M42 Block Reconditioning

[KenC]

My #4 cylinder died (fouled plug, stuck open injector or a combo of the both), so I decided to just re-ring all of them and recondition the block a bit.

I'm planning on buying a flex-hone (dingle-ball hone), and de-glazing the cylinder walls. I think the cross-hatching still looks pretty good, so it shouldn't need a machine shop hone. What do you guys think?


#4 is the closest one to the camera. The little jagged line near the top of the bore isn't palpable at all... I'm not sure what it is.





Again you can't feel that little line at all, so I'm thinking the flex hone will clean it all right up.

[dude8383]

The hone will probably clean that up, might as well go up a size for the pistons.

[twistednut]

Yes you need to hone the cylinders for the new rings to properly seat. I am using one of those flex ball hones.

[StereoInstaller1]

If the cross hatch was that clean in my block, I would measure for round and put it together, assuming it passes.

Ken, I think your rings never seated.

Luke

[KenC]

The hone will probably clean that up, might as well go up a size for the pistons.

Up a size for the pistons? I'm assuming you mean bore it, and get larger pistons. Not doing that.

[KenC]

Yes you need to hone the cylinders for the new rings to properly seat. I am using one of those flex ball hones.

PM sent

[BenM]

Just an FYI, Honing and flex honing are 2 different operations. But to answer your question, a flex hone should clean up and even it doesn't is an inexpensive thing to try before having a machine shop rehone and/or bore and hone the block.

Also make sure you order the right grit you need to achieve your desired finish.

HTH,
Ben

[KenC]

Just an FYI, Honing and flex honing are 2 different operations. But to answer your question, a flex hone should clean up and even it doesn't is an inexpensive thing to try before having a machine shop rehone and/or bore and hone the block.

Also make sure you order the right grit you need to achieve your desired finish.

HTH,


Ben

Any recommendation on the grit. I've seen 240 as a pretty common one.

M42 stock Goetze brand rings aren't moly, are they?

[dude8383]

Up a size for the pistons? I'm assuming you mean bore it, and get larger pistons. Not doing that.

correct me if i'm wrong, but shouldn't you go up one size if you hone the block? you'd have to go up a size so that the seal remains within spec. right?

http://www.realoem.com/bmw/showparts.do?model=AF93&mospid=47305&btnr=11_1336&hg=11&fg=20

i might be wrong, i've only built one motor

[BenM]

Any recommendation on the grit. I've seen 240 as a pretty common one.

M42 stock Goetze brand rings aren't moly, are they?

Can't say I have experience with building engines so I can't say for sure, but it seems that 240 grit is relatively mild and I'd start with that. If that doesn't do it, I would lightly try 180 or even 120 if you're bold, but just be very careful if you are using an oversized flex hone. 240 should take the mark out after a few swipes.

I work with swaged and machined (slots, holes, grooves, etc.) aluminum tubes and we typically use flex hones to remove burrs that worn mills or drills can leave in the inside of the tube, at the bottom of particular slots or holes.

correct me if i'm wrong, but shouldn't you go up one size if you hone the block? you'd have to go up a size so that the seal remains within spec. right?

http://www.realoem.com/bmw/showparts.do?model=AF93&mospid=47305&btnr=11_1336&hg=11&fg=20

i might be wrong, i've only built one motor

You'd have to be pretty damn aggressive to hone out a block +.25mm or about .010"! I mean it could be done, but typically you wouldn't take that much off. You would just bore it to .001-.002" less and then hone it to size.

Flex honing is completely different than honing.

[dude8383]

You'd have to be pretty damn aggressive to hone out a block +.25mm or about .010"! I mean it could be done, but typically you wouldn't take that much off. You would just bore it to .001-.002" less and then hone it to size.

Flex honing is completely different than honing.

You're right, I'm a noober goober. Flex-honing is probably what Ken is going after.

Am I right that if one were to hone the cylinder bore, you'd have to go up a size?

[StereoInstaller1]

You're right, I'm a noober goober. Flex-honing is probably what Ken is going after.

Am I right that if one were to hone the cylinder bore, you'd have to go up a size?

Depending on just how out-of-round the bores are to begin with.

Old school BS rebuilds get "knurled" pistons, as when the grooves are cut, it makes the piston "larger" so it can fit the bore...for a few thousand miles if you are lucky.

[KenC]

Just bought the 240grit flex-hone... I'll take pics for you guys. Thanks for the input.

[3bvert]

yes knurled is old school, but it does work a bit
decent rings make a difference
out of round is a possible to happen

but sometimes you can just hone em, new rings and get many thousand out of a old engine

for a cylinder that ws done to 40 pounds pressure, the walls look pretty good,

honing stone will remove the top ridge better then "dingle-berries"

werent you geting the engine hot tanked ? wht did the machine shop think