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Spark Plug Thread Size
#788936 11/02/19 7:39 pm
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I purchased a used head off of eBay and the spark plug was frozen into it.

After some penetrating oil and a breaker bar, I got the plug out.

The threads are pretty much destroyed, but they “might” clean up with a tap.

Does anyone know what thread a B44 head has?

Thanks


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Re: Spark Plug Thread Size
Norcoastal #788937 11/02/19 7:42 pm
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I don't know, man .... if I had a cylinder head in my hand with the threads "pretty much destroyed", I wouldn't go for any "mights" with a tap. You won't really know if the "might" worked until the bike raps you on the knee with a spark plug as you head down the road.

I'd carry it to a shop (or my shop) and install my favorite insert. No more worries.

Lannis


"Until it's safe" means "Never".
Re: Spark Plug Thread Size
Norcoastal #788938 11/02/19 7:43 pm
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A 14 mm spark plug thread.


Amateur Loctite enthusiast.
Re: Spark Plug Thread Size
Norcoastal #788939 11/02/19 7:45 pm
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Are threads on an aluminum head easy to repair?


1973 Norton Commando Project
2016 Ducati Xdiavel
1968 Ford GT40 Replica
Re: Spark Plug Thread Size
Norcoastal #788954 11/02/19 9:38 pm
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Originally Posted by Norcoastal
Are threads on an aluminum head easy to repair?


yes they are but not just by running a tap through them if the thread form is torn out. I agree with what Lannis said above.........easy fix with a thread insert ......best to get someone to do it for you

its not a big or expensive job, specially since the head isnt on the bike.


"There's the way it ought to be and there's the way it is" (Sgt Barnes)
Re: Spark Plug Thread Size
Norcoastal #788955 11/02/19 9:46 pm
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+1 for getting a proper insert installed at a shop.
An insert fitted by a pro should last, I'd recommend to stay away from DIY there as after all the insert and the setting tools are quite expensive for a one off. Helicoil will also not necessarily work for a longer time.
By the way, the spark plug thread is metric, M14*1,25 mm.

Cheers!

Ph.


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'62 A 65 Star (disassembled)
'69 A 65 Lightning
'71 A 65 Firebird
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Re: Spark Plug Thread Size
Norcoastal #788956 11/02/19 10:00 pm
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Originally Posted by Norcoastal
Are threads on an aluminum head easy to repair?


Not if you haven’t done thread repair before.


Amateur Loctite enthusiast.
Re: Spark Plug Thread Size
Norcoastal #788971 11/03/19 12:00 am
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and 3/4 reach. there must be a independent HD shop in your area that will have the insert and the proper way for the install. If you just chase the threads the plug will probably blow out.

Re: Spark Plug Thread Size
Norcoastal #789012 11/03/19 10:53 am
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The threads creep and when you drag a plug out they crack at the root and then you end up with what Lannis outlined.
Also if you go the insert route, a solid insert is better than a wire one in this application and make sure you use a little nickel ant-sieze on the plug threads from now on.
And most important DO NOT OVER TIGHTEN THE PLUG .
Wound in till it seats the 1/4 turn to crush the washer, no more.
Most of the damage is done by gorillas thinking they are sealing an atomic reactor, not a motorcycle engine.
After that carbon build up on the end of the thread.
The latter can be avoided by turning the fuel off & starving the engine rather than just switching off.
The final few revolutions will be lean and tend to burn carbon deposits off the plug.


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Re: Spark Plug Thread Size
Norcoastal #789020 11/03/19 1:07 pm
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I contacted the guy I purchased the head from and he’s going to take it back.

I’m back on the hunt for a decent head.

Thanks for the advice tho...


1973 Norton Commando Project
2016 Ducati Xdiavel
1968 Ford GT40 Replica
Re: Spark Plug Thread Size
Norcoastal #789022 11/03/19 1:14 pm
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Originally Posted by Norcoastal
I contacted the guy I purchased the head from and he’s going to take it back.

I’m back on the hunt for a decent head.

Thanks for the advice tho...


I think that the reason that heads don't come with spark plug inserts already installed at the factory is because it's too expensive for mass production.

A properly installed solid insert will be stronger than just running threads into the aluminum head, and will be less subject to wear from installing/deinstalling spark plugs over the life of the motor.

So if you find a really nice head with buggered threads, I'd get it and sort it out!

Lannis


"Until it's safe" means "Never".
Re: Spark Plug Thread Size
Norcoastal #789038 11/03/19 5:43 pm
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Nice that the vendor took the head back. I had an A65 head fitted with a plug insert about 45 years ago and have had no problems with it. The bike was only 5 years old when I got it and one of the plugs was really loose. A local machine shop did not charge too much as I recall.

Gordo


The roadside repairs make for the best post ride stories.
Re: Spark Plug Thread Size
Gordo in Comox #789065 11/03/19 8:12 pm
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there are good spark plug insert Kits , that work well .
they are just a little bit too expensive for a one-off fix ... 200 bucks and more .

there is time-sert kit ... rental service online for 30 bucks .

but if you can find a repairshop locally ... use it .
The fix isn't motorcycle specific ... it's any aluminum head with a bunged spark plug hole .
this makes the fix somewhat more Universal and easier to find someone local .

the insert needs to be locked ... which means helicoils don't quite do it .
The time-sert brand , a personal choice , is expanded slightly into place by a chasing tool ...
and a top-hat that sits in a new seat .
the chasing starts when the top hat seats ...
you want the new threads to be permanent and transfer heat .

Last edited by quinten; 11/03/19 11:31 pm.
Re: Spark Plug Thread Size
Norcoastal #789078 11/03/19 10:12 pm
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Plus one on Time serts. Think a lot about making a rig for a drill press to hold the head square and true when drilling out and counter boring. A professional shop will take a lot of the stress out of it.


Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (undergoing restoration)
67’ D10 sportsman (undergoing restoration)
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Re: Spark Plug Thread Size
Norcoastal #789084 11/03/19 10:44 pm
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I’m sending the head back because besides a bad spark plug hole, it had a broken fin.

I have a feeling most heads will need spark plug repair, so I’m going to find the best head and go from there.

If it needs a repair, now I’m better prepared.

Thanks for all of your help and advice.


1973 Norton Commando Project
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Re: Spark Plug Thread Size
Norcoastal #789133 11/04/19 11:21 am
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Plug inserts are standard fitment on some car engines from new.
Again it is a cost thing & BSA did not design the engine with the thought you will still be riding it 60 years latter.


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Re: Spark Plug Thread Size
Norcoastal #789213 11/05/19 3:07 am
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One thing I've learned (the hard way) is that you never want to remove or install spark plugs from/in an aluminum head while it's hot. So if you get a good cylinder head and you want to keep it that way...

I had solid inserts in my '67 (see Paragraph 1). When I had that done it was relatively cheap to have an automotive machine shop do the drilling and tapping. Those inserts had a flange on the outside edge, which set the plugs a little farther back in the head. I thought this may have contributed to later pinking problems, but there could have been other factors involved.


Mark Z

'65(lower)/'66(upper, wheels, front end, controls)/'67(seat, exhaust, fuel tank, headlamp)/'70(frame) A65 Bitsa.
Re: Spark Plug Thread Size
Norcoastal #789236 11/05/19 10:57 am
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I think a lot of you lot are a bit anal,, i've fitted successfully dozens of helicoils to cars and bikes over the years
and never had any problems with them. If you are careful and stake the top they work fine.
Just my 2c of course.
I agree inserts are nicer but i've not got any.

Re: Spark Plug Thread Size
NickL #789312 11/06/19 1:58 am
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Originally Posted by NickL
I think a lot of you lot are a bit anal,, i've fitted successfully dozens of helicoils to cars and bikes over the years
and never had any problems with them. If you are careful and stake the top they work fine.
Just my 2c of course.
I agree inserts are nicer but i've not got any.


Right Nick, and the helicoils don't have that flange on the outside, so you get the correct reach on the spark plug.


Mark Z

'65(lower)/'66(upper, wheels, front end, controls)/'67(seat, exhaust, fuel tank, headlamp)/'70(frame) A65 Bitsa.
Re: Spark Plug Thread Size
Mark Z #789319 11/06/19 4:59 am
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Quote
think a lot of you lot are a bit anal,, i've fitted successfully dozens of helicoils to cars and bikes over the years
and never had any problems with them. If you are careful and stake the top they work fine.
Just my 2c of course.
I agree inserts are nicer but i've not got any.

if it works for you its all good
half assed is still anal , just not as clean .
for a number of reasons
i think
a spark plug thread is worth the extra effort .
.

Last edited by quinten; 11/06/19 6:09 am.
Re: Spark Plug Thread Size
NickL #789323 11/06/19 7:36 am
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Originally Posted by NickL
I think a lot of you lot are a bit anal,, i've fitted successfully dozens of helicoils to cars and bikes over the years
and never had any problems with them. If you are careful and stake the top they work fine.
Just my 2c of course.
I agree inserts are nicer but i've not got any.


Helicoils are by nature not oil or pressure tight so my general rule is solid inserts when oil tightness or pressure tightness is essential, wire inserts everywhere else.
Having said that I do fit Recoils to the plug holes on mowers & chainsaws but a leaky plug on your lawnmower aint going to leave you stranded in outer whoop whoop.

All of the head bolts on the M20 are helicoiled as are most of the gearbox holes.
However the sump gets solid inserts.


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Re: Spark Plug Thread Size
quinten #789328 11/06/19 12:18 pm
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Originally Posted by quinten
Quote
think a lot of you lot are a bit anal,, i've fitted successfully dozens of helicoils to cars and bikes over the years
and never had any problems with them. If you are careful and stake the top they work fine.
Just my 2c of course.
I agree inserts are nicer but i've not got any.

if it works for you its all good
half assed is still anal , just not as clean .
for a number of reasons
i think
a spark plug thread is worth the extra effort .
.



Im of the same opinion, Unless I make up a rig so that I have the head fixed and angled at the same drill angle as original (regardless of if that angle is correct or not) I'd rather make sure that the hole drilled is clean and inline with the original thread. having it off plum could mean that the time-sert is not in contact with the head all the way down, worst case scenario is you'd still have a leak point!

My 2c


Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (undergoing restoration)
67’ D10 sportsman (undergoing restoration)
68’ D14 trials (undergoing transformation)

Re: Spark Plug Thread Size
Norcoastal #789372 11/06/19 11:09 pm
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https://1drv.ms/u/s!AsKcYdC1qRK7jkMVNVG_Nn4NzgR2?e=d22HZv

Picture showing a no good insert leaking and coming loose in a bevel Ducati 900. Had to make a very special insert or the head would have been binned. I never had a problem with helicoils and have had them in use in high mileage. When re-threading for them they usually cut less metal out too and if done right never come loose, and the plug will sit in the same depth it was. I prefer them.


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Re: Spark Plug Thread Size
Norcoastal #789511 11/08/19 5:12 pm
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The Time-sert tools come with a chamfer to seat the insert. You should be able to tell when using the tool that the insert will seat all the way around.
Another option is Cal-Van tools 880 spark plug repair which also has a threaded tube insert. K-D tools makes a similar kit. The reamer-tap eliminates the need to drill the hole first. Inserts come in various lengths including 19mm (880-5).
[Linked Image from toolsource.com]

Re: Spark Plug Thread Size
Norcoastal #789530 11/08/19 8:20 pm
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I was wondering about a spark plug thread repair insert kit I've seen on eBay similar to the one Dmadigan mentioned above. The kit contains 12 inserts and a 16 mm tap but no drill or other tools.

[Linked Image from i.imgur.com]

What not clear to me is whether you need to drill out the old hole and then use tap or whether the tap is sufficient by itself before using the inserts.

Also I don't know how the inserts are installed and secured in place, perhaps high temp loctite?

Would be interesting to hear comments from others if anyone has used something similar.

Last edited by gunner; 11/08/19 8:22 pm.

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Re: Spark Plug Thread Size
Norcoastal #789537 11/08/19 9:58 pm
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With a helicoil you get a sized clean up drill, Timesert the same. Both are way better than fuucked threads. I thought it would be a good idea to fit Timeserts into my old head, the threads were OK, but I knew the plugs had been in and out a lot, there was a bit of waggle about 1/2 way My LBS put Time serts into my A65 head, I watched Ali do it , proper job. , I thought they might be better than helicoils, the plugs are still not a grade A fit , somewhat loose , OK , but some perceptible waggle at 1/2 in ( same as before). I cleaned the plug , combustion chamber interface up, the plugs were more recessed than I like and an old thread was in free space , this would have invited pinking. YMMV. Unless your threads are totally fecked , dinnae bother. A helicoil might be better because it will give original plug depth. If you must do something, have the head bolt hole shoulders spot faced, my centre mount was miles off the batter.

Last edited by gavin eisler; 11/08/19 10:00 pm.

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Re: Spark Plug Thread Size
BSA_WM20 #789539 11/08/19 10:12 pm
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Originally Posted by BSA_WM20
Originally Posted by NickL
I think a lot of you lot are a bit anal,, i've fitted successfully dozens of helicoils to cars and bikes over the years
and never had any problems with them. If you are careful and stake the top they work fine.
Just my 2c of course.
I agree inserts are nicer but i've not got any.


Helicoils are by nature not oil or pressure tight so my general rule is solid inserts when oil tightness or pressure tightness is essential, wire inserts everywhere else.
Having said that I do fit Recoils to the plug holes on mowers & chainsaws but a leaky plug on your lawnmower aint going to leave you stranded in outer whoop whoop.

All of the head bolts on the M20 are helicoiled as are most of the gearbox holes.
However the sump gets solid inserts.



No parallel thread is guaranteed to be either gas or pressure tight, that's why sealing washers exist. I've never seen a tapered threaded spark plug but itv wouldn't surprise me if
the idea was tried at some stage. Most plug threads are stripped due to over-tightening, for some reason people think they are required to be 100 ftlb.
The last time i had to personally use a helicoil was at a race meeting, on checking plugs after practice my passenger was a bit heavy handed when replacing one.
I used plenty of grease on the helicoil tap and did the job in-situ. We then went out and won both our races for the day. The head still had that heli-coil in when the bike
was sold many races and years later.
I suppose you blokes would have abandoned the race meeting, driven home, taken the head off, taken it to a machine shop, etc. etc. (No bloody way .)

Re: Spark Plug Thread Size
Norcoastal #789543 11/08/19 11:26 pm
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i helicoiled a spark plug once on a small block chevrolet motor without taking it apart. never saw it run afterwards but the job was straightforward.


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