Stripped 550 cylinder spark plug thread

[ecovandal]

Hi,

I've just discovered one of my 550's has a stripped out thread for the spark plug.   Does anyone have any specific recommendations for the repair.   Presumably a helicoil type of insert.   I want to make sure I get the size right for the tapping tool and insert.   If anyone knows the correct sizing that would be very helpful  .... as well as  links to a good kit to do it ( in the states they seem to have a 'save the thread' kit.

 

Thanks

[Stubby]

2 minutes ago, ecovandal said:

Hi,

I've just discovered one of my 550's has a stripped out thread for the spark plug.   Does anyone have any specific recommendations for the repair.   Presumably a helicoil type of insert.   I want to make sure I get the size right for the tapping tool and insert.   If anyone knows the correct sizing that would be very helpful  .... as well as  links to a good kit to do it ( in the states they seem to have a 'save the thread' kit.

 

Thanks

Spud has done a few with a helicoil type ( only a different make I think ) . Its a smaller diameter spark plug I think . @spudulike

[openspaceman]

2 hours ago, Stubby said:

Spud has done a few with a helicoil type ( only a different make I think ) . Its a smaller diameter spark plug I think . @spudulike

I've a feeling he prefers timeserts which are a threaded bush rather than helicoil which are a diamond section wire coil.

 

I think the 550 will be 14mm by 1.25 pitch but some small saws have 10mm plugs.

 

The thing to be wary of is that even the 1 diameter length threads may be too long for the spark plug hole so count the threads and see if a bit needs cutting off with a dremel. Also I don't like carrying the 16mm tap all the way through so the helicoil cannot impinge into the cylinder but have not actually had a problem of the helicoil moving.

[adw]

They are 10 mm x1.0

[Khriss]

They aint foolproof, used ones off ebay with varied results  🤔  K

[openspaceman]

1 hour ago, Khriss said:

They aint foolproof, used ones off ebay with varied results  🤔  K

I'm no expert and I think I could almost count how many plug holes  I have done on the fingers of my hand and I think only three on chainsaws. I only use the stepped reamer taps for spark plugs but drills and taps for smaller threads,

[spudulike]

ADW is of course, correct....I use helicoils or Stainless inserts but would use helicoils on a 10mm repair.

My recommendation - use a decent tap - I use Vokel and I would attempt to use a pilot nose tap as if you have enough thread left, it eases the tap in and getting it straight is damn important.

If you use a cheap crap tap....you may as well save your money and throw the cylinder away now! A helicoil needs a well cleanly cut receiving thread. If it is knobbly rough and poorly formed, you will get poor heat transfer and it may even pull out giving you a bigger headache.

Probably easier to take the cylinder off but if you are precise and catch all the swarf, I have done successful repairs without stripping the engine. 

Here is the tap you need (Haven't checked best price). You will need a bit of thread left in the hole to receive the tap but it is your best option.

M10 x 1.0 Helical Pilot Nosed Repair Spark Plug Repair Tap | Engineering-Supplies.com

ENGINEERING-SUPPLIES.COM

---

HSS-G Spark Plug Taps Pilot Nosed To suit wire inserts ISO (6H) Tap tolerance ISO 1 (4H)

 

[ecovandal]

On 20/02/2022 at 19:37, spudulike said:

ADW is of course, correct....I use helicoils or Stainless inserts but would use helicoils on a 10mm repair.

My recommendation - use a decent tap - I use Vokel and I would attempt to use a pilot nose tap as if you have enough thread left, it eases the tap in and getting it straight is damn important.

If you use a cheap crap tap....you may as well save your money and throw the cylinder away now! A helicoil needs a well cleanly cut receiving thread. If it is knobbly rough and poorly formed, you will get poor heat transfer and it may even pull out giving you a bigger headache.

Probably easier to take the cylinder off but if you are precise and catch all the swarf, I have done successful repairs without stripping the engine. 

Here is the tap you need (Haven't checked best price). You will need a bit of thread left in the hole to receive the tap but it is your best option.

M10 x 1.0 Helical Pilot Nosed Repair Spark Plug Repair Tap | Engineering-Supplies.com

ENGINEERING-SUPPLIES.COM

---

HSS-G Spark Plug Taps Pilot Nosed To suit wire inserts ISO (6H) Tap tolerance ISO 1 (4H)

 

Thanks very much.  What sort of helicoil should I be looking at ? ( I know its M10 X1) .  Free running or screw lock, thread length  ...... asking for an idiot !

[spudulike]

Helicoil inserts generaly come in 1diameter, 1.5 diameter, 2 diameter.................

You just need to work out the length of the thread and work out if it is 1, 1.5 or 2 diameters etc

You obviously need a 10mm 1.0mm insert as you said!

Best go slightly short rather than longer!