To hone or not to hone?

rorz12 · 08-25-2023, 12:36 PM

I recently switched out my stock downpipes for cattless downpipes, and now I have white smoke coming out of the exhaust whenever I'm idle. When I had the stock cats on, I'd only see the smoke if I idle for like 10min and then give it a hard rev.

I tried some oil additives to recondition the valve seals and it worked great until I did another oil change. So it was only masking the issue by thickening the oil and it didn't really solve anything.

I decided to have the valve seals replaced. Dropped off car at the mechanic and he went one step further and removed the heads. The drivers side bank cylinder walls have some scratches which he thinks have been caused by bad piston rings. The passenger bank walls are pretty much fine with no scratches.

If you run your fingernail over the scratches you can feel them. Fingernail doesn't get stuck/caught in them though. Mechanic is saying we can have them polished/honed without having to go to oversized pistons and rings.

My understanding though is that these alusil blocks are difficult to hone and so I am wondering if I should just change the piston rings and rod bearings and don't recondition the walls? safer? The interwebs seems to say that replacing the valve seals should resolve the white smoke issue. And I'm wondering how much difference I'll actually benefit/feel by honing the walls..

What do you think?

Opie55 · 08-25-2023, 02:47 PM

That's probably a question for an experienced engine rebuilder. Only real-world experience can tell you the effect of scratches like that. But question one is how many miles does the car have and how long are you planning on keeping it? And question two is how much will he charge to do it?

rorz12 · 08-26-2023, 03:09 AM

Quote:

Originally Posted by Opie55

That's probably a question for an experienced engine rebuilder. Only real-world experience can tell you the effect of scratches like that. But question one is how many miles does the car have and how long are you planning on keeping it? And question two is how much will he charge to do it?

It has about 111K KM or 69K Miles. I'd like to keep it for a few more years but depends if I'll have to relocate for my job or not which is a bit unknown right now.

So my mechanic will send off the cylinder heads to a specialist to press in new valve guides (because there is too much play in the valves and new seals would wear quickly again) and recondition the valve seats for $550. He reckons he can get the guy to polish the cylinder walls for no extra cost

So strange that the scratches are only on the driver's side.

SWFLf10 · 08-26-2023, 06:49 PM

I would definitely hone while it’s all apart. I would worry that the damage will only grow if left as is.

08-25-2023, 12:36 PM	#1
rorz12 Private First Class 19 Rep 106 Posts Drives: 2013 BMW 650i Gran Coupe Join Date: Sep 2022 Location: Qatar iTrader: (0)	To hone or not to hone? I recently switched out my stock downpipes for cattless downpipes, and now I have white smoke coming out of the exhaust whenever I'm idle. When I had the stock cats on, I'd only see the smoke if I idle for like 10min and then give it a hard rev. I tried some oil additives to recondition the valve seals and it worked great until I did another oil change. So it was only masking the issue by thickening the oil and it didn't really solve anything. I decided to have the valve seals replaced. Dropped off car at the mechanic and he went one step further and removed the heads. The drivers side bank cylinder walls have some scratches which he thinks have been caused by bad piston rings. The passenger bank walls are pretty much fine with no scratches. If you run your fingernail over the scratches you can feel them. Fingernail doesn't get stuck/caught in them though. Mechanic is saying we can have them polished/honed without having to go to oversized pistons and rings. My understanding though is that these alusil blocks are difficult to hone and so I am wondering if I should just change the piston rings and rod bearings and don't recondition the walls? safer? The interwebs seems to say that replacing the valve seals should resolve the white smoke issue. And I'm wondering how much difference I'll actually benefit/feel by honing the walls.. What do you think? Attached Images
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08-25-2023, 02:47 PM	#2
Opie55 Colonel 1195 Rep 2,907 Posts Drives: '15 650i Convertible Join Date: Apr 2018 Location: US iTrader: (0)	That's probably a question for an experienced engine rebuilder. Only real-world experience can tell you the effect of scratches like that. But question one is how many miles does the car have and how long are you planning on keeping it? And question two is how much will he charge to do it?
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08-26-2023, 06:49 PM	#4
SWFLf10 Captain 374 Rep 639 Posts Drives: 2016 Alpina B6, 2015 535i Join Date: Jun 2018 Location: Florida iTrader: (0) Garage List 2016 BMW Alpina B6 ... [10.00] 2015 BMW 535i [8.83]	I would definitely hone while it’s all apart. I would worry that the damage will only grow if left as is.
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