stripped spark plug threads

[patrickd]

Hi I have stripped threads in the #3 cyl. Is there any way to fix this? short of replacing the head? Would a helicoil work? if so would the head need to be removed?

Also anyone have any idea how much it would cost to have the top end rebuilt?

[cbRider]

You should be able to do it with the engine in the frame.
A Helicoil is a good reliable repair. Rolls Royce uses Helicoils on all of their aluminum engines
right from the factory.

[Polymer-2]

They make special inserts for spark plugs. You can get the kit at Autozone or similar parts store. Comes with tap, inserts and installation tool. You also need to get some red high temp silicon to seal the insert to head threads.

[patrickd]

Wouldn't the silicone  screw up the ground between the plug threads and the head? Will it still fire?

[Polymer-2]

patrickd wrote

Wouldn't the silicone  screw up the ground between the plug threads and the head? Will it still fire?

That's according to the instructions that come in the kit but the answer is no. When you tighten down the insert the silicon will be squeezed out from between where the threads torque together and there is metal to metal contact.. The silicon is just to fill in any inconsistencies in the threads.


Jerry's World of Restorations.  http://www.polymer52.webs.com

[patrickd]

While silicone will no doubt seal it up I'd think it wouldn't glue the insert in like loctite would.. Any thoughts on the subject? Just wondering if it would unscrew when the plug was removed.

[Polymer-2]

The end of the insert is knurled and once fully inserted it is then flared in place with the supplied tool thus locktite isn't necessary. I said earlier that my kit was from Autozone but after thinking about it I remembered I got it online (much cheaper) and is called "Save-A-Thread" and made by HeliCoil.
HeliCoil part number 5334-14. Just follow the instructions. Extra inserts are also available so you only have to buy the entire kit once. I've used it several times on several different air cooled engines and never had a problem.
Note these are not the regular helicoil thread replacers. These are small collars.
Here is a site with a picture..http://www.sjdiscounttools.com/hel5334-14.html

And another http://www.globalspec.com/FeaturedProducts/Detail/MetricScrewTool/Helicoil_Spark_Plug_Thread_Repair_Kit_14mm_x_125/23773/0

[cbRider]

Be careful, the kit shown in the above post is for a 14mm plug.
My CB750F has 12mm plugs. Make sure you get the correct size for your engine.
Instead of using silicon I recommend "Loctite 620" it is good for 200ºC or 400ºF, temperatures you can get in the cylinder head.

a site for Loctite 620:
http://contrails.free.fr/fichiers2/620-EN.pdf

Karl

[Polymer-2]

<quote author="cbRider">
Be careful, the kit shown in the above post is for a 14mm plug.
My CB750F has 12mm plugs. Make sure you get the correct size for your engine.
Instead of using silicon I recommend "Loctite 620" it is good for 200ºC or 400ºF, temperatures you can get in the cylinder head.

a site for Loctite 620:
http://contrails.free.fr/fichiers2/620-EN.pdf

Yes your right..Sorry..
Here is the link to TimeSert for the 12mm stuff.
http://www.timesert.com/html/sparkplug.html

[patrickd]

The problem with it is that it is an inside cylinder and there is no room to use the punch to set the insert. Also they are 12X1.25 That kit is 14mm

[cbRider]

I can see a problem with the insert pictured on the above site.
http://www.timesert.com/html/sparkplug.html
Their longest 12mm insert measures .690 in length
while the plug measures .750. The insert should definitely not be shorter than the spark plug. That would create a pocket for carbon to accumulate and you will have problems removing the plug in the future.
It also deforms the shape of the combustion chamber. Not a good idea.
Just my opinion.

Karl

[genesound]

Actually, I just measured a D8ES plug with a caliper, and they have 0.6" of thread, so the 42123 TimeSert kit is the correct one.

[holysmokes]

if you need your engine head rebuilt, get ahold of ray[fasterspider] over at www.cb750c.com

he resides in CA and is a quailified honda mechanic

[jinshiyang]

You may refer to this website (http://www.xhcljx.com/eng)