Author Topic: Noisy tappets - how bad can it be ?  (Read 5156 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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