Hi guys,I want to ask is there any different threaded glow plug for 2 stroke glow engines?I mean,when I decide to change my OS 8 glow plug on my TT 42 GP engine with a Fox idle bar glow plug,in order to improve idling of my invert engine application,I feel I cant screw it manually after 1.5 -2 turns into engine head.I have to use wrench to screw it down totally and tighten.But when I try OS plug,I can screw it totally by hand until need tighten.I m sure I didnt make it wrong to eat head threads but I wonder if it could be different type glow plug thread that I forced it down.Can anybody have an answer?
Thanks

I mentioned, that fox plugs have wery soft washers. they need to be tightend to end.

There are more threads on a Fox Idle Bar plug than that on a OS #8. Set them side by side and you will see that the threaded part is longer on the Fox.

Enjoy,

Jim

Thanks W8ye,I understand what u mean but,if I could screw it until those extra zone by hand, I would have no worry at all.I only could screw it for 1.5 turn, not much 2 turn by hand then it got stuck.Made me use wrench.So I worried if thread could be different than my engine's head.

The OS#8 and the Fox Idle Bar plug are supposed to both be US thread extra special fine at 1/4" X 32 threads per inch.

Thanks. That was the answer I hope to get.Thank u.Though I could tighten it without problem, was still worrying about any damage of head.

The Fox plugs are a very precise fit in the plug hole which is a very good thing.

I always run plugs through a die first to avoid enlarging the threads in the head.

Good advice, but I m living in a metric state so it s hard to find some suitable nut,etc.But logically there must be no difference at all between all kind of glow plug threads to avoid such problems , could potantially be very dangerous.I saw that precise machining difference feeling with hand.
Anyway, thanks for your kind answering guys.U made me feel better.

The 1/4-32 taps and dies are hard enough for us to obtain here in the US. They have to be ordered. They are not at the local store.

Enjoy,

Jim

turn i know. I had such problem on magnum 91 4c. I guess what u told us. just tighten it.

Turk:

As W8YE said, all glow plugs, other than glow "Heads" and Nelson plugs, are 1/4-32 UNEF.

You can wait until one of your Fox plugs fails, then saw a couple slots across the threads and use the result as a thread "Chaser" to be sure the threads in the head are clean before you put a new plug in.

Bill.

Hi!
This is due to different manufacturing tolerances!
Therefore I always use a 1/4-32 tap and die to really be sure that I don't destroy the treads in the head.
Regards!
Jan K
Sweden

Inexpensive tap I have, http://www.microfasteners.com/catalo...cts/TNMTAP.cfm

Thank u so much guys.Now I know there will be no real harm but only tolerance nuance on my engine head.So no need to worry further. Whenever I need any plug change,I know let it screw down and tighten only,dont think further.
Thanks again .

For those in the USA, Harry Higley makes a 1/4 x 32 tap and die set which should be available at your LHS. I think, but don't know, that you can get it from Tower or similar supplier.

Jim

If you has own lathe or your friend has a lathe, you can make own 1/4-32 tap of drill rod (some time called for silver steel) or carbon steel and hardening the tap before use.

See in article about make own tap: http://easyweb.easynet.co.uk/~chrish/homepage.htm see after the list: 7. Make a tap and die from carbon steel.

I has maked 2 tap and works well as original tap.

Jens Eirik

It seems that the TT engines use a much "tighter" plug thread than many others.

I've found quite a few different glowplug brands that won't thread past a turn or two by hand into the head of my TT engines (Glo-devil for instance), but the OS#8 always goes in all the way.

The same plugs thread all the way by hand into my GMS and other engines without any problems at all.

I suspect the TT heads have slightly undersized threads (perhaps hoping to achieve a better gas-seal as a result) and some plug manufacturers produce slightly overseized threads (for the same reason). Unfortunately, when you get the combination of a head that's threaded too small and a plug that's threaded too large -- problems occur.

I just stick to those plugs that actually fit my TT engines and use the others in my other engines.

Hmm that link dont work no more. darn !

KnarF,


Yes it does.

Check your PC's settings...

Just as there are differences in thread sizes in different engines/glowplugs there are also tolerances for the construction of taps/dies. Some taps/dies, especially 'el cheapo' ones, can leave little to be desired. I bought my set of 1/4-32's from Rex Supply...a supplier for the machine shop industry. Yea, they cost a bit more...you get what you pay for though.

The OS and the FOX plugs are made differently one is rolled the other is not. FOX threads are more accurate sometimes a OS plug will end up at 33tpi instead of 32.

Are you sure?? Checked with tread gauge there are 33 tpi??

Treads can be tight or loose depend on tolerance between treads in clearance.

Jens Eirik

Rolled threads are much stronger than cut threads, just as a forging is stronger than a casting, and for the same reasons. As the metal is reshaped under heat and pressure the grain follows the new contour.

I don't know of any glow plugs that are not rolled threads, glow heads are different. They are usually cut threads.

Regarding an error to the point of 33 tpi, it's not going to happen whether rolled or cut.

Bill.