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Best Way To Repair Crankcase


gazzaecowarrior
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I wish i had spotted it when i bought the bike but i didn't. There is about an inch square missing from the bottom outer edge of my right hand crankcase where the flywheel cover meets the crankcase. Bike is an 04 125 Beta. What would people recommend to fix it ? Could the case be welded in situ or would the case have to be split and then welded ? Anybody had any success with chemical metal type materials ? Any ideas would be most appreciated. Gareth

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Welding crankcases can be difficult. It can warp them and cause problems with fitment against the other half, and also bearing seating etc.

It can be helped by pre heating the cases before welding to help spread the heat dispersion. If you are missing a whole section, it will require a lot of welding to build up the missing area, and this will generate a LOT of heat. If you want to attempt it, I would personally split and strip down the case half.

Make sure you find a good TIG welder, and discuss your concerns about warping.

On the other hand...that is a lot of work. I would probably look into a way of repairing the hole with, say, a thin curved piece of alloy or plastic and epoxy metal. It only needs to stop dirt getting in. I have a 2012 evo, and the flywheel cover lets loads of water in. I just take the cover off after every trial, or wash, squirt WD40 in, blow it out with the airline and let it dry. I would make the repair on the outside though, as you dont want anything picking up on the flywheel and doing damage.

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Welding crankcases can be difficult. It can warp them and cause problems with fitment against the other half, and also bearing seating etc.

It can be helped by pre heating the cases before welding to help spread the heat dispersion. If you are missing a whole section, it will require a lot of welding to build up the missing area, and this will generate a LOT of heat. If you want to attempt it, I would personally split and strip down the case half.

Make sure you find a good TIG welder, and discuss your concerns about warping.

On the other hand...that is a lot of work. I would probably look into a way of repairing the hole with, say, a thin curved piece of alloy or plastic and epoxy metal. It only needs to stop dirt getting in. I have a 2012 evo, and the flywheel cover lets loads of water in. I just take the cover off after every trial, or wash, squirt WD40 in, blow it out with the airline and let it dry. I would make the repair on the outside though, as you dont want anything picking up on the flywheel and doing damage.

Thanks for that info. Totally agree with you regarding the welding. If it were a

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If you weld it strip the case of all parts and then put the empty cases back together, this would help eliminate warpage

But if it were mine I would use epoxy of some sort, don't try to do it all in one gob, do some let it dry then lay another strip

Or cut an adequately sized piece of aluminum to fit as well as possible then glue it in place

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There is an epoxy metal solid that comes in tube and is two sections of modeling clay consistancy that one kneads together. It is tough stuff and may ground, sanded and painted when hard.

May be moulded into any shape, prolly would need to rough up surrounding metal to get some adhesion. Think of using something of ali beer can to maintain inside radius of the form, remove it later.

Just thoughts!

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If you do the epoxy bridge method you could use a very fine gauze on the inside (so it does not catch the flywheel) and build up with epoxy liquid metal. I am guessing that as the damage is next to the mounting rubber and therefore bolt hole??

If it is it will always be weak and probably flex which will mean the epoxy plate will fall out when the bash plate is next whacked hard. A flexible method may be better but I can't think of a decent method just now.

Edited by pindie
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If you do the epoxy bridge method you could use a very fine gauze on the inside (so it does not catch the flywheel) and build up with epoxy liquid metal. I am guessing that as the damage is next to the mounting rubber and therefore bolt hole??

If it is it will always be weak and probably flex which will mean the epoxy plate will fall out when the bash plate is next whacked hard. A flexible method may be better but I can't think of a decent method just now.

Thanks for that

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One product I have used consistantly over the years is J-B Weld (see jbweld.com). It is a two part epoxy and once hardened you can drill, grind or machine it. Works great on engine cases.

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  • 2 weeks later...

One product I have used consistantly over the years is J-B Weld (see jbweld.com). It is a two part epoxy and once hardened you can drill, grind or machine it. Works great on engine cases.

Just used the JB Weld.Amazing stuff. Took a day to go off properly as it has been so cold. . Looks good after sanding. many thanks.

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