Mike Powell's 125 Engine...

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

[/quote]

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

mjpowell wrote:

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?

Mike

Hi Mike
thanks for the info, I built a water cooled barrel but they both distorted too much, we put it down to Brazing the ports on as you have explained, and boring too large.

we are currently building another, but we will cast weld it this time, then silver solder it to plug any leeks,
braze ! the route of all expansion and distortion problems in a cylinder you are trying to keep round, well as round as possible

JB made some really interesting comments on distortion (excellent references to ) when he spoke about distortion of a cylinder when bolting and clamping it down we have been honing the barrel on a clamped dummy spigot prior to honing since 1981. I probably new a lot more about this subject then than I do now

Not really had chance to respond to the theory on how this barrel was manufactured, certainly some very interesting aspects, the transfer port area is huge!, so to is the transfer ducts volume, also the exhaust port appears very short/stubby,in a different position, I’m sure these are all important aspects of the design criteria originally laid down.

for anyone building water cooled cylinders, the Original bantam Tuning manual specifies a maximum it should not be bored past when using a 175CC cylinder for a short stroke it make it week it says.

our new cylinder for my water cooled engine, is based on a D5 150CC cylinder and will have a liner but the top part will be exposed to the water, reference my dad’s sketches loaded on here somewhere, we intend to re weld the top half back on and the re-use both top and btm fins, the original stud holes top half will hold the head studs.

an interesting subject

Derek

Are there any aluminium water cooled barrels around? I really fancy making one. Water cooled barrels do seem very complicated though.

Hi Rob
you can get the 1mm rings for the tz piston from vic eastwoods at swanley kent he is the wisco dealer but if you want to change the piston they is a TM kart piston that will fit and has oversize as well it may be the tz piston has been turned down so if you could get a new one it would go straight in

Hi Robbie

what is a TM piston? as I need to look at a longer skirt piston, as a longer term fix. one made for a 125cc. !

Derek

Hi Derek and Rob
Tht Tm piston is some of the tz 250 boys are useing as they are have trouble getting yamaha pistionshttp://www.ebay.
found this pic of one on ebay http://www.ebay.co.uk/itm/tm-racing-125-k7-new-unused-Kart-engine-genuine-piston-/110759552742
also theys a Tkm piston which is a kart piston try this web site for piston data http://www.shop.titan-piston.com/TM/
http://www.kartstore.co.uk/shop.cfm?cat=1550&node=138
http://www.kartstore.co.uk/shop.cfm?cat=1577&node=125
hope tis is some help to the both of you
Robbie
back to the house work
ps have not forgot about gearbox problems coming soon

Thanks Rob

Will check it out, sounds like helpfull information for other too.

regards Derek

John. B.

at our recent meeting, you were Big topic of discussions, ref your comments about the shape/colour of the piston crown, On Mike Powells engine, for the record could you first clarify you were refering to the piston crown not the combustion chamber, and please tell us what we should be looking for, on the piston crown, ref Pic 9. and please give us more information on what you are refering to exactly.

Kind Regards Derek

Sorry, just got back from Xmas Hols....

Wretched weather and really tired now and just going thro´ the multiple messages and saw your note.

I must look back at those pics but off the top of my head the inside of the combustion chamber looked as if someone had polished it and hadn´t got out to the squish area yet where there are two burn stains suggesting an oddity with combustion squeezing outwards non-uniformly in only two places.

Certainly the combustion chamber doesn´t -- or didn´t rather, at 1st look -- look as if it belongs to the piston crown which -- I think (thinking back, about it now) -- looked as if the heat release (expansion of combustion gas) was fairly uniform under the squish band where it then did look a bit odd at the front (exhaust) edge of the piston. If everything was perfect I would expect there to be a band of at least 5mm width of no burning stains at the outer edge but it has to be remembered that this engine works well so maybe JayBee hasn´t got it sussed out properly...???? ....

I MUST LOOK AT THE PICS AGAIN -- tomorrow....

2012 belated Cheers!

Hi John

Thanks for that I will look fowards to your comments after your next look,

I was actually hoping you would be able to tell us some subtile difference that could help us read better the crown, or points that show differences in ign/transfer/exhaust - Imbalances? or what it can show has happened, or what to look for if imbalances present.

regards Derek

Hi Derek! I am likely to end up asking more Questions than giving adequate answers on this MP engine exposure...

...re the advice concerning the piston crown discolouration I can say a few words from experience -- and from having at one time instrumented a piston with thyristors (fine wire temperature sensing elements enscapsulated in 3mm dia glass beads) to get an idea of the temperatures in the piston during dyno test running. This means I MIGHT have a bit of a rough idea as to what might be happening to the piston & head during combustion.

Re Imbalances you suggest -- much depends on the octane rating of the fuel as to whether you can achieve optimum settings for carb jetting and ignition timing because there´s one hell of a difference in the heat-release-period and maximum combustion pressure with a <100 octane fuel (petrol) and a >101 octane fuel. And re the head´s combustion chamber -- as shown here -- the combustion chamber bowl looks more like running on the latter fuel -- with the piston crown looking like it had run the former -- low octane fuel, although a lot of that is attributable to burning oil in the petriol-mixture.

We (Henry Ford & I) bought the thyristor equipment from AE Engineering which was too archaicly mechanical (needs a long paper to describe...!!) to last any great length of time during dyno test....

...uh oh! I am nostalgigating again (I made a 2012 resolution not to ...).

... but it did work -- for about twenty hours of dyno running and we got some good results ....

OK! Back to basics. Firstly we do plug-chops to get an idea of running rich or weak -- (having first checked for too retarded or advanced ignition) -- but how often do we check that the piston crown tells the same story? On the Wednesday I did plug chops at Brands with the Gardner expert and with a new needle at a new setting went to Snetterton on the following Sunday where the 250 ABS flew faster than any other two wheeled missile ever has -- for three laps of practice -- and then seized with a hole in the piston and its crown sunken.... The sunken section was the diametre of an old half-crown with the surface Grey/WHITE around the hole with the surrounding squish a light brown to grey band -- not at all like the plug!

It was one of the really old school -- might have been Roy Bacon or Mick Scutt² -- who said, "They go their best just before they seize!"

With this experience behind me I went to Brands with Icarus-2 Bantam, leaned-off the mixture by plug-chop test until it was really motoring well and then gave it a half-an-hour´s hard thrashing. Surprise surprise! With the head off the piston told a different story. The middle of the piston crown was grey with a very light brown fringing instead of the chesnut brown of the plug -- and it looked as if the surface was rougher -- sort of sandy texture -- which had me thinking it had been close to collapsing disaster and had me replace that piston. They were, of course, STANDARD BSA pistons I used in those days!!

So, to this very strange looking combustion chamber of the MP engine? To me, it does not look as if the head belongs to that piston. Such indication of fiery activity on the piston crown is not shown in the surface of the combustion chamber? In fact it looks as if the head had just been taken off a lathe face plate after polishing the bowl surface.

IS IT AN OPTICAL ILLUSION I am seeing? There´s a thin ring of burn at the spark plug hole and then little indication of combustion heat until the squish band, where there´s just a bit of lop-sided burn-stains at the exhaust and inlet sides where the Bump-Clearance (piston-crown to head clearance) has varied -- OR the non-uniform cooling has created distortion of that clearance.

As I said before the explanation I have is for the head to be non-uniformly, over-cooled.

Back to the piston crown. Of course, petriol-mix oil is being burnt on the hot piston crown and the burn-stain indications are that the Loop-Scavenge effect is working well*** with black in the middle and brown surround...but I think I would be a little worried if it were my motor with the black covering going right to the piston edge at the exhaust area. OK, that -- as with the piston crown centre -- is where you expect the most heat but I would expect -- in a properly cooled piston -- that there´d be a band ( as I said before) of unstained/cooled ring all around the piston-crown edge.

The reason behind that statement is that the top ring transmits the piston heat -- at the edge -- to the cylind barrel wall. The barrel wall at this point might be say at 180°c temperature and the piston at 220°c, 5mm in from its edge, thus providing a good heat transfer path for the 40°c... The fact that during hot gas expansion the top ring is being pressed hard against the upper ring groove facilitates this heat transfer.

As I already mentioned, I´d be concerned at the black patch on the piston edge adjacent to the exhaust port but on the other hand that could possibly be only surface heat of the rush of exhaust gas....??

I´m gonna take another decko at the pics because there might be indications of surface metal erosion -- I have seen this on overheated, failed pistons where it looks as if a patch had been sand-blasted. It is as if the metal breaks up locally -- not melts -- but disintrgrates, maybe because of the overheating -- grain-growth weakens the metal such that it crumbles into powder....


This might end up as an eternal debate because there are conflicting opinions on spark plug readings, head cooling with combustion chamber shape and piston discolourations by many experts in the auto racing business. Much of the work done is in respect of fuel economy and pollution as much as in competition,.


²- humble apologies Mick -- for the "really old" -- of course YOU are NOT!!

***probably why it is winning races.

Uh oh! Did I write all that??