I'm doing some work on a friends bike who has bought one of Ian's special pistons. He gave me an un-linered barrel to replace the one on the bike, which I've given to my engineer for boring out to size 90mm + 5thou skirt clearance. Out of interest he measured the outside of the barrel below the fins = 96mm .....which leaves a wall thickness of just about 3mm. When I got home, I measured the linered barrel = 98mm ?
New main bearings coming from Darren!
Any comments please? Ron
email (option): ronpier@talk21.com
3mm wall thickness ? Have you got one of those Shelley jacks with the Big 4, Ron ? Will it fit between head and frame tube ? Just as a precaution, like :-)
I've never had problems with the barrels...There is some variation in barrel diameter but the narrowest part of the barrel runs for a very short length before it tapers outwards...Also, the substantial tappet chest casting gives a lot of additional support...The head steady makes a contribution as well...Ian
email (option): ian@wright52.plus.com
3mm wall thickness using a generally considered poorer quality of material during the war too risky for me. Pat Jeal raced an M.20 which was substantially over bored and his father who was very knowledgeable in respect of BSAs would never stand on the drive side of the bike when it was running.
If you want to get more power out of the bike why not modify the cylinder head and use an M.21crank assembly.
email (option): keithchandler@clistandchandler.co.uk
Well firstly, the un-linered barrels are of post war better material.....Hence the no need for the liner. The other thing is you have to use an M21 crank to achieve the 700+ cc. I'm satisfied with my own M21 600cc conversion and I do have a B33 piston in stock to bring it out to 635cc one day....Just for fun.
But in this case, I'm only doing what someone else has asked for and he already has one that has covered considerable mileage.....and there are quite a few more out there. But when I ride with him, as you suggest, I'll keep on his right side:laughing: Ron
email (option): ronpier@talk21.com
Pat Jeal used a linered barrel and removed the liner, accepting that the quality of the casting was poor and aware that there might be faults in the casting...His father was paranoid it seems, as Pat raced and sprinted the bike in that format (though I understand he did have some problems with porosity of the castings....)
I've run my own M20 as a 720 for around 15 years...I've also run my B33 as a 720 and that doesn't have the benefit of the cast in tappet chest for support, though the barrel is slightly thicker at about 98-100mm at the narrowest point...It does, however, produces considerably more power than the side valve... Ian
email (option): ian@wright52.plus.com
As Ron mentions the owner of this bike has another 720...He bought that one from me and I did 38,000 miles on it before I sold it to him!...Ian
email (option): ian@wright52.plus.com
It's probably important not to have any stess raisers or sharp edges where the cylinder flange is blended in. I've seen a number of Norton twins pull the flange off and they usually do it at low revs (isn't that when cylinder pressures are highest ?)
It still amuses me that so many M20 owners feel the need to increase capacity by almost 50% and yet I can think of no other WD motorcycle where the owners are not content with the style of power delivery as part of the machine's character. Standard M20s do look slow on the road though.
Most Norton twins blow up easily hence the Triton, dont even mention the Atlas or Combat Handgrenade engines. I am satisfied with standard M20 performance though, but most M20,s need gearing up only to make them rideable in modern traffic.I had a civillian ZM20 which I had for years and it went well but when I first road tested my newly rebuilt 41 WM20 it was useless with standard gearing once I had changed the engine sprocket for a 21 tooth one it transformed the bike! now will sit at 65 mph easily if you want too..
Dave T
My experience with my own WM20 which I've had for 30 years, is that the standard engine on WD gearing was acceptable, but still often required a change down a gear on hills and any up sizing of engine sprocket only amplified the problem......OK if you live in Norfolk or Holland I guess. So I went for a standard M21 flywheel and piston with an M21 carb and a 21T engine sprocket. But I then found that gearing was too tall for my use, 55mph max cruising speed and convoy duties. I wanted it a bit more buzzy, so I dropped it to a 20T sprocket. It has loads of grunt on hills and plenty of overtaking acceleration.....Suits me fine like that. Ron
email (option): ronpier@talk21.com
Its possible that not all unlinered castings are from the mould, maybe some are thicker than others.
Rob
email (option): robmiller11(a)yahoo.co.uk
can you measure yours Rob? Ron
email (option): ronpier@talk21.com
As Oddball didn't say...'A 720cc M20 can give you a certain...edge'...:laughing: As Rik did say the standard M20 is a bit pedestrian, particularly going up hills...I altered mine to a 600 and then a 720 because it vastly improved journey times on longer journeys and as a bonus it actually improved fuel consumption as it wasn't being revved as much up every hill in one of the lower gears...
It can be done to an M20 because a] Parts from different models are easily interchangeable and readily available and b]The basic engine design isn't limited by any particular mechanical weakness and will take that degree of enlargement without affecting reliability...
IMO the bike is vastly improved by the changes for todays road conditions and as I've had various M20s and M21s over the last 40 or so years I don't really feel the need to experience the 'real thing'...I'd already done that over multiple thousands of miles...Ian
email (option): ian@wright52.plus.com
When I had my engine built (currently standard configuration 600cc) I had it enlarged by a well known local builder.
The bore was about 91mm, the inlet port was enlarged & tidied up a bit, a big Concentric went on & it was geared up. Cams & ignition stayed standard.
In that form it didn't know what a hill is, & it would lunge up to the early 50s but after that it was obvious the motor was confused.
It went through pistons faster than Trump goes through advisors but the barrel stayed OK. Engine balance was poor, presumably due to the huge piston & there was a lot of vibration. All in all not a success.
I'm throwing this in as an example of problems that might arise, I stress that the builder knew his stuff, but the engine needed a lot more development.
Not the usual way to acheive 600cc Bob, but I guess it saved taking the whole engine apart! A straight forward M21 crank with it's longer stroke will give 600cc on the standard 82mm bore. Ron
email (option): ronpier@talk21.com
A standard M20 crank with a 91mm piston gives 611cc...I'd be interested to know what piston was used...If the difference between the weight of the standard piston and the oversize one was more than approx. 1 1/2 ozs. the crank assembly should have been rebalanced to account for that...That may well explain the excessive vibration...
I don't understand why the engine should have consumed pistons any more than a standard one..Again I'd be interested to know what happened to them in an effort to try and understand that...As the engine vibrated badly and consumed pistons I would question the abilities of the builder in this case as he has produced an engine that doesn't really work well...Perhaps he was unfamiliar with the type...
Personally I like to have the cranks dynamically balanced anyway. They were balanced statically originally and I imagine a production tolerance was applied, so rebalancing them dynamically usually leads to a smoother running engine...A balance factor of 60% works well...Ian
email (option): ian@wright52.plus.com
I should've said the engine was fitted with a 600 crank like the other projects mentioned here, in writing the post I concentrated on the actual modifications.
The pistons were from a local firm in South Australia & originally intended for a car. They were all that could be obtained at the time. This was over 20 years ago, but from memory the pistons scored badly for no obvious reason. Perhaps clearances?
While not a specialist on these engines, the assembler had a good reputation as a motorcycle engineer & mechanic. I don't know what he did to "balance" the engine but it definitely needed more work.
As I said in the first post, the engine wouldn't pull through the mid 50s & that needed to be explored & sorted.
But without the ability to do most of it myself, it was all going to cost a lot & I settled for the charm of a 600 plodder.
In fitting a 91mm piston to a 500 crank I would've gone fairly close to creating a square M20, some sort of achievement I guess.
Well Bob you've got the cc wrong for that engine. Ian has calculated that with one of his special 90mm pistons and an M21 crank, the cc is about 720. so your 91mm piston would have been even more 730 or something. Ian's pistons are quite short so I guess the weight is similar to an original piston but there was no 82mm piston with this bike so I can't check. No doubt Ian can confirm.
I put the previously prepaired M21 crank (new big end) into the cases with new main bearings yesterday. The oil pump was seized as often the case with a bike that's been stood for a long time without oil. Also the pick up spout had fallen out (I've seen this before) so I acqured a new bottom plate from Russells and worked on the pump to free it up.
I'll be building the rest of the engine/magdyno in the frame when I've re-sprayed it (Earth Brown) as there's no way I can lift a complete M20 engine these days. Ron
email (option): ronpier@talk21.com
Ron
I never worked out the exact capacity of the engine when it was enlarged, 730 seems about right. When I gave up on it the 600 crank was retained with a standard barrel & M21 piston fitted to give it 600cc.
I've still got the bored out barrel & am not sure what to do with it. I don't think I'd try to reuse it as is so a bespoke liner would be needed. For my purposes it'd be best to have it as standard.
If the large engine's top end had worked better, I'd maybe have persevered with it. What modifications do you think should be made with cams, carburetion, etc?
Bob, Ian has messed around with cams and timing and such, so he is one of the best blokes to comment about that. My own 600cc conversion consists only of a bigger (1 1/16") standard M21 carb. It wouldn't really matter what I did to mine, I'm still more than happy cruising at 45-55 mph.
But I guess in your case, with the vast open roads and long distances you might incure, some tuning and higher gearing might be benificial
Ron
email (option): ronpier@talk21.com
Don't know any thing about the bike in this photo,only that it was taken at Mallory Park in 1978/9. 
A very nice picture, typical for the 1970's when there seemed to be a lot of creativity. And bikes and parts were cheap and availible, I guess.
Not much rivet counting then.
Or junk the Beezer and get a Matchless! Just saying.........(could not resist!).:grinning:
You need a new needle...That one keeps sticking...:laughing: ...Ian
email (option): ian@wright52.plus.com
Ron
For interest's sake I'd like to know what others have done with big bore conversions , but back now in standard 600 form my bike's quite suited to its local environment. I like to think it's still doing what its builders intended, 45-50 mph cruising seems about right.
I am new to this but have been reading posts and collecting cheap bits on eBay.I have an m21 crankcase, a barrel bored out to 88 mm, a 90.5 mm VW piston, an M20 Conrod and a B33 crankshaft with shot big end .I have a cast iron head and was thinking of moving the plug to the tdc hole. It looks like with a bit of work . Boring out the barrel, stripping the big end and using the m20 Conrod it will all fit together and will give around 572cc and a roughly square engine . Any thoughts would be appreciated .
I've built a 90 bore by 94 stroke engine (598cc) but haven't run it yet...From memory the last time I looked at VW pistons they seemed overly heavy...That was a long time back though. Have you weighed the piston?...and what size gudgeon pin does it have?...
I work out the dimensions you have given to produce 566cc...M20 flywheels would give you 604cc and M21 flywheels 720cc...Ian
email (option): ian@wright52.plus.com
When I bought my WM20, it had a car piston installed, on a barrel with a liner.
I did not measure the piston, but the 90mm piston was few mm smaller...
The liner had the thickness of a tin can.
I did not know it was like that till I took the head off, few months later,
But the bike run very well with no issues, and had 13T final sprocket, and I beleiave a 19T flywheel sprocket.
.... And a sidecar :smiley:
Noam.
Noam I think someone may have fitted a bigger liner to your barrel. I have a NOS standard liner here that measures 88.9mm OD.
Ron
email (option): ronpier@talk21.com
email (option): keithchandler@clistandchandler.co.uk
Hi Ian I have weighed it now 1lb 8.5 oz about 6oz heavier than standard piston, including the gudgeon pin .It has a large gudgeon pin but the hole in the centre is slightly smaller than a standard gudgeon pin so could be bored out a bit and cut as a spacer . I have another crankshaft which I think is from a B32 judging by the Conrad reference number which is heavier I think it is 23 lbs.
It depends how much diameter difference (of the gudgeon pins) that you have to play with but you may be able to sleeve the gudgeon pin bosses in the piston down to the size of the BSA pin...This saves weight overall as the smaller pin can then be used and the small end bush remains unaltered.....
You can either machine circlip grooves into the boss sleeves if there's enough material or press domed bronze 'buttons' into each end of the pin...The pin will obviously have to be shortened in that case to provide the required space. The bronze buttons run on the cylinder walls and keep the pin in place...This was a common set up in the past and I've run it in BSA engines without problems...
If you can get the total piston/pin/rings weight within 1 1/2 ozs. of the original no crank rebalancing will be required..(if you choose not to)....
Remember though..If you fit a longer M20/21 conrod to a B33 crank the weight of the extra conrod length (and bigger top on the rod) also has to be taken into account for balance calculations which will probably lead back to a requirement for rebalancing...Finally,don't forget to carefully check the centreline of the gudgeon pin to the piston crown dimension when considering changes such as you describe...
Are you planning this engine for road use?...Ian
email (option): ian@wright52.plus.com
Hi Ron,
Thinking of it again, you may be right.
I may have tried to fit in a regular O/S piston, not the 90mm one...
It was very long ago. I will try to have a look soon (It is stored somewhere) and share pictures.
What I do remember, is that I was surprised of the liner thickness.
It was about 1mm, if memory serves.
The smallend bushing was also drilled to receive the much ticker piston pin. :confounded:
Cheers,
Noam.
Bob I am guessing you were using JP pistons, they did not have a good reputation years ago and needed extra clearance plus they were heavy. I have never used one of there pistons only rings, for them to still be in business they would have had to improve a lot over the years has anyone used their pistons recently. Never heard a complaint about car pistons they make.
Hi John
Yes JP pistons were used. With no prior knowledge of this particular conversion the builder rang around local suppliers & these JPs were all that could be found. I remember they had a bad reputation at that time, don't remember why or whether the're still around.
I guess what I was trying to get at in these posts is that for someone without the ability to do the work themselves, it was expensive as you essentially pay for experiments.
But I think things are much better now, a lot more information & appropriate parts.
John you'll have to add "oop't north" or "'erriot contry" to your tital. Ron:relaxed:
email (option): ronpier@talk21.com
Weight is a bit hit & miss as he machines pistons from common blanks
So one batch can be a different weight to the next if they were made from different blanks.
The rings he supplies is a totally different kettle of fish.
They are not suited to cast iron bores and will take forever to bed in.
They will do it eventually but we are talking a couple of thousand miles of smoke screens.
I never ever fit the supplied rings.
And the club members who have taken this advice have never had any problems.
Better still is he will make batches as low as 10 so a couple of members just had him run up some model H sloper pistons
One is on the road for over a year without problems, the other is still waiting for his head to get welded.
email (option): bsansw1@tpg.com.au
Bob; my experience goes back to the 70's, early 80's knew a few mates that bought them for an AJS and BSA B33 both nipped up that's when we learnt they needed more clearance. Why, no idea they looked and were heavy never worried me as I always found UK pistons in Melbourne. I did buy two sets from the UK, BSA M20 and M21 I have found easy to get parts for.
JohnB; I have added AU will change to something else if you think it is to similar, probably won't post often as both my sidevalves are post war.
trevor; My outfit is running JP rings put them in 3+ years ago and she has never smoked. My experience with JP pistons was from the seventies-early eighties would imagine everything in that factory has been changed since then, good to hear you have had no issues with the pistons. Going to need a piston for an old Calthorpe if I have trouble finding one I will give them a try.
Hi, As the guilty(?) builder and rider of "Claudius" which I think is still the fastest M20(ish) BSA I suppose I should bung in my comments. The paddock photo of the army coloured M20 special shows it as raced before I went sprinting. I based the bike on what could be done with WD BSA bits. So that meant a B-type frame and rear wheel, an M20 gearbox, motor, forks and front wheel. Alloy rims as per the Army ISDT M24s. The Vintage racing rules allowed only the standard inlet tract so I couldn't use an upswept one.
The motor had an M21 crank. As has been said it used a linered barrel with the liner removed. The barrel was initially bored to use a 90mm Triumph car piston. Strong but heavy. There were a few holes through between the fins which had weld laid between them. Special small end bush and alloy end plugs on the pin. These melted in a queue awaiting a sprint run. So it was over-bored a bit more for a Honda XBR piston which gave 749cc. Again pin end plugs and this time methanol to cool it a bit.
I fitted the bike with a "Nero" type dustbin fairing and it ran 109mph for the flying 1/4 with a terminal of 112.
The best standing 1/4 was 14.95sec.
It was built with was available. 1 3/16 Amal TT with drilled out jets. Cast iron flywheels. Steel would have been better, and possibly a non-linered barrel. Using twin spark plugs in an alloy head worked well. It revved to about 5,100rpm. It had standard valves with the heads turned down thinner. With steel flywheels I'd have revved it more so would have increased the inlet valve diameter.
If you are doing an M21 with a big bore don't neglect Japanese bike pistons. I know the idea will upset some people but the pistons are very good. Short and light.
Cheers,
Pat
Good to here your comments Pat. What did you do with cams and valve springs. One forum member has fitted C15 valve springs inside his standard M20 springs. Ron
email (option): ronpier@talk21.com
Delighted to see you post Pat - long time no see - the last time you kindly rescued me with a new head gasket at Berkeswell late at night after the M.21 special had blown the gasket coming up the hill after the level crossing. You even turned up with a flask of coffee for the weary travellers. Brilliant.
Anyway to your M.21 surely you modified the head to raise the compression ratio? I altered the head on my M.21 to follow the design of the SWD Norton Big 4 head which also runs an 82mm piston as standard. I believe it raises the compression ratio to around a staggering 6:1.
All the best and by the way I still have the WD M.20 your Dad helped me so much with.
Great to see Pat Jeals comments on here...I have read all the published material on the development of Claudius so have a file of photos and information gleaned from various sources in my side valve tuning archive.
Also, Harley K Model information, an article on the Australian M20 run by Bill Gough, an article on Nigel Fox's Norton 16H, Peter Crespins articles on side valve tuning, information from KNS Cycle in America on Harley tuning and the same from Patrick Delli, car tuning info. and even patent copies from the Patent Museum on side valve developments...
It's an interesting subject and a bit of a 'black art' but Pats efforts are to be admired as he managed a fantastic result on a 'hobby' budget...Ian
email (option): ian@wright52.plus.com
Just found a 1954 m20/m21 bsa engine price list for cylinders m20/m21 66-88 £7-0-0 and AA cylinder £8-15-0 what's the difference are these a better casting mal.
email (option): Malmotorcycles@gmail.com
Hi Pat, Phil in Clarence Gardens Adelaide South Australia. Am building a WM20 to go salt lake racing. Am using twin spark & big bore/M21 crank to get capacity. Loved the story, thanks.
email (option): tilbrookphillip@gmail.com