Alloy head spark plug threads

[RichardL]

Very interesting, these last two. Keenserts will take a real leep of faith.

Richard L.

[Brian]

I think any of these will work ok, even the normal recoil insert will be ok.

The plain wire Recoil coil insert actually has one advantage over the others in that it is impossible to fit incorrectly. Both the others require the person fitting it to drill and tap the hole perfectly square but the standard Recoil kit comes with a tap that starts off with the 14 x 1.25 and then steps up to the size required for the insert, there is no drilling required. You just wind the tap in to whats left of the original thread and keep going. There called pilot nose taps.

I went out to my shed to take a pic of the tap but then remembered my kit is at my son-in-law's place so had to find a pic on the net. Whats that about never lending tools.

[BSA_54A10]

1) Expecting the copper washer to make two joint faces gastight is an act of faith.
2) the special self aligning and drilling tools are available for just about every insert made.
3) if you have a good look at the angle of the "V" in a helical you will see that it is not the proper angle for any thread form.
Solid inserts are cut to the correct profile for the thread that they are replacing.
Both Timeserts & kleenserts have locking pins and they are what Rolls Royce fits to their alloy heads from new so good enough for RR will be just alright for my BSA.

[RichardL]

1. Really? Nevertheless, the act of faith I was referring to is the permanence, not the effectiveness.

2. ---

3.  I have helicoils and no apparent compression loss.

4. I will be taking your good advice (thank you) and replacing the helicoils with solid inserts when the helicoils fail.

Richard L.

[RichardL]

This thing with the copper plug washer has me stumped for understanding if it is, indeed, leaky. We use broad solid copper head gaskets with very little plastic deformation to seal not only cylinder pressure around that large circumference, but also the oilways. I am rather certain that the PSI on the copper causing the head gasket to seal (with its wide-spaced bolt pattern) is far less than on the plug washer sealing a smaller circumfernce with a smaller surface area and a  washer designed for deformation. I know, I know. I'm completely wrong. How can I be so stupid and mechanically naive?

Richard L.

[iansoady]

I've never had a problem with helicoils or recoils myself. And according to this helicoils are used in Rolls Royce engines as well......

[bsa-bill]

I know, I know. I'm completely wrong. How can I be so stupid and mechanically naive?

No mystery Richard I find it easy enough -- often

wouldn't argue that more modern insert could be better than the good old Helicoil but they have been good enough for our old bikes for a long time now and a bit easier to do for those of us not quite up to A grade mechanic standard

[warmshed]

I think in the end any thread repair kit should be suitable.  Here is a cheapish one that you may wish to consider. http://www.ebay.co.uk/itm/Helicoil-type-Spark-Plug-Thread-Repair-Kit-M14-x-1-25-/271002603399?pt=UK_Hand_Tools_Equipment&hash=item3f19038f87#ht_3046wt_1163   Get a bit of practice and you could recoup your money loaning it out to similarly affected bike owners.

[BSA_54A10]

Don't know about jets but every thread into alloy on the 6.7 V 8's is helicoiled with the exception of the spark plugs which have solid inserts.

As for the plug sealing washer it is designed to seal much like an O ring between two flat ( ish ) solid surfaces being that it starts life as a round or oval section washer which gets crashed to make the seal