Previously repaired cylinder stud

[gog]

Well I finally got around to removing the heads on the R80. I have long suspected the top front cylinder stud on the left side to have a problem, as it appeared to have been cut at the end just after the rocker.

As the bike was running fine, I decided at the time not to tempt fate just yet.

I have new cylinders to go on so they had to come off now. As far as I can see, its a previous repair. The stud is definitely cleaner than the other three and has far more threads proud of the crank case than the others. It looks like its been turned down to a thinner diameter, and maybe not the correct stud. The thread on the other end has been cut short as you can see in the pics.

I have no idea how much thread is actually in the hole and engaging to hold the stud in the case. The rockers seemed to get oil and the bike ran just fine.

I cant see any oil galleys around the stud, or where it would feed from the back, but then again i dont know what im looking for.

Should I just leave the repair in place and hope that it stays in when i torque the heads back on, or remove it and see whats going on? I have a complete set of replacement studs in the spares box.

Anyway, have some pics. Likely to explain things far more clearly than me wittering on:

On the plus side, the valves look in decent shape (i think) showing no signs of creeping into the head. Feel free to tell me otherwise

 

[solidstate100]

Hi

I think I would have undone the nut and re-torqued it BEFORE I stripped it down - that way you would have known it if was OK before you got into it. As it stands I would trial fit the cylinder and head (use the old head gaskets, not need for pushrod tube seals, case seals etc) and see it if will hold a torque. If it will I would probably leave it alone (as you say it was running fine before) - if not.......well, looks like another (better) repair needed.

 

[ianboydsnr]

Re fit the new stuff, then torque up to the correct figure,

if it pulls out, then repair, if it doesn't then your good to go

you may want to replace the unusual stud, that's probably ok to do as well!

 

[gog]

In hindsight, that would have been a good idea

Ill remove piston rings and grotty pushrod tubes and slide the old cylinder and head back on and see if it will take 25lb/ft tonight.

Valve spring compressors arrived so ill be able to get them off and clean everything up in the heads. If valves come out, do they need lapped when theyre put back in?

 

[ianboydsnr]

In hindsight, that would have been a good idea

Ill remove piston rings and grotty pushrod tubes and slide the old cylinder and head back on and see if it will take 25lb/ft tonight.

Valve spring compressors arrived so ill be able to get them off and clean everything up in the heads. If valves come out, do they need lapped when theyre put back in?

there's no guarantee that even if it takes 25lb/ft, that when you fit the new stuff, that it won't strip out,

fit the new then torque up, your only risking a cheap head gasket,

I had similar issues to yours, I torqued it up to 29lb/ft, which it held, I wouldn't want to strip it down and try again!

 

[gog]

thanks ian. im still waiting on rings for the new pistons arriving. ill see how i get on with the rest tonight, doing this all in 2 hour evening stints between kids going to bed and mrs leaving for nightshifts. very frustrating not being able to just crack on and get it sorted!

 

[Rob Farmer]

I'd be taking that out to have a proper look. There is a proper helicoil that goes in there if needed.

 

[gog]

do you know where i could get the coil in the UK Rob? anywhere that rents out a jig would be handy too, as my drill skills are not as accurate as might be needed.

 

[Voyager]

Its a long time since I had the barrels off my 100GS . . .

Do the studs (or the threaded holes) extend into the interior of the crankcase ??

I.E. can you feel the end of the hole / stud with a finger ??

That might give you a clue as to what has been going on in there.

I'd be inclined to get it right while its apart. If you don't it will always be at the back of your mind as you ride .

Bob.

 

[gog]

I couldn't bring myself to ignore it and hope it would be ok. took it out, turns out it's been repaired before, job looks ok. looks like a 10, maybe 15mm helicoil in there. this stud doesn't go right through the casing, but whoever drilled it has gone deeper than it was previously, and have put a longer stud in (I tried one of my spares in the hole and it was too short by the time it bottomed out). it looks like it's been done to a decent standard and the oil passage is clear, the helicoil starts just behind it.

 

[gog]

here's the longer stud (standard 297mm longer stud cut down at rocker end). the black bit of the threaded section is how far it was in

 

[DrFarkoff]

There are two x studs that are different to the other 6

I think They fit rear Right vertically BUt I need to check

Yup 6 x 275 mm and 2 x 297 mm

http://realoem.com/bmw/showparts.do?model=0457&mospid=51630&btnr=11_1688&hg=11&fg=11

Parts 6 and 6

 

[gog]

cheers jay. yep, what im saying is whoevers done the fix had put one of the longer studs in the repaired hole as they have drilled deeper than they should have. the shorter stud correct for that position would have been too short when fully seated in the now deeper hole, so they used one of the longer 297mm ones and then cut it so it was same length as others. bit of a hack but seems like it's done the trick.

 

[Rob Farmer]

That's much clearer now.

Bmw make replacement thread insert but the problem is in drilling it square. Www.cycleworks.net make a jig but it isn't cheap and is hard to justify for a single repair.

http://www.cycleworks.net/index.php?main_page=product_info&cPath=29_33_51&products_id=20

 

[gog]

Looks like the drilling has already been done for me Rob so fingers crossed I wont need the jig, even if the present coil doesnt hold when i put it back together. If it pulls out, ill buy the right insert (longer than the one thats in it now) and replace. Thanks for the link - I had seen them before but youre right, it is a lot of outlay for one repair. Worthwhile for those with a fleet of these bikes or those working on them professionally.