Mike Powell's 125 Engine...

A neat engine stand -- 9 marks out of 10...

... 9marks out of ten for the engine stand Mike, but you must stand in the corner for being a Bad Boy!

That CDI ignition rotor is a flywheel and you NEVER mentioned it when you started that ruckus about
Rossi mentioning his Ducati flywheels ...

Now, what dia is that rotor and how much does it weigh?... and please confirm the flywheels dia and weight as shown here?

Cheers!

John.. which do you think is front and rear on the cylinder head pic?

I'll weight ignition rotor and measure diameter, why did you assume it didn't have
an ignition rotor? in your 'Heavy crankshaft' posts ??

Whats your next question?

Hi Mike

1) Timing side bearing what type is it? a/c
a) The cage appears to have over heated?
b) Is it a fibre cage type? I think I can see inner /outer supports.
c) I have never seen one like this only rollers look similar

2)Inner transfer walls please explain! The shape and/or reason ? “what difference” does it make? and do you alter the shape at all while experimenting., “I noticed you said dev-con” they look like cast Iron.

3)Have you identified each shot with a number to show you are showing us something or is this to be able answer questions on each one, or are you pointing that we should be looking for something on each photo,? I think there are so many aspects on each shot I will send you a PM with some other questions.

4)Please explain the gearbox ratio’s on top gear ? I have counted these several times, I even asked another to do so who like me could not believe this, does this actually work ? I just could not believe it, at first, but it is 22/24. ? so I’m very interested to put this through (John Senddle) – gears ratio /calc table on this forum a while back, to see what ratio it gives between the gears, but it would be so much easier if you just told us why? And the reasoning behind this, Mike but more importantly what difference it makes when changing between 1st 2nd and Top obviously this will be different for others but , my give a clue?

5)There are so many other questions, and gems I have spotted, but I can not ask all the questions, I’m sure others would like to have a go, at spotting the other more critical gems in these photo’s “some very interesting aspects, I have never seen inside this engine before. Amazing I can see no braze too on this cylinder.?

6)All we need now is for "Trevor Amos "to strip and photo his engine in the same way and post it too.

“I feel the engine stand, Is a step forwards for us “just got to get one of those”.

Derek

I assumed it didn´t have an ignition rotor because we had a contact breaker there and on some race bikes I´d seen the Hall Effect sender, gapped wheel -- or holed wheel with battery and coil ignition , of course.

Another question relative that snapshot -- the rotor has 6 circular things in a plate on the outside that look more like clutch spring covers than anything else I can think of...?

... you sure you haven´t got a KERS (Kinetic Energy Recovery System) on there that you clutch-in
during the race when the time is ripe???????

CDI -- I take it means capacitor-discharge-ignition -- `scuse me for being a simplrton!

Cheers!

Interesting engine internals being exposed , could be brave or foolhardy , depends upon what the competition seize on or eliminate !
One thing i have noticed which is common to all the engines shown , bronze bushes in the sleeve gears ! Am i the only one to install
needle rollers here or are there others doing this ? I did this in Nov 97 and, incredibly, the originals are still in place , a real fit and
forget mod .

Cheers for now , Trevor

-Pic #8 -- re front & rear ? of cyl head in pic 8 -- is difficut to be sure because of the head´s symmetry but if pic 8 and pic 9 are related then it is the left side which does not show much `burn´ as does the piston crown on what is the exhaust (left) side. Where the four circular patches show as clean there are indications -- I think?? -- of the head, momentarilly lifting clear, letting some combusted gas thro´there, then sealing properly later -- when properly WARMED UP!!???

So, just another GUESS on the Mike P... 125 -- there´s a slight leakage there on start-up which obviously goes away once the head has warmed up*** -- yet I still think it is running too cold under full load conditions.... .

***otherwise there´d be more carbon and the leak would worsen until disaster took over!

Cheers!

Fantastic amount of clever work on this engine. Lots of aluminium welding on the crankcases -- -- and the padding?? Mike? -- what is the crankcase compression-ratio??

The clutch looks different. The centre bit looks "worked-on" -- something to do with the push-rod bearing??

Re the flywheel dia and weight -- I have, I think, already included it in the treatise Peter has -- but ALL rotating parts of the engine must be included in calculations and the clutch and any other rotating parts are effectivly acting as the engine´s Flywheel.

So the question is how heavy is that clutch?

Its all a bit of guesswork anyway and my interest is the question, that won´t go away -- why the `big´ flywheels on the 175?
I thought the conclusion I came to was satifactory but doubt has crept in and I´d like to get to the bottom of this one.

We all know why the flywheel is needed. It is as Trevor once said, on here, during one revolution to provide energy to overcome the resistance to rotation***. Which means that from TDC -- during expansion of the power stroke -- the speed of rotation is faster than when the piston is travelling from BDC on compression stroke towards TDC. Long long ago I made a single-acting steam engine model which, without a flywheel, would only run at 1 to 2 revs per second and its exposed crank could be seen to move rapidly from TDC to then slow to hardly moving as the piston moved from BDC to TDC again... The indication was that the friction losses during that period were more than the inertia of the crank assembly could provide to keep it moving fast.

So, for the Bantam 125//175 difference -- I concluded -- perhaps wrongly -- that friction losses of increased piston dia were the reason...!!

***not his exact words but having same meaning. Trevor quoted the amount of ' Cyclic Velocity Variation´ at a given speed and I forget what that was.

If someone knows WHY -- then I´d appreciate being put out of my misery before it is too late!!!

Cheers!

Sorry JB haven't done rotor measurements yet - forgot (work gets in the way you see)

Trevor, true enough, just thought I'd let some secrets out as I can't expect the class to
thrive if new starters/old hands haven't thought about other ways of doing things. Hopefully
people after viewing other 'engines' and will improve there lot and performance, I do it for the
good of the class.

Derek I will answer your points but not tonight as about to go out. I'll answer all messages on
open forum not private pm..

Regards Mike

We (me and my father) dont normally go in for an opinion but felt it was time,


Apologies if it is in the wrong post/Topic,


Without a doubt we think it is great with all the engine pictures and show's what is and can be done, but also surely a good rider compliments a good bike?

This is an open forum and so may the better person win as im sure everyone gets the gremlins!. Without help from the experienced riders and builders then how are newcomers meant to progress with a build as complete race bikes come up very very rarely.


Kind Regards


Edward & Malcolm

Just to answer some points:-

Main bearings SKF featuring nylon cage.. less friction...
must admit I didn't notice difference.

I used the term Devcon (like hoover for vacuum cleaner?) was
actually Loctite metal set 3475(aluminium).

Transfer ports - trend was a while ago to have long 'jug handle' passageways
and I tried to copy that trend - however trend now is short direct passages?
or has it changed back again? These things seem to go in a 5 year cycle!

Gears - yes it featured 24/22 output pair!! At Mallory (using 24/23) i was losing out to
Ian and Snowy, so for Pembrey I changed to 25/22 output pair to get more poke out
of the corners but unfortunately gap between gears to large for my narrow powerband
motor. However shearing a layshaft I rebuilt the motor(at Pembrey) with a 24 sleeve gear while not
'good practice' it did improve gear ratio. I think I only got away with it because I race with a lot
of mechanical sympathy.

Mike

JB something for you -

Flywheel 2lb diameter 3 3/8"

I know you like imperial!!

Thanks Mike! Yes, I had twenty years of Newtons and Kilopascals -- and was truly sick of such units -- but we have always had bore & pistons in ccs and being truly British I want to use as much Imperial units as possible to the END!

As I said before the two wheels (except when wheelying) when "acting as flyWHEELS" dwarf the engine´s inertia during acceleration. That addition of rotor´s weight & dia makes only a tiny difference -- and thanks anyway -- I am just hoping the light will come as to why the 175 -- seems to positively need a larger flywheel inertia than does the 125... Something other than bore size must be involved.

By the way, you mentioned the IoM again, when you don´t really want to race there yourself, and when I spoke recently of Slick´s comments on here there was no response -- so I shall tell it to you that Phil Edge of the Southern 100 Club wrote to me to say that he has given my comments to the
race secretary, George Peach, who is monitoring the entries for their suitability/eligblity/capability to race in three possible Billown road races that are being put on in 2012.

It would do a power of good -- advertising wise -- to have a couple of Bantams finish the Billown course which is near Castletown....

Cheersm,
JayBee.

Derek you said you had more questions from your observations?

Stand is a D3/5 cut short in its prime? It came with a Bantam Racer Rick bought in 1980.

[quote
pic10

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hi Mike
I would like to know more about how you decided the radius on the transfers, and who actually did this.

I also point out there are two critical radiusses missing of the new barrel nick had made for his backto front barrel.

I'm sure Nick asked recently about the manufacturing process of such a water cooled 125cc iron barrel,

I know I asked about this before and got no reply!.

The liner looks very thin, ? and it looks like its just been Honed ?

Is that silver solder on the base of the cylinder, if so why? silver solder,

I would like to know more about how this barrel was made.

Regards Derek.

Hi Derek.

I bought Nick's bike from this year and I am interested in your last comment as to how the porting can be improved. I have not really made any changes to the engine yet as I want to dyno it first but I am very keen to develop it after. I will upload some pictures soon though I can't seem to do it from my phone.

Cheers

Rob

Derek are talking about the radius in the port windows or in the 'devcon' inserts?

Port windows done by Tom.. Devcon passageways.. I guessed after looking in books
and on the web. Seemed to have a radius or a 45* chamfer.

Cylinder made by Tom 30years plus ago so I wouldn't know how its made other than
:- D1 (55) remove top fin leave next fin m/c all the others off, make exhaust port from
lump of cast iron- braze on make inlet port sheet steel - braze on, make transfer ducts
sheet steel braze on while watching the exhaust fall off etc, If you manage to stick all
ports on, silver solder a jacket on quick!! Silver solder lower melting point so ports
shouldn't fall off when putting jacket on?

Yes v thin, If you look closely on the sleeve bit that drops into the cases there from inside
- liner, D1spigot then machine steel/cast? to fill the gap when fitted to D7 cases. Also has
had a hone down it. Base flange looks strange because it is beetween fins hence lots of braze!

Mike

If you can not do somthing your enthusiastic with, on what better day than Christmas day to do it. she is in the kitchen "I'm cooking the turkey" so I have a few hours to kill.

Hi Rdus - Mike is absolutly spot on, ref the radi chamfer reputed to give a minimum 2HP !! /(amazing you can feel it like a good exhaust when you get it right) has such an effect on torque too. Mike makes a very interesting comment about Book,s I would certainly like to Know which and were this is covered in a book and what the book is called "Mike please", and check out page 13 to 23 on Bitstop.BUZZ Under RSA 125/250

Derek

Hi Rduesbury
will pm you

Derek

I appreciate your help derek! I didn't take your comments badly at all.

I felt it could perhaps be improved when I stripped the engine. I have made several other improvements but nothing performance enhancing really. Generally the engine seems to e very good but there are always things that can be developed. I feel that the porting in the crankcases can be improved too but until I dyno it I am reluctant to make any changes. Is there an optimum gas velocity I should be aiming for through the transfer ports? I expect the volume of mixture to be transferred through the ports can be calculated, say 125 cc + some to be compressed back from the exhaust.

Hi Rub

Velocity of the transfer ducts ? "flow can be measured, lots of poeple know a lot more about this than me, what I do know is most flow benches made for 2 strokes dont work accuratly, or give proper correlation.

calculating it well lots of maths, even then too much guess formula work and factors involved, even then thay are all too dependant on temp whch is almost impossible to deal with so a average Temp is used - meaning its not accurate, but a great subject -

Flow benches have been talked about extensively on Biz.buzz for the RSA - its said the best type is a pulsating item. I have limited knowledge of this subject. im sure there are others that will hopefully have far more positive and technical interesting things to say on here.


Derek

hi Ru

just read page 23 on biz, he says if you connect a normal vacume to the exhaust with an engine assembled, and put in smoke pellets to the inlet side, (you will need an bit of rigging with pipes) glue on a glass plate to the head, then rotate the crank till it uncovers the transfers.

you should be able to see the flow, all interesting stuff, but what does it show you, we did this a long time ago and placed a spacer under the glass to mimic the cylinder head.

regards Derek

Hi Derek

Struggling to find the site. Do you have a full adress for it or what can i type into google to bring it up?

Rob

Hi Rob
The first thing I would do is get out on the bike and do some testing and get to a track day and get used to the bike before you start play with any the port timing
This engine was rebuild /remade by Tom Miller wen carl coombs had it
this bike is quick in the right hands like all bantams they have to be riden hard to get the best performace out of them
in the past i have had some very good battles with this bike wen carl was riding it it is NOT slow
so I would be very careful if you start changing the port timing
get to know your engine first
play with carb setting and ing timing but the golden rule is only change I thing at a time a write it down LIKE I do somtimes
and PS if the gearbox works leave well alone
the only thing i would say is try and get away from the tz 250 pistons as they are like rocking horse S--t they is a cr 125 piston that is peg at the back this may have all ready been done by Nick hope these words of wisdom help

Robbie

I think the piston in it is a tz yeh. The piston ring gap seems huge so I know that want changing but the piston looks in pretty good shape. The bore looks pretty worn though so I was going to give it a rebore and fit a different piston. I think someone suggested an rm piston too.

I have only ridden the bike once but it seemed great. I would have ridden it more however after inspecting the clutch I notice a main bearing was slipping so I stripped the engine earlier than planned. The bearing was slipping on the external diameter so i had a friend turn a bush, bore the case to a transition fit and froze the bush in before then reboring to the correct diameter for the bearing. Has worked great and the engine build well. I have plenty of pictures. I will try and upload some.

Rob