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Lower valve guide removal

gwild

Active Website User
VOC Member
This is my first post so before we start I'd better get the hello everybody proceedings out of the way. Hello everybody. Now to business

I'm currently trying to rebuild a C Comet.
Over Christmas it was together enough to enable me to start the thing for the first time in my care (also my lifetime) which was a good feeling, but what was not was the lack of compression through my right foot. The valve guides were worn, so the valves weren't sealing against their seats.
I've taken it apart to put new lower valve guides in the heavily worn existing, but how do I get the old ones out?
This is the head:
head.jpg
I made a crude fork with short fat tines to fit in the lockring, but after heating and twisting the head all I accomplished was shearing off the tines.
To my limited experience the lock rings don't look punchlocked in:
exguide.jpg
The only mess around there is the working to relieve the oil flow to the rocker:
extunnel.jpg

Any help would be appreciated!
Many thanks,
gwild

Previous photos of the rebuild start here
 

CollingsBob

Well Known and Active Website User
VOC Member
I highly recommend that you fit valve guide seals...and while you are at it, fit new rocker arm pivots. Those things, along with modern pistons & oil control rings will transform your bike.
 

gwild

Active Website User
VOC Member
progress so far

I made the tool as specified in KTB, which was successful in getting the old lock rings out.
lockrings.jpg

Unfortunately the hole in the head for the lower exhaust valve guide is oversize, so I'm having a go at making my own guide. I've got a lump of colsibro to make it from, a normal size sealable guide and the old oversize but worn guide to copy (l-r, figure below)
newguide.jpg

My next question is what tool should I use to line ream my new guide and the upper valve guides? I've been looking in tool catalogues but cannot find the undersize 3/8" reamer (that will also have a suitable arbour to fit through the upper valve guide to keep all concentric) needed. My only idea is to take a 3/8 reamer and make it fit using a centreless grinder, but this seems a bit drastic. Is there another way?

As an aside, my exhaust valve seat has a few nicks in it. Does anybody have an idea where I can find the correct 30 degree cutter? I have some new valve seat rings but do not think they are necessary.

Collingsbob, the liner is re-bored to fit my newish piston with gapped rings so should be good.

thanks and shall update with progress,
Gwilym
 

ogrilp400

Well Known and Active Website User
VOC Member
G'day Gwilym,
Hey mate your well on the way, keep it going.
Turn the od then bore the id so that the guide is about .002" to .003" under the size of the valve stem. This makes sure the two are concentric. Don't go any smaller on the od than the old guide. If the old guide shows any signs of black oil carbon where it fits the head then I would go about .0005 larger.
Now the line reaming. There is a couple of ways of doing this. Get yourself a new up to 3/8" adjustable reamer. Machine yourself up a small top hat bush to fit in the top guide and around the shank of the adjustable reamer. After fitting the bottom guide put the bush and top guide in place and ream from the top down.
Or, get about 4" of 3/8" round solid. Drill and tap into the end the same thread as the adjuster on the reamer. Screw the 3/8" RS tightly onto the reamer and place in the lathe and turn down to 5/16". Put the top guide in place and ream from the combustion chamber side. A tip here. get a valve spring and a screw on cap and put it on and it will hold the top guide in place whilst you ream.
Now the reaming. Go very carefully and ream until the valve can just be tightly hand pushed into the guide. Once that is achieved use metal polish to lap the valve and guide to a free fit. When final assembling, coat the guide and valve stem liberally with molybond grease. You may have to run upper cylinder lubricant for a while but it will cut your oil consumption. The exhaust valve side can be a slightly looser fit.

Phelps.
 

ogrilp400

Well Known and Active Website User
VOC Member
Oops forgot to mention. The valve seat cutters should be available in 30 degree. 30 degree cutters are used for top cutting the usual 45 degree seats.

Phelps.
 

gwild

Active Website User
VOC Member
Question for materials specialists

With help I've been looking at my exhaust valve in detail. The head is slightly bent, and the shank looks as if it has caught on the lower valve guide at some point, so the head got bashed by the piston?.
I was going to replace the valve guide with some colsibro (copper, nickel and silicon alloy, often used in valve guides), but I have been advised by a restorer of Austin 7s to use cast iron instead. Which should I choose?!

I am cautious as his area of expertise have cast iron heads, while the Comet is aluminium. I don't think I should be worried about the expansion coefficients, as cast iron is less than aluminium or brass, but what are the other pros and cons? It doesn't help that I am having trouble finding proper material data sheets for colsibro. I've never heard of cast iron being used as a valve guide for Vincents, but why not? It would require a tighter inteference fit when cold?

many thanks,
Gwilym
 

gwild

Active Website User
VOC Member
Burman gearbox problems

I put everything together today, and it worked! Well, it ran, and first gear worked with a bit of fettling.
But there seems to be a problem: second and third gear of the Burman box don't appear to do anything. Shifting upwards from 1 just gives a neutral, and again, until into fourth. I've 'timed' the shifter so the selector quadrant is in the correct position, but is there anything else to adjust? Or do I need to pull it all out and have a look?
I drove the bike to the top of the hill just because it goes, in first, and found that I couldn't then select neutral at the top. Only after the engine had stopped was I able to select, push the bike around, restart engine and motor home. Should this be part of the symptoms?
I'd like to be able to make it work tomorrow, but this is seeming increasingly unlikey...:(
 
Last edited:

stumpy lord

Well Known and Active Website User
VOC Member
HI,
to make a reamer for the lower valve guides buy 11/32 to3/8 expanding reamer, a piece of 5/16 silversteel rod, one 1/4-32 teeth per inch [model engineers tap.
drill the silver steel rod and tap with the said tap. The rod now screws on to the end of the reamer and behold you now have a piloted reamer, which fits the upper valve guide.
the reamer and tap are available from tracys tools.
hope this is of help.
stumpy lord
 

timetraveller

Well Known and Active Website User
VOC Member
There is an alternative for those who have access to a lathe and are confident in their ability to use it. That is to make up a replacement for the top guide which has a central hole the same size as the hole you require in the lower guide. This replacement does not need to have the same detailed shape as the original top guides. It can just be a thick piece of metal which sits in the recess in the head to take the bottom of the top guide and is so deep that either on its own, or with the help of a spacer, it can be held in place by the valve spring cap. Then one can use the reamer to do both the lower guide and the temporary upper replacement at the same time. You just have to be sure that you can make a hole in the true centre of the new part. If, like many of us, you have lots of old top guides lying around then you can bore out an old top guide, insert a steel sleeve and bore that to the correct size to take the 3/8" reamer. Good luck
 

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