Small defect in cylinder wall, getting opinions

[cmsanford88]

Hi All, working through a restoration on my first 2002. I recently got the engine back from machining and was looking everything over. I had the block bored to 89.5 for 9.5 piano top pistons. I found this small casting defect or pit in Cylinder 1. It's about 2 inches from the top of the block, can just feel it with a finger nail. This is the first engine I've done a full teardown and rebuild on, wondering if this is acceptable or if I need to call up the machinist. 

 

Thanks

Chris 

 

 

Edited July 22, 2023 by cmsanford88

[tech71]

Yeah some pitting there, others may disagree but since you are already committed  and have the pistons (I assume)

I say press on, I've seen worse in engines that ran and performed just fine.

Nothing the machinest can do for you cept bore up to last oversize, then the search for pistons begins again.

Edited July 22, 2023 by tech71

[visionaut]

Surface roughness = .003-.004mm

 

I assume that’s 2nd rebore at 89.515mm

[jimk]

If it is used as it, it'l be an oil burner.  To salvage the block and use the pistons you have, it will need to be sleeved.  And sleeving one hole doesn't work because when boring for sleeve install, Cyl 2 becomes distorted.

Been there.

 

[cmsanford88]

Thanks for the input guys. I do have pistons already, and yes they're 2nd oversize. What's people's take on sleeving vs a new block? The thought of sourcing, shipping and machining another block only to have a similar problem is obviously not appealing. 

[jimk]

11 minutes ago, cmsanford88 said:

What's people's take on sleeving vs a new block?

Sleeved one, no issues.

[Conserv]

1 hour ago, jimk said:

Sleeved one, no issues.

+1

 

Sleeved the #1 cylinder of my ‘76’s block. No problems have arisen. But, to Jim’s point, the re-boring was done after the installation of the sleeve, so we’ll never know what effect the sleeve installation had on cylinder #2.

 

Regards,

 

Steve

 

 

[Mike Self]

2 hours ago, Conserv said:

But, to Jim’s point, the re-boring was done after the installation of the sleeve, so we’ll never know what effect the sleeve installation had on cylinder #2.

Isn't that's what an interior micrometer is for?

 

This situation is a strong argument for wet liner engine blocks...

 

mike

[Conserv]

3 hours ago, Mike Self said:

Isn't that's what an interior micrometer is for?

 

This situation is a strong argument for wet liner engine blocks...

 

mike

I wasn’t clear, Mike,

 

My point is that, if inserting a sleeve in cylinder #1 had an effect on cylinder #2 — I don’t know if it did or did not have any such effect — the re-boring of all four cylinders to second oversize corrected it, because it occurred after the sleeving.

 

But if you’ve already re-bored to second oversize, you do need to be concerned that the sleeving process could conceivably have an effect on the adjacent, freshly-bored cylinders.

 

Best regards,

 

Steve

 

[Mike Self]

1 hour ago, Conserv said:

But if you’ve already re-bored to second oversize, you do need to be concerned that the sleeving process could conceivably have an effect on the adjacent, freshly-bored cylinders.

Agreed...what I was saying that after sleeving the one offending cylinder, using an internal micrometer could determine if the sleeving process had distorted any adjacent cylinders, which would require sleeving them even though their original cylinder walls were not pitted.  Sleeving only one cylinder to correct a problem or damage isn't uncommon...I have a spare B model Fiat Topolino block with a very bad gouge in #3 cylinder, but I know it can be bored and sleeved with a standard-sized dry liner to match the three good cylinders; otherwise it would be scrap iron.

 

I wonder if those pits in Chris' cylinder wall could be arc welded with a nickel rod, then have the boring bar run back through to smooth the weld down.  I once watched a machinist weld up the teeth of an 8 foot diameter punch press gear using nickel alloy welding rod.  Once the teeth (well over 150) were built up, they'd each be machined back to size.  The punch press (originally steam powered) dated from 1865 (!) so spares were NLA--and this process was a whole lot cheaper than buying a new punch press.  Could that be done to a cylinder wall?

 

mike

mike

[TobyB]

I would be soooooo tempted to try building an engine from that block.

 

But I'm an outlier.

Sleeving's a good idea, in this case.  And Mike's right on- since it's already bored,

you may be in for 4 sleeves IF the process distorts the other bores.  But this is

a machinist- level question for a machinist who's comfortable with sleeving.

Not necessarily a BMW specialist, fwiw.

 

t

 

[visionaut]

On 7/22/2023 at 11:50 AM, tech71 said:

I say press on, I've seen worse in engines that ran and performed just fine

1 hour ago, TobyB said:

I would be soooooo tempted to try building an engine from that block.

Me too, lol.

 

becuz:

there’s only a small total radii loss (swept area) on only one cylinder

 

that cylinder is fresh honed and not worn around the pitting 

it’s not severe vertical scoring, it’s not near the top of piston travel 

 

the splotchy geometry of the larger right pit switches the leak radially as the piston travels

 

the purely horizontal geometry of the small gash lowers the leak exposure time seeping past it

 

i’m thrifty and stubborn

 

the party was all ready to go

 

how much oil we talkin’? 🫠

 

Tom-too

 

 

[tech71]

OP what does/ did your machinist say about it?

Seems that would be a pertinant opinion.

[66Vette]

I agree with tech71.  Talk to the machinist, better yet, take the block to him.  If it is just a pit in the cylinder wall and doesn't suggest anything more serious, I believe your machinist will have zero concerns.

 

It is hard to tell, but the pictures show some other marks.  Have your guy bless it.

[Preyupy]

The problem with using a block with rusty bores is you don't know how deep the pits are until you bore it.  I usually have the machine shop do a rough bore and keep going until they get clean metal THEN order the pistons for the closest size over that.  Then do the final bore and hone to fit the pistons once you have them in hand.    The horse is already out of that barn.  I would talk to your machinist and see what he says.  I'm a bit surprised he didn't mention this when you picked up the block. 

 

The options are 1) assemble it as is and see if it smokes.  If not, you lucked out and you are good to go.  2) Find another block. THAT WILL CLEAN UP at 89.5mm bore!  3) Sleeve it, one cylinder and see if it changes the cylinder(s) on either side of it.  More than one cylinder if needed.  By the time you put in 4 sleeves you have more than paid for a different block and had it bored.