Motorcycle crankcases

[RED1]

I have a problem - the two pics that follow are the alloy upper crankcase of my Honda CB750 made in 1973/4 or thereabouts.

The bike was apparently used for engine testing in the 70's by a London based dealer and various bits of equipment/sensors were fitted - hence the drilled holes in crankcases - now filled with the three brass bolts shown in photos.

My question is how best to plug these holes? I'm currently rebuilding the bike and as the brass bolts are a relatively loose fit - would like to have the holes welded up if possible. What do you think? Is this a goer or should I resign myself to trying to make the bolts oiltight or ditch the cases and get replacements?

Can I weld the material with my Clarke 100e using appropriate gas and wire? The alloy at each hole is approx 5mm thick.

cheers all

 

[runnach]

Hi Red, personally I would tig weld, cast looks clean enough, so can't imagine any probs filling up the holes. if you do decide to use your mig machine, you will require pure argon shielding gas, alloy wire, 5053 grade is best, as not as soft as 4043 grade. Using either process, make sure cast is clean as possible prior to firing up.

HTH n cheers.........

 

[shenion]

Hi Red, personally I would tig weld, cast looks clean enough, so can't imagine any probs filling up the holes. if you do decide to use your mig machine, you will require pure argon shielding gas, alloy wire, 5053 grade is best, as not as soft as 4043 grade. Using either process, make sure cast is clean as possible prior to firing up.

HTH n cheers.........

5053 is not supposed to be used on anything that runs at over 150F. Something about the magnesium causing cracks in the edge of the weld.

Although I have seen users that claim it worked fine on alum heads. It seems to be dependent on the base metal.

Use 0.9mm 4043, it will feed just as well as regular MIG wire.

 

[Drains]

It'd be worth making ally plugs to fill the holes and welding them in, rather than just filling the holes with weld:- less weld, less heat, less potential for weld-related problems.

 

[Paul.]

Thats a job for tig, I do quite a few repairs like this, & rebuilding broken lugs, repairing stripped threaded holes etc, I would probably cut a round plug from a piece of ali bar and weld it from both sides, at least then you have new clean metal in part of the weld,

 

[fingers99]

I'd go with TIG Paul: the alloy on bike castings is usually very good quality (especially on Japanese and Italian stuff).

MIGing it with a home MIG and without a lot of experience is likely to make a mess.

Depending on the finish of the castings you can either polish or tap a peice of glasspaper against the cases to get a sandcast effect.

 

[snowcat]

Are these a pure casting then??? rather than Mazac, Die Cast etc

 

[Paul.]

Engine & gearbox casings tend to be cast ali, its usually the smaller castings such as carb bodies that are found to be zinc based die cast, a quick touch with the tig torch or even a gas welding torch will soon determine what it is,

 

[Hitch]

Yep, i'd deffo go with the TIG. As said, stuff like this normally welds nicely. If it doesnt, its proabably down to oil contamination. Yours lokks nice and clean though.

 

[RED1]

Thanks folks - the message is loud and clear then - TIG only, now all I have to go is find a good local TIGger as the job seems a bit delicate for moi.

OK next daft Q - anyone know a REALLY GOOD welder (tig obviously) within the Glasgow/Edinburgh/Inverness triangle

I'll explain the geography later

 

[rja52]

I've only just joined this site and wouldn't want to disagree with anyone...but are you sure welding is the best way...personally, I'd cut an approximate thread on a piece of ally bar, screw it in, cut it almost flush and peen it over both sides...I'm assuming you're going to repaint the cases. I'd try as hard as possible to avoid any distortion....see from the pic that it has the usual oil leak from the case bolt by the way!

 

[Paul.]

I've only just joined this site and wouldn't want to disagree with anyone...but are you sure welding is the best way...personally, I'd cut an approximate thread on a piece of ally bar, screw it in, cut it almost flush and peen it over both sides...I'm assuming you're going to repaint the cases. I'd try as hard as possible to avoid any distortion....see from the pic that it has the usual oil leak from the case bolt by the way!

That may be an alternative on a difficult to weld material, or even threaded insert as well as welding, Id still weld where possible though, the casting would need to be thick enough to get a decent thread in, and peening may cause stresses around the repair area, peening compresses and stretches material, welding shrinks it on cooling,

 

[runnach]

Thanks folks - the message is loud and clear then - TIG only, now all I have to go is find a good local TIGger as the job seems a bit delicate for moi.

OK next daft Q - anyone know a REALLY GOOD welder (tig obviously) within the Glasgow/Edinburgh/Inverness triangle

I'll explain the geography later

If yer no in too much of a hurry I can nail it nae bother

 

[RED1]

If yer no in too much of a hurry I can nail it nae bother

No hurry apart from my impatience - mind you it has been waiting for 10 years or so to get done

I'll PM ya
cheers
Iain

PS - I have relatively infrequent Oban - Edinburgh jaunts. Do you dive over this way at all?

 

[SC_BK]

Thanks folks - the message is loud and clear then - TIG only, now all I have to go is find a good local TIGger as the job seems a bit delicate for moi.

OK next daft Q - anyone know a REALLY GOOD welder (tig obviously) within the Glasgow/Edinburgh/Inverness triangle

I'll explain the geography later

I'm nr Inverness and a couple years ago had a brake calipper lug snap on a cast alloy casing on one of my bikes. Spoke to a lad I knew at a local fab shop, he said it was do-able with a tig but would never be as strong as original so I ended up getting a whole used casing off ebay.
BUT that had to take a lot of stress.
I'm sure they'd be able to weld up that holes for you, though I feel runnach might be the cheaper option

If it's any help I'm constantly doing laps of Scotland, rare for me to be in the Oban area though

 

[runnach]

No hurry apart from my impatience - mind you it has been waiting for 10 years or so to get done

I'll PM ya
cheers
Iain

PS - I have relatively infrequent Oban - Edinburgh jaunts. Do you dive over this way at all?

G'mornin Iain, I have done the Edin>Oban red eye jaunt on many occasions, not been for a while though, due to other commitments unfortunately. Drop me a line and we can sort something out for plugging yer holes

Cheers...........

 

[runnach]

I'm sure they'd be able to weld up that holes for you, though I feel runnach might be the cheaper option

Oh cheers SC_BK, someone told you I'm cheap as chips

 

[Weldingartisan]

I do quite a lot of ally gearbox casing repairs (mainly VW diffs exploding). Difficult to tell the ally quality/oil saturation by looking. With holes like yours I would clean with B.C. (brake cleaner) countersink the hole to leave a 1-2mm root face, pre-heat and TIG using 5356 filler. Access is often restricted to one side, hence the prep. W/A

 

[warp speed]

I had an old RM250 casing tig years ago, the butcher didn't line up the edges before welding. it would only have taken a few minutes on a flat surface to get it right.
oil-leak-tastic.

--
Warp factor zero
www.daviddudgeonstudios.com