Good evening all,
The head is off and there is evidence of exhaust valve guide damage. There is play in the valve and the guide is oval.
I intend to remove the guide and replace - anyone know where I can get a new guide? (1933 Model 8 - part number 3012G).
When removing the old one, I have seen a video of the head being boiled for a while to expand the metal - is this something that is recommended or just give it a good bash with the drift tool?
Thanks in advance
Andy
I had to make mine. I used the old ones as a pattern..Mehanite, which is a form of cast iron, is what I used..John
Hi Andy,
It depends how severe the problem is. You could ream the existing guide and fit a valve with an oversize stem if not to worn. Failing that and If it's too far gone then remove it. You obviously have to take care not to damage or fracture the head in the process of removal. The existing guide should be an interference fit and shrunk in. You could push it out if its not too tight with a home made puller/pusher. Yes you may be forced to knock it out with a soft metal drift and hammer. I am not one for using uneven heat as it could lead to head fracture better to put it in an oven and warm it up gradually and even (when the misses is out of course remember to clean up). If it won't move you may have to resort to cutting a slot or two by hand with a junior hacksaw blade on the inside of the guide taking care not to mark the head and brake the guide up.
Re getting a new guide you are very unlikely to get a new one from anywhere. It's a case of using the old one as a pattern and making one or getting one made. Such is the way with most pre-war and Vintage machines. Likewise with the valve(s). Its a case of think outside of the box and modify something which is similar to suit to keep on the road.
I wouldn't be tempted to use any sort of impact tool on a head as rare and irreplaceable as that, Andy. Cast iron is brittle and sod's law says it will crack ::) I'd echo the the use of a home made puller - a length of threaded stud with a spacer tube over the top of the guide should do the trick. If the head and the guide are both of cast iron, there's probably little benefit in heating the head as they will both expand at very nearly the same rate anyway.
My first decision would be to make a judgement on how bad the wear really is and would it be likely in its present condition to last several more years anyway. Monitor it and measure again after another couple of thousand miles to see if it is getting rapidly worse.
Only my two penn'orth of course ;)
Steve (wot is well aware of the difficulty in obtaining spares for Sunbeams)
Hi Andy.
Have you considered having the existing guides lined? I've never used this service myself but have heard good things. It saves all the potential problems of releasing 80-odd years of adhesion of the old guides with possible consequential damage. I've replaced several guides in my time but all in alloy heads.
Have a look here: http://www.hthoward.co.uk/engine-machining-services/how-do-ht-howard-ensure-the-best-for-your-cylinder-head/bronze-valve-guide-sleeving/