Hi,

I've recently started a complete restoration of my M21 with the aim of using it as a relaxed tourer to take over to Europe. (The slower you go, the more you see!!)

I'll soon be starting on the bottom end of the motor and would like to add one of those widely available spin-on oil filter mounts and potentially an oil cooler aswell.

Does anyone know if the standard pump is capable of handling these modifications or if the pump in any of the other pre-unit singles might be of a higher capacity? (Having to supply oil to the head aswell) ABSAF.nl make a higher capacity version of their own but it is a little pricey.

Does anyone know the flow rate of the pump (out of interest)

Thanks guys!

Also, does anyone have experience with a 720cc M21? What sort of cruising speed can you realistically expect?

email (option): mad_king_soup@hotmail.com

Personally I wouldn't use either a filter or a cooler on my M21. These engines can get pretty hot but often the oil is still quite cold.

Henk.

email (option): ahum@quicknet.nl

No real need for a high capacity pump either, if you think that most wd engines that are being restored now are probably having their big ends replaced for the first time! So I guess you can say that the pumps must work well enough in standard form, all in all on the M20 M21's it only has to pump the oil along the timing side shaft, then centrifugal force takes over and force feeds the big end, the oil pump does no more than that, everything else is either splash or mist lubricated, with regards to the oil filter, the standard oil filter is adequate if set up properly with the top cap fitted (as so often they aren't) so once again, no real need for one of them either.
The only thing I'd fit is the magnetic sump and oil drain plugs

email (option): davmax@ntlworld.com

Sounds like it would be a lot of effort for no real benefit then!

This is my first british bike & other than a quick ride before stripping down I have no experience of it on the road. While it's completely in bits I'd like to try & improve it wherever possible.

Thanks for the advice. It certainly saves me finding out the hard way!

Cheers, Ben

email (option): mad_king_soup@hotmail.com

Just an idle thought further along these lines;

If the engine runs hot but the oil is still cool. (I suppose the oil doesn't reach the hottset parts of the engine in a sidevalve design)

What about coming out of the tapping for the oil pressure button, running copper hose back & forth between the cylinder head fins and then through a cooler?!

email (option): mad_king_soup@hotmail.com

It's a side-valve engine and you could do more harm than good by running "radiator pipes" through the head fins. There is nothing to lubricate in the head so the comment in your original post about lubricating the head is a non-starter.

More importantly, if you provide cooling pipes to the head fins but not to the barrel fins, one of two things would happen (and I don't know which is more likely, as I've never heard of this being done). One possibility is that the cooling pipes will be ineffective to reduce the temperature, either because there is not enough contact area or cooling surface, or because the holes you drill to put the pipes through would reduce the effective area of the existing fins and the pipes will not carry away enough heat to make up for the reduced area, or the pipes will impede air flow through the fins and the pipes.

The other possibility is that your system will be effective and this may be even a worse problem: you may reduce the temperature of the head to a point where there is a severe temperature difference between the head and the barrel and you run into problems with, e.g., head coming loose, warping, etc.

There is also the technical problem of how you do this. Simply making holes in the fins and running pipe will not do as there will be no contact between the pipes and the fins, to transfer heat. You will probably use copper pipe, so brazing is out as it requires too high heat. Soldering is out because it will probably come loose when the head heats up (remembering that the head will get much hotter than hot coolant in your car radiator). Using steel pipe means less efficiency, since steel is much less conductive of heat than copper, plus additional work as you will probably not be able to bend the steel but will have to weld individual runs into a matrix and then weld them to the head fins.

As for using oil to cool the engine, there is no significant amount of oil going to the hot parts of the engine so this would be ineffective to reduce the temperature but, if you have an oil cooler, it may reduce the working temperature of the oil, thereby increasing viscosity and reducing lubrication where it is needed.

I wouldn't mess with it. Until recently I was riding my M20 as a daily commuter in New York City stop-and-go traffic, without any adverse effects from overheating. If you will be using yours as a tourer, which I take to mean that a steady stream of cooling air will be going through the fins most of the time, the temperature of the engine or the oil are the last things that should be of concern to you.

email (option): jonny.rudge@verizon.net

Hi Ben,

If those bikes ran in N. African desert with no improvements, (Minus air filter) with iron heads and old primitive mono oils,
It would easily run as a truer with a modern good oil much easier.

You could fit an aluminum head, if you have a cast iron one, but it is also not really necessary unless the engine is improved for high compression ratio / high displacement / high rev.

Noam.

email (option): noam10@gmail.com

Blimey..this post is covering some ground!...Here's my 10 penceworth. The M20/21 engines basically have a bombproof bottom end if correctly assembled and it is a high mileage low maintenance assembly. Modifications to the pump capacity and lubrication system generally are unneccessary..IMHO the BSA bottom end is one of the strongest, is well lubricated and has very good cam gear. If the engine is being totally rebuilt (and therefore will be absolutely clean internally) an additional oil filter is not essential, but modern filters probably do take more burnt carbon and smaller particles out of the oil than the original set up, so I would consider that as an option. The unit fitted to the Norton Commando is suitable,readily available and simple to mount. Fit it in the return side of he system if you decide to go for it.
I would also fit a hardened seat to the exhaust side...These engines will run on lead free without any particular problems but the hardened seat will increase the service intervals in that area. This is a particular advantage if you are going to do a lot of motorway miles at cruising speeds..This type of work does wear the valve and seat more rapidly.
The alloy head certainly helps dissipate heat better than the iron one..but if you use one get the gasket face lightly skimmed before fitting to ensure a flat face. Also, if not already present fit a steel spark plug thread insert and timing plug thread insert to avoid potential thread failures.
Heat is wasted combustion energy and the 'hot running' of a sidevalve engine is an indicator of it's inefficiency.
An impossibly 100% efficient engine would remain completely cold when running as all the energy (heat) of combustion would be converted into rotation of the crank.(kinetic)
The unused heat is destructive to engine components so has to be removed and that is why, in the case of the air cooled sidevalve, it is radiated through finning.
One way to increase the efficiency of a sidevalve (or any fourstroke engine) without structural changes is to 'insulate' the combustion chamber internally, allowing less heat to escape the combustion process. To achieve this the inside of the head, top face of the barrel, the heads of the valves and the crown of the piston would have to be ceramic coated. This contains more of the heat and also protects the internal components. Claims of 15-20% efficiency increases are claimed for this process and it is commonly used in competition and increasingly, modern road engines....but it could be reasonably deemed OTT for the humble M21. I just mention it as a possible 'improvement'
There are a couple of options for increasing cylinder capacity. However, the inherent limitations of the sidevalve porting and combustion chamber etc. mean that top end gains are limited. Cruising speeds are improved slightly over the standard engine and can be achieved on taller gearing with less revs.
The main benefit of this activity is a sharp increase in the torque figure...Hill climbing is very much improved and there is less need to 'drop a gear' and use revs on inclines. Less gearchanging, less running in the lower gears and cruising speeds achieved at lower revs also lead to improvements in fuel consumption.
On the whole there are few improvements that are really required...the basic bike is a plodder, but a basically reliable one. There are points to be aware of when assembling these engines, particularly in relation to the oil pump and the assembly of the lower half of the engine..best to address those when you are into the job. One final point..I would recommend the fitment of a solid copper head gasket..they are far more reliable than the pattern composite types currently available...Ian

email (option): ian@wright52.plus.com

Wandering slightly off topic, but have recently heard of (but not actually seen the result) someone locally having a new M20 head CNC machined from alloy. Upped compression and internal profiling inspired by the Harley sidevalve. Will keep my ear to the ground for results.

Hi Iain..I'd be interested in any info./pictures on that project..also the intended application for such an exotic part.. ...Ian

email (option): ian@wright52.plus.com

Count me also in !

Noam.

email (option): noam10@gmail.com

Will see what i can do, the guy i spoke with was not the owner.
I suspect it was for race (or at least performance) use.

I think Ben's comment about oil pipes around the cooling fins was tongue in cheek Ron

email (option): ronpier@talk21.com