Spark plug thread recovery

[geewhizz]

Last time I rode the bike the right hand spark plug jumped out. I can't get it to thread back so I'm guessing I may have cross threaded it at some point and now the threads maybe shot all the way.

Can anyone confirm the thread size - M10 x 1.0 ? 

Secondly what the best fix, any alternatives to the helicoil? I saw this reverse action thread repair tool on youtube/ebay (although I've yet to find an M10)

Is it an en engine out job?

Thanks,

[Beresford]

The thread is bigger than M10, (that is the normal size for mirror stems), but I could be corrected on this. If you look on youtube for " time sert spark plug repair " there's a lot of info there on how to fix it properly. Also comparisons between helicoils and timeserts. Helicoils are adequate for non-critical stuff, but for the plug I'd choose timeserts .

I don't think that there is much to choose between them except for the installation process. With the timesert it is much more precise, and accuracy of installation alignment is far superior.

[geewhizz]

Thanks for the lead on the time-sert Bereford, it certainly looks the part. I'm tempted to do both cylinders if I can get that tool but it looks to be ££££. 

'time-sert how to' video if anyones interested > https://www.youtube.com/watch?v=ygT0XZZald4

Looks like it may be a fiddly job as the spark plugs are fairly recessed and I don't have access to compressed air. I've ordered a cheap endoscope to try see what going on first.  

For anyone interested the NGK spark plug codes for out machine > CR8EH-9

C=Shell thread = 10mm x 1.0mm pitch
R=Construction = Resistor
8=Heat Range = 8 (between 2hot 12cold)
EH=Reach = 19mm Half Thread
-9=Gap = 0.9mm

Cheers

[geewhizz]

I'm keen to know if anyone has heard of or used a 'US PRO Spark Plug Thread Repair Kit' before? I've linked below. Looks like it sits between the time-sert and the helicoil. There's a lip on the female thread so should stop it dropping inside the cylinder. There is not an attachment to rebore the seat/lip so I'd guess the spark plug would sit proud by a millimetre or so further than stock. Certainly cheap...Any thoughts welcome ! 

https://www.ebay.co.uk/itm/US-PRO-Spark-Plug-Thread-Repair-Kit-M10-X-1-00-5872/153742280405?epid=6024255209&hash=item23cbc106d5:g:NFUAAOSw-0xYiMAF

[motofan]

Hi there , have you fixed the problem? I just thought, have you tried to refit the plug?If you stripped the threads (naughty boy) then it won't tighten back in, if you hadn't tightened it up enough (naughty boy) then the threads might be stripped with the hammering they would have received OR (if you're lucky) the plug might just have unscrewed itself. So try to refit it if you haven't already and you may be pleasantly surprised!
Dave.

[geewhizz]

Problem not fixed yet. I'm confident the threads are damaged, it's been a good excuse to buy an air compressor so its not all bad news. I suspect I under tightened them and they came loose damaging threads on the way out. 

I picked up the kit linked above just to have a look at it as its ruffly 1/20th the price of a Time-sert kit.
 
I'm not convinced this will work. The issue I see is that the spark plugs in our machine has a shoulder instead of being fully threaded like some others. The shoulder seems to act as a stop for spark plug - if it gets seated that far when installed. The concern is if the insert is in but the lip isn't flush to the head, the crush washer on the spark plug won't seal down on the cylinder head before the shoulder of the spark plug hits the lip of the insert. Makes sense? Will post a pic later to illustrate the query.

Hopefully I'm just over thinking it.

[motofan]

Hi there Mr Whizz, as you say those inserts are probably not good unless there is enough meat in them to open up the top part i.e. remove the internal thread to allow the plug to sit onto the top rim, then it would be no bother! I've just replaced all of the plug threads on my 1975 400f with standard "springlike" helicoils, they were 12 x 1.25 mm so a bit more chunky than the 500 threads, but I removed the head to do that, are you doing yours in situ?

[geewhizz]

I'm a bit nervous about helicoiling the cylinder head. The time-sert tool comes with a cutter so the lip sinks in flush, I'm just not sure if it would fit down the narrow plug recess. I was hoping to avoid taking the head out but it's starting to look like a safer idea.

[motofan]

Measure the space at the plug entry, if you can get a plug spanner in there then the insert will fit sshurely?

[tt fan]

Just want to add that i would definitely spend the extra on a time-sert thread repair. Preferably solid carbon steel insert and use a high temp thread lock when you fit it. I dont envy you, personally i think removing the head is the only chance of getting a good result. Wish you luck

[geewhizz]

Thanks for your input TT fan, time-sert does appear to be the favoured method however the kit is eye wateringly expensive even with current £10 off and free delivery, its £186 inc vat direct from Wurth   Hoping its one of those companies where its cheaper to avoid buying directly.

[geewhizz]

If I can find an m10 x 14-15mm counter bore to recess the sleeve, id be very tempted to give it a go with the us pro thread repair kit sleeves

Need to counter bore 14mm diameter x 0.8 mm to make sleeve flush

An example of the type of tool. Ideally just want the counter bore with a narrower diameter to make hand cutting a bit easier

[tt fan]

Wow how many inserts come in that kit?
If it's 5 or 6 you could probably use one and sell the kit on to recover (i guess) half your money. This is the trouble when you factor economics into repair of cheap / old bikes and stuff.
Just a few other ideas - good used head / possibly engine should be available on here or the bay. That's the way i'd go. Or ask someone who repairs small engines professionally (think chainsaws) if they would replace the threads in your head as a one off??

[geewhizz]

Decided to take the head off, now realise I should have done so to begin with. The tolerances with the US Pro inserts + tap seem too baggy for my liking. I'm going to use a V-coil spark plug kit with a tapered tap and go at it from the cylinder side up and JB weld the insert. At £35 seems like the right tool for the job.

[tt fan]

How did you get on with the Vkol??
I hope you got it sorted  

[geewhizz]

V coil seemed to work really well thanks although I've yet to test the engine running. I'll update in a cpl of weeks with a vid when its back in action.

[geewhizz]

Just want to say a big thank you to all the members that gave me advice and parts recently while I got my bike back in order. Went for test ride this avo after finding out theres been a 6 month extension to due MOT dates at the mo. First ride in many months and the bike seems better than ever. Never started so easily and sounding very smooth. Below is a note of all that got changed > mainly writing it here so I know I have a note of it somewhere.

50300 miles on the clock - both spark plug cylinder head threads V-coiled, re-cut spark plug seats, new spark plugs, new valve stem seals, valve cleaned and valve seats lapped, valve clearances re-done, cylinder head resurfaced, ports and piston head cleaned, new cylinder head gasket, new carb to head rubbers, carbs degreased, new radiator, fan, hoses and stainless rad cover, new engine casing bolts and gaskets, new sump gasket, engine resprayed, front half of frame resprayed, down pipes resprayed, new fuel, vacuum and carb to head hoses... think thats about all. Will post a pic later.

   And the lesson is, better to take care when changing your spark plugs

[tt fan]

Sounds like a major spruce up. Well done on getting it sorted. Post thst pic

[geewhizz]

see if this link works for photos + walk around vid on dropbox

https://www.dropbox.com/sh/mvd2o2czextmku0/AADNQUAIfArh54powM0KwLRJa?dl=0

[tt fan]

Link works.
You made a really nice job of that.
What did you use to paint the engine?
Bike looks great!

[burudi]

to remember that there is a video in this post on how work is done and without removing the cilinder head ... and if it is also a home service, I think it is unnecessary to overheat your head because there are professional experts in this work and all over the uk .... looking and asking, of course.

the coronavirus is enough fever and anguish .......

[geewhizz]

TT Fan > Thank you, I'm happy with the way it's turned out. For paint I used Simonez Engine Enamel Matt Black (engine) Gloss (frame). The gloss air cured to a decent finish, the matt needs heat/baked (which I didn't realise at the time) If I were to do it again I'd probably use a 2K spray can for better durability, chemical resistance and air curing. I think 'Engine Enamel' is an enticing marketing phrase, i'm dubious of its long term durability however. 

Burudi > I'd say by having a go, its the only way to learn, part of the reason for my bike ownership was to become more mechanically able. Hopefully next time I won't be half as flustered ( I'd also choose head off + V-coil over Time-sert in situ ) and it has provided some welcome distraction from the current Global chaos!

[jonnyteabag]

Well done sir!

Garden looks fantastic too  

JT

[Beresford]

What are the rear shocks ? I have similar alloy TECs with the remote reservoirs , but I wouldn't have thought of mounting them upside down like that.

[geewhizz]

They are made by TEC so probably the same shocks. If memory serves, I had to mount them in that orientation because they were fouling against the side grab handles the proper way round...been a while since they were fitted 

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