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D7 / D10 engine mish-mash
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NeilB
Kidderminster
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December 14, 2019 - 11:48 am
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So, it appears I have a D7 barrel, but a D10 piston and head. The rings are scrap (gap well above the 13 thou limit), but the piston  (+20 thou) is very good, and the barrel is decent. I would gladly replace just the rings, but they're probably going to be harder to find and most the cost of a complete piston, in which case am I better off the +40 thou piston and honing the barrel out to make it perfect. 

The rings as I measure them are 1.62mm thick and 2.50mm wide, although obviously being worn, the width may be misleading.

 

If I do replace the piston for another D10 job and keep the D10 head, does that mean the carb is going to be too small and need work or replacement? Added to that, how do I tell the difference, and I think I'm missing the plunger on the carb, although not quite sure what the function of this is anyway.

Thanks for reading!!

IMG-20191214-WA0000.jpegIMG-20191214-WA0002.jpegIMG-20191214-WA0004.jpeg

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sunny
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December 14, 2019 - 12:52 pm
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carb  dawings  always  show  all parts   that  can be   be  fited  some  carbs  are   fited   with   alll  the  bits  like  plunger choke   its   not  needed  as  the  air  filter  has  a  choke  on  your  carb        ,,  bantams  can  be  a  miss  mach  in  the change  of  a  MODLE    so  get  wot  you  have   going  befor  binning    good   parts   the  D  10   number    aplys  to  the  crankshaft    as  some   had   3  or  4  gaers   ,the   D10   3  g  cases are  also   able   to  cary  a d 7    crank  as  i  found   out

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NeilB
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December 14, 2019 - 1:39 pm
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Had it running, sounded horrible and wouldn't rev, but that was because of worn big end and piston rings more than anything I assume. The engine itself is an FD7 so I was wondering if it was best trying to go back to standard D7 parts as I'm looking at possibly a new piston anyway, or stick up minimum spending and keep the d10 piston and head. 

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cocorico
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December 14, 2019 - 1:46 pm
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We've just been talking about piston rings - have a look back.

1956 D3 running, lights to sort. 7 other bikes in the Barn. 1950 D1 engine being rebuilt (slowly).

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Stoo63
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December 14, 2019 - 1:52 pm
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Might give you some ideas on carbs, Neil.

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'52 D1 direct lighting plunger, '58 Square Four (project), '59 D1 direct lighting plunger,  '59 Tiger Cub, '60 5TA,  '76 FS1-E

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NeilB
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December 14, 2019 - 2:29 pm
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Thanks Stoo!

Coco, I had a look at the discussion on 2 vs 3 piston rings and got a bit confused I think, maybe I should re-read when I'm not so tired zzzz

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cocorico
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December 14, 2019 - 3:42 pm
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NeilB said
...I had a look at the discussion on 2 vs 3 piston rings and got a bit confused I think...

No, it was about availability - this one. ** Please log in to view **

1956 D3 running, lights to sort. 7 other bikes in the Barn. 1950 D1 engine being rebuilt (slowly).

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mike p5xbx
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December 14, 2019 - 4:05 pm
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that looks more like a D14 cyl head it has a slightly wider squish band to the D10
has your conrod small end a bronze bush or a needle roller bearing
will make a difference as to what piston you can fit
has the piston a flat top or slightly domed
the problem will be ignition timing the D14 has a higher compression ratio to the D7 so needs to be retarded more then the D7
and you dont really have enough movement on the stator to do that

D? - D10- D14 Bantams 350 AJS -500 Triumph http://bsanotru.....lfire.com/

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NeilB
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December 14, 2019 - 4:30 pm
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Coco - thanks, I'd seen that, but was planning to modify to size if necessary anyway, just trying to find a starting point to work with. 

 

Mike - the piston had two rings and a slight dome on it, the small end bearing is a roller type. I think I'm leaning towards just changing the rings, as long as I can find the right width and thickness, I can modify the circumstance and add the notch if necessary. 

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