190 plug cross threaded

[stuarth]

I am changing the plugs on a 190e. I took out the old ones and in putting in a new one, it does not screw in properly and gives the impression of being cross threaded. Is this possible (yes I suppose) and do you have ANY suggestions what to do. I can screw in about 4 mms but then it gets real tight and since the head is aluminium (?) and the plug is steel...
Anything I can do before I ruin the head?

help!! Or should I just drive it home and hope for the best?

 

[lofty]

stuarth hold fire don't screw the plug further, or you will damage the internal thread beyond normal repair, a suggestion which may work, use one of the old plugs and check to see if that winds in finger tight, only using the extension bar and 10mm socket NO wrench If you only get the old plug as far as the new one i.e. 4mm then you have cross threaded the plug! Although I have not used this method myself on plugs I have used in other instances of cross threading, if you have a grinder taper off the first few threads on one of the old plugs, make sure that where the thread starts it is clean so the thread makes correctly, if you can get that started making firstly that it is completely square with the engine block. If it runs easily then run it backwards and forwards a couple of times to clean the thread. Then try the new plug again, But don't put it under any real pressure.
The worse case scenario is that you may have to get the car to a garage or have a helicoil fitted, this device replaces the original thread but if you have only gone 4mm? the situation should still be recoverable but it might cost. I really do hope that helps keep us infd.
Lofty :cry:

 

[tom7035]

Fair advice above, but I would also suggest cutting a hacksaw slot across the threads of the old plug first. This has the effect of cleaning up the damaged thread and also gives the small amount of metal swarf it creates somewhere to go as the 'cleaning up' plug progresses down the threads.

Even better of course, can you not borrow a proper plug tap from a friendly mechanic to ream it out with?

As stated, the worst case scenario is a helicoil. Good luck.

 

[panason1c]

I would add to the above replies....apply grease to any 'tap' you use so that any swarf sticks to the tap and doesn't fall into the cylinder.

 

[OlafMaxwell]

Do your best but don't worry too much if it goes wrong. A Helicoil repair will work, they are very effective and most small motorcycle engines suffer their alloy heads being ruined by overtightening etc by overenthusiastic DIY teenagers!!. Its a fairly simple repair and most garages will be able to do it, no head removal or anything like that as long as you can ge tthe Helicoil tool into it!!