Stripped spark plug hole

JimNH said:

Aircraft engines have Heli-Coil plug threads from new. They’re a little different than thread repair Heli coils in that they take special tooling to install them. There’s a serrated edge that is forced into the aluminum, they don’t come out. Having removed and replaced thousands of spark plugs I’ve never damaged one or seen one damaged but since there’s a kit to repair them it must happen. Here’s the tooling at almost three grand. Only a big engine shop would likely own one as a new cylinder is around $1600. Or so. Anyway, the heat transfer is apparently accounted for. Older radials used a bronze insert to hold the plugs but all modern use heli coils.

HELl-COIL 18MM AVIATION SPARK PLUG THREAD REPAIR KIT from Aircraft Tool Supply

HELl-COIL 18MM AVIATION SPARK PLUG THREAD REPAIR KIT - Using Heli-Coil serrated aviation inserts is the only FAA approved method of repairing damaged spark plug threads. It is also the only method certified by engine manufacturers such as Teledyne-Continental and Textron-Lycoming.

www.aircraft-tool.com

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$1600 for a new clyinder you say? Peanuts compared to the new Commando head

Fast Eddie said:

You gonna do both whilst you’re at it ?

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Hopefully both at the same time , yes , protection to avoid a roadsise failure .

Tornado said:

$1600 for a new clyinder you say? Peanuts compared to the new Commando head

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Actually around $1900. now and that's for the assembly including piston, pin, rings, valves, springs less rockers. Economy of scale. One of the best values in aircraft engines , but, my engine is going out for overhaul in November. Quote is for $45,000. That doesn't include new propeller governor which has never been overhauled for another 2,700 plus a myriad other things. Shipping $425 each way to Nova Scotia.
I know the camshaft is deteriorating. I've replaced all the lifters due spalling and cam is tired. Last overhaul was in 1996 and was a field OH. They did not OH the Carburetor, magnetos are obsolete with few parts available so can't OH them. TBO in its present configuration is 1500 hours. I'm at 1700. I've changed 4 of the six cylinders since I've owned it. During this overhaul the configuration will change the TBO to 2200 hours. Time Between Overhauls is not mandatory for non commercial use and things like compressions, borescope inspection, oil analysis, and doing things like 500 hour magneto inspections are more important. I'd keep running it but I fly in the clouds and at night and it's been almost 30 years since the engine had a complete internal inspection. The plane's value will increase a good percentage of the engine cost. Since I'm a licensed A&P mechanic with an Inspection Authorization I do all my own work. I'd do a field OH on a simple engine like an A65 out of a Cub but these really need to go to a big shop.

marshg246 said:

But have you ever put on in a Commando head? Hitting the intake valve seat at 3/4" long is a real possibility.

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Hey Greg, didn't mean to ghost you but immediately after last post went for a two week ride in greece. In answer to the question I never tried on a commando because never had bad plug threads. Did not think of seat question although the inner edge or normal timeserts is not really larger than a helicoil. Know this was addressed already but did not want to ignore you. Best. Michael

About to try the Timesert spark plug cut and then inserts in a few days at Acadian's . On the bench .
Any tips ? The left side threads fell apart , but the right side are good , I intend to replace both at the same time . Instructions illustrate a 2-stroke head not pulled from the motor . My Norton head is pulled and cleaned . Light oil for the cuttings , 10 W 30 .
Nervous .

marshg246 said:

As long as you can drill straight, without wobble, at the right angle, and stop at the right point then DIY is fine. Drill too deep and you will likely hit a valve seat especially if you get the angle slightly wrong. The intake seats are close to the hole and exhaust seats are not much further away. The hole required for a timeset is a good bit bigger than the sparkplug hole.

A good machinist doing the work on a mill is unlikely to make the mistake.

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Freehand if you must but it's inviting trouble. Drills just punch a hole and are not that accurate if you need a precise hole. Hand holding a drill? Lots of wobble. Take the head to a reliable shop. Also, be easy when installing sparkplugs. I never use the recommended pressure.
15 ft/lbs seems like too much.

seattle##gs said:

Freehand if you must but it's inviting trouble. Drills just punch a hole and are not that accurate if you need a precise hole. Hand holding a drill? Lots of wobble. Take the head to a reliable shop. Also, be easy when installing sparkplugs. I never use the recommended pressure.
15 ft/lbs seems like too much.

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I will follow the instructions . I trust Acadian .

With the less than perfect metallurgy of those old heads I would definitely have it done in a shop where they can keep everything square.
The granular, somewhat porous nature of some of that metal is inviting tearing during drilling and tapping.
I have done exactly that to a gearbox shell.
Just my view though - I wish you well!
Cheers

Went over to Acadian's with the head and Time-Sert kit . He noted this Kit for spark plugs repair contained some 12mm brass inserts when I need 14mm ( short ) . He said the Norton head is trickier than Triumph or BSA ones , the plug holes come very close to the valve seats . I'll try to get a hold of Gord Bush this week to see if he can do the job if he has the proper inserts .

Torontonian said:

Went over to Acadian's with the head and Time-Sert kit . He noted this Kit for spark plugs repair contained some 12mm brass inserts when I need 14mm ( short ) . He said the Norton head is trickier than Triumph or BSA ones , the plug holes come very close to the valve seats . I'll try to get a hold of Gord Bush this week to see if he can do the job if he has the proper inserts .

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You bought the set for our 14mm thread plugs, no?

Edit: Just checked that number you quoted for your kit on 12 October with the Timesert site and it's for 10mm plugs. Bugger!! Sorry I didn't check your number at the time.

Seems you need https://time-serts.com/store/m14x125-washer-seat-spark-plug-repair-short-pn-4412-321/

robs ss said:

You bought the set for our 14mm thread plugs, no?

Edit: Just checked that number you quoted for your kit on 12 October with the Timesert site and it's for 10mm plugs. Bugger!! Sorry I didn't check your number at the time.

Seems you need https://time-serts.com/store/m14x125-washer-seat-spark-plug-repair-short-pn-4412-321/

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Yeah , the comments window on my order says " For a Norton Commando motorcycle " .
Guess no one read that . Instructions in the kit illustrated a 2- stroke head .

I'm going to box up and return the pricey kit . The driver , inserts , etc. , are wrong for a Norton .
Mo money , mo time , mo gasoline , mo postage and customs fees .
Gord Bush intelligence tomorrow in Etobicoke shop .