Glow plug tightening torque

Thanks, Phil,

do you think the values in the chart apply to non-.ferrous materials like aluminum alloys the OS head is made of?

I can't offer any advice on torque specs... but I'm curious about approximately "how often" you remove and replace the plug? You mentioned applying after-run oil through the plug hole. Does OS recommend this be done frequently on their 4-strokes? If you're following their maintenance schedule.. then you probably haven't done anything wrong yourself. The head could have been tapped with a worn tap at the factory... perhaps it was a faulty casting.. or you may have been unlucky enough to have a plug with a bad thread.. who knows. Aluminum is not real forgiving when it comes to repeated threading into it.. with any force.

There "is" something you can do, to check your plug threads... and it's well worth doing with every plug you have. You can obtain a 1/4-32 "die" for the purpose of "chasing" the threads on your plug(s) before you screw them into an expensive and possibly irreplaceable cylinder head. Keep the plugs that have been chased/checked in a labeled segregated storage area, protecting their threads from contamination or being accidentally "dinged-up". Some guys screw them into holes drilled in a small rubber block-type "caddy" that's easy to store in your flight tote too.

Lastly... whenever I assemble any threaded parts; I "rotate" the part(s) as if to "loosen" them... while also applying light pressure, until I feel the leader-thread "drop-in". This results in a "click" that can be felt through your fingers when it happens. Tightening can then be commenced with the assurance that the threads are engaged properly.

I am guessing that the thread-repair you're having done, may be what's known around these parts as a "heli-coil"... although I'm not sure about the uncommon 1/4-32 thread application. That would be the easiest way to do it. Another alternative would be to TIG-weld the hole closed.. but this requires re-grinding/polishing in the combustion chamber.. and re-drilling/re-tapping the plug hole at the correct precise angle. I'll be very curious as to how the repair is made.

I hope I've given you some advice that you can apply Balogh. Best of luck with the engine when you get it back from the cook!

The first link is a Holly carburetor reference (most carburetors are aluminum alloy), the second splits out different materials. The aluminum alloy column agrees with the carburetor reference, but the thread size on the second is 1/4-28 instead of 1/4-32.

After-run oil can be put into the exhaust without taking anything apart. Just support the model in the appropriate attitude and rotate the engine through several times. If the exhaust is really challenging using the pressure tap may be easier, just route the fuel line with a connector somewhere useful. An additional pressure tap can also be installed with little fuss for the purpose of PM (preventative maintenance)

Phil

I tighten plugs with a socket on a nut driver handle. That helps me to not over do it. I'm famous for giving it one more twist for good luck, so the last thing I need is more leverage.

I can add one more comment about applying after run oil. I oiled the engines in all of my planes last month by filling the venturi a couple of times and rotating the shaft while tilting it nose up and then some more inverted. Before I went flying Saturday I borrowed a plug from one of them and it was dripping wet with oil. So no real need to remove the plug or muffler to get it thoroughly oiled.
Rusty

RknRusty wrote:I tighten plugs with a socket on a nut driver handle. That helps me to not over do it. I'm famous for giving it one more twist for good luck, so the last thing I need is more leverage.

I can add one more comment about applying after run oil. I oiled the engines in all of my planes last month by filling the venturi a couple of times and rotating the shaft while tilting it nose up and then some more inverted. Before I went flying Saturday I borrowed a plug from one of them and it was dripping wet with oil. So no real need to remove the plug or muffler to get it thoroughly oiled.
Rusty

Good to know!
Phil

Thanks to all of you for the useful advice. OS states oil is to be applied either through the venturi or through the glow plug hole. I followed this latter so as not to flood the carb having all those tiny bores inside in oil as this I thought may make the engine start later difficult. And the glow plug is at least - or I thought was - accessible through the cowling, anyways..

Now I will have to drill a hole on the other side of the cowling to make the venturi accessible and will apply the oil with  a syringe.

I am not sure how the kitchen-master will heal the ripped thread in the engine head. It is placed way too close to the valve seats and I am afraid drilling a larger hole for a brass bushing into which the new thread is to be cut will not fly.

Roddie, what do you call heli-coiling?

Anyways Tower Hobbies has those OS parts on stock (cylinder head and gasket) and already shipped them - it takes at least 5 weeks if it ships at all.

Thanks again for the valuable advice.

A helicoil - if you can get one that provides the correct thread - is the neatest way of repairing a stripped thread because the original hole does not have to be enlarged by very much.



It does need a "KIT" to perform the operation.



I have done this on motorbike cylinder heads and it has worked a treat.

Thanks, Roddie,

one cannot be old enough to stop learning...I like it but doubt if the kit is available in my area, so I just wait if the surgical repair will prove right.

The 1/4-32 kt usually requires order for everybody as it is an unusual size used by models and carburetors.

Phil

Just a thought, by the time your order the kit and ship it, you may find a replacement head to be cheaper or the same price.

Something to consider anyway.

Ron

On the other hand, the kit is complete - drill, tap, insertion tools and, usually, over 10 inserts.

The kit cost me (many years ago) £10.

I found that after I had repaired the head - about 10 minutes - no other cost, I repaired one for a near neighbour and one for a chap at work - I was compensated with a bottle of wine from one and a six pack of Guinness from the other.

I sold the kit with the remaining inserts when I was having a clear out (about 10 years later) for £12.

More than a free repair.

That is OK, but where is the wine and the Guiness today?

balogh wrote:That is OK, but where is the wine and the Guiness today?

Eventually, after "processing" - it went on a trip down the River Thames.   

Balogh, even if you need a new cylinder head.. it will be worth the wait to have it. Many of our engines have parts that are no longer available. If this is an engine that you really enjoy and run often... you may want to research other common "wear-parts" while they're still available from OS... and order some "spares". I don't know much about 4-strokes.. but there must be valve-train components that incorporate multiple small precision parts; camshaft, valves, gaskets/seals etc., that will wear-out eventually from prolonged use. Does the case use bearings? If so; it may be worth having a replacement set of those too.