Ariel Owners Motorcycle Club

Only back on the road a month or so since rebuilding the head (long before necessary) due to a dropped valve insert, I almost didnt make it home after a club run on the VH when out of the blue, it “popped and farted” to a standstill somewhat inconviently between towns and on my own.
After considering my options and which mates were nearest with a trailer albeit probably an hour away, I did the right thing and went through the “I reckon it could be this” checklist.
No spark led quickly to Magneto points had come loose and the gap had disappeared. Thankfully I carry my original toolkit and hence saved by a 50c magneto spanner
Happy to get home without a trailer!

I find its often useful to look at the `last thing you fixed' - its often the cause of problems.

Too right. A couple of years ago, I stopped to clear a blocked main jet. All was fine until a few days later, and the bike was bogging down as I tried to get a move on.

The jet I had cleaned had mysteriously fallen out...

Could have been the origin of the id jet. Ahh Roadside restorations are the worst kind especially in front of a large audience who have all the answers they read of somewhere. The Pain worse than death. Proper preparation prevents pathetically poor performance, hopefully. Never be rushed or talk to people as you are doing it. A GOOD bike is not always the shiniest. It's the one that goes nicely the whole rally . Nev

hi Michael ;
i had similar occurence on my NH , i found that the points had closed up because the thread for the bottom contact was worn to point of being stripped , the alloy material used in the casting is very soft and its not hard to do the locknut up too tight to the point of pulling the thread out with it .

the thread used is same as uk electrical wall sockets use and what i did was use one of the brass threaded bushes/sleeves from a metal wall socket and fit it into the points carrier , i turned it down slightly to give it a slight step at one end , then i drilled the carrier out to allow me a tight fit , then loctite and press the brass "bush" in place , i turned the bush in a lathe so i had a slight lip on it to stop it "pulling through" , its only small but can be placed on a long 3.5mm screw and then gripped in the chuck and then turn it down from left to right lightly using a small sharp tool ..

i think thread is 3.5 x 0.6 mm for the standard Ariel points contact , as well as the uk electrical sockets .

ian

MGriffin wrote: ↑Sun Jan 15, 2023 10:47 am Only back on the road a month or so since rebuilding the head (long before necessary) due to a dropped valve insert.....

Michael
I'm a bit late on this, but I'd be interested to know how you fixed the valve insert.
I've also got a head with a dropped inert, I think it's because the insert is too thin (it's happened twice, the original guy put in a new insert but it was the same wall thickness).
Any idea what the dimensions of your new insert are?

SG

Thick walled inserts don't have enough "give". Thick ones can also crack the head for that very reason. The new type (that's been around for years now) is more likely to stay in place. A good finish on the mating surfaces and the correct interference is needed.. In alloy I go deeper. Even some cast in ones hammer and come loose in alloy. Liquid nitrogen is used with Porsche heads. Cryogenic Don't use plain cast iron for insert material especially in the exhaust. The HEAT can shrink it and it will come loose. Nev

Simon.Gardiner wrote: ↑Mon Jan 23, 2023 4:08 pm

MGriffin wrote: ↑Sun Jan 15, 2023 10:47 am Only back on the road a month or so since rebuilding the head (long before necessary) due to a dropped valve insert.....

Michael
I'm a bit late on this, but I'd be interested to know how you fixed the valve insert.
I've also got a head with a dropped inert, I think it's because the insert is too thin (it's happened twice, the original guy put in a new insert but it was the same wall thickness).
Any idea what the dimensions of your new insert are?

SG

Hi Simon,
Yes the insert was too thin but in my experience its often best to leave good looking inserts alone….this was the exception though.
Either way, it failed slowly thankfully when trying to re-start after a petrol stop.
The new inserts (replaced both) are much thicker and now a bit deeper aswell. Down side is that because my head ports and throats are a little “worked” from years of tuning and use etc I couldnt open the inserts up to match the throats as I would be back in the same situation as before. The result is there is a small “step” behind the valve that has been “softened”.
I believe the inserts are high performance unleaded type.
I can find out the size and type if that helps?
Regards
Michael.

Michael

I'd be very grateful for any dimensions so I can compare with my failed one (and get a guide for what might be used as a replacement).
I think my failed exhaust insert was something like 1.775" OD, 0.125" thick and 0.275" deep. (The inlet is a similar size and that seems fine.)
These were fitted 'cryogenically' but maybe with dry ice was used rather than liquid nitrogen.

I'd like to reclaim the head if I could!

Thanks

SG

Thinner ones are BETTER if they are of the right metal and fitted with enough interference. Thick inserts have no give and can split the head or just crack it. If Inserts come loose it will generally be the exhaust ones affected as if the heat does not get out of the insert it will SHRINK itself by getting red hot. Good finish ensures good contact and heat flow. A roughly formed recess could be the trouble. All the GAS and Unleaded use insert are good. Nev