shells whilst it was apart. Refitted and now the knock has gone.

So the knocking was effectively "piston slap" on no. 2. But why?? Well when I got the new set of pistons (County like the old ones) I measured them and compared to the old set I removed. According to some numbers I found somewhere there should be around 2 thou clearance piston to bore on the pistons maximum dimension. The new set had exactly that. However, when I checked the "good" pistons from the old set I couldn't measure any clearance, they were effectively tight in the bore. I did measure all the bores top and bottom and all were spot on the dimensions for a +40 bore. So my conclusion is the old set of county pistons were oversized and after a fast hot run to Reading and back the skirt on No. 2 got a bit "tight" and picked up on the bore and then wore rapidly - leading to the sloppy fit and piston slap. I drove the car for a good few thousand miles with it knocking and it it didn't get a lot worse. I would also add that the car did not get hot - temp gauge stayed fairly central on the whole trip and it was filled with a good quality oil which had been recently changed.

PXL_20230430_174459221.jpg no 2. piston at TDC, note how clean it is around the top edge!

IMG-20230501-WA0013.jpg Severe scuffing and wear on the skirt.

[jbuckl]

I am pleased to report that I did eventually find the cause and effect a cure!

A brief history. The noise started a long, long time ago, think it was in 2010, after I had returned from trip to Reading, (around 250 miles at motorway (ish) speeds). At this point the engine had only done a few thousand miles since the previous owner had a full engine rebuild at a renowned Stag specialist. Over the intervening years I replaced timing chains, tensioners, oil pumps, relief valve springs, jack shafts, water pump , heads (two different sets) etc. Nothing made any difference. Earlier this year, after 13 years of being embarrassed by the loud knocking, I decided to sort it once and for all. Tried process of elimination, shimmed the jackshaft "C" plate as I thought it could be end float of the jackshaft, removed oilpump drive temporarily to remove strain on the jackshaft, checked cam buckets for "slop" etc. all made no difference. So removed the heads, no evidence of valves contacting pistons. Then I noticed No. 2 piston was sitting proud of the block on one side. Further investigation revealed that I could rock the piston side to side. None of the other pistons did this. So pulled the block and stripped it all down. I found No.2 piston skirt badly scored and worn. Fortunately the bore was not too badly damaged and a light honing cleaned it up nicely. So I rebuilt it with new pistons, fitted new shells whilst it was apart. Refitted and now the knock has gone.

So the knocking was effectively "piston slap" on no. 2. But why?? Well when I got the new set of pistons (County like the old ones) I measured them and compared to the old set I removed. According to some numbers I found somewhere there should be around 2 thou clearance piston to bore on the pistons maximum dimension. The new set had exactly that. However, when I checked the "good" pistons from the old set I couldn't measure any clearance, they were effectively tight in the bore. I did measure all the bores top and bottom and all were spot on the dimensions for a +40 bore. So my conclusion is the old set of county pistons were oversized and after a fast hot run to Reading and back the skirt on No. 2 got a bit "tight" and picked up on the bore and then wore rapidly - leading to the sloppy fit and piston slap. I drove the car for a good few thousand miles with it knocking and it it didn't get a lot worse. I would also add that the car did not get hot - temp gauge stayed fairly central on the whole trip and it was filled with a good quality oil which had been recently changed.

PXL_20230430_174459221.jpg no 2. piston at TDC, note how clean it is around the top edge!

IMG-20230501-WA0013.jpg Severe scuffing and wear on the skirt.

That will do it.

[Rog13]

Very interesting & thanks for all your responses.
Rog.