I had the barrel of my m20 bored, bigger piston new bearings. So far so good. I drove about 1000 mls no problems suddenley there is coming a lot of oil out of the breather. The breathervalve was very thin so I renewed it. Didn't make it better. No power loss. Eventhough I removed the barrel. No dammage there. Pisgtonrings are OK. No scratches on barrel or piston and a nice play between barrel and piston. I use Sae50 oil. I changed it after breaking in with the same oil. I can drive about 50 mls then my rear-tire is getting wet. It puzzels me for quite some time now. No smoke out of the exhaust when driving. Who knows the answer. Something internal in the engine? I want to know before dismantling the engine again.

email (option): mail@clemensvandusseldorp.nl

Hi Clemens...I don't think the oil loss is related just to the size of larger piston you have fitted.(though you don't say what size it is)

I've run a 90.5 mm piston in mine for over 10 years now (with a 112mm stroke crank) and at 720cc capacity I've had no breather problems at all..

By comparison my B33, which is also at 720cc but revs more than the M20 did have breathing problems until I fitted a second breather...

However, it seems like you may have a problem relating to the piston rings/bore clearance as the problem appears after you have done enough miles to get the engine really hot.

What type of rings are fitted, are the gaps correct and what bore clearance are you running?..Also, did you fit a new small end bush?

It seems you are pressurising the crankcase excessively either due to a piston/bore or a valve seat/guide problem.

One other possibility is that the oil pump is worn and is not scavenging the crankcase effectively or that the ball in the pick up tube on the bottom of the pump is not moving freely, reducing the amount of oil being picked up by the pump...

If the scavenging side is not functioning correctly oil can build up in the crankcase and will eventually be ejected through the breather...

I have to say though that neither of those problems are common on the BSA (but are possible)...Ian

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

I forgot to mention. I did check the oilpump, nothing wrong with it. I changed the oilfilter (maybe to much obstruction) I even rode without the filter. Then I drove for about 30 miles, and directly after that I pulled out the drainplug. There was not much oil coming out of it. So the pump must be working OK. The piston is 0.60 (was 0.40) oversize. clearance between piston and barrel 0.09 mm. When I dismantle the pipe from the breather you can see the oil coming out.
Is there someting inside the cranckcase that prefents oil getting into the breather? (my B33 has a little pipe on the breather sticking into the engine) Did I miss something building up the engine? Can it be the oil itself?
Or do I have to live with it and make a reservoir to catch it?

Do you have a fibre disc in the breather? This disc should shuttle inside it and opening and closing the breather while the piston goes up and down.

I have some NOS discs laying around if you need one.

Henk

email (option): ahum@quicknet.nl

The M20 breather fittings don't have the internal pipe fitted...This was added to OHV models due to problems with the breather when it was fitted in the timing cover...

There shouldn't be any problem with the oil you are using...If I was to try anything it would be to fit another set of rings...What about the ring end gap?...Is that within tolerances...?

If you are losing oil excessively from the breather yet you are sure the scavenge side of the system is OK then you must be pressurising the cases...

You can only do that by a malfunction of the breather itself or by compression pressure reaching the crankcase...

That can only be the result of a problem with the piston/rings/bore assembly or a problem with valve seats/guides, where compression reaches the cases via leaking past a defective seat or valve....

Those things can't all be right or there wouldn't be anything wrong with it... Ian

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

In the breather is a new brown fiber valve, no ring. Valve guides are ok . Leaking valve should cause less power and that isn't the case. Any ideas left?

email (option): mail@clemensvandusseldorp.nl

Hi Clemens, Just a thought but are you sure your tyre is getting wet from engine-oil or could it mainly come from the gearbox?. The gearbox is known for it leaks along the big bearing and bronze bush around the mainshaft.

Good luck, Michiel

email (option): m.wijbenga[at]hotmail.com

I can see the oil flood coming out when I dismanle the pipe that is pointing to the rearchain. It's surely coming out of the breather. I think I am going to dismantle the barrel and piston again maybe a crack somewhere.....

Oil discharge from the breather, initially at high revs , indicates excessive blow by.
So my guess is hat the rings have not yet bedded in.
I used to have this problem a lot because I used to flood the rings when I fitted them.
However I am now a dry fitted rings nam and have never looked back.
When new rings go in it is a case of strat the bike & if it can sort of jun, jump on & ride like you just stole it.
Rings will bed in a few miles then you can go home & fiddle with the carboy as it will need adjusting after rings have been installed.

email (option): wariron@tpg,com,au

It goes against the grain for me, but I have heard this before. Someone had smoking and excessive oil consumption after a rebore. He stripped the barrel off and washed everthing with thinners and assemble again dry. Never had a problem again

Ron

email (option): ronpier@talk21.com

I oil the rings and piston on assembly and it has always worked for me.

Whilst I might consider driving the engine a little harder to bed in only a set of rings if I had a problem I wouldn't, under any circumstances, do that with a rebore and a new piston fitted unless a larger than standard tolerance had been applied...

This was done with the competition Triumph engines I used to be involved with and they could be driven hard right off the bench...However, the pistons were fitted with a clearance that just allowed the engine to smoke a little from the outset...In other words pretty slack...Of course that didn't matter on engines that might be rebuilt more than once during a season of pre 65 scrambling...

I have built numerous BSA single engines for myself in the last 40 years and also for customers in the last 17 years and have never recommended 'ride it like you stole it' as a sensible strategy for running in rebuilt engines.

Apart from the piston and rings there is the small end bush, timing gear bushes, outrigger plate bush and valves and guides guides to be 'run in' as well...Not to mention the gearbox if that has been overhauled...

IMHO and experience, if a cylinder has been rebored to the lower manufacturers tolerance in particular, you are tempting fate by ignoring the manufacturers recommendations for correct 'running in' by driving it too hard, too early....Ian

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

I agree with that, and I also oil everything on assembly.
The bloke who told me about the thinners was the boss at Draganfly

Ron

email (option): ronpier@talk21.com

I have been using this method for years with great success.
Prior to changing I would start the engine, warm it up then adjust the carb with the engine idleing most of the time.
However It was explained to me why idleing a new motor is not a good idea and excessive idleing ( while you are adjusting the carb (S) ) is even worse.
Done better than 50 engines motorcycle engines and about 200 mower engines without a single failure to date.
The only lube I use during the rebuild is Penrite assembly lube.
Currently the boys are trying to convince me that I should also be changing the ring gaps.
I have been using tight 2nd rings with fairly open tops .
While I am not convinced by the arguements to date, I feel is is possibly more fashion than fact, Ihave done a few engines the "new way" and am waiting for the second & third services to see if it actually makes a difference.

The "ride like you stole it theory" goes like this.
In order to get a good seal between the rings & bore you need heavy pressure behind the rings to get hard contact between the rings & bore.
To do this you need wide open throttle to get full volumes into the cylinder and full pressure against the bore.
This is even more important with our machines as the compression ratios are so small.
So it is hard around the block, right through the gears ( no over revving ) & the job is done.
The customer can come back, start their bike, then take 10 minutes to get his gear on & I am not worried about having a "glazed bore" warrantee job in a couple of weeks.

email (option): wariron@tpg,com,au

I can see the logic behind the method you describe Trevor...However, now you have described it in detail it becomes clear you mean 'once round the block' only (so for a relatively short distance) and without excessive revs....

So giving the instruction 'ride it like you stole it' to an inexperienced owner or one who doesn't understand the specifics of the method, without any further qualification, is actually quite misleading and the end result could well be a 'cooked' engine.... ...

It is enough of a problem defining running in procedures under normal circumstances as peoples interpretation of 'don't overload the engine', don't slog it in the lower gears' etc. etc. is not necessarily the same as your own...

Personally, for that reason, I don't think I would recommend this method to an inexperienced owner..
Also, no manufacturer, to my knowledge, noted this method to be a requirement as part of the running in procedure....Ian

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

I have been driving once more. Normally topspeed is about 55 mls/h (with duo) now I could barrely get it to 50mls/h (solo). No smoke coming out of the exhaust so I'm going to dismantle the barrel and piston again.. Mayby a little crack or something like that. Now I'll go to an expert with it. An expert with tools to find cracks..... Something must be wrong.

The third dismanteling and inspection of all parts concerning this leakkage showed that the gearwheels of the oilpump are, compared to some other ones, thinner and not straight anymore. Should that be the cause? It's normally the best lubricated part of the engine....Isn't it !?!?!

email (option): mail@clemensvandusseldorp.nl

Hi Clemens...Nothing lasts for ever...and although well lubricated the gears of the oil pump might have spent years running in dirty, contaminated oil...

Back when the bikes were worth nothing people just ran them and poured in a bit more oil every so often...Also if the bike came from the far east it will have seen much more use than was ever intended for it..

Worn pump gears and housings will certainly ease the passage of oil through the pump when stationary...though it still has to get past the anti drain valves..

Another possibility is that the return gears are worn to the point that they do not return enough oil, leading to an oil build up in the cases..

However you look at it though, it may be a contributory factor...and as it seems to be worn badly you would be wise to replace it anyway...Ian

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

Odd, but sort of related question....
Could a broken quill in the timing chest cover create these symptoms as well?
Mike

email (option): yankee1865@msn.com

Hi Michael..If by 'broken' you mean missing or damaged to the degree that most of the oil doesn't go where intended, I would think the life of the big end would be pretty limited...Ian

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

Pretty good question but inside the timing chest cover everyting is as it should be. I think the return pump is worn and insufficiant in higher revs that explains a that there is not much oil when draining but flood when driving. Loss of power was little and probably due to too many oil in the cranckcase. Until now its theoretic deduction.... a ride will prove it (I hope). Now I'll look ffor the right parts.

email (option): mail@clemensvandusseldorp.nl

ERRRRR......
Well, its there, but broken off in the shaft.....most of the oil seems to be getting where it needs to go.
The tube portion is fractured right at the bottom, but the tube is still there...if that makes sense. Sorry to hijack...
Is there a source for the quill? What is its official name?

Mike

email (option): yankee1865@msn.com

Sorry Michael...I thought you were proposing a hypothetical question for Clemens to check...not describing your own engine...

First you need to get the remains f the quill out of the crank..The quill itself is swaged into the cover and not easy to remove...

If it is available as a separate part I would think Russell Motors are the best hope..However, you then have to fit it..

I can probably provide a good replacement cover if you decide to go down that route ultimately...Ian

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

Thanks Ian! I might give replacing it a go....cheaper to ship a quill to the states than a cover!
I thought it might be a similar issue, since mine is doing the same....so hypothetical with a basis in reality
Mike

email (option): yankee1865@msn.com

The quill will come out of timing cover easy enough. When you put in the new one use a centre punch to dot a couple of times the alloy near the quill to stop it coming out. Draganfly Motorcycles list the quill part number is 66-698.

Re Quill

I have 2 covers,both with different diameter quills,.18 & .22 dia,both fit up
the shaft,is the bigger dia better for oil flow ? Thanks.

Well the go would be to take the bike out and when it starts to go oily do a quick clutch stop and check the oil tank.
A slightly more complicated method would be to add a length of clear tube to the return line long enough to be able to see how much oil is returning.

I will still go with the rings and on that subject which rings did you fit ?
A friend bought a JP piston for his bike & despite me telling him a dozen times no to, he fitted it with the supplied rings.
The result was an oil tank emptying itself all over the rear tyre.
Three times he stripped the barrels off & honed the bore due to insufficient clearance and the engine nipping up when hot.
Finally he got adequate bore clearance so the nipping up stopped but the oil flow did not.
Eventually he confessed that he had fitted the rings JP supplied to him and he was adrent that they were fine as they showed good compression and reasonable leak down ( cold ).
I convinced him to do the same hot after which he bought a new set of rings.
What a difference the new rings were thicker, wider & much more springy than the original set and where it was really noticeable was the oil scraper.

email (option): wariron@tpg,com,au

Clemens you don't say what oil you are using I understand that some of the modern oils are to good and make the bedding in of rings a longer job also for a while see if you can put a plastic pipe on the end of the breather pipe either taking it away from the back wheel or into a small container which would tell you how much is coming out of the breather

email (option): roger.beck@node6.com

'[ A friend bought a JP piston for his bike & despite me telling him a dozen times no to, he fitted it with the supplied rings.']...

It amazes me that a piston manufacturer not based in the third world either makes the pistons too heavy or fits sub standard piston rings..or both....

GPN in Italy are equally guilty...It would be better if they sold the piston cheaper and let you find your own ringset..

No excuse for either company in my opinion as, in fact, neither of them sell a particularly cheap piston and their products should be fit for purpose....

It's a sobering thought that piston manufacture seems to have gone backwards from 70 years ago..So much for modern materials and production methods and CAD.... ....Ian

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

This piston ring issue is a warning to all
My mate Tony bought a high compression O/S piston from Hitchcock's for his WD/CO. (Indian I dare say?). The barrel was rebored correctly to size and it has never nipped up. But I doubt he did 200 miles before we started losing him in clouds of smoke and oil. A new set of rings from John Cox fixed the problem, and he now has one of the fastest CO's that I've come across with about 1500 trouble free miles........Apart from he locked the back brake on a bend and fell off it last week Ron

email (option): ronpier@talk21.com

Well yes & no
No excuses for the garbage rings and when all is said & done a lot of damage to the companies reputation results.
Bare pistons or better still fitted with your choice of rings ( at appropriate prices ) would be a better business model.

Piston metallurgy has barely changed since the 30's when they found that 12.75% silicon alloys expanded fairly closely to the amount cast iron expanded at the operating temperatures of petrol engines.
In the 40's they found out why, the silicon rich phase contracts as temperatures rise due to a change in morphology.
In the 60's when electron microscopy became available they tweaked this phase change and the grain structure.
In the 70's when spectrochemistry became available they tweaked the allowable amounts of impurities to get a better structure and started innoculations with Ti to reduce grain size even further .
In the 80's ultrasonic dendritic modifications were found not suitable ( replacing the Ti ).
In the 90's thermionic investigations allowed for more stable shapes during cooling which allowed for thinner side walls , lighter pistons and cheaper mass production methods.

However to take advantage of this you need runs in the order of 100,000 units which when you consider the total number of M20's made over the entire life span of the engine would not be an economic proposition.
Further more ultra modern manufacturing makes only 1 size piston per casting so you would need to make another 100.000 @ + 10, then + 20 etc etc etc.

So yes it is a case of "back to the future" with foundries making very heavy thick walled piston blanks from which you can machine a dozen or so different finished products.

Now AFAIK JP do in fact use Cad/cam methods for machining their pistons as it is much more economic to wack a blank in the machine, punch up WM20 + 40 then come back in 10 minutes and remove the finished product.
Machines are cheap, skilled lablor is expensive which is exactly the opposite to the days when our bikes were new.

email (option): wariron@tpg,com,au

Hi Trevor, Interesting info. about material developements and testing methods...

Ref. piston weight though, the thicker, one size fits all, castings could be machined to the correct weight,to match the originals, at a marginal extra cost..
This is done with the forged pistons I have made as due to high forging costs each forging blank is used for various different applications...

Stripping the crank on a single cylinder engine and rebalancing it to suit an overweight piston costs far more...

it is not impossible to produce a piston in low volumes at the correct weight...For example, there are pistons for Triumphs and others on the market that are not like that...Also, the situation with the rings is completely unwarranted.

It's really a question of how much determination there is to do it right and to sell a quality component..

If we are going to condemn parts from India that are sub standard and not fit for purpose then we should do the same with defective parts from any source....Ian

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

No argument from me on that front.
JP & GP could very well machine off enough to bring pistons to the correct weight and still be balanced.
I do balance pistons before I fit them so heavier is better then lighter but It would be with an extra $ 10 not to have to do it.
I support JP because they do a big range of low volume pistons and the quality of the pistons is good save the excess weight & crap rings, Further more they are consistent .
I got a pair of "tiwan" pistons for my A 65 which I would not fit.
The surface finish was way too coarse.
They were different sizes by .003" in diameter
they were odd weights.

they sat on my shelf for 20 years to remind me . If the maker, retailer is making a good product they will put their name on it. If they don't want any one to know where this rubbish comes from they will not put a brand name on them.
I have been using this method for a very long time and rarely have I been caught out paying good money for landfill.

email (option): wariron@tpg,com,au

['rarely have I been caught out paying good money for landfill.']...


Wassells pistons sold currently under the 'Hepolite' name are Taiwanese manufactured with American sourced Hastings ring sets fitted...

I think currently they are doing A7/10, A65, Trident and Rocket 3 and various Triumph Twin pistons...

I have a friend who has fitted a number of sets and he reports good results to date, though I haven't used any myself...However, I will try them if Wassells go on to do the BSA single pistons...

So, it seems the Taiwanese might have 'raised their game' in the last 20 years...Ian

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

It is not the person who is making the product, it is the person who contracts them to do it.
China has more satellites in space now than any other country and in a few years will have more up there than the rest of the world combined, so they can make stuff which is not landfill.
Every country in the world will have some skilled tradespesons there who can make a good product.
Go to any country with some drawings and material specifications to put out to tender and there is a better than avarage most of the tenderers will be making a high quality product.

Go to the same country with 1/2 sample pistons & ask who can make some just like this cheaply and most of what will be on offer will be landfill.

More Honda stepthroughs ( CT 's ? ) have been made in Tiwain than ever were in Japan.

I got a drive sprocket from a local supplier here who sources from India
Most of his stuff is good and he asks a fair price for it ( A bit more than on evilbay ) however is this case the sprocket simply did not fit. Eventually I worked out that the splines had slightly slopped sides so did not mesh properly with those on the output shaft.
After some pressure tha supplier confessed that he had gone to a cheaper maker as the previous one had put up his prices ( firt time in 15 years ). SO the result was 300 sprockets that could not be used. He then asked me if I could give him mu worn out one, plus the tp gear so his maker could copy them better & test them all before despatch.

The defective sprocket were put on evilbay at landed cost price with the caption "not sure what they will fit " and a they all sold within a week.

email (option): wariron@tpg,com,au

That's a bit naughty isn't it?...
He knew the sprockets were defective (as a result of his own actions) but 300 people ended up picking up the tab off the back of a vague e bay sellers description... ...Ian

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

Not ethical in my books but made me look a lot closer at what gets offerred on evilbay and the attitude of retailers to it.
"If it is cheap enough some idiot will buy it"

email (option): wariron@tpg,com,au