The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: sean on 29.10. 2012 03:32
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hi
1962 super rocket [alloy head] is it necessary to change valve guides or seats due to only unleaded being available if so which guides are best for this head ?
thanks
Sean
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Not unless you are considering doing 16,000 rpm @ 30,000 feet or running nitrous enrichment.
All of valve recession data came from the aero industry & then got incorrectly applied to surface vehicles
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I had a valve seat replaced in 1961 due to ...................... , oh did we call it something else back then, it wasn't worn out, it had picked up resulting in a track on the seat that allowed the gases out into the ex pipe before it should be there, so little whistles and pops that BSA didn't design in
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I to have never understood this debate about the use of unleaded and valve seat recession.
1/ Lead has always been added only because it was a cheap way of counteracting pre-ignition when engine compressions went up
2/ I very much doubt the theory of lead forming a protective layer on the valves and seats. If I remember well from my school days, the melting point of lead is about 300 and some degrees Celsius. The temperature around the exhaust valves can be 3 times as high, so any lead should be burnt away immediately
4/ A couple of years ago I had to take off the head from my Morris because of a blown head gasket, and as it's a 6 cylinder 2.6 engine and you don't want to take the head off to many times because it's so heavy, I also replaced the exhaust valves. I found them heavy pitted, in spite of running on leaded fuel all of there life.
It seems to me that a lot of people are abusing the abolishing of lead in petrol to sell there products, whether it's something to add to your fuel, or to earn some money in converting engines.
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There has never been any lead in petrol ever. Lead is insoluble. The compound that was added was tetraethyl lead which has properties completely unlike metallic lead. I think the compound that results after burning is a form of lead bromide, which coats the valve seats.
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I'm happy to use the best octane rating I can find on the forecourt, then add Castrol Valvemaster octane boost and lead replacement; this on my iron head. The cost of all this remains negligable in the grand scheme of things for me.
Now my Guzzi V50 is of more concern. It will not run right on anything other than high octane fuel and although the seats should be recession proof (unlike my 'pension' it would seem), given that they have a reputation for stretching and snapping the heads off the valves how do I know what's happening when I find the clearances closing up - seat recession, or valve stretch?
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Cyclobutch you shouldnt have any issues at all with your V50, they are almost indestructable. The Guzzi with the reputation for valve problems is the V65 lario which were a 4 valve design.
I had a V50 Monza which the last time I heard of it had done 330,000 k's and was still going strong. I ran it on pump remium ULP (95 octane here) and it ran perfectly.
I've been running all my old bikes on unleaded since it came on the market here in the 80's and have never had a issue with valve recession. I dont use any addatives. I use the higher octane stuff when it is available but that is to stop pinging, fortunately here in AUS we can get 98 octane from the pump just about anywhere.