Hello all,
A couple of years ago I gave my M20 a top end overall, there was only a couple of threads left on the spark plug hole so I decided to recut the thread and use an insert, everything was OK until a few weeks ago when I removed the spark plug and pulled the insert out at the same time 😖, the plug was a lovely colour but obviously the insert is stuck fast on the plug, I can't risk a plug failing on the side of the road and I can't fit a new one.
Sorry about the long winded story but I know we all like a back story.
Does anyone have a cylinder head for sale
email (option): Alwyndart@gmail.com
A quick look at Ebay, shows eight M20 heads for sale at the moment.
I'm in the UK,
Thanks
Alwyn
email (option): Alwyndart@gmail.com
I expect it can be repaired, but another head might be cheaper.
Mark
email (option): pes.sales@btconnect.com
I'm not so sure. They don't often come up in the UK. All the Ebay ones are overseas, and once P&P has been added... Their rarity might be due to owners substituting Cast Iron for ally, which blow the gasket more regularly. 16H heads are more common and cheap.
email (option): jeremy@clogmaker.co.uk
Stuart Bray has one £120... https://www.stuart-bray-motorcycles.co.uk/parts/bsa-wm20-spares/
['Their rarity might be due to owners substituting Cast Iron for ally, which blow the gasket more regularly...']
It's not the case that the alloy heads have a tendency to blow gaskets if properly prepared and fitted and a solid copper gasket is used...The latter is also a requirement with iron heads these days if gasket unreliability is to be avoided...That is due to the elimination of the asbestos in modern pattern gaskets which formed the center part of the original gaskets....
Make sure the gasket faces are flat on both head and barrel, use a 1mm thick solid copper gasket, use heavy washers under the bolt heads and tighten down evenly..Torque to 28-30 ft/lbs...I don't use any kind of sealant..I've run them reliably for years on a number of M21/21s, also with a higher than standard compression ratio...Ian
email (option): ian@wright52.plus.com
Yes but I can't recall solid gaskets being available in the 70s...
email (option): jeremy@clogmaker.co.uk
Solid copper gaskets were most certainly available for my BSA Super Rocket in the 70s as I used them.
email (option): ian.clare1@virgin.net
As Ian mentioned, the copper/asbestos gaskets worked fine back then (As long as the head bolts were tightened and re-tightened according to the book) The modern composite gaskets are absolute crap. TT John on this site usually has a good stock of solid copper M20/21 Gaskets.
Ron
email (option): ronpier@talk21.com
Yes well I had a couple of M21s. My first one at school, the second attending college. Ally heads had a reputation. My present bike should have an ally head . It came to me with a ferrous one. A casual perusal of late 50s M21s for sale show many with iron heads.
I stated this was the reason back then. Believe me for your average rider a torque wrench was a piece of exotica. Tools cost far far more and a lot of us were skint. If we weren't so skint we'd have been driving a car, not a sidecar. Engines run a a lot hotter with a sidecar. At night my exhaust junction often glowed dull red.
If you can think of any other reason why BSA heads are so expensive [Given that the design went on for decades] compared with war specific 16H ones, let me know.
email (option): jeremy@clogmaker.co.uk
['If you can think of any other reason why BSA heads are so expensive [Given that the design went on for decades] compared with war specific 16H ones, let me know...']
I think the answer to that is just supply and demand...There are a lot more surviving M20s that have done a lot more work so there are more that have lost/damaged/corroded heads...To illustrate that, on the first Normandy Tour of 144 bikes 58 were M20s and 7 were Norton 16Hs....
Personally, I don't think alloy heads are intrinsically less reliable IF they are correctly fitted and maintained and the mileages I've done with one fitted bear that out.....What they are is more prone to problems caused by incorrect fitting which is not the same thing...A cursory look at many alloy heads will indicate that many have been misused in the past...Having spent many years rebuilding engines etc. for other people I lost long ago the belief that everyone knows what they are doing...and I include myself in that for many years after I first acquired a bike....So, the alloy heads have suffered and the (IMO) false idea has arisen that they are unreliable by virtue of their design..Regarding torque wrenches they are a modern 'luxury' that wasn't avilable in the past but they aren't an absolute requirement to achieve reliability...I ran M20s for decades before I bought one...Ian
email (option): ian@wright52.plus.com
Jeremy I have no idea about the relevant costs of an M20 or 16H head, other than there are probably 10 times more M20's existing now than 16H's therefore more demand for spares??
Regarding Torque Wrenches. They were a crude spring pull device back then and not in general use in ordinary workshops. Hence torque wrench figures are not included in the manuals. They were tightened by experience and even different length spanners to adjust the pull.
Figures today are quoted either from experience or by comparisons from more modern vehicles with a similar fitting or charts giving figures for different threads and sizes etc.
The biggest culprit of blown composite head gaskets is after fitting a new one, failing to re check tighten the bolts as many times as required during the first warm up sessions until it is compressed to it's maximum. Even then, the cardboard in the modern gaskets will still often blow out. Ron
PS typing at the same time as Ian!
email (option): ronpier@talk21.com
These can be helpful to those with machinery.
https://pesltd.uk/?product=02-0861
Mark
email (option): pes.sales@btconnect.com
Marks washers are exactly what's required for an M20/21 head...iron or alloy...Ian
email (option): ian@wright52.plus.com
The numbers could be it, but try finding an ally head. They seemed to have been binned when replaced by iron ones. Sidecar outfits were owned by folks that generally couldn't run to a car, not keen mechanics
email (option): jeremy@clogmaker.co.uk