Reseating cylinder studs

[Kookaburra]

Getting prepared for the 2016 Scrapheap Ride and just as you think you have things sorted and going really well - it happens. The cylinder studs on the left (upper exhaust and lower inlet) have gone finger loose and very soft. I know the signs, previously had the lower left exhaust stud do the same. Looks like they will need a reseat of steel into aging aluminium.  I am probably victim of my own good work. Significantly improved performance putting increased stress on the 30 year old connectors.

The specialist thread repairer who did the last one was awesome but that was on a non oil carrying stud. I'll get him to come and do these but a bit concerned about this one. Any experience or tips?

[Tony Smith]

I was browsing BMW parts online only yesterday and saw mention of a special thread repair insert for studs that have oil-ways. Just don't ask me where I saw it, hopefully the fact that they exist will assist.

[Kookaburra]

Thanks Tony, i went looking on the net and  I found an after market BMW stud tool kit designed and manufactured by HPD in Baltimore. Looks like a great fix but at US$500 (plus AUD conversion rate and the postage), it is a bit over the top. HPD claim their oversize thread inserts are superior to helicoils in this application.

Gunsmoke Engineering says "BMW sells a longer Helicoil with which to make the repair." Cycleworks has these at $4 a pop and a $225 jig to get the drilling business straight. Someone in WA has used one and reckons they are the go. (No mention of the oil way though.) The BMW helicoil p/n  is 11-11-1-338-630. Apparently they are loctite coated and have a special length of 12 coils, and a locking cord.

So now I am a little better informed on some options but not yet clear on the best way to proceed.

[Tony Smith]

So now I am a little better informed on some options but not yet clear on the best way to proceed.
 

Fessing up time. The two times I have had to repair studs I used "std" helicoils (actually "recoil" brand).

As regards the drilling jig I simply made one out of a large-ish piece of timber left over from our home construction (yes this was 25 years ago) Take two pieces of Australian native hard-wood stair tread and glue them together. Then drill 4 holes with the same spacing as BMW head/barrel studs. To secure the drill guide I made up pieces of tube of sufficient length so that I could use a nut and washer to secure the drill to the engine block.

The most expensive part of the while process was locating and paying for an extend length drill, but I'm sure you will agree the long drill is much, much cheaper than making or hiring a low profile steel drill guide plate. The advantage of the depth of mine (approaching 120mm) was that the additional "guidance" given when starting the drilling.

This is not a complicated procedure.

The QLD BMW club used to have a drill guide for hire by members, perhaps check with your local club to see if they have one.

I loaned mine (which in any event was for an R100 so it may not fit an R65) and it was never returned - If I ever have to make another I would try and find some pipe with the correct internal diameter to slip over the studs and then drill the timber so that I could drive (perhaps using a little glue) the pipe into the timber block - that would be a tool for life, but possibly a little overkill.

[Kookaburra]

Tony you are so confident and it seems mostly competent. Yes, i also I used a 'recoil' keysert on the rocker dome stud.  However I have decided the cylinder stud job is critical to not stuff up and is beyond my competence level so I am going to get the stud doctor in.  I now have the left cylinder and the piston off and I am confronted with trying to get the studs out. Have tried the double nut thing but the 2 offending studs (upper exhaust & lower inlet) will not budge in either direction.  Despite my attempts at double locking it is the nuts that are turning not the stud. Worried it will do in the threads on either the stud or the nuts. Need some advice on what to do next. Try harder to double lock?

[georgesgiralt]

Hello !
There are special tools to remove studs. They are made of a sturdy cylinder with a hole in it and a high tensile steel cylinder with a 1/2" drive square. When you turn the square drive, the cylinder press the studs and seize it solid. It then has one option: move.
With this tool you can act on the cylinder part, not the threaded part and can grab the stud at the base near the engine block. You risk less lateral forces and damage this way.
Keep in mind that Manfred in Germany may have used Loctite on these studs... So a little heat with a propane torch may help some...
I, for one would not disturb the not problematic ones... if it's not broken, don't try to fix it.

[montmil]

.... if it's not broken, don't try to fix it.

Excellent counsel! [smiley=thumbsup.gif]

[Tony Smith]

Stud removers that do the job can be had quite cheaply

The one in the photo below is less than $AUD12. I have one of these types and it has outlasted several much more expensive devices - its major drawback is the amount of access room it needs around the stud in question - not a problem with an airhead cylinder stud.

The more expensive types however are overall not so robust....

[Kookaburra]

Totally agree if it ain't broke don't fix it.  The two suspect studs (upper left and lower right) are both  significantly longer than the other 2 and have loose tell tale finger nail parings of aluminium coming out so they definitely need fixing!

I was also worried about the alarming lateral forces generated by double nutting on the end of a very long stud; so thanks Tony for the heads up on the stud remover which I will attempt to acquire today.





    

[georgesgiralt]

Tony, This is exactly the device I own and was talking about.
I got mine not cheap from the major French tooling company so I paid for the reputation more than for the tool itself..  
Kookaburra, be gentle when removing the offending studs. You do not want too much aluminum removed with the stud...

[Kookaburra]

Got the Sydney thread doctor in and he used the aforementioned device to take out the studs and a fair bit of aluminium thread came with it. He put a helicoil in the upper stud and a timesert in the lower.  We went to great lengths to clear the swarf from the oil gallery as well as keep it out of the engine cavity. I have now refitted the studs and locked them at the right length with a couple of drops of the green bearing locker. Now waiting for the gasket, circlips and o-rings to arrive so I can reassemble and carefully torque to just under spec .
Questions: why is it now three studs on the left cylinder which have pulled? Is it commonly the left? Any theories gurus?

[Barry]

Don't know about all 3 but BMW effectively acknowledged that the front left hand studs threads were weak by starting to fit helicioils in those positions from new at the factory.

[Kookaburra]

Barry, do you know was it only the front left to which they fiitted helicoils as standard from the factory?  IE is there something different about the casings or forces on this side of the 248 engines?  In idle thoughts, the cylinder is of course mounted marginally further forward in the casing than the right. My thread doctor mused it could be the engine may have been running hotter on the left cylinder. PO owner used to leave it on the side stand as he had a bad back.

[Barry]

There was a service bulletin but it gave no detail just the statement that the factory had been helicoiling left fronts.

[Kookaburra]

Well left front is exactly where i have been having the problems.