555 stripped thread.

[Aled Hughes]

What are your views on repairing a stripped sparkplug thread on my 555, helicoil? Thanks 

[Muddy42]

How bad is it?  I've never done this, but I've heard of people butchering a new spark plug to make a tap to clean out and restore the threads.  Basically you cut grooves at right angles to the thread.  I've done this successfully with a normal bolt and threads, but never to an engine. 

[openspaceman]

40 minutes ago, Muddy42 said:

How bad is it?  I've never done this, but I've heard of people butchering a new spark plug to make a tap to clean out and restore the threads.  Basically you cut grooves at right angles to the thread.  I've done this successfully with a normal bolt and threads, but never to an engine. 

Yes it does depend on how badly it has stripped.

 

If you can still wind a plug loosely in then it's a cinch to use the stepped tap tool, not familiar with 555 but done a few Stihl and Huskies and a car or two.

 

 If the hole is badly misshapen and you need to drill and then tap conventionally you need a steady hand.

 

It is possible to do it with the cylinder in situ if you bring the piston up past the top of the exhaust port and fill the cylinder with grease.

 

The helicoil has to be exactly the length of the thread or a fraction less as it must not extend into the cylinder or have any thread left out above.

 

When done you break off the driving tang and then expel the grease, tang and swarf.

[adw]

The 555 has a 10mm x 1.0 thread, I have Heli coiled a few, the others comments  are correct its all about drilling and tapping absolutely square and a decent coil kit, I hate the cheap kits they are not very good.

[Aled Hughes]

Well you can almost push the plug in, threads are quite feint. Ordered a kit and intend on giving it a go, i have a useless cylinder so ill use that as a tester thanks for your replies I'll keep you posted on results 🤞

[adw]

Watch the length of the insert, if too long it will protrude into the cylinder, you would then have to wind it all the way through and start again.

[Aled Hughes]

3 minutes ago, adw said:

Watch the length of the insert, if too long it will protrude into the cylinder, you would then have to wind it all the way through and start again.

Ok great thanks 

[Aled Hughes]

17 hours ago, adw said:

Watch the length of the insert, if too long it will protrude into the cylinder, you would then have to wind it all the way through and start again.

I take it the heli is left hand thread to insert so as not to push it in further when inserting spark plug? Suppose loctite on the heli wouldn't be a bad idea?

[Stubby]

4 hours ago, Aled Hughes said:

I take it the heli is left hand thread to insert so as not to push it in further when inserting spark plug? Suppose loctite on the heli wouldn't be a bad idea?

No . RH . Or you would have to get a LH spark plug ! The out side of the helicoil cuts into the parent metal and the inside forms the new thread for the plug . Oh and loctite would be a bad idea .

Edited July 7, 2023 by Stubby

[Dan Maynard]

Go down to stores and get some left hand thread spark plugs, young lad.....