Yes i agree with you, it can be done welding but how much fun is it paying for welding and when you come home you cant get the rockershaft in... Tommorow iam taking the bike out for fun again, i also hate to have things like that hanging around with everything else in perfect condition. Looking forward to hear what happens JJ.

Jens you have over 100k on your bike and no crack?

I've got no oilleak's, havent looked for cracks, but didnt notice any when I rebuild the topend at around 125.000km. Im around 148.000 now.

I will look next time im messing with the bike.

As someone suggested, mount some bolts from inside, and mount nuts on the outside, so you dont overload/stress the top cover.

But I must say, this is the first I've ever heard about this. Theese bikes has been around for ages, even the newer ones are over er 10 years old.

Cant wait to se the solutions you guys come up with, and if it helps.

Damn 148k thats amazing, in my early days there was this transalp with 200k with no rebuild. I dont know about putting weight on each ear like that, better off with sleeve inside. What did you do in the rebuild?

The XT600 Thread - Page 359 - ADVrider

Look here for solution to your cracked rocker box.

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'84 XT600 is now bored to 2nd oversize and new OEM pistons and rings installed. No more smoking.

Bored/honed the cylinder, new piston with rings, and a new camchain since I was in there.

Theres an xt600 here in Denmark which got 250.000km on the clock before the first rebuild. A think it was from 1986, its one owner, and used for commuting.

well, couldnt resist the urge to, first check if my xt600 suffered form the same crack (even if there were no leaks) and second, check if the solution of two bolts in order not to compress the ears could work.

Well, it does! about one hour of work, not exactly super easy, but reasonable for anyone with good hands.

So the easy way of fitting from the inside two M10 allen bolts like i did in my XTZ/TZ supermono racer can not work. the distance between the ears in the XT motor is smaller and after you fit one bolt there's no room to fit the other one.
So went the other way around, with nuts on the inside! thing is that the width between the ribs is about 15.8 mm, smaller than the width of an M10 nut which is 17mm. ground two nuts on a sanding belt + some dressing, and it works like a charm. A bit tricky to put back because of lack of space around but it's all back together and i could hear the head releasing a sigh of relief for not being stressed between her ears

Took photos too, just bit busy this evening, Brazil vs. Germany in TV, will post in the next few days.

It wont help those with the crack, but could be good prevention for all others. Maybe the admin will want to make out of it a sticky: "Turboguzzi's head fix"

Good show, anxious to see it.

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'84 XT600 is now bored to 2nd oversize and new OEM pistons and rings installed. No more smoking.

ok here we go, first pic shows the xtz top ears and you can see that hey are wider spaced so i could fit two bolts form the inside.

so this is how i modified a normal M10 nut, sanding it down to about 15mm and also rounding the two corners as the cavity has some radius from the inside.

you really have to make sure that the nut will fit freely in there and seat over the flat area. if it's too it will wedge the two ribs appart and crack them... take the time to dress it until it fits well.

used two M10 X 25 bolts to bolt it all back together.

BTW, the original long bolt has fine pitch, so no surprise that it will puts so much compression force on the ears... i used two normal pitch M10 bolts and some loctite.

Nice!!

How about using two buttonhead bolts and grind them down? That way one could have the nuts on the out side... could that work?

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Yamaha XT600E '01, Honda XR400 '03, Yamaha XT550 '83

The solution you have on the xtz is good, if you only have bolts in each side and use same bracket as original i dont like the idea. You get no support from the other side and the center, if there is a small twist when riding it will brake of the ear fast. Iam not a engineer but just my 2 cents..

I would think a bushing between the mounts to squeeze against would be better as you can use the same bolt and get the same amount of support but not squeeze the sides together, breaking them. The bushing would need to be a tight fit to be effective.

my 2 cents

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'84 XT600 is now bored to 2nd oversize and new OEM pistons and rings installed. No more smoking.

Either solution is better than stock , my 1/2 cent.

I actually have a degree in engineering and did aeronautical structural design for five years, but didnt get around to do any finite element analysis before doing the mod

the tube fix is just as valid, but you'd need to find a tube with 15mm OD X 10mm ID (very unlikely) or turn one on a lathe (as well as hand fit it so it's really tight and takes the load). what's nice about the two bolt solution is that it's really DIY, you need only a bench grinder or file the nut till it fits.

but there's another angle to it: with a single bolt & tube solution (but also in the stock situation), when the head expands under heat, the single bolt creates an even bigger bending force on the ears (the steel bolt expands less). who knows, that might be part of the stress that cracks the weaker ear on the right (it has a shorter base with a deep 90 cut at the front that creates stress concentration, really bad design practice).

With the two bolt solutions, the ears can easily expnand (the 3mm steel plates are not that stiff) without any thermal expansion stress.

so there are pros and cons, but surely both are better than the stock solution where the ears are ALWAYS under a bending load from the bolt.