Hard Chrome Plating Main Bore Repair

[MotorMouth93]

I have a semi-rare block (Honda C30A from an NSX) with a substantial amount invested in it that has main bore issues. I bought the core block sight unseen and had it sent to a shop for MID sleeves, main studs, line hone, and timeserts in the decks and later a block shows up at my house several states away with beautiful sleeves and a main tunnel that's tapered by 0.0010", straight edge shows misalignment by about 0.0010-0.0015", and its out of round by 0.0030" at the parting lines. Would have been nice to know the block was garbage before slamming wet sleeves in it but whatever, have to work with what I have now. The caps show no signs of being clipped so I think they just ran the mandrel in long enough to make it sort of straight and called it good. I might be able to get away with running it but at this point I've been trying to get this block put together for almost 3 years so what's another few months to do it right. (Best investment ever was a 2nd engine for my car so I can keep driving it)

I've heard of plating (hard chrome, nickel maybe?) inside the main tunnel and building up maybe a 0.005-0.010" layer then line boring back to the proper size/shape. That seems like an excellent option compared fabricating a repair sleeve or welding and dealing with probably warping. Has anyone done this before or know of a shop that can do it? Or have any other suggestions for repair methods?

(The obvious solution is oversize OD bearings....but those don't exist for this engine. In fact, no aftermarket bearings exist, except for some from a Japanese company that cost $50/shell and only come in STD sizes.)

[Tom68]

Dunno about hard chrome, it obviously can be welded, but I'd be looking at boring it oversize to suit a thick wall bearing from another application.

[mag2555]

Go read up on something called hydrogen embrittlement.
This is a bad side effect that takes place whenever something is chromed, which makes me think that you will not want to go that route to repair/ get this block right.

I know this effect takes place with steels and cast iron, but I am not sure about Aluminum.

I think your best bet while certainly not cheap would be to over bore the housing for a bigger OD bearing of which when installed in the block could be cut back to its steel backing layer and then leave you with the needed straight housing bore needed to once again run stock bearings .

This is from what I recall was done years ago with SBC blocks to run a 350 main size crank in a 400 cid block.

[lefty o]

industrial hard chrome is a decent gun finish, im 99.999999999999999% certain it would not stand up to use inside an engines bore.

[PackardV8]

I have a semi-rare block with . . . a main tunnel that's tapered by 0.0010", straight edge shows misalignment by about 0.0010-0.0015", and its out of round by 0.0030" at the parting lines. . . . The caps show no signs of being clipped so I think they just ran the mandrel in long enough to make it sort of straight and called it good.

So what information are we missing here? If it wasn't properly line honed to your standards, why not just get it done right?

BTW, can't speak for the NSX, but most used blocks (especially aluminum) from good running engines will be out that much when pulled down for a refresh/rebuild. Like you, I wouldn't want to build it that way, but it would most likely run and last.

Mahle bearing crankcase tolerances:
•.001” bore out-of-round:
•.001” maximum if horizontal is larger than vertical
•.002” maximum overall misalignment (.001” for highly loaded engines)
•.001” maximum misalignment on adjacent bores (.0005”- for highly loaded engines)

[MotorMouth93]

So what information are we missing here? If it wasn't properly line honed, why not just get it done right?

The main bore is wider than spec by 0.0030" at the parting line and there are no oversize bearings available, so a huge amount of material would have to be cut off the saddles and caps to bring that back in which would move the crankshaft way up in the block.

There's a school of thought that says I should just run it. And it might be okay. But I don't want to do that even if the alternatives cost a lot.

[PackardV8]

The main bore is wider than spec by 0.0030" at the parting line and there are no oversize bearings available, so a huge amount of material would have to be cut off the saddles and caps to bring that back in which would move the crankshaft way up in the block.

Line boring can be done so as not to change the crankshaft centerline nearly as much as does line honing. When indicating the block, move the bar .0005" towards the block, then bore the cap, not the block until the last .001" and Mahle says that last .001" can stay wide at the parting line.

[KnightEngines]

Ignore the width at the parting line.
Get 80% clean up & call it good.
Line bore is preferable rather than line hone.

If being a bit wide at the parting line was a deal breaker then pretty much every line bored subaru is junk, but it's never a problem & I've done probably 100 or more of them.

[ec1]

Sounds like it just needs a typical line hone or line bore job. Who cares if the parting line is little wide is correct. But if you are picky and want to go down the rabbit hole of plating with hard chrome - it might be an option to copper coat it. Much easier to machine or hone back in. Just like the OEM's used to do with big or small ends of connecting rods and then rehone back to spec. Talk to a local chrome shop that can chrome aluminum wheels. Any decorative chrome shop uses copper and nickel under a very thin outer layer of chrome. I would probably dip the whole block in wax like the hard chrome shops do and cut off the wax where you need to add copper or whatever. I have used hard chrome for fixing camshafts in hard to find Industrial diesels with success. As in where the cast iron cam rides in the cast iron block with no cam bearings. In the end, line bore the cam tunnel till it cleans up and regrind the mains of the cam larger than original to fit. But when needing to fill space on an aluminum main bearing housing. I would use something softer than hard chrome. Basically you really need to know what you're doing and so do all of the other parties involved regarding plating a fully machined block.

[rebelyell]

So what information are we missing here? If it wasn't properly line honed, why not just get it done right?

The main bore is wider than spec by 0.0030" at the parting line and there are no oversize bearings available, so a huge amount of material would have to be cut off the saddles and caps to bring that back in which would move the crankshaft way up in the block.

There's a school of thought that says I should just run it. And it might be okay. But I don't want to do that even if the alternatives cost a lot.

seems you're no stranger to long-distance
Charlie Weston has a well-established reputation for solving complex "problem" block issues; Weston is at Piscataway, New Jersey.
couldn't hurt to call
http://www.westonmachine.com/

[MotorMouth93]

Thanks for all the suggestions guys, lots of interesting ideas here.

I like the copper idea, I've come across a lot of aviation bearing housing repairs using brush plating of softer metals like nickel and copper in my research so that is seeming like it might be a better option than chrome, it'll be in the saddles in the aluminum block only with new steel caps so load capacity shouldn't really be a concern. I need to call around to various machine shops and plating companies now as well as order a set of billet main caps. I'll give Weston machine a call too to see if they've dealt with something like this before.

[hoodeng]

Packard's suggestion of offsetting the line bore process to keep the upper bearing seat as close to original location is probably the best way to go.

As has been pointed out, hard chrome would be very difficult to apply and machine [you won't be line boring chrome] copper is the primary coating when chroming aluminium, this would still be difficult to achieve as you would be at the mercy of who is doing the plating knowing exactly what you need at the outcome.

Pictured is some chromed alloy covers that had plating over run in the rocker spindle bores [the platers were asked to mask out this area but didn't, i also know why] the only way to remove this material is to hone it out, very carefully, you don't want it to lift, this stuff destroys stones but it can be done,,, it just goes on the bill.

[modok]

I'm not familiar with that particular engine but I have line bored the main housings of many kinds of engines.
I'm imagining it is an aluminum block with iron caps, dowels in the caps......?
if so
It will be mainly the block side that has gone out of shape (both the housing and the parting surfaces)
Thus can be easier AND better AND faster to cut the block registers rather than the caps. Alarmingly simple when done the easy way.
Boring it should give far better results than attempting to only line-hone it. The crank might be moved up .003 approx, give or take depending on what is needed, but probably not a big deal besides possibly the oil pump or main seal might need to be manually aligned.
I'd say find somebody like me and have them fix it.

OR....if it is the type of design where the lower caps are all one piece aluminum casting and cutting that would ruin the alignment of everything then my enthusiasm may be reduced, but I have fixed those too.

Hard chrome or elecroless nickel on aluminum is very possible, but not practical. no need for it to be so hard. Copper would be fine but I've never seen that done either. You might be the first.

[ec1]

Oooh I forgot about the "brush plating"! I would love to see you try that along with line boring... I can't recall how much coating thickness you can achieve with the brush on...but I do know the regular copper electroplating like what they use at a bumper shop can go on plenty thick.

[MotorMouth93]

Hard chrome is no longer on my radar, just seems overly problematic compared to nickel or copper. Brush plating seems like a good option if done properly. I've talked to a few shops about it and nickel seems to be the preferred metal for brush plating on aluminum for bearing housing bore repairs , and I suspect that's because the process is simpler than copper if being applied with a brush rather than full part submersion. Thickness can go up to a few hundredths of an inch so building up 0.0050" or so shouldn't be an issue. Dipping the block in wax for a standard submersion type copper electroplating might not be a bad way to do it either though so I'll look into that as well.

I could just have the block line bored as a few have suggested but that'll still leave me way too much width at the parting line. Which is *probably* fine, but this particular motor family tends to put a lot of strain on the mains so I'd rather just try to get the dimensions as close to perfect as possible even if it takes a lot more work. This is my project engine, I've got a reliable running engine in the car and it only sees a few thousand miles a year so this can drag on forever if need be.