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D14 engine seizes as soon as a little warm
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Roarn
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June 12, 2020 - 1:58 pm
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Thank you for all help / tips - I will get back to you with more info, engine number and more pictures during the coming weekend! At least I know he said the engine were marked with D14B.

It came 2 cylinder units - on the bantam now a cylinder with more squarish inlet port - and a little smaller ports ( i think) than the other who sat mounted on the bike when purchased, that had a inlet port with a more "heart shaped" ?? - but damage beyond repair.

Will come with more this weekend! 

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cocorico
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June 12, 2020 - 3:03 pm
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Roarn said
... worked all his life as car mechanic / bodyshop repair / painter and last 25 years certificated buss mechainc....He also has a passion for 2 stoke mopeds and involved in local club. When he found this Bantam 6-7 years ago he fell for it - a British 2 stroke,,,, ultimate,,

I think we can assume this gentleman has a pretty good knowledge of engineering and 2 strokes, just needing pointing in likely directions.

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cocorico
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June 12, 2020 - 3:15 pm
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Roarn, it might help if you can identify what barrel & head is fitted (as you had two different ones). Here are a couple of links to previous posts on 175 cylinders and heads. There is quite a lot to wade through.

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Roarn
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June 13, 2020 - 3:31 pm
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"Double check that carb model is ok for a B175, if that is the full engine designate, not just B175 parts fitted to a D14 engine. As mentioned in previous post, please check engine number for confirmation"

 

Hi again, now I think I have all info, though the owner is a skilled mechanic he did clearly not have enough skilles about these engines,,,,

 

IMG_18133.JPG

Engine number D14B 6617 - assume original as also frame number corresponds.IMG_07522.JPGIMG_07533.JPG

THIS cylinder were onto the engine when purchased but damaged beyond repair,,, IMG_18188.JPG

THIS is how last piston look like after last miss fortune, barely run - have just removed cyl.

 

It has a 26 mm Amal mounted, larger exhaust adapter/ring and when inspecting earlier sized pistons mainly sized at exhaust port and also slight signs at inlet port.,,,

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cocorico
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June 13, 2020 - 4:30 pm
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Can you post similar photos to the above of the cylinder now in use?

Can you see a casting number on the cylinder you are using? - should tell us what model it is intended for.

Were all the seized pistons damaged in the same area and is the damaged area facing one of the ports?

Is there a number on the carb and can you see whether the diffuser protrudes into the venturi or is flat? (2 strokes normally have a protruding one, cut away towards the engine)

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Roarn
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June 13, 2020 - 8:58 pm
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Hi,

Yes, the head issue is also noted, and will track down more casting numbers of the 2 cylinders he has to identify their origin. Someone mention earlier that the bike seems to have a B175 head fitted? straight plug hole?,, that one should be better regarding compression issue, or still might need machining? Will also track down more info regarding Amal carb fitted as requested, all this to sort out every details about this bike and eliminate every possible problems / faults!      

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nickjaxe
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June 13, 2020 - 9:11 pm
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Did your Pal buy the big bore piston from Rex...instructions should detail whats req.

My Bantam video              https://www.you.....jpOFmzRZRI

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wildun
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June 13, 2020 - 10:06 pm
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I am making no suggestions here but, Nickjaxe has pointed you towards investigating whether the compression ratio is too high. You say that you are using only a 0.5mm, 0.020" gasket. Rex Caunt sells a 1.5mm 0.060" gasket for this engine, easy to fit and worth a try.

I use 1.5mm head gaskets on my 175 four speed engines, it results in a very flexible engine with no pre-ignition at low rev high throttle openings.

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Sponge
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June 14, 2020 - 10:09 am
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Having looked carefully through this thread I would beg to make a couple of late observations please:

At 160 the mainjet is probably too small - B175 spec Amal 626/17 carb for a B175 should be set at 180 main jet - this is significant - overheating is caused by a lean mixture. 

With a big bore kit fitted there will definately be a need to review the compression ratio - even with the B175 head - unless machined out the C/R might still be too high.  Once teh compression ratio is under control you will need to look back at the carburettor again. 

I am concerned about the barrel - on a 4 speed bike we should be seeing the additional stud in the crancase face.  Might be the angles but I cannot see it so would be interested to know the provenance of the barrel.    

Whilst the barrrel is off a bit of work with a little file will get those sharp edges rounded off - to give extra peace of mind. 

As previously stated - this is likely to be a multiplication of small things that all add up to a more significant thing.  

Its fun isn't it ? 

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nickjaxe
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June 14, 2020 - 10:36 am
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Les but the OP is using a D14....the main jet on the D14 is much smaller that the same on a B175.

From memory...the D14s main jet is 150 or 160.

My Bantam video              https://www.you.....jpOFmzRZRI

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cocorico
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June 14, 2020 - 10:46 am
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It's all a bit 'in the air' until we can identify what cylinder, head and carb is actually fitted. Then there's the added factor of a big bore kit to consider.

Lets give him time to sort that lot out first, eh?

No use telling him to use such and such a jet / gasket / etc until then - one step at a time.

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bantammad
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June 14, 2020 - 8:21 pm
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Hi bantammad ere as sponge said lm out

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Roarn
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June 15, 2020 - 7:19 am
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Hi again, some more info as he is taking it apart. Cylinders. - the only marking he find is this:xxx.JPGIMG_18744.JPG

 

Is this "L" marking, this is cylinder used while having problems - model?IMG_18858.JPGIMG_18900.JPG

 

This "M" marked cylinder was on the engine when bought but damaged beyond repair (might it be B175)

 

And for the record, dont mind the "spinn offs" - have found all info here useful and highly interesting, AND an eye opener for the owner!!!  

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BantamBaz
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June 15, 2020 - 8:02 am
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Morning, 

I've been following you thread with interest.

I did enquire of Rex about a big bore piston at one time, he suggested that it would leave a very thin skirt & advised a smaller oversize with a standard barrel.

The skirt on yours does look very thin.

Do you have photos of the piston & it's sieze points.

Barrie.

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bantammad
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June 15, 2020 - 9:26 am
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Hi bantammad ere (I’m back in ) regarding the thin wall of the barrel as shown l take it is 64.5 bore unless I’ve missed the point my 64.5 bores look the same for reference , regarding my previous post on the big bore subject I’ve actually built five 186cc engines but have only had one of with a seizure problem as l made reference to earlier.as stated by others may l suggest relieve the damage from the piston as mentioned by filing the damaged areas l then think all should be ok but do use a 1.5 head gasket from the shed Les 

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Stoo63
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June 15, 2020 - 10:10 am
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Didn't realise we were playing "The Apprentice"?

 '55 D3 Battery; '58 Square Four (project); '59 D1 direct lighting plunger; '59 Tiger Cub; '60 5TA;  '76 FS1-E; '91 GTR 1000;  '97 Honda Sky SGX50.

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bantammad
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June 15, 2020 - 11:34 am
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hi bantammad ere the Apprentice you’re Fired 😷

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Blue Heeler
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June 15, 2020 - 11:41 am
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I`m in. I was addicted to the hokey-cokey, but I`ve turned my life around...and that`s what it`s all about.

L = Not ideal, too thin, have been known to overheat around the exhaust port and bores have been known to distort, but like anything in life, could get away with it. Counter-argument could be that bore is cooled by close proximity to port gases...excluding exhaust, and I covered that.

M = ok if piston-to-bore tolerances, ring gaps, radiused ports are all good. Mixture & ignition timing ok and run-in properly...ie temperatures kept down. BSA weren`t happy for folk to take some Bantam models out to +.060. B175 will run cooler than the D14. Mixing & matching components can have an engine running hotter or cooler, eg my +.060" bore D14 fitted with a flat-topped piston, ran cooler than with a domed piston.

That "M" was stamped on set of D1 crankcases owned by the chap in Texas. Would be interesting, and maybe even helpful for our friend in Norway, to know what the M & L markings denote...anyone know? 

(Jeg er inne. Jeg var avhengig av hokey-cokey, men jeg har snudd livet mitt ... og det er det det handler om. L = Ikke ideell, for tynn, har vært kjent for å overopphetes rundt eksosporten, og det er kjent at borehullene forvrenger, men som alt i livet, kan komme unna med det. Motargument kan være at boring blir avkjølt i nærheten av portgasser ... unntatt eksos, og det dekket jeg. M = ok hvis stempel-til-bore-toleranser, ringhull, radierte porter alt er bra. Blanding & tenningstidspunkt ok og innkjøring ordentlig ... dvs. temperaturer holdt nede. BSA var ikke glade for at folk tok noen Bantam-modeller ut til +60. B175 kjører kjøligere enn D14. Blanding og matchende komponenter kan ha en motor som går varmere eller kjøligere, f.eks. Min +0.060 "boring D14 utstyrt med et flatt toppet stempel, kjørt kjøligere enn med et kuppelstempel. Den "M" ble stemplet på sett med D1 veivhus som eies av kapellen i Texas. Ville være interessant, og kanskje til og med nyttig for vennen vår i Norge, å vite hva M & L-merkingene betegner ... noen som vet?)


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cocorico
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June 15, 2020 - 11:41 am
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There appears to be no dowel hole in the 'top' cylinder (the damaged one) so maybe an incorrect one anyway (** Please log in to view **), probably from a D5 or D7. The topic also shows the difference in port shapes and sizes if that helps identify what's what.

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Roarn
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June 15, 2020 - 4:20 pm
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IMG_18922-1.JPGtopp-1.JPGIMG_18977-1.JPGIMG_18988-1.JPG

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