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Centre plug head on D14
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carpetralph
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September 25, 2019 - 9:27 am
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I have a spare centre plug B175 head. Is it worth putting on my D14. Would it make any difference?

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Bee175
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September 25, 2019 - 9:59 am
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I frankly don't know Ralph.

Is your D14 running ok anyway? Any improvement is going to be minimal. I tend to think that if something is running ok, leave well alone.

Gary.

BSA Bantam B175 1971 and BSA C15 1966

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JulianS
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September 29, 2019 - 6:11 pm
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An interesting factory parts service bulletin dated October 1968 on the D14 and centre plug head.G53-October-1968-D14-centre-plug-head-General-information2.jpg

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carpetralph
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September 30, 2019 - 6:45 am
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Interesting.  Do we know what a 70-7799 barrel looks like?. Is this a standard D14 item?

I have a parts list for B175 that lists the barrel as 70-9618, and shows the gasket as 90-1515, presumably a copper gasket?. Mention of only 1 gasket to be used, so does one assume that at some earlier stage there was a recommendation for 2 gaskets to be used on the D14.

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JulianS
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September 30, 2019 - 9:18 am
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90 1515 is 25 thou thick and 70 7967 is 50 thou thick . Below from parts bulletin G48 dated January 1968. G48-January-1968-General-information-D14-head-gasket-RM213.jpg

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Ignore the Champion N9Y plug because they changed in back in August that year.

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Sponge
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September 30, 2019 - 11:59 am
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Hi Ralph, 

Having owned several of both machines in my youth I found, through many frustrations),  that the D14/4 with standard (rear plug) head is a fussy engine that overheats with consequent side-effects etc. Reason for this has a lot to do with the relatively high compression ratio and you can see that BSA attempted to remedy the situation with thicker head gaskets etc and then a top end re-think with the new B175 engine.   Also, I found that the D14/4 engine is intolerant  of small irregularities in timing, petroil mixture, carb settings, air temperature etc  - anything that your D14 engine is not happy with will manifest itself as overheating and heat related side-effects.    

I found that the D14/4 engine ran better with two head gaskets fitted, a bit cooler, but then had a tendancy to blow them out. Not difficult to fix but a pain all the same.   I was not aware of the thicker head gasket.  My local BSA dealer advised using two gaskets. 

I did fit a B175 head and gasket to my D14/4 and it made a noticable difference to the engine's manners, because the engine was running cooler, less coughing and banging and 4 stroking on the over-run etc.  There was no discernable loss in performance but also no discernable improvement in power or speed (just better manners).    I eventually got my hands on a Todd head - which made a small difference all around ( more torque, ran cooler and quieter).  

The B175 was a much nicer engine to run because the centre plug head had better heat dissipation, a lower compression ratio and better design (squish band etc).    

So my advise is - if you have a B175 head - fit it and see what it runs like - I doubt you will be disappointed.   Some extra tips though - 

Always make sure you have the tufnol spacer between the carb and the barrel - this prevents the Carb from getting too hot. 

Ensure that your exhaust is in top condition - no excessive carbon or dents etc - this makes a big difference to a D14 engine.     

Ensure that you have the correct inlet tract  ( standard air filter and volumetric tube etc ) these engines seem to be very fussy about changes to their inlet tract and any changes will , once again, lead to overheating and a need to re-tune your carb.  

Hope this helps

Sponge 

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mikef
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September 30, 2019 - 3:24 pm
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Hi All.
      We live and learn, as they say. I never knew that BSA ever fitted a straight plug cylinder head to a D14.
Maybe they never actually did. Back in March 1969 I had a D14, brand new, it had the slanted plug head, but of course no idea when it was manufactured.
Anyone else got ideas on this?
It had the usual D14 traits, overheating and pinking when hot. Having said that I was a spotty teenager then and thrashed all heck out of it.
I do remember having to fit two head gaskets though, as even back in 1969 the 0.050" gaskets were not available. Interestingly now I have seen 0.040" head gaskets advertised and 0.060" head gaskets but 0.050" seem unavailable.
I agree with just about everything that Sponge has mentioned above, so won't repeat that.
Mike.

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mike p5xbx
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September 30, 2019 - 4:32 pm
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I have a 0.05 head gasket on my D14 dont have any problem with it at all
and it has 150psi compression
but agree that timing and mixture need to be absolutely correct
also helps if you use the correct amount of 2T oil sorryout-a-here

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

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carpetralph
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October 1, 2019 - 6:48 am
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Thanks for all your replies, all very helpful.  Mention of the tufnoll carb spacer was interesting, as my bike does not have one, so that needs sorting. 

Given Sponge`s informed answer I think it could be well worth while fitting the B175 head, and this I will do as soon as I can find a 50thou head gasket.

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mike p5xbx
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October 1, 2019 - 5:45 pm
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Rex does a 1mm head gasket which is 0.040 maybe near enough

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

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carpetralph
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October 1, 2019 - 7:51 pm
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mike p5xbx said
Rex does a 1mm head gasket which is 0.040 maybe near enough

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Ta. Just ordered a 1.5mm item, which is 59thou. Thought as I am on +60 piston would err on the bigger side. Also found a 1/4 inch tufnol spacer on ebay and a couple of new carb studs. That may be the reason I don`t have the spacer because the threads are stripped on the first part of the carb studs and I think the spacer may have been removed so that the nuts gripped lower down. I shudder to think how tight the nuts must have been to strip the threads, its a wonder the carb survived.

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carpetralph
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October 6, 2019 - 10:21 am
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Well, got all the bits, so had a good session in the garage yesterday.

Took the old head off, and whilst it was off I took the opportunity of setting the ignition timing. Didn`t use a degree disc although I do have one, but set it at 60 thou btdc with a dial gauge. De coked the piston top and fitted the centre plug head and 1.5mm gasket from Rex`s.

Took the carb off and fitted new studs and 1/4" tufnol spacer. A little too thick really, should have gone for the 1/8" version as I had to leave the washers off to get a full thread on the nuts, but I can change that later. whilst the carb was off I changed the slide back to a no3, as the bike had felt to be running weak with the 3.5, but found the reason as it turned out I had fitted the needle on the top groove instead of the middle groove. I am sure I had put it in the middle, but its such a struggle getting it back in with the return spring getting in the way I may have dislodged it. Does anyone have any tips as to doing this easier.

Anyway, the result of all this effort, the bike took longer to start than it used to, and a lot longer to warm up before I could take the choke off, and when I took it down the road it is definitely smoother running with no apparent loss of performance at the top end, but I have now lost all the bottom end torque, and have to rev it and slip the clutch to pull away.

I am going to go out today and put the new 3.5 slide back in, as I suspect that the worn no3 is letting air past and weakening the mixture at the bottom end.

Stay tuned, as they say, 

Ralph.

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carpetralph
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October 6, 2019 - 1:55 pm
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Think I found a lot of the problem,20191006_115139.jpg20191006_115210.jpg 

I spent a bit of time rubbing the carb back and forward over a flat file placed on a flat surface. I started out with a 48 thou gap at the worst point, but managed to get it down to less than 2 thou (my smallest feeler gauge wouldn't go under) see below,20191006_121615.jpg20191006_121642.jpg20191006_121821.jpg

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N.D.James
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October 6, 2019 - 1:58 pm
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Looks much better but all the little bits make a big difference

 

Nathan 

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carpetralph
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October 6, 2019 - 2:07 pm
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Yes, must have been sucking air, there was a thick squidgy cardboard gasket which I removed to fit the tufnol spacer yesterday, with 2 thin paper gaskets. Now its back on and the faces are flat I am sure it is sealing, and it now will pull away from low revs. Still seems a little weak on the first third of the throttle though, so going to invest in a new no3 slide as old one has visible wear and may be letting air past. I will get there in the end.

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SpacedMarine
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October 6, 2019 - 2:51 pm
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Is that a surface plate or the missus kitchen worktop?🤣🤣🤣

What's 7/16 in mm again?

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cocorico
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October 6, 2019 - 4:21 pm
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Shouldn't the seal be made by an O ring? The flange of the carb appears to be machined for one.

1956 D3 running, lights to sort. 7 other bikes in the Barn, including a Morini 250 now insured and on road testing.

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carpetralph
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October 6, 2019 - 5:29 pm
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SpacedMarine said
Is that a surface plate or the missus kitchen worktop?🤣🤣🤣  

cocorico said
Shouldn't the seal be made by an O ring? The flange of the carb appears to be machined for one.  

That is a cast iron surface plate Spaced Marine, I am fortunate to have a pretty well equipped workshop, inbetween playing with cars and bikes I am building a half size steam traction engine, and have lathe, milling machine etc. See pics.

Cocorico, correct there is an O ring, but it is very thin, probably no more that 1.5mm thick, and of course half of that sits in the groove, leaving little sticking out, less I think than the distortion in the carb.little-samson.jpg20181025_064232.jpg

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mike p5xbx
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October 6, 2019 - 6:11 pm
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carpetralph said

, I am fortunate to have a  

and a Triumph TR2/3 as well smile

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

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N.D.James
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October 6, 2019 - 7:01 pm
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carpetralph said

cocorico said
Shouldn't the seal be made by an O ring? The flange of the carb appears to be machined for one.  

That is a cast iron surface plate Spaced Marine, I am fortunate to have a pretty well equipped workshop, inbetween playing with cars and bikes I am building a half size steam traction engine, and have lathe, milling machine etc. See pics.

Cocorico, correct there is an O ring, but it is very thin, probably no more that 1.5mm thick, and of course half of that sits in the groove, leaving little sticking out, less I think than the distortion in the carb.little-samson.jpg20181025_064232.jpg  

What an amazing piece of engineering

I would love to have that in my garage but i might have to work harder for a few more years yet 

Very nice 

 

Nathan 

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