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91
A7 & A10 Engine / Re: Engine misses and loses power
« Last post by chaterlea25 on 23.02. 2020 15:39 »
Hi Jim,
A reamer can be bought for a few quid don't *** about with abrasive paste as it will imbed in the bronze guides
Is there any engineering shop or even another classic bike owner near to you that would have a reamer
John
92
Frame / Re: Mounting problems with rear fender for BSA A7, 1951
« Last post by martinh on 23.02. 2020 15:35 »
I have found the new one exactly the same designe as mine. So I think that mine is the original one.
https://vintagesteelfenders.com/mudguards/bsa-plunger-rear-1949-53
93
A7 & A10 Engine / Re: Engine misses and loses power
« Last post by Swarfcut on 23.02. 2020 14:41 »
Inlet valves have marginally larger heads than exhausts. Hard to tell by eye.  Stamp 67-0324 identifies that valve as  A10 Iron Head Exhaust. V18 is the corresponding reference number in  both the Alpha Bearings and G&S Catalogues.

I would describe that valve as "witnessed", by no means the concave hammered pit I was expecting, like mine. But not what you expect after a short run. But then to be honest, it is not something usually examined after such a short time. Have a look at the state and suitabilty of the tappet adjusting screws.

Inlet valve A10 Iron Head is 67- 0323.  The zero is sometimes omitted on the component.

 Valve Spring Length. A10 Iron Head.     Inner 1.531" Outer 1.875"

Swarfy.



Additional.  Valve Head Diameter  Inlet 1.312"   Exhaust  1.062"       Valve Stem 0.31"

 Source. Roy Bacon Twins & Triples.
94
Frame / Re: Mounting problems with rear fender for BSA A7, 1951
« Last post by Swarfcut on 23.02. 2020 14:33 »
  Martin...    I may be wrong, but picture 4 shows a couple of indents more associated with a front fender ( mudguard ), to clear the fork legs rather than to clear rear frame members, so thinking this actually started life as a front mudguard. Anyone else know if early A7 rear guard has these indents?

 The rear section was originally designed to be hinged, yours looks to be a bolt on homespun adaption. The lower edge usually flares out at the bottom. The number plate mount for the year is an open type, rather than the post  '53 boxed in type that you have there. Rear light is also a later type, more suited to the later boxed type with an indent to the pressing to make the lens lie more in line with the top of the box.

 So, first decide if you can source a better mudguard, one correct for the year. Otherwise making yours fit is not impossible, but will be a real test.  To be honest it isn't far off, bolting the guard to the stays will improve things. Aim for the guard to follow the wheel and tyre when off the stand.

  The upright arm of the  rear mudguard stays are moved slightly forward of true vertical, and bolt inside the mudguard. The rearward arms end up horizontal or more often pointing very slightly down at the rear. Behind the gearbox are two horizontal steel strip mounting stays.

  This leaves the awkward to describe arrangement adjacent to the seat spring lower mount. Here the bolt through the frame  passes through a cylindrical spacer and supports a bridge piece under the mudguard.  The bridge has rivets to mount the guard.  The spacers fit into cutouts in the side of the mudguard blade, the bolts do not  attach directly to the mudguard blade.  See how this compares with what you have.

 Lots of pictures available, and maybe some helpful Forum Members can post some as well.

 Swarfy.
95
A7 & A10 Engine / Re: Engine misses and loses power
« Last post by berger on 23.02. 2020 14:21 »
jim quick test is inlets are magnetic, and won't stand the heat as exhaust valves *beer*
96
A7 & A10 Engine / Re: Engine misses and loses power
« Last post by BigJim on 23.02. 2020 14:09 »
Not really in focus sadly but you can see the mark which is a slight indent. 30 miles approx. Also pic of writing on bottom. What is the difference between exhaust and inlet valves, can they be swapped?
May dig out some old ones from my leftovers box and see how they slide into the guide.
Cheers
97
Frame / Mounting problems with rear fender for BSA A7, 1951
« Last post by martinh on 23.02. 2020 13:48 »
Hi, I am step by step solving small issues on my new BSA, I did some work on clutch, harness change,... but now I am trying to fit correctly rear fender. The end part with rear light does not fit very well to the second part of the fender, therefore I am trying to rework it. But still I am not successful. Do you have some similar experience? Should be BSA A7, 1951 plunger, but I have some suspicion that some parts are from a10. And it is visible that previous owner has got the same issue and he tried several options.
Thanks for any help and advice.
Martin
98
A7 & A10 Engine / Re: Engine misses and loses power
« Last post by Swarfcut on 23.02. 2020 12:08 »
Jimbo
    The design is basically unchanged from Plunger/Semi Unit to the end of S/A.  That centre bolt is only slightly inclined to the rear, so much so it is often overlooked, but for true perfection it's this one first out, last in. Also there are variations in the lengths of the  head bolts.

 Centre and Front   1  1/2"        QTY  3

 Front Outer           2 11/16"     QTY  2

 Rear Outer            2 3/8"         QTY 2

 Rear                     2 11/16"      QTY 2     All bolts 3/8"

 Source: BSA Service Sheet 204  These variations accommodate the different positions within the cylinder head casting, but lengths are useful to establish you have the correct size bolts, not some spurious assortment. All have washers.

 You can also try cleaning up the top of the valve stems with an oilstone. This area is normally hardened, and the hardness should extend deep enough to allow a light refinish of the top surface. Be careful, keep it square with the stem. If you find the material relatively soft, I would suspect the quality of the valve. A good, old genuine item is to be preferred over a modern repro, as you have a greater confidence that the metallurgy of the old component is at least up to the required standard as originally specified. We like to think newer is better, but it's not always so.

 Swarfy.
99
A7 & A10 Engine / Re: Engine misses and loses power
« Last post by BigJim on 23.02. 2020 11:14 »
 Thanks for that Swarthy , will try to post a picture of inlet valve tops. This is a pre-unit engine and head. Is that centre bolt angled in both semi and pre-unit?
100
A7 & A10 Engine / Re: Engine misses and loses power
« Last post by Swarfcut on 23.02. 2020 11:01 »
Jimbo.
     Head gasket should have no bearing on your problem. Make sure threads are clean, lightly lubricated, no muck or oil at the bottom of the blind holes. Centre head bolt is at a slight angle, always loose off first, tighten last. Someone should be along with a suggested torgue figure, BSA just say "really tight."  Clean matched surfaces and the correct clamping force on gaskets is the key.

   Replace valve springs with new, and  yes you can try T-Cut, but you may find a high silica whitening type abrasive tooth powder or paste a little more aggressive. Next up the scale is CIF bathroom cleaner. See how your new valves fit before you start polishing inside guides...and to state the obvious, check the guide bores are nice and clear.

 Hammering to the top of the valves is interesting. Soft? To much clearance? Too tight in the guides?  Coil binding?  Always thought mushroom adjusters a good idea as the original parts seemed to only have a small contact area to the valve tip..all my valves have had a slight hammered dip, so setting a clearance is a bit of a guess.

 Swarfy.
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