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Head and Barrel ID including stud spacings
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PeteMcD
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June 5, 2012 - 10:00 am
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This thread nicely highlights a number of anomalies that have cropped up before concerning the somewhat bizarre parts numbers that seem to have been allocated to these items on D7s, D10s and D14s.

 

I have been confused about this in recent months since discovering that the cylinder head on my own late 1968 D14 was fitted with a long reach plug head carrying the part number 90-1304.

I have also found other D14s fitted with identical heads showing this part number. The BSA parts books lists the correct D14 head number as 70-7804.  The same reference allocates the afore mentioned 90-1304 as belonging to Bantam D5 –D7s which would be short reach plug fittings, have a different combustion chamber and no squish band; clearly this is not the case with the heads in question.

I had my 90-1304 head checked by an expert who identified it as off a D10, but that should be a 90-1514 according to the manual - the plot thickens!

 

I recently acquired a nice new shiny D14 head embossed with the “correct” part number 70-7804 which has allowed a close comparison with my original prior to fitting the newer one to my D14.

 

I can say that, apart from the embossed part number, the two heads are identical and that includes measurement of the combustion chamber.

 

In summary I think that BSA Bantam cylinder head part numbering went a bit haywire towards the end of their era and that D14s (and probably D10s) were fitted with “correct” heads but for whatever reason (same castings, different machining?) carrying the “incorrect” part number 90-1304 from earlier models.

 

PS.  The performance from both heads is identical.

 

dunno

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Piquet
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January 28, 2013 - 1:42 pm
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D1 1948 – 1954: stud centres 52mm Bore 52mm std (original pineapple and early square barrel, 1" stub inlet)

Head part numbers

90–2 is listed as '49 – '53 D1 (Pineapple)

90–287 is listed as '49 – '53 D1 Competition with de-compressor (Pineapple)

90–714 is listed as '54 D1 (Square)

90–726 is listed as '54 D1 Competition with de-compressor (Square)

Barrel part numbers

90–1 listed as '49 – '53 D1 (Pineapple, 5/8" bore inlet)

90–713 listed as '54 D1 (Square, 5/8" bore inlet)

D1 1955 – 1963: stud centres 55mm Bore 52mm std (square barrel, 1" stub inlet)

Head 90–814 is listed as '55 – '63 D1 (Square)

Head 90–834 is listed as '55 & on D1 & D3 Competition with de-compressor (Square)

Barrel 90–820 listed as '55 – '63 D1 (Square, 5/8" bore inlet)

D3 1955 – 1957: stud centres 55mm Bore 57mm std (square barrel, 1" stub inlet)

Head 90–731 is listed as '54 – '57 D3 (Square)

Head 90–788 is listed as '54 D3 Competition with de-compressor (Square)

Head 90–834 is listed as '55 on D1 & D3 Competition with de-compressor (Square)

Barrel 90–732 listed as '54 – '57 D3 (Square, 11/16" Bore inlet)

In the '54 -'56 D1/D3 parts catalogue there are different crankcases listed

'54 D1 (90-743) stud centres 52mm

'54 D3 (90-779) stud centres 55mm

but identical cases for '55 and on D1 and D3 (90-828) stud centres 55mm

D5 & on 175cc 1958 – 1971: stud centres 60mm Bore 61.5mm std (square barrel, flange inlet)

There are a variety of cylinders for the 175 models all with the same 60mm stud centres and 61.5 std bore.

Differences appear to be in the size of the various ports, later models having bigger ports.

D5/D7 inlet 7/8ths, D10 early inlet 1", Later D10 onwards inlet 26mm.

D10 onwards fitted with a cylinder locating dowel.

 

Various heads were fitted but the cast in numbers (where present) cannot be relied upon for identification (see post above).

There seem to be at least 3 basic types,

  1. Plain hemispherical combustion chamber with no squish band and a short reach plug hole machined at a backwards facing angle. D5 & D7 type matched with flat top piston.

  2. Hemispherical combustion chamber with squish band around the outer edge and long reach plug hole machined at a backwards facing angle. D10 & D14 type may have different compression ratios but matched with dome top piston.

  3. Hemispherical combustion chamber with squish band around the outer edge and long reach plug hole machined centrally upright. Head also has a horizontal cooling fin below the standard vertical fins. B175 type matched with dome top piston.

Fitting a dome top piston with an early non squish band type head may result in the piston contacting the head.

There were also after-market 'performance' heads, usually with a centre plug hole manufactured for most models by George Todd and others.

I believe this information to be correct but if anyone has additional information or spots errors, please contact me so the post can be updated.

I'm not a complete idiot ............................................ some parts are missing.

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Piquet
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January 29, 2013 - 3:07 am
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The dowel is fitted from D10 onwards and I assume it is purely to align the cylinder on the crankcases (avoid a step in the transfer ports?) or maybe it is to signify the higher tuned barrels hoping to avoid fitting a D5/D7 barrel to a later engine.

Below is an abstract from the D10 Parts Book showing the dowel as item 14.

D10Plate3.jpg

 

Third picture down in The Bushman's post

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you can see the dowel hole in the base of the cylinder.

hope-that-helps

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I'm not a complete idiot ............................................ some parts are missing.

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Piquet
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August 15, 2013 - 1:23 am
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Further to Pete's post above regarding 175 cylinder heads, I have just compared 3 I have.

Left to right.

D7 head with the cast in number 90-1304 short reach plug hole.

D10 head with the cast in number 90-1304 but on the opposite side, long reach plug hole.

D14 head with the cast in number 70-7804 long reach plug hole.

rsz_p1010059.jpg

rsz_p1010060.jpg

 

D7 is the lower one here with the recessed plug hole.

rsz_p1010072.jpg

 

Disregarding the close attention from a broken piston ring around the outer edge, it can be seen that the D7 head has no squish band whereas the later heads do.

The difference in the combustion space which sets the compression ratio can also be seen. The shallower the space, the higher the compression.

I made a rough comparison using a digital vernier to measure the depth of the combustion space (a better comparison would have been to use a burette to measure the volume).

 

D7 = 18.41mm

rsz_p1010061.jpg

rsz_p1010071.jpg

D10 = 19.73mm

rsz_p1010062.jpg

rsz_p1010069.jpg

D14 = 16.29mm

rsz_p1010063.jpg

rsz_p1010068.jpg

 

A further complication here is that the D7 piston is flat but the D10/D14 pistons are slightly domed which would account for the D7 head having slightly less volume than the D10.

 

I also noticed that my D14 head has fins right up to the front of the plug hole whereas Pete's two D14 heads are more like my D10 in that respect.

rsz_p1010055.jpg

rsz_p1010058.jpg

rsz_p1010074.jpg

rsz_p1010073.jpg

 

So there are quite a few variations in this range of castings.

It's probably safe to assume that a head with the 90-1304 number and a short reach plug hole is a D5/7 head but any head with a long reach plug hole and that 90-1304 number could be either a D10 or a D14 head.

More pictures

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I'm not a complete idiot ............................................ some parts are missing.

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mike p5xbx
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May 13, 2019 - 4:45 pm
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I was going to post this on the end of
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but it is Locked please move if you think appropriate Mod edit - moved.

D7 to B175 Barrel identification from the inlet port
Barral-ID.jpg

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

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mikef
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May 13, 2019 - 7:24 pm
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Thanks for that Mike. I have never seen the barrels side by side before. A picture paints a thousand words.
We now have a positive ID on the barrel type.
Mike.

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