increasing tappet clearance

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
Chris Berry
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Location: QUEENSLAND AUSTRALIA

increasing tappet clearance

Post by Chris Berry »

Hi all
I have just got my head back for a second time having fixed the exhaust valve and am now in a position where I have found that the distance between the rocker and cam on both valves has progressively increased to the degree now where I do not have sufficient adjustment on the push rods to take out the slack. I have checked:
the cams - all good
removed the head and checked valves - again - all seems good
push rods are not noticeably bent
The relationship of the push rod height and rocker cover still seems to be the same. The only possible thing I can think of is that the rocker arms have moved on the spindle. I checked the nuts on the end of the spindle and all are tight. I fear undoing them to check the spindles as they are so tight I may damage the alloy rocker cover. I must stress that the clearance has PROGRESSIVELY increased. I do have a back up where I can put the hardened valve stem caps on the valves but this is treating the symptom not the cause. Has any one come across this problem before
Mick D
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Re: increasing tappet clearance

Post by Mick D »

Hi

It's unlikely that the rocker arms have moved on the shafts - they're splined.

Has the case hardening on the rocker arm where it bears on the valve stem worn through? the arms would then wear and give the symptoms you have.

Is the oil supply to the rocker box OK? If not this will also accelerate wear.

Did the valves come from a reputable source?

Regards Mick
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clive
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Re: increasing tappet clearance

Post by clive »

Are the valves the earlier type that need the end cap? Sounds like they might be. If you use them without the ends are not hardened and will wear giving the symptoms you describe.
clive
if it ain't broke don't fix
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Rob Harknett
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Re: increasing tappet clearance

Post by Rob Harknett »

I was about to ask, have you got valve stem caps, which would solve your problem. The 1948 parts list does state you should have them pt. no. STD 685 that's 000685 new pt. no.
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Pharisee
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Re: increasing tappet clearance

Post by Pharisee »

Has one of the steel end caps become a loose fit on the alloy push rod. I had that happen once on a Triumph and it 'hammered' the end of the alloy tube and opened up the clearance.
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SPRIDDLER
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Re: increasing tappet clearance

Post by SPRIDDLER »

I assume you have the Parts List for the '48 Ajay (and Matchless) singles:

http://archives.jampot.dk/book/Spares_l ... s_List.pdf

which shows valves caps to be used, unless the valves you bought from Club Spares don't need them (e.g. have longer than standard stems):

Image

In the same parts list you will clearly see on page 11 that the cams (FE59 and FE 60) and shafts (FE 57) are splined together so cannot 'slip'.

Image

Later:
:?
I've just had a look in my shed at some NOS pushrod bits for a '47 and there's about 7/8" of thread on the adjustment ends. The caps can only be around 3/16" thick but are there to protect the tops of the (originally fitted) stems from cam wear as mentioned elsewhere.
Image
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Which taken at the flood............'
Chris Berry
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Re: increasing tappet clearance

Post by Chris Berry »

Thanks although it is a 1948 frame the engine is a 1951. These are new valves I purchased from AMOC and had fitted. its got me beat
Chris Berry
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Re: increasing tappet clearance

Post by Chris Berry »

I have found the problem. It seems that the bottom of the barrel has split allowing the barrel to lift and thus the extra distance between cams and valves. Right now I am in desperate trouble as I don't think the barrel can be repaired. Does any one know where I can get hold of a 1951 barrel with the back cut away for the rear mounted magneto. Am willing to pay anything to get the bike going again
Mick D
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Re: increasing tappet clearance

Post by Mick D »

Hi

Ouch!! - My first phone call would be to Steve at AMC Classic Spares, He's helped me out in the past with used parts.

If you post a photo of the damage I might be able to suggest a repair but it's not that likely, is the barrel sleeved do you know?

Regards Mick
SPRIDDLER
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Re: increasing tappet clearance

Post by SPRIDDLER »

Oh, Lordy. You've had more than your share of problems.
I overlooked that it has a later engine.

Back on May 6th you wrote:
Chris Berry wrote:I have just had my G80 resleeved and taken back to standard. The engine rebuilders advised me that they had bored the sleeve to allow 0.005" piston clearance. On my first run after around 6 miles i came over a reasonable hill in third gear (so as not to labour the engine) at around 20 mph and the was coasting down the other side in top gear at 30 mph when the engine stopped. It appears the engine temporarily ceased (to be confirmed when I lift head).
It's rare for a cylinder base to crack. It could it be due to stresses imposed on account of the re-sleeving or the seizing (or both).

As Mick mentioned, Steve Surbey at AMC Classic Spares may be able to help.

http://www.amcclassicspares.com/

If not you could try Les at Russells Motors in Clapham, London. He only does new or NOS but it may be worth enquiring. He doesn't do email, only fax and phone:

http://www.russellmotors.co.uk/

If a repair isn't possible (a photo might be a help) look on eBay or maybe put a 'Wanted' ad on this site?

As a wild and off-the-wall thought and since you're far from suppliers with potentially high shipping costs perhaps someone on here could comment whether it's possible to have a later (non cutaway) or AJS cylinder barrel machined to accept the rear-mounted mag (you'll have the old one as a pattern) which would give you more options to find a replacement cylinder in Australia.
'There is a tide in the affairs of men
Which taken at the flood............'
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