I have been sorting out cylinder heads from in my shed and they are all slightly duff in some way. One has been helicoiled and it looks rubbish/bad job... looks like the thread has split in two?!



picture from inside head...

is it recommended to helicoil plug holes? if so what size are they and would it be recommended to try and fix this one again!?

They are only a temporary solution Tim. They are not an answer to a bad thread. Unless the head has sentimental value, throw it away.

wind it out and put a new one in

wurth timeserts get a good rep but horrendous costs if you buy the kit

altho ive seen 2 let go

sean

Tim,
looks as though someone's bunged in a 3/4" reach helicoil, rather than the correct 1/2" type.
( That's a surefire way to create a hotspot to encourage pre-ignition, amongst the other reasons why it's a poor job )

It should be possible to wind the coil through 'inwards' by gripping the tail of the spiral of wire. Once it's out, have a look at the thread in the cylinder head to see if it's OK, or not...

Taps/threads for helicoils are usually 2mm up on the original size, so I'd guess that would be a 16mm x 1.25.

ken

Just for the record .....

.....helicoil on the left,timesert on the right..... [pic from last time this subject cropped up]

T.

stripping threads has always confused me
so i get the do it to hard and youve stripped the thread bit
how could you tell a helicoiled thread without removing the engine to pieces, and how much is it to replace the part (ive forgotten technical names right now which is why im asking) which would need replacing with no thread??

3 heads stripped and binned today... all sick in some way or another. One more currently being analyzed but looking like that will go in the bin too! shame as that leaves me one LHS in the shed and one LHS on the bench... not quite a full engine.

ooh don't bin them

oil feed can be helicoiled
sparkplug holes either helicoiled or welded and re cut

not by me.... I don't have the tools, machines or skills to do the repairs.

The heads aint that good condition generally with chipped fins etc... if they were no longer available then I would be thinking twice ( no I'm not usually one to bin stuff but you cant keep everything!)