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Valve caps


My Inter's exhaust valve head is bruised by the tappet. It has no chamfer (oddly?) and I'm going to grind one using a Dremmel before I extract it.

Do others use valve caps? Or are they too likely to escape? The top of the exhaust valve is one of the places on my Inter that has least oil, so I need to remember to grease it regularly (moly grease probably). Also...make certain the tappet tip is dead square to the rocker...


Spreads the load, protects the stem and machinable to adjust the rock angle.  Why wouldn’t you....


cheers Jon


The top does not look very pretty. I'm certainly going to replace the tappet, and assumed I should replace the valve. But if I do add caps, it will need to be a bit shorter anyway.


To wear that profile into the stem suggests a lack of rotation of the valve, probably due to lack of lube at the guide, a partial seizure and then a reluctance to turn.  I guess the guide is fairly worn also.  The cap solution is the way to go, there were a set of 4 on EB up to today with little interest at £12.  PS; the adjuster is not the tappet, that’s the bit that contacts the cam.... they are also replaceable should you have a wear issue there.

good luck Jon


Thanks Jonathan.  The guide is fine - relatively new bronze.  I'd be surprised if the valves turn in service - with hairpins etc.  (after writing this I see from elsewhere that they are supposed to rotate..don't understand how - unless it's later engines?)  But I think I'll go for shortening it and adding caps.  I might even make my own - they'd better be hard (or hardened) but off the shelf sounds good.  I've just looked at the spares list - part 3046 'rocker adjusting screw' needs to be changed.  Now to work out how to cut 80 thou off the valve stem and keep it square.  I think they had caps post war - but that's a bit of hear say.

Franks lists 20thou clearance for exhaust valves.  I wonder why so much?  The impact must be huge.  There's very little to expand differently in the cam box, so the hot clearances must be similar.

Now it's worn, the rocker surface in the adjuster slides nicely in the worn surface of the stem - could have been designed that way!  I bet that's how a lot of them work - these engines are well known for flogging on well after they should be described as worn out (allegedly).  Perhaps because of the amount of oil that surrounds everything apart from the tops of the exhaust valves!



Hi David,

   The reason the valve clearance is so much on the exhaust valve is because the valve material is austenitic steel which has a very high expansion rate and was originally KE965 grade. Another factor is an OHC engine is a fixed measurement as opposed to a push-rod engine where cylinder expansion affects the valve clearance. This alloy of steel valve is non-magnetic and has a high temperature stability. These were machined to give a 4 thou clearance in a 3/8th inch guide and appear loose when new. A bronze guide in a cast iron head in not the best fitment as the bronze expands quicker than the iron and distorts, this may be why the valve has not been rotating. A cast iron guide is much better as this material requires very little lubricant to work satisfactory. As a rule of thumb, cast iron head/cast iron guide, aluminium head/bronze guide. Do not use an austenitic valve on the inlet as this valve is constantly cooled by the incoming fuel. If you want to get a working clearance run the engine until spitting hot, have a set of feeler gauges ready and measure as soon as you stop the engine, minimum at this temperature should be at least 2 thou. The valves are relatively soft and can be filed by hand. Beware of modern valve material as this may have been intended for a water cooled fitment, so do some checks.


Thanks Richard. To be honest I don't know  the guide material...I thought I could see some yellow on the inlet but exhaust is black. I'll scratch it off and check. It was built by a well known Inter expert so I hope and expect it was correct. On Doddington web site are some assembly notes, where they say valves begin to rotate at maximum revs. I doubt if this engine has been over 4500rpm. I don't know if that's relevant! Now it's apart I want it to be as good as possible, but there's no point in buying a new valve if I shall shorten it and fit a cap anyway. They don't seem to be much marketed in the UK.

I'll start a new post shortly about meshing the top bevel...


What a wealth of knowledge we have access to. I always found the 12 /20 thou settings a bit  extreme and tend to reduce them to a noise level that sounds right after a piping hot run. But I've  not ventured down to 2 thou yet...

 They can take a lot of hammer if they are set up right, Any motor that can take the punishment of a TT will be fine on the road, we rarely if ever get to those extremes nowadays. As you believe the guide is a recent replacement is it so for the valve?  Is it a soft material replacement as Richard suggests.  Magnet test would give some indication, and get a magnifier on the   removed valve to check there is no stelite cap friction welded to the stem. 

Take off the burr with a file first.  I would say a grind would be the best way to resurface.   As its such a light touch I would use the side wall of a wheel mounted in the lathe chuck and the valve stem located in a fixture (fit sized hole in a block) mounted to your tool post would work.  Don't let the heat build up and cool quickly after dressing.  How  much to  take off  depends  on thickness of  cap and  your  Half  lift  measurement (at half lift your adjuster should be square and central to the valve stem/cap)

How many of the valve grinding machines from the repair shops have gone in the bin...  

 The caps are termed by our american cousins as "Lash Caps" should you be searching the  internet for some.


Go steady





While I was repairing the head on my 31 model 20 I asked Mike Pemberton if I should use iron guides again , his replay was to use colisbro guides..Reading up on these guides I see they can be used in iron or alloy head.

I used Chevy big block valves cut to size and like my Ariels I used  valve caps only because they do make sense.




Interesting, Ian. I can't find any 3/8" ones in UK. I'm not buying from Aus...£57 postage for a start! I have read on the ever unreliable web that stainless valves must be used with bronze and not chrome stems. I don't know what kind is the one I ordered. I'm going to reassemble with the old one becauseI know it works. I'd rather go back to it later if it wears annoyingly quickly, than have a bike resting in the shed! It's a single..much easier to remove and replace the head than it is for a Norton Twin!


Thank, Michael. USA and out of stock! The last item I bought from US had a price of $16, but cost with postage about $40, and took four months to arrive! International trade is somewhat vague it seems to me. I think it was lost for weeks in a post office in Michegan.

I've just been told a friend of a friend has one. I hope it will arrive in the post. 

I've also been told by a long time owner and racer...they all do it, so put up with it for as long as possible! I'm going to use moly grease on it from now on.



Thanks Michael - no joy.  A friend tell me his friend has some...I'm hoping one will turn up in the post. Otherwise I'll just keep the tip greased with moly grease and keep on adjusting when I need to.


Hi David / all,

   The NOC shop has a couple but they are not cheap at £35 each plus post and VAT. Paul Norman at racingnorton has a large selection of new valves at around the same price


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