I recently acquired a junked MS440 which was advertised as having a stripped spark plug hole. I got lucky on this one. The cylinder and piston were in pristine condition, with a cylinder/skirt clearance of .002". Just needed some new Cabers and it would be like new. The bottom end was also great. Just needed a spark plug hole repair.
The only machine shop in my area didn't do automotive work, so it was DYI or get a new cylinder. I obviously wanted to save the cylinder, so I took a chance on the Helicoil Sav-A-Thread.
It came with three inserts, the smallest being the perfect depth for the cylinder.
Insert:
The cutting tool starts with a standard 14mm tap which leads into a beveling section and then a thread cutting section for the insert.
Here's the problem: if you are repairing a deep spark plug hole, the 14mm tap will pull you automatically into the cutting area and continue to act as a guide. With my cylinder, by the time I was through the original spark plug depth, the tap was also through, and I was left without a guide, except for hands and eyes.
I continued on, putting pressure on the tap and being very careful to make sure the tap was plumb. I used grease to lubricate the cut and catch the shavings (the cylinder was not on the saw, but the grease did a good job of keeping the shavings on the cutter). After several starts and cleanings, I broke through to the other side (Cue "The Doors"). I cleaned all surfaces, liberally applied Permatex Red Thread Sealer, and seated the insert flush with the plug seating surface. At that point I seated the expander die and smacked it with a hammer to drive the upper spikes into the aluminum threads.
It wasn't absolutely plumb, but was just a hair off, so it looked OK. Considering there was no real guide for the threads, it was surprisingly good. The thread hole had acted as a sort of guide by pushing the thread cutter toward the path of least resistance.
This is how it looked when finished:
This concludes Part I.
I will follow up when the saw is complete and tested.
So far,
PROS:
The kit is not difficult to use and so far has done the job it was intended to do.
The price for the kit is reasonable; less than $23, delivered, and can be reused for
only the price of the insert.
The design and quality appears to be good.
CONS:
When using with short spark plug holes, the major benefit is lost, that is, the
14mm tap acting as a guide to keep the cutting tap positioned exactly. This is a
substantial drawback.
The insert threads into the hole easily (with a finger holding the insert). I would
prefer that the fit be more snug. I doubt that this will pose a problem, just my preference.
This concludes Part I. I will follow up when the saw is complete and tested.
Part II to follow.
The only machine shop in my area didn't do automotive work, so it was DYI or get a new cylinder. I obviously wanted to save the cylinder, so I took a chance on the Helicoil Sav-A-Thread.
It came with three inserts, the smallest being the perfect depth for the cylinder.
Insert:
The cutting tool starts with a standard 14mm tap which leads into a beveling section and then a thread cutting section for the insert.
Here's the problem: if you are repairing a deep spark plug hole, the 14mm tap will pull you automatically into the cutting area and continue to act as a guide. With my cylinder, by the time I was through the original spark plug depth, the tap was also through, and I was left without a guide, except for hands and eyes.
I continued on, putting pressure on the tap and being very careful to make sure the tap was plumb. I used grease to lubricate the cut and catch the shavings (the cylinder was not on the saw, but the grease did a good job of keeping the shavings on the cutter). After several starts and cleanings, I broke through to the other side (Cue "The Doors"). I cleaned all surfaces, liberally applied Permatex Red Thread Sealer, and seated the insert flush with the plug seating surface. At that point I seated the expander die and smacked it with a hammer to drive the upper spikes into the aluminum threads.
It wasn't absolutely plumb, but was just a hair off, so it looked OK. Considering there was no real guide for the threads, it was surprisingly good. The thread hole had acted as a sort of guide by pushing the thread cutter toward the path of least resistance.
This is how it looked when finished:
This concludes Part I.
I will follow up when the saw is complete and tested.
So far,
PROS:
The kit is not difficult to use and so far has done the job it was intended to do.
The price for the kit is reasonable; less than $23, delivered, and can be reused for
only the price of the insert.
The design and quality appears to be good.
CONS:
When using with short spark plug holes, the major benefit is lost, that is, the
14mm tap acting as a guide to keep the cutting tap positioned exactly. This is a
substantial drawback.
The insert threads into the hole easily (with a finger holding the insert). I would
prefer that the fit be more snug. I doubt that this will pose a problem, just my preference.
This concludes Part I. I will follow up when the saw is complete and tested.
Part II to follow.
