Spark plug problem

[TheSkinny]

I tried to change spark plug today. Got replacement identical to original but I cannot get the spark plug to screw in. In fact I tried to get the old one I took out to screw back in (just to experiment) and it wouldn't go back in either. I don't think I have stripped the threads to this point. Any tips for making the screw threads turn? The only thing I've seen on the Internet so far is a suggestion to put soap or wax on the threads to lubricate them-- however, this was for wood screws in lumber.

FYI, What is happening now is that I get the spark plug to screw in for a couple of turns, then it tightens and seizes up. Same place every time. My mower has always been serviced by mechanics. In fact, I couldn't say for certain that the plug has ever been replaced.

Troy-bilt Pony mower. Briggs and Stratton 17.5 hp engine.

I'm thinking there may be some really good lubricant built just for this purpose. Is there a way to make sure you line up threads correctly? I don't think there is grime in the threads but there may be. Best way to clean the threads. Any other tips, etc.

Thanks,
Richard

 

[exotion]

Me thinks you have the wrong plugs. And someone shoved it in there when it wasn't supposed to.

 

[ILENGINE]

I would say either a plug has been crossthreaded or seized in the threads, which pulled the threads. You will need to chase the threads out and make sure they are clean. They make thread chasers available at auto parts stores. If you want to use a tap instead of a chaser it is 14mm 1.25. Just make sure to blow out the chips really well afterwards.

 

[TheSkinny]

Folks,
Thanks for the comments. The phrase "Chase the threads out" is new to me but I am guessing from looking on the web (and the way other people use the phrase) it means to use to use a tap to go back over the threads. I have a tap set (if I have the right size) but have only tapped a few holes before (maybe five or six). This is a great suggestion but any tips on the way to do it right? I think I'll try getting the spark plug in once more this afternoon and then try that. Thanks also for mentioning the size of a lawnmower spark plug hole! I'll try finding the correct tap if I don't have one already.

Also thanks for the suggestion about cleaning out the hole. I should have thought of this. I'll use a toothbrush and go round the grooves, pulling anything i find out of the grooves towards me first so I don't foul my engine internals. Or would a small metal wire brush be better than a toothbrush?

A MacGuyver thing I thought of: One morning I couldn't budge a screw. Later that day I tried again and it came right out. The only thing I could figure was the outside temperature had changed. So the idea I got is to put the spark plug in a plastic bag and submerge it in ice water for a couple of hours. It may contract enough to go into the hole. What do you guys think?

(BTW, I also thought of blowing hot air on the engine to expand the size of the hole but then I realized it is the metal that will expand and this may have the opposite effect by swelling the metal into the hole rather than expanding the hole itself.

Thanks again for the good ideas. Anyone else out there got comments?

Richard

 

[Fish]

Try a chaser first, you can get one cheap at an auto parts store. Like 3 bucks or so. Then before chasing, smear some semi-solid grease on it, and any metal chips will stick to it.

 

[TheSkinny]

Exotion,
I thought about the fact that someone might have put the wrong plug in and then forced it, messing up the threads. But the two spark plugs, the old one and the new one are the same - and both match what the user's manual calls for.

Richard

 

[TheSkinny]

Fish,
I'll try what you said. Is there another term for semi-solid grease, a brand name or something? Will the girls at the car parts store know what I'm asking for (they usually seem bewildered).

Also, I'm thinking that before I try the spark plug again I'll use the "soap the threads" idea. But instead of soap or wax like carpenters use on wood screws, for an auto engine I will brush some motor oil on the threads before I try to screw in the spark plug.


Sorry I'm so long-winded on this thread but, I'm afraid the more I mess with the spark plug the more I could damage the threads - I'm trying to get as many ideas lined up as possible and try them all at the same time.


Richard

 

[exotion]

There are always larger spark plugs that can be gapped I've had to do this a few times. Temperature is a good suggestion can try a heat gun on the plug hole (DO NOT get it red hot you can get it hot but not to hot) the metal will expand allowing room for the plug. Also do not use flame...... And make sure all flamables are not around.

 

[TheSkinny]

I found what looks like excellent info on crossthreading problems. One tactic is turning the screw counterclockwise instead of clockwise to straighten threads up. There is a lot more, too. If you have similar problems, I think this would be a great resource. The info is on the Goldwingdocs forum at How to prevent cross-threading fastenerso

Richard

 

[Fish]

Stihl have to strongly suggest the thread chaser. That is what they are made for.