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nigel breeze

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PostSubject: mallory...   Sun Apr 22, 2012 1:11 am

[img][/img][img][/img][img][/img][img][/img][img][/img][img][/img] well any comments/observations would be appreciated..looks like running lean?? the engine cut out on the practice lap but restarted in the paddock, in listening i felt the engine didnt quite sound the same,but i soldierd on , warm up laps ok, standing start on the grid couldnt control the dragging clutch and keep the bike from bogging out, consequently stalled,not once but twice affraid i did consider not entering at mallory due to not having spent anytime testing / riding the bike and it proved to be right as it looks like i have some engine problems amongst others (poor front brake, possible buckled front wheel maybe warped disc,dodgy tyre i havnt looked into that yet). happy days study scratch thanks to the riders who helped with advice and providing me with a iridium plug as my b10es,s just kept oiling up, adjusting the clutch properly, pushing me to start for the last race and the comedy duo eddie and malcomb for making me laugh.
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Edward Pickering

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PostSubject: Re: mallory...   Sun Apr 22, 2012 6:36 pm

Hi Nigel,

Hopefully the experienced guys on here will be able to help with your questions, as for raceday due to the fact we were about as much use as a chocolate fireguard we thought that mild abuse was the order of the day! lol!


Kind Regards


Eddie
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john bass

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PostSubject: Guessing again...   Sun Apr 22, 2012 9:33 pm

Guessing again -- Nobby1! It was postively running weak at full throttle opening -- or the ignition timing was wrong for the type of fuel in use -- or the compression-ratio too high for the type of fuel... Positive scuff followed by rings not working properly and also running rich at some lower throttle opening which had your earlier plug oiling-up!! i.e. Rings no longer sealing all the way around... That´s why it sounded different after the tightening-up ...

... -- another couple of pics around the piston circumference would verify this.

There are signs of `combustion-washing´ on the head. That´s where there are no burn marks. This "cleaned look" does not mean there wasn´t any combustion there -- it is a function of the combustion movement stripping the carbon off the surface (particularly when using a high octane fuel). This is backed by the circular-streaking-stains meaning there was a lot of turbulence which may mean unequal transfer port flow causing hefty swirl....
Swirl is necessary for optimum combustion but a two stroke relying on Loop Scavenging for its efficiency requires a uniform up and over swirl and not of a rotary nature as indicated.


Better to have Trevor or Sticky Mick or some other expert analyse this and comment -- also criticise my statement -- which would be helpful to US all....

I know how you must have felt at Mallory, Nobby1 -- I suffered too and spent time watching everyone else having fun whilst I sweated just to get a ride ... I know that if I had been more dedicated I would have FOUND the time to make sure everything was well-prepared before the meeting but my life was overfull at that time -- --- ---- long, long ago.


Better good fortune at Cadwell.


Cheers!
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ROBBIE

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PostSubject: Re: mallory...   Mon Apr 23, 2012 12:35 am

Hi Nigel sorry I did not get time to speak to you at mallory. but I had big problems with my and michaels bikes but that's another story Embarassed looking at your pics looks like you had a little nip this is quit commen looks a little tight for the bore my bike sometimes nips first time out with a new piston. what we do is check the ring is nice and free and a light horne through the bore.as you have run it after it cooled down it may be ok but check you Don't have any aluminium left in the bore or it will seize again.it looks too rich to me try starting the bike at home put some load on the engine try putting the front wheel up to a wall and see if you can get the back wheel to spin up up this may also help you get that clutch set up.wen you get it on the track if it's too rich at top end wen going down the straight try rolling throttle off just a bit and if it picks up it's too rich at the top end.as a good staring point Ing timming 60" and compression no higher than 9.5.1 I am running at 8.5.1 on Avgas also check you got no air leaks now get out at cadwell you got all weekend to get that first finish under your belt Hope this helps see you at cadwell
Robbie


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nigel breeze

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PostSubject: Re: mallory...   Mon Apr 23, 2012 1:03 am

john thanks for your observations and robbie for your input too. ive decided to try the bike with a four plate standard clutch, some may feel it wont last long but what the hell. some of the debris inbeded in the head looks like a bit of detonation and possibly wrong ignition setting. alan said the bike would be better off with a power jet on the carb to improve the carboration and ill see to this too and also some dyno time .. during the practise lap before the bike nipped up i felt pretty pleased with myself as the power developed over standard was very noticable and no jumping out of gear, as john has pointed out the improvements in the transfer port dept can only improve the scavenging and possibly the power further. not sure when ill be out again though, cadwell date too close but you never know.
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mscutt

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PostSubject: Re: mallory...   Mon Apr 23, 2012 1:42 am

Nigel its not lean at all in fact its really rich and it looks like you were close to oiling up that plug too!

Due to being rich its not run at any great temperature and there's plenty of oil about so I'm sure the light sieze marks are due to insufficient piston clearance. Its a common problem but one you can fix.

The usual way to cure this by hand is with a carburundum*** stone with a little oil. Keeping the stone as flat as you can, try to remove about a thou from each side (of the piston) and try again. All barrels are different so the only way is to find your optimum size by repeating the operation until its safe.

As Robbie said, make sure there is no alloy in the barrel. If you don't have access to a hone several options spring to mind - a strong solution of caustic soda painted on the alloy will dissolve it, gentle scraping with a hard edge scraper or just a bit of emery and your index finger will do the trick if its not too severe a plating.

Not sure about the dragging clutch - do you get enough lift? Is the top plate bending as you draw the clutch in? Are the plates all flat?

Re the bits embedded in the head, inspect them with a strong magnifier and a sharp edge to scrape them. If they are metallic where have they come from ? could they be shards of alloy from the sieze? I don't believe there's been any detonation everything is too cool.

*** I was recently shown a much better tool - a diamond lap. About 2" wide and covered in a pattern of diamond dust ovals it worked quickly and because of the width stayed level - I've seen them on the internet at about £16.

Mick


Last edited by mscutt on Mon Apr 23, 2012 7:05 am; edited 1 time in total
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Derek

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PostSubject: Re: mallory...   Mon Apr 23, 2012 2:46 am

Hi Nigel some interesting comments from you.

Alan always gives good sound and solid advice, seems like Rob has a few ideas on what he does too all helpfull Im sure!.

my advice is do your own thing, I dont know what your settings are, I doint think any of them on their own are that important, looking at the crown I would certainly disagree with Rob as the combustion colour looks a great colour "or too cool", however I think John is far more experienced than me in looking at swerls on the crown of a piston.

If I were you I would do a number of things. but ther are many things that should be simply checked first, your only down the road from me, so I would be more than happy to assist with some of this checking.

but first
1) pat your self on the back, you made it out, what an achievement this alone is, this is what Alan said to me on my return in 2010, so well done to you, as it is an achievement to just make it out, these little bikes are not designed for racing, you have succeeded where many have given up, and you had no gear box issues. so you have many positives from your first outing.

Alan Brown gave me great assistance when I first returned, his help was invaluable before I started back, you can not go wrong if alaan says you need it just find a way to do it he is never wrong.

regards Derek


Last edited by bettsd on Sun May 06, 2012 8:10 pm; edited 1 time in total
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john bass

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PostSubject: Last bit ...   Mon Apr 23, 2012 4:56 am

Last bit on this from me:-

What Mick & Rob said reminded of the hours I spent at Brands `profiling´ two pistons in a day of practice before start of season... Running with rich carburration I´d "Run-In" the pistons for several minutes each -- by poodling around and blasting now and again -- then coming back into the pits and reviewing what had happened with them. There´d be obvious high spots and the bore might show a sign of a slight scuff. Whilst sidecars or cars were out doing their half hour I´d do what Mick said and stone off the apparent high places and make sure the bore was still OK. Some people say using a fine riffling file is better because that doesn´t leave tiny grit in the piston but I think that is overstated. At the end of a day at Brands, I´d blast one of the two pistons for the full half-hour and if nothing went awry I´d have a spare piston ready for changing. On my Icarus-1 -- my first Bantam -- that worked well for a whole season*** but on Icarus-2, where I got too clever with dubious tuning, to go to higher revs (11,000 instead of 8,400) still using Standard Bantam pistons, I suffered an enormous lack of piston reliability. Enough to make a stone Buddha weep!!

That clean bit on the cylinder head is typical of the "combustion washing" effect that comes with methanol or high octane fuels where the combustion chamber is kept relatively cool so I agree with what was said about piston clearance being your trouble and that backs up what was said about the `piston profiling´... I hope it is relatively clear now as to what went wriong and how you might put it right....

***You know the old saying, "If you have a spare, the original never goes wrong..." (it did of course but usually near the end of the season...)!!

Cheers & chin-up again...!


Last edited by john bass on Mon Apr 23, 2012 5:08 am; edited 1 time in total
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Derek

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PostSubject: Re: mallory...   Mon Apr 23, 2012 5:06 am

just had another look at what John is on about, can not discount him just becase he rambles on about flywheels, seems he is onto somthink , I agree with him, on MICK is talking through the little oriffice lol.

it seems your piston profile needs adgusting, need stoning, clearence across the gpin those pistons do expand a lot and in my opinion are not profiled correctly for any purpose other than snow racing.

anyway stone some 0.003 thou ovality more in this area than the skirt clearence, and it should be enough, this may seem a lot but its a forging and these are dence so expand a lot,

and yes its rich but i already said this before. ??????

Derek
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PostSubject: Re: mallory...   Mon Apr 23, 2012 5:18 am

hi nigel when you have the engine back together bring it over one evening we can adjust the clutch i have a lathe so can make anythink needed to get it set up correctly, Alan has a 18 spring conversion i got off him, this works great on the steel set up but is very heavey on the hand and cable.

regards Derek
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Derek

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PostSubject: Re: mallory...   Mon Apr 23, 2012 5:27 am

mick could you give us the dimond lap details to google i seen flot items but never for bores

derek
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john bass

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PostSubject: Oh Gawd Derek!   Mon Apr 23, 2012 5:28 am

Oh Derek -- did you have to mention flywheels again???

But memories of practice days at Brands must be re-lived. I just didn´t just `profile´ pistons and sort out exhaust pipes there (among a dozen other things) -- there´d be real practice and actual dicing with road-hacks -- big ones, like Dominators at that. More fun than racing in Bantam events...!!


But getting back to flywheels -- did we ever come to a reasonable conclusion on the subject??

Cheers!
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mscutt

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PostSubject: Re: mallory...   Mon Apr 23, 2012 7:03 am

Derek

a small misunderstanding there. I was talking about a flat one for doing the clearance on the piston by hand.

I just googled "diamond lap".

The one I used was less like a stone and more like this -

http://www.ebay.co.uk/itm/Double-Sided-Diamond-bench-stone-Ideal-sharpening-gravers-400grit-1000grit-/220871413669?pt=UK_Crafts_JewelleryMaking_GL&hash=item336cf64fa5

Mick
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nigel breeze

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PostSubject: Re: mallory...   Mon Apr 23, 2012 7:14 am

thanks again for all the replys...anyone got a picture of a bantam175 piston crown showing correct colour and transfer patterns?seen ones for pistons with multiple transfers but not with two.
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Derek

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PostSubject: Re: mallory...   Mon Apr 23, 2012 10:21 am

its quite interesting that Mick has picked a diamond type lap to profile his pistons - I would also add when a high silicon piston scuffs, its not agreat bearing surface, so should be stoned however in some cases the mixture of pressure and heat on silicon produced by scuffing, is enough to duplicate the components that produce diamond in its natural state. so looks like
Mick and the london boys found another great way to resolve this issue, when trying to relieve the piston.

Derek
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john bass

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PostSubject: A fine stone...   Mon Apr 23, 2012 9:00 pm

There are several grades of grind-stones for sharpening tools and I used three of coarse to fine -- with a very fine one at the finishing strokes -- left an almost polished finish. I know some people who´d pooh-pooh that notion and would declare a rough finish was necessary to keep the piston lubricated by retaining oil in the rugosities*** but Icarus-1 was remarkably reliable where Icarus-2 was awful. That´s understandable, of course, when you think of Icarus-1 putting out a lowly 12 horsepower at 8,400rpm.

*** Scuse et moi! I love this word and don´t get to use it very often.

Cheers!
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alan
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PostSubject: Re: mallory...   Mon Apr 23, 2012 10:57 pm

Hi Nigel,
The problem you have is piston clearance, note that the piston scuffing is mainly to the "four corners" this denotes that the clearance on the piston is too small, or that the taper on the piston is insufficient to cope with the expansion.
Cure? the only real course of action is to clean the bore (As per Robbie's description) and stone back the piston in the scuffed areas.
In future rebuilds you will need to "pre stone" the new piston when fitting.
You should be OK in this part of the engine then.
Also the carb is seriously rich and you are flooding the motor, it was really obvious at Mallory, you need the power jet system and to get the mainjet down or you will always choke up as the motor warms up.
Good luck and do keep asking for help.
Cheers,
Alan
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Derek

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PostSubject: Re: mallory...   Wed Apr 25, 2012 5:18 am

Robs Idea of checking out the clutch, but beware, we had a smal dwarf wall Ed let out the cluch a bit quick while testing out Robs theory, seems he never had the front wheel realy tight against the wall, the bike vitually jumped the wall as it stalled, while taking the top three courses off with it, and I have a nice flat exhaust that im scratching my head at what to do. on the down side it was the nabours wall at the end of the drive, so I have a repair bill to deal with too "thanks Rob" anymore great ideas!,

so beware if your testing clutches make sure its against a large and secure wall, preferably not your nabours, and dont let your 19 year old son do it.!!!

regards Derek
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Edward Pickering

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PostSubject: Re: mallory...   Wed Apr 25, 2012 5:43 am

Derek,

You should of set up his front brake to bind like yours.......................


Eddie
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