Motorcycle cylinder head

[Screwdriver]

Just to finish this off: the bike turned up today and I ground back the broken casting with a Dremel carbide bit. Looks like the previous stud had snapped off and been ground flush before being drilled out (off centre). Knocked out the remaining half crescent of steel thread and cleaned the alloy.

Then with 120A (foot pedal strapped to a log) started laying down some 4043 beads. Argon whacked up to about 25cfm because we're outside, heavily weighted -ve offset (position 2 out of 4 on the KEMPPI) to give me better cleaning.

Paused in between beads largely because I kept blowing the tip, either where a gust took away the shielding or the awkward angle meant I either dipped the tip in the puddle or touched the filler. Also to allow the head to cool. It never got too hot to touch because the head is of course water cooled anyway.

Once it was filled, filed down to flush and made a little jig from box section to match the existing (badly fitted) stud so I could drill it out and tap. The jig is bolted through the existing hole and lined up by eye, braced with a length of bar.

Plenty of meat on the newly welded piece but just look at the other stud hole! eww. it was tempting to re-do it out of principle but if it ain't broke...

It's a good solid repair though. Job done.

s.

 

[Pete.]

Good job!

Looking at the opposite drilled-out bolt it's not hard to see how they wrecked that one.

 

[Richard.]

Not an easy repair by any means doing it in situ. Very well done.

 

[RichardM]

Nice job, give it a clean-up and a bit of silver spray!

Race chains are made to last the race, any longer and you are wasting HP.

 

[arther dailey]

Thats a good repair, would it not be possible to add some weld to the thin side of the "good" stud hole, realise its virtually paper thin, and in one sence its just making work, just asking to gain more knowledge, if you fitted stud in hole first would that work? thanks Arther

 

[chevy2]

I do a lot of odd welding jobs for a local motorcycle repair shop,
done this or similar jobs plenty of times, often caused by overtightening by owners,

Always repair the heads in situ,
Normal rules apply of good precleaning before welding,

Clamp the broken piece in place and gently warm the surounding area with the tig torch for about 30secs to a minute using a fair bit of AC balance to remove the oxidants from the casting,
You don't need a huge amount of amps for repairs like this as the bosses are near the edges of the head, just over 100 amps is generally enough once its warm,
Only then start to add filler, always 4043, gradually creaping up on the heat so the weldpool doesn't become mudlike which is common on cast ali,
Once the boss has a full weld all around, then add a fair bit more heat and wash the weldpool out a bit wider for insurance.

 

[Screwdriver]

Thats a good repair, would it not be possible to add some weld to the thin side of the "good" stud hole, realise its virtually paper thin, and in one sence its just making work, just asking to gain more knowledge, if you fitted stud in hole first would that work? thanks Arther

Thanks. I had considered fixing the surviving bolt hole but that's a lot more awkward to get to. As it was , I was lying on my back, legs under the bike with the foot pedal strapped in the upright positing on an old tree stump. I would have to grind away a ton of rubbish, pull out the remains of the badly drilled out/off centre old stud (it was still in there on both sides). So on balance, since it was still solid, we decided to leave it. if it ever fails, then I can fix it...

I think you can weld aluminium around a steel stud but you'd have to get it pretty damned hot or the weld will freeze immediately. Again, more trouble than it's worth.

S.