CV461S Stopped running.

Rule of thumb
Std bolts get a std insert which is 1 diameter
Medium strength bolts use 1.5 d
High tensile bolts get 2 D
When used in alloy go up one lenght .
 
d = diameter of the bolt
so for an 8mm head bolt 3D = 24 mm
Getting a 3D insert in is a lot more difficult that many would believe
It has to be shorter than the threaded section of the original hole by 1 thread top & bottom ( if hole is through ).
I mostly use 1.5's and 2's on push mower head bolts
 
bertsmobile1 said:
d = diameter of the bolt
so for an 8mm head bolt 3D = 24 mm
Getting a 3D insert in is a lot more difficult that many would believe
It has to be shorter than the threaded section of the original hole by 1 thread top & bottom ( if hole is through ).
I mostly use 1.5's and 2's on push mower head bolts
Click to expand...

These are 10mm x 1,5 bolts. The measured (roughly) original thread length is 30mm with about 10mm unthreaded past that. Suggests I can just use the standard tap. I have my concerns about the longer lengths, mainly just the ever increasing torque needed to thread them in. Maybe that is not really a problem.

This is a ride on mower, single cylinder. as you probably know. I think then going with 2.5 D max would be the ticket here?
 
Just to close this out, the inserts installed fine. I went with the 25mm coils.

The used head I got on Ebay turned out to have a warped exhaust valve, discovered when I decided to "lap" in the valves prior to installing it. I used the valve from the head with the dropped seat and it lapped in nicely.

Installed, with very few left over parts . . . . and it seems to be running fine. Though it did give me a scare as it warmed up and began billowing smoke. Panic set in until I remembered how much penetrating fluid I had used trying to get the head bolts out to begin with.

All in all a learning experience, having never done heli-coil before. Thanks for all the tips.
 
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