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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

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

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.

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

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.

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

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

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.

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

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

Just to let you guys know how my lawn tractor adventure came out. Actually everything worked. I got everything finished and the tractor reassembled yesterday and the mower now runs better than new! I'm surprised since this was about my first foray ever into fixing a lawn tractor.

I do have some troubled thoughts about one aspect of the job and I'd like your comments.

When I chased the threads in the engine block my plan was to use a brush to clean out any metal shavings. I also planned to only do 1/8 turn at a time and back the tap out. First, it wasn't so clear cut since the tap never went smoothly in the hole and I was never quite sure where the problem started and where the threads straighted out. So I got a lot of shavings. The main thing I wonder about was the fact that I overestimated the size of the spark plug hole and the brush I used was too large. I have a feeling I probably pushed metal shavings into the engine when I put the brush in. I then got a smaller brush but figure it was too late.

However, I did get a lot of the shavings out with the smaller brush --- and at least for now the tractor is running beautifully.

I dont' really know for certain that I did push any shavings into the block but I'm just surmising I did. Questions-- If I did push a few shavings in how long would it take for me to start seeing problems with the engine? Anything I should do in the meantime to diminish any problems? Is this an inevitable problem? Should I just not worry about it since the engine is now running well and maybe I won't have any problems from this after all?

Thanks in advance for any comments,
Richard

Yeah, that grease on the chaser really works pretty good, you should have tried it.....Hell, Vaseline, butter, Crisco...... Better than metal shavings anyday....

Air compressor or dentist vac works good.

Update on my lawn tractor situation:
I've used the mower twice now and it continues to run well. However, I have had a mysterious little episode that some of you might be able to comment on. The last time I was using the tractor I suddenly got a puff of thick blue smoke that I think came out of the muffler -- I'm not sure as the muffler comes out the front of the mower and I was sitting on it at the time. It seemed to be up front of the engine but it surprised me and I couldn't tell for sure. The smoke went away as fast as it appeared. The engine kept running and it seemed fine. About fifteen minutes later it happened again. Again the engine continued to run fine. It may have labored a second or so when the smoke appeared, but then everything seemed okay again.

It has never done anything like this before. Any ideas?

Thanks in advance.
Richard

Carbon deposits coming loose?

Skinny, Tips . Aluminum should not be heated. At 390F it softens and will not hold valve guides in place and threads will pull out. Carbon is depositied in the spark plug bore at the chamber side and works its way outward . This can be felt when screwing in a plug by hand. Sound like your situation was damaged threads. I NEVER START ANY FASTENER WITH A POWERED DRIVER OR A CRANK HANDLE. If the threads are ok , square up and slightly reverse the normal screw- in motion until you feel a slight drop. Then continue by hand clockwise (rt hand thread) until you feel the threads are engaged properly.

The experts tell us not to use a tap to chase threads because the tooth profile is too agressive and will weaken the threads. Of course I use taps, but it is like chiseling with and striking a screwdriver (I do this too)-don't do it if possible. A chaser is best. I put it on a socket and extension and try to complete the clean out by hand without a handle. Observe plug torque (e.g. 10-20 ft lbs ??) and reduce the torque if you lubricate. The galv surface is a lubricant itself . I usuallly squirt WD 40 onto the threads and dry the threads with rag.

Over the years I have often cut or ground on an engine with risk of entry. Sometimes you can plug (rag) and vacuum. The effect of chips dropping may not be catastrophic as some may have left on the first few engine cycles thru the exhaust port. Let's hope.:thumbsup:

Fish said:

Yeah, that grease on the chaser really works pretty good, you should have tried it.....Hell, Vaseline, butter, Crisco...... Better than metal shavings anyday....

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You're right. I should have tried that.
Richard

exotion said:

Air compressor or dentist vac works good.

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Interesting idea. A friend of mine told me (after the deed was done) a magnet works well. I'm sure that's a good idea with a steel engine. However,, I don't think aluminum is attracted to magnets. I'll have to try it.
Richard

exotion said:

Carbon deposits coming loose?

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You might be right. I would think this would be the most benign possibility. - Richard

motoman said:

Skinny, Tips . Aluminum should not be heated. At 390F it softens and will not hold valve guides in place and threads will pull out. Carbon is depositied in the spark plug bore at the chamber side and works its way outward . This can be felt when screwing in a plug by hand. Sound like your situation was damaged threads. I NEVER START ANY FASTENER WITH A POWERED DRIVER OR A CRANK HANDLE. If the threads are ok , square up and slightly reverse the normal screw- in motion until you feel a slight drop. Then continue by hand clockwise (rt hand thread) until you feel the threads are engaged properly.

The experts tell us not to use a tap to chase threads because the tooth profile is too agressive and will weaken the threads. Of course I use taps, but it is like chiseling with and striking a screwdriver (I do this too)-don't do it if possible. A chaser is best. I put it on a socket and extension and try to complete the clean out by hand without a handle. Observe plug torque (e.g. 10-20 ft lbs ??) and reduce the torque if you lubricate. The galv surface is a lubricant itself . I usuallly squirt WD 40 onto the threads and dry the threads with rag.

Over the years I have often cut or ground on an engine with risk of entry. Sometimes you can plug (rag) and vacuum. The effect of chips dropping may not be catastrophic as some may have left on the first few engine cycles thru the exhaust port. Let's hope.:thumbsup:

Click to expand...

These are good tips. I;m keeping them until I change my next spark plug. Thanks-Richard