I am in the middle of stripping the bike to clean it up and make it shiny. (86RT)
Just about to drop the engine and have the frame cleaned and resprayed.
I have had a cross threaded spark plug since I got the bike.
Took them out one day and number 4 plug turned 1/2 - 3/4 turn and fell out so I am guessing a crossed thread.
Should I remove the head (timing cover already off to check the chain condition) or helicoil or ignore?
The plug seals well and does not leak anything out from around it.
thanks
rossco

You may be able to get someone to helicoil it while in situ but it is a very deep spot to get at. Fix it, one day it will come out and it will be a long way from home you can bet on that.

I drove my '69 Beetle around for a week or so after cross threading a sparkie, which was only a 1/2" reach compared to our bike's 3/4" reach. When the plug let go, as I crossed an intersection at the lights, it sounded like a gunshot as it blew out, taking all of the threads with it. I didn't know about Helicoils in 1980, or if they even existed back then, so I threaded a steel insert in and it was good to go for another year or so. I'd fix it, as Rick suggested, lest you find yourself with a four cylinder K75 at the roadside, only it won't be as smooth.

"lest you find yourself with a four cylinder K75 at the roadside, only it won't be as smooth."
Good call mate.

Find qualifi ed metal workshop and ask there. Maybe could be enough to remove plug and renew the thread. Once I had same problem with old boxer 50/5 on one of the cilinders. We removed plug put the thread tap, drove it through the tread and that was enough.



Regards

nino wrote:Find qualifi ed metal workshop and ask there. Maybe could be enough to remove plug and renew the thread. Once I had same problem with old boxer 50/5 on one of the cilinders. We removed plug put the thread tap, drove it through the tread and that was enough.



Regards

Put grease on the tap to pick fine debris from thread

If I am pulling the head off I was thinking of running the plug or a tap from the inside out?

rossco

rossco wrote:If I am pulling the head off I was thinking of running the plug or a tap from the inside out?

rossco

Its much easier with head out of place, but you can try with head in place. Thread is deep inside if you do it for first time, ask somebody skilled to do it. Grease tap and run it down and back. It probably should be enough

So after I ask the question, if I said I had less than no idea about removing the head I would be over stating how much I know.
I just spent 30 minutes staring at it wondering how in the hell do I know how it goes back together.
If I take off the timing chain (as I will have to) and if the camshaft gets turned while the head is out, how the hell do I make sure its all in the right spot again.
Crap.
Just realised.
The phrase 'bitten off more than I can chew' comes to mind

Stop. Don't do it without help. If you run a tap through the threads in the head you are only recreating a non-crossed thread in the tiny bit of aluminium that is actually holding the spark plug in there....It needs to be thought through carefully, and you need advice from someone 'on the ground', and looking at it. Removal of the head is the last resort. A Helicoil or steel insert is what is needed to be considered first. I urge you to get some help.

Find yourself a good bike shop or one that rebuilds engines. They should be able to do it insitu. The engineering shop i last worked at had one, its a special kit for rethreading spark plug holes. It comes with a cutting tool the screws into the head (It has a self centering thread to go into crossed threads) it cuts a new deeper seat in the head and comes with special threaded inserts that lock themselves in once installed.
As GITH said if your not confident don't tackle it on your own.

The BMW manual is very good (I think) in taking you along the process. If you have a mate who does more wrenching the better! If not, talk to a bike shop and ask for an estimate. We can help you remotely, but you'll need to do the work then!

I think I can take that advice. Off to the bike shop I go.
Thanks guys.
rossco

Guest in the House wrote:Stop. Don't do it without help.

+1
Read on another motorcycle forum I follow about a guy who's bike spat a plug at him. Caused a huge welt in his leg that ached for weeks. Apparently, the PO tried putting in a Helicoil to repair damaged spark plug threads and did a botched job of the repair. You don't want the same result for your bike. Seek a pro as GITH suggests.

Booked in with the local bike shop.
Thanks again

rossco

Case closed.
Mechanic greased up the thread and put a tap in it. Runs in and out like a charm. He said he cleaned it out, but going to blow some air through it to be sure.

Thanks for the advice all.
rossco

rossco wrote:Case closed.
Mechanic said... he cleaned it out, but going to blow some air through it to be sure....
rossco

Ooh, I wonder where that blast of air will direct the tiny bits of aluminium and such? That's a robust combustion chamber but the shards of aluminum that don't immediately get exhausted out upon start-up will be flying about and can make some interesting primitive cave paintings that'll could be there for eternity. I'd just use a bit more clean grease twisted onto a clean rag and carefully wipe it in and out of the 'new' threads until clean and debris-free. It's important to remember that a tap does remove some of the necessary aluminium in order to make those 'new' threads, so be extra careful when turning a new plug in and use the proper torque setting....but not too much...

rossco wrote:Case closed.
Mechanic greased up the thread and put a tap in it. Runs in and out like a charm. He said he cleaned it out, but going to blow some air through it to be sure.

Thanks for the advice all.
rossco

Congrat Rossco. Its easy. Only problem position deep inside.