Decompression valve problems Ariel NG

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william.forsth
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Decompression valve problems Ariel NG

Postby william.forsth » Mon Sep 03, 2012 9:10 pm

​Hi all, I lime to ask for a favour, I need a picture of a corect docompression valve setup , wires and valve. I cant get mi e to work, I have another wire fitted to it, and I got an original one, seems pretty straight forward, but cant get it to work. Might be tha valve is to worn or somethingas well. Pleas post picture here, or email me :-)

William.forsth@gmail.com
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Re: Decompression valve problems Ariel NG

Postby Silas.S » Tue Sep 04, 2012 8:42 am

Commonest failure of Ariel decompressors is the lever to spindle joint. It is a taper fit. It is probably loose, or fitted at the wrong angle. Undo the nut at the end of the spindle. If the arm falls off you then know why it is not working. If it stays tight see if the little peg that presses down on the valve collar works when you move the lever by hand. No? then tap the lever off the spindle and adjust it until it does. If this fails I probably have a diagram to scan somewhere. Silas.
sas.

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keith.mettam
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Postby keith.mettam » Tue Sep 04, 2012 9:59 am

Hi William,
Try this DraganFly link it shows the decompressor assembly components which may help you :-

http://www.draganfly.co.uk/shop/pi44443 ... egoryId=63
(Open the link in a new window if it doesn't work).

With my 57 NH the unit started leaking oil badly recently and when I stripped it the leather washer was hard and disintegrating. Of more concern to me was the excessive wear to the spindle and body of the assembly. I have put a new leather washer in it and re-assembled it and at the moment it seems ok. I expect I will have to get a new unit from DraganFly if it leaks again.
One point to watch when setting the de-compressor clearance at the rocker arm is that it is not too tight so as to affect the exhaust valve clearance. Although it can't change the clearance it can make it impossible to accurately set the clearance if the de-compressor is too tightly adjusted so that it has very little or no free play between it's operating lug and the rocker arm. This will then prevent the rocker arm seating fully back into the pushrod when checking the valve clearance. Ensure your exhaust valve clearance is correct before you start assembling the de-compressor unit. Then fit the de-compressor. Once you have got it working (it doesn't need to open the valve much at all) just re-check your exhaust valve clearance is still correct. If not re-adjust the de-compressor and then check the exhaust valve clearance again until ok.
When the body and spindle wear on these units you can end up with a lot of 'lost motion' and it may be impossible to get the unit to work, so you might need a new one, William.
All the best with it,
Keith Mettam.
Last edited by keith.mettam on Wed Sep 05, 2012 10:43 am, edited 2 times in total.

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william.forsth
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Postby william.forsth » Tue Sep 04, 2012 11:47 am

Hi - the thing is, I am not even sure it is the right assembly fitted on the bike. I know it is not the corect cable, but the one I ordered woorks even worse than the one fitted. It might be German parts. I get the feeling this bike been patched together and then shipped of in bulk to sell in Sweden in 1947 or 48. There is a german WWII tail light on it, and there was a very nice Pagusa passenger seat on it from wartime BMW I think.

Image

However, this is what it looks like today. And the valve mechanism , Ijust cant get it apart for the life of me.

Image

I am not even sure it is the right one ?????

The problem seems to be that it does don to back enough (forward) but rather stayes in an backward position, which after a while due to vibrations etc makes the valve open, and the engine decompresses and stops. There is a bit of wear and tear in the assembly so it is not that tight fitting.

Any thoughts ?


and while I am asking away, I got two different rocker box caps, is that correct? or is this also just a fluke of wartime scrap engineering
No 1 correct one I guess!
Image

Not a correct one I am guessing
No 2
Image
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brenton.roy
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Re: Decompression valve problems Ariel NG

Postby brenton.roy » Tue Sep 04, 2012 2:01 pm

Hi Will,
it's just going to be a matter of adjusting the setting so that the pin on the inside of the decompressor arm is near the tab on the rocker arm - as Silas has said - so when you pull the cable, the pin pushes the tab, the valve opens.
You can see how it works by moving it around. The nut (that should be) on the thread that faces up in your photo is a lock nut. You put a srewdriver in the slot at the end of this shaft to adjust where the pin should be, get it right, then tighten the lock nut. If it's all tight, it should not come out of adjustment. Check the taper ( also re Silas).
If the taper is totally stuffed - you tighten it and it still slips, you may need to take more drastic measures.. You may need to grind a little here and there. Usually, a washer with a hole that is wider than the taper will work, if it has clearance to pull up.

A 350 probably doesn't need a compression lift. A healthy kick should work OK. - You might choose to adjust it so it doesn't work at all.

The sping you have should work OK. The correct one is like in a pair of garden secateurs. You might be able to find one in a hardware shop.

The worn rocker cap is the right one for early motors. You can either buy another new pattern one or file the shoulders square. Worn but working is good.
Keep smiling, it's all good!
regards, Brenton
'51,'56 Squares, '48 VH, '27 Model C, R67/2, Mk IV Le Mans, '06 Super Duke and Ariel projects.

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Re: Decompression valve problems Ariel NG

Postby Silas.S » Tue Sep 04, 2012 2:15 pm

Valve lifter.jpg
As you can see the Ariel item ends in a disk with a pin protuding. It is this pin that presses down on the valve retainer to open it. As far as I can see from your photograph this disc and pin is absent [?]. Also the screwed portion that goes thought the rocker cover looks far to long to me, but I havent had one of these out for a while. The diagram also answers your rocker cover question. Draganfly had some of these when I last bought some. There was also [on some models] a sprung finger that prevented the rocker cap unscrewing with vibration. It also prevented them being unone with a spanner. A lot of the sprung fingers got thown at the cat as a result. In comon with others who got fed up with lost rocker caps I lock-wire mine via a small hole drilled in the outer part of the rim. It looks as if your valve lifter also has an arm that is a taper fit on the shaft. I expect it would tap free and you could then dismantle it. Silas.

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Re: Decompression valve problems Ariel NG

Postby Silas.S » Tue Sep 04, 2012 3:07 pm

If we are getting really anorak-technical the 'secateur' type spring is a "volute" spring. No doubt so-called because of its ability to volute into the darkest corner of the workshop. Silas.

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william.forsth
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Postby william.forsth » Tue Sep 04, 2012 7:26 pm

HI all, and thanks for the marvelous feedback. I am pretty sure it is an adjustment thing, and my current assembly will not come apart, so I ordered a new one. If I can adjust the arm/lever I guess I can get it to work better with the spring and make it press down the valve retainer and get back and stay clear from it. Right now it does not go back enough, and therefore forces the valve to open and decompress. Well that is my theory at least.
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Re: Decompression valve problems Ariel NG

Postby john.nash » Tue Sep 04, 2012 7:59 pm

exhaustlifter.jpg


Here is one of mine.
Unfortunately they are all under the tank so not easy to get a picture

ok. so

Take off the exhaust cap, over the valve.
Roll the bike up to compression TDC, so that you can feel the play in the exhaust valve rocker.
Loosen the lifter arm by undoing the nut over the screwdriver slot and then hitting it with a small hammer ( try to get the nut far enough over the end, where the screwdriver slot is, so that the hammer doesn't round off the end). The arm is on a taper and should now be loose.
The spring will hold the arm in place.
Turn the nut back in BUT don't do it up.
Now, get a flat screwdriver in there and turn the lifter so that it's just off the valve. You will feel it hit the valve (and can tell there is no longer play in the valve either). The knack is to get it JUST off the valve (not easy; needs practice) and then hold the screw to stop it moving while tightening up the nut.

It's a pain the arse.
The book says to operate the lever a bit, when doing it (whick kind of takes the place of my thing about adjusting so it's just off the valve). I find that needs one more hand than I have.
John "Josh" Nash
webmaster@arielownersmcc.co.uk
AOMCC No.4119
2009 royal Enfield,1978 t140 bonneville, '67 CJ750, 196-ish Ural M62 outfit, 1960 k750, ''51 kH500, ''49 soon to be Ariel bobber, 47 VH twinport, '44 Ariel WNG, '43 Ariel WNG, '41 Ariel WNG and piles of rusty scrap ....

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Postby ian.scott » Wed Sep 05, 2012 9:05 am

Are you sure the outer cable ,which is what actuates the lifter is not getting caught under the tank ?
I have had a lot of problems with that and in the end had to raise the tank slightly in order to give the cable more room to slide back and forwards as you lift the valve.
Ian


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