Sad day when the bike you picked up has stripped sparkplug holes(91 zephyr750)

Literally every sparkplug hole is stripped, i noticed it shortly after i brought her home. The plugs in cylinder #1,2,&4 screw in and get barely tight but then if you cant actually tighten them down, you try to atleast make them snug then they just loosen and then you can keep on turning them in and they will only go back to barely tight, its horrible... #3 sparkplug hole is so bad that when you disconnect the plug wires and crank over the engine you can hear pressure blowing past the plug and it doesnt grab even the littlest bit like the others. Its all quite depressing.. I was thinking of ordering a time-sert sparkplug hole rethreading kit with inserts since the inserts seem to me that it would be a more permanent fix and better than helicoils. It also doesnt require drilling which I like since I would be to worried about the angle while drilling out and I don't like the possibility of metal shavings falling inside the cylinders.... does anyone have experience using this time-sert no drill with inserts thread repair kit? I was wanting to know which insert length i should get.? The ngk d9ea sparkplugs i use are m12x1.25 but they have a reach of 19mm. So what inserts should I get? Obviously 12x1.25 but what about length? I see one inserts length is 15.0,  another that is 17.5, another that is 9.0. So what length inserts should I get? I would think the the size that is closest to the sparkplugs reach of 19mm but I don't know because I don't know how far they would be sitting in the cylinder head once installed, or if the would be partially covering the sparkplug causing it to not spark properly or whatever, but also don't want to get to short of one's since I want there to be as much thread contact as possible. If anyone can let me know I'd appreciate it. 

Bummer but fortunately a simple fix. 
Take the head off to do it properly and it'll give you a chance to check and measure the bores and to see if it needs a rebore. Personally if the plug threads are that butchered I'd want to put new rings and hone the cylinders at the very least. Those plug threads are an indicator of previous poor maintence so while the heads off why not check. You'll also need to sort the valve lash due to poor maintenance so head off again not much more effort. 
Do it properly do it once. 
Regarding timesert length it depends if you intend to recess the the timesert lip into the head as you should or leave it proud. 
DO NOT USE A HELICOIL. 

Pretty sure you will want full depth threads, so that means the longer insert.

And while there may not be drilling needed, there are plenty of chips created by installing Timeserts.  I agree with Warren, I'd pull the head.


 

I really do not want to pull the head haha if I pull the cylinder head that means I'm going to have to re time it, replace the valves and would make me want to bore the engine, which means I'd then have to also upgrade the bottom end etc etc and it's only a $500 bike. The engine is in poor condition already, the whole generator cover is covered on jb weld or something and I don't think there's even bolts or atleast you can't see them because all the jb weld stuff.. I would rather do a quick fix just to get it running good enough so I can ride it till it dies and then just get another engine. I seen alot of these engines with very low miles on ebay and other sites for around a grand. 

The guys are absolutely right, whichever repair method you chose there will be debris that isn't magnetic (so you can't fish it out) doing the repair with the head "in situ" will 99.9% guarantee cylinder damage and a larger chip could get caught under a valve holding it open ready to "make love" to the piston crown 
You have another thread running ref blanking the "smog control" system which also involves tapping to insert the bungs which will also create debris - do the smart thing and "pull the head" It's your choice but you will regret it later if you don't

Robby2894 wrote:

I really do not want to pull the head haha if I pull the cylinder head that means I'm going to have to re time it, replace the valves and would make me want to bore the engine, which means I'd then have to also upgrade the bottom end etc etc and it's only a $500 bike. The engine is in poor condition already, the whole generator cover is covered on jb weld or something and I don't think there's even bolts or atleast you can't see them because all the jb weld stuff.. I would rather do a quick fix just to get it running good enough so I can ride it till it dies and then just get another engine. I seen alot of these engines with very low miles on ebay and other sites for around a grand. 

If the engine is in  as poor a condition as you say and the plug threads are shot and there's jb weld holding it together, to me it sounds like you've reached or surpassed the tipping point to replace it already.

Personally I would rather put the money into the engine I already had and end up with one of known good condition than potentially wasting it on an unknown quantity. Ask yourself why the engine for sale is not in a bike if its "good".
Every engine for sale is advertised as "running before removal". They all ran when they left the factory which was before removal. 

 

Wookie58 wrote:

The guys are absolutely right, whichever repair method you chose there will be debris that isn't magnetic (so you can't fish it out) doing the repair with the head "in situ" will 99.9% guarantee cylinder damage and a larger chip could get caught under a valve holding it open ready to "make love" to the piston crown 

You have another thread running ref blanking the "smog control" system which also involves tapping to insert the bungs which will also create debris - do the smart thing and "pull the head" It's your choice but you will regret it later if you don't
 

Huh?  Wait just a minute here, guy's...

I say if men have balls, they may do well to use them.

daveo wrote:

Wookie58 wrote:

The guys are absolutely right, whichever repair method you chose there will be debris that isn't magnetic (so you can't fish it out) doing the repair with the head "in situ" will 99.9% guarantee cylinder damage and a larger chip could get caught under a valve holding it open ready to "make love" to the piston crown 

You have another thread running ref blanking the "smog control" system which also involves tapping to insert the bungs which will also create debris - do the smart thing and "pull the head" It's your choice but you will regret it later if you don't

 

Huh?  Wait just a minute here, guy's...

I say if men have balls, they may do well to use them.

 confused Wookie ?

Wookie58 wrote:

daveo wrote:

Wookie58 wrote:

The guys are absolutely right, whichever repair method you chose there will be debris that isn't magnetic (so you can't fish it out) doing the repair with the head "in situ" will 99.9% guarantee cylinder damage and a larger chip could get caught under a valve holding it open ready to "make love" to the piston crown 

You have another thread running ref blanking the "smog control" system which also involves tapping to insert the bungs which will also create debris - do the smart thing and "pull the head" It's your choice but you will regret it later if you don't







 

Huh?  Wait just a minute here, guy's...

I say if men have balls, they may do well to use them.

 confused Wookie ?





 

  Bang em out, and be done with it!

Obviously it's easier with the cylinder head removed, but very achieveable with it on.  Just gotta be determined and know what the entire process involves before doing anything.

Gird up ye loins, men!

Must-have proper tooling for the job, or I would not attempt it...



I chose the M14 size 44111 insert for it's 16.8mm length, being the longest available for 3/4" spark plug thread reach.

 

I don't agree with what was said up above. There are videos on how to do it with the head still on the bike. Grease on the tap, blowing out the chaff with an extension on the air spray tip then turning it over with the plugs out will get rid of most of it. Like what Jeff said, "What's left will turn into little molten balls and exit out the exhaust valves." I've done it with no problems. The one thing that would make me remove the head is the valve guide seals will be old and hard causing it to burn oil. Also removing the head could cause carbon particles to drop into the rings causing deep scratches in the cylinder walls causing more damage. If it were my $500 bike I'd fix the spark plug threads, ride it and see if throwing more money at it is a viable option. Chances are it would be. 
Steve

As with so many things "you pays your money and makes your choice" good luck with whichever route you chose to go down
PS: there is a process to do stem seals with the head still installed 

I would not do it on a more expensive bike ,but maybe you can take the headers off and make sure the exhaust valve is open on the cyl you are working on.Then place a vacuum cleaner in the exhaust port while drilling and use lot of grease on both the drill and the tap..Another thing could be placing the bike upside down and using same method.