Replacing crankcase bolts.

[stevo as b4]

My KMX 125 has a few crankcase bolts where the plating has corroded and they've furred up on the heads. I know I could try cleaning them up in situ with a mini wire brush etc and painting them.

But if I wanted to replace them with stainless steel bolts, would it be possible to change them in situ one at a time without risking either warping the cases or causing an air leak?

I'm dubious of this idea, and just wondered if it's madness or not to do this in the same way you do with aftermarket engine casing bolts?

[pepperami]

[MarJay]

I don't see an issue. You normally have to use quite a bit of force to separate crank cases anyway so removing one bolt at a time is not going to do any harm. As long as they are torqued correctly, and you don't try to ride the bike like that I can't see a problem.
____________________
British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.

[Robby]

Yes, your method will work. I wouldn't use stainless bolts though.

Stainless has three big pitfalls when used in aluminium alloy cases:
1. It causes the alloy to corrode more quickly. Aluminium oxide (corrosion) has around twice the volume of alloy, so the bolts get very tight.
2. Stainless is harder than mild steel, but more brittle - at least in the grades typically used for cheap-ish bolts. This means it snaps off more easily, and with less warning - often as a consequence of point 1.
3. Stainless is pain in the arse to drill. So when points 1 and 2 have happened, and you need to drill it, you have a much harder job.

I would either remove the existing bolts and clean them up then reinstall, or replace with new mild steel (preferably plated or galvanised) bolts.

For the sort of home project that I expect you would enjoy, because I know I would, you can buy home plating kits on ebay. So the original bolts can be cleaned up with acid or electrolysis (metal kitchen sieve to hold the bolts and avoid wiring each one up in electrolysis) and then plated.

As a very lazy man, I prefer to clean things using chemistry than wire brushes.

[Islander]

Use passivated high tensile steel rather than stainless. If you use stainless with alloy then you're likely to get galvanic corrosion that may cause the bolt to sieze in the block.

[stevo as b4]

Cheers folks for the input and advice, and the wisdom about stainless bolts too.

I can probably just take out and clean up or replace the 3-4 bolts with the issue, and I'll do them in the old one at a time method so hopefully won't have any issues with air leaking or warping of the faces.

Robby, your actually right and have given me a good idea of what to get myself for Christmas too. If a diy cleaning and plating tank is not too huge, then yeah I'd really like to have a go at renovating my old bolts. I've got 2spare engines and a another bikes worth of bolts I could put it to practice on.

Would be nice to do more in house restoration on some bikes too, like paint spraying (have a compressor and a hvlp gun already). Wheel building too, as that would save a packet on a cheap and cheerful off roader resto project.

Out of interest, what types of plating can you do diy, I.e is there a choice of plating solutions available for diy set ups?

Oh and final question is, how does titanium compare with stainless for corrosion resistance in alloy castings? Is it better or worse?

[Islander]

Titanium? Why?

Imagine one becoming seized for some reason. Now imagine trying to drill it out...

Passivated steel.