Author Topic: Noisy tappets - how bad can it be ?  (Read 8078 times)

carrera

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Re: Noisy tappets - how bad can it be ?
« Reply #90 on: 09 February 2020, 02:36:08 PM »
Prepare yourself for distressing pictures :)

Head off, sump off, pistons released into the wild.

As I mentioned number 4 had noticeable rock, here's a photo of it.

On every piston the oil control ring seems to be stuck in the groove. I haven't tried releasing the rings yet. Small emds seem perfect with no play on the gudgeon pins

The bore is also scored, I have yet to measure it up so see if it will hone or needs more drastic action

First thoughts are that infrequent oil changes / lack of oil cause the oil control ring to jam in the groove causing this type of damage ?



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sgould

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Re: Noisy tappets - how bad can it be ?
« Reply #91 on: 09 February 2020, 07:38:56 PM »
Ouch! :(
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carrera

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Re: Noisy tappets - how bad can it be ?
« Reply #92 on: 09 February 2020, 08:43:35 PM »
I've seen worse !

The scuffing is on one side only.

I put a bore gauge down, and it seems that the bore will clean up with a hone.

Rings have been removed from number 4. I'm really quite impressed that the oil control ring is a 3 piece item

The little end and gudgeon pin have been separated and are practically perfect.

Initial measuring showed that the piston itself was an AB piston and dimensions seem standard. I'm coming to a view that low oil led to loss of the oil protection on number 4, causing the scuffing and a bit of metal exchange between the bore and piston.

Question is, will a replacement piston (assuming weight match) solve the problem. I think I need to drop on of the other pistons into number 4 bore to see if it rocks or not.

I also found a good read here http://www.boosttown.com/engine/piston_damage.pdf, not Saab specific, but a decent guide none the less.

Any other ideas or experience ?

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sgould

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Re: Noisy tappets - how bad can it be ?
« Reply #93 on: 09 February 2020, 09:46:45 PM »
My only experience of this sort of thing is on the diesel engine that had the piston I posted earlier in the thread.  The engine needed a rebore though, and the engineering company bored the damaged cylinder at the limit of tolerance on the offset to remove some scoring caused by the broken ring.  I rebuilt the engine with one size oversize pistons.  The crank was just polished.  The engine ran for a year or two later and was still going well when I sold it.

If you do need to go oversize, I've heard that there have been attempts to bore out the engine to 2.5 litres but there are no head gaskets to suit, and if the standard 2.3 litre gasket is used the projecting edge gets burnt. It's quite a pronounced overhang, a bit over 1.5mm, which is a lot more than an oversize piston, but I don't know how much gasket overhang is allowable.
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carrera

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Re: Noisy tappets - how bad can it be ?
« Reply #94 on: 02 March 2020, 12:09:01 AM »
A little progress today.

Having found my piston ring compressor (don't ask), I popped number 1 piston in the number 4 bore. Though there was some piston rocking it was clear that having all three rings working instead of just one provided the support to prevent the piston touching the bore.

The hypothesis that stuck rings allow the piston to pivot on the small end and make wall contact seems to be viable

Now I just need to know the wear limits for the bores, see the other thread I made just for that question.
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carrera

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Re: Noisy tappets - how bad can it be ?
« Reply #95 on: 14 March 2020, 05:57:36 PM »
I have managed to get a couple of hours on this again. Haveing measured the bores up I decided to hone number 4 to see to what extent it could be cleaned up and what it measured when done. My honing stone reached end of its life so I had to stop and this is what it looked like at that point. An awful lot has been removed, but there are still some scratches visible.  They are quite hard / virtually impossible to feel though.



And just for interest I noticed evidence of the same piston slap at the top of the piston stroke on the other 3 cylinders. Is this "normal / expected", or unusual, caused by having the oil control rings in the pistons stuck in the groove on all the pistons. Yopu can just see it in the photograph, just below where the original cross hatchings disappear



« Last Edit: 14 March 2020, 07:02:06 PM by carrera »
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carrera

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Re: Noisy tappets - how bad can it be ?
« Reply #96 on: 22 May 2020, 06:11:26 PM »
I bet you had almost forgotten about this little task  ;D

JTC has provided me with a piston from a broken engine which I cleaned up and made was of the same class as the other pistons in the engine. The good news is that they are of the same "AB" piston type.

I cleaned the piston and weighed the piston (with rings and one gudgeon retaining ring), and then the combined assembly with rod, details as follows:

Original            422g + 943g = 1365g
Replacement    424g + 942g = 1366g

When I do replacement piston + old rod the answer becomes 424g + 943g = 1367g

That's good enough for me at the moment  :thumbsup:, and it indicates that the original piston has lost 1-2g of material onto the bore walls. Time for some evidence:

I haven't worked out what the discolouration marks are yet on the replacement piston ???

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carrera

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Re: Noisy tappets - how bad can it be ?
« Reply #97 on: 21 June 2020, 08:05:02 PM »
Another month and no real progress, but I do have a shopping list for a full rebuild because that's what this is looking like

Block
s/h Piston
Big Ends
Mains
Head gasket kit inc valve stem oil seals
Timing chain kit
Balance chain
Balance shaft bearings
Clutch
Slave / release bearing
Oil
Coolant
Subframe bushes
Crank polish
Piston rings
Oil pump
Head bolts

Some of the things are "while you are in there" type stuff.

I'm not intending to put Wossner pistons in

Have I missed anything ?

Any other thoughts
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sgould

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Re: Noisy tappets - how bad can it be ?
« Reply #98 on: 21 June 2020, 08:52:43 PM »
Engine mounts?

While it's all out and you have plenty of room, I would be looking at the aircon pipes and the power steering pipes.  My aircon failed when the pipes were removed, possibly by the dealer replacing the power steering, and they broke all the plastic clips and the aircon pipes rubbed through on the auto gearbox cooling pipes.  It won't be these that it rubs on if you have a manual gearbox, but there are other bits around.  The garage that fixed the aircon fitted all the clips but still got it wrong and the pipes rubbed through on the bodywork... ::)

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