Stripped thread [spark plug]

Bobber

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Jun 3, 2024
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15
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Location
Bucks
Hi All
I have a Honda cd 175 I’ve been working on, it had a few issues but with a little knowledge and great advice from this Forum I have it running.
I took it out yesterday and she ran well 😊
I do have a problem though !!
I have a stripped Thread on one Spark plug !!
I wrapped Ptfe tape around it and it is holding up ok. I know I have to do a permanent fix with a Helicoil !!
Looking for Advice for what type and do I have to remove the Head to fix ?
Regards
Bobber
 
jensen said:
These in only one good way, remove the head, al other methods are less good, but worth the risk if time and costs are your enemy....
Click to expand...
You have an aluminum head so the leftovers are soft and will not hurt the motor. Having said that I would not want a lot of filings to fall into the cylinder as some COULD hold the intake valve open. I would liberally coat the tap with grease to catch the cuttings, and remove the tap and clean it several times. This should catch most of the cuttings.
 
On top of the debris problem, to place a helicoil, you must work precisely when it comes to alignment. To me, too difficult with the head on the engine in the frame. I take the engine out, head off, and do the repair on the workbench. If it fails due to too much damage and or not enough material. you can also use an insert.
 
Well I’ve just got back home on One Cylinder !!
The Spark plug blew out of the head and was only held by the Ht lead.
It was quite Amusing 😂
Luckily I was close to home !!
I think looking at the comments I will remove the Head.
Longer is sometimes Quicker.
Any recommendations for the right Helicoil Kit.
Advice is much appreciated 👍
 
jensen said:
These in only one good way, remove the head, al other methods are less good, but worth the risk if time and costs are your enemy....
Click to expand...
You have a choice of the style of insert you use. For sparkplugs I prefer to use the SOLID INSERT over the wire insert. They are harder to find but I see them on Amazon.
 
I don't have one, but I have seen one at a local shop. I'm talking about a tool that can be used when there is some residual thread left in the spark plug hole. The tool has leading threads that screw into what is left of the original thread. This gets the tool started perpendicularly to the washer seat. Further up the body of the tool is a reamer, and above that are thread cutting flutes of the size needed for the solid threaded insert.

Look here
 
fxray said:
I don't have one, but I have seen one at a local shop. I'm talking about a tool that can be used when there is some residual thread left in the spark plug hole. The tool has leading threads that screw into what is left of the original thread. This gets the tool started perpendicularly to the washer seat. Further up the body of the tool is a reamer, and above that are thread cutting flutes of the size needed for the solid threaded insert.

Look here
Click to expand...
I have seen a couple of YouTube videos and they look really good, it looks a fairly easy operation.
The videos I have watched have been done with the Head in place to.
One greased up the thread and one blew out the Swarf !!
Not sure which method is better ?
Would you happen to know what kit I would need ?
Regards 😊
 
fxray said:
I don't have one, but I have seen one at a local shop. I'm talking about a tool that can be used when there is some residual thread left in the spark plug hole. The tool has leading threads that screw into what is left of the original thread. This gets the tool started perpendicularly to the washer seat. Further up the body of the tool is a reamer, and above that are thread cutting flutes of the size needed for the solid threaded insert.

Look here
Click to expand...
This is what I’ve seen on YouTube
And they look great.
Not sure what size I need yet ?
Thanks 👍
 
I use the solid inserts for spark plugs, lots of kits available without going to the name brands.

With the head in place I put 2 swiffer dusters into the cylinder with the piston about halfway up. Some grease on the threading tool and the tool should pull itself in using the remaining existing threads ... hopefully there are some. Pressure on the tool as you work it in is important. You need to make sure all the grease is off the new cut threads. Use some hemostats to carefully pull the swiffers out. You do not want pieces caught between the cylinder and piston.
The inserts I use say to use high temp silicon for the install and to let set for 24 hours.

I have even salvaged heads that had helicoils in them using the solid inserts but it is trickier.
 
Hi all
Looking for recommendations for a repair kit for my Honda cd 175 12mm thread 1.25
I’ve seen YouTube video on Timesert kits.
Any advice appreciated.
Internet is a minefield !!!!
 
Bobber said:
Hi all
Looking for recommendations for a repair kit for my Honda cd 175 12mm thread 1.25
I’ve seen YouTube video on Timesert kits.
Any advice appreciated.
Internet is a minefield !!!!
Click to expand...
Moved your newest post here because you already had an open thread for it.
 
Bobber said:
Hi all
Looking for recommendations for a repair kit for my Honda cd 175 12mm thread 1.25
I’ve seen YouTube video on Timesert kits.
Any advice appreciated.
Internet is a minefield !!!!
Click to expand...
Since sparkplugs are removed on a regular basis it's best to use a sleeve type insert like Time-Sert rather than a Heli-Coil. I will suggest using a machine shop to do the work as the kits are quite expensive and most machine shops already have them so you only pay for 1 insert instead of a whole kit. Amazon shows a kits w/5 inserts for $115 USD
 
I wonder how the cost of having a thread insert fitted compares with buying a second hand CD175 cylinder head ?

There's a couple of ones on Ebay UK that look as though they'd clean up OK, for 30 quid, and there's a couple of nicer ones that some optimists want 90 quid for.
 
Richard Pitman said:
I wonder how the cost of having a thread insert fitted compares with buying a second hand CD175 cylinder head ?

There's a couple of ones on Ebay UK that look as though they'd clean up OK, for 30 quid, and there's a couple of nicer ones that some optimists want 90 quid for.
Click to expand...
Perhaps a valid option. Machine shop work for a small job like is more expensive than most would think. I wouldn't be surprised if it costs US $50-$100, unless you live in a somewhat economically depressed area. I know job shops around here charge around $100/hour.
 
esh21167 said:
Perhaps a valid option. Machine shop work for a small job like is more expensive than most would think. I wouldn't be surprised if it costs US $50-$100, unless you live in a somewhat economically depressed area. I know job shops around here charge around $100/hour.
Click to expand...
Yeah. Around here a lot of them have a table minimum. $200 to even put it on the bench.
 
Twin Town said:
Had one fixed at a local small engine shop for $40 a few years ago.
Click to expand...

That was a deal. Those type of shops are getting tough to find. I think there are probably two 'small engine shops' like that in my tri-county area. And they are mower shops, so I don't know if they would even do something outside of power equipment. Motorcycle shops for sure, but then again, their labor rates are astronomical. One wanted $180 LABOR for an oil change on my wife's Can Am spyder in addition to a $150 'oil change kit.' Probably takes 30, maybe 45, minutes.
 
Hi Bobber, thought I'd bump this thread to continue the repair on your 74 CD175 and the spark plug hole. I gather from your message that the head is now off but there may also be a problem with a head stud.
If you found a shop to do the spark plug thread and there is a way to get the broken or stripped bolt or head to them, see what they recommend.
 
Here is your pic from the PM you sent. Let's all converse here in this thread about it.

Looks like the rocker shaft is slid further than needed. You may want to remove the rockers and cam shaft to take your head into the machine shop for the spark plug thread repair.

Untitled.png
 
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