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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?
A7 & A10 Engine / Re: Engine misses and loses power
« Last post by Swarfcut on 23.02. 2020 11:01 »
     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.

A7 & A10 Engine / Re: Timed breather, what is the actual timing?
« Last post by Superflash on 23.02. 2020 10:52 »
Thanks for the explanation. The problem I have is that I've never actually seen a complete running A10 in the flesh so figuring out how things work or where they fit into the greater scheme of things has been a real eye opener and a bit of a buzz if I'm honest. Cheers
A7 & A10 Engine / Re: Engine misses and loses power
« Last post by BigJim on 23.02. 2020 10:17 »
Iron head and new springs. new guides etc. Had fitted expensive SRM valves. Will be replacing with cheaper ones in the exhaust only. Top of inlet valves show signs of hammering from rockers. The engine showed signs of over run which i assumed was due to poor cable routing. Beginning to think inlets binding too.
Who thinks giving them a bit of sliding up and down with t cut to loosen them a touch is a good idea? I do not have access to reamers or whatever is the correct method. Have thrown so much money at this bike that i am loathe to spend a lot more.
A7 & A10 Engine / Re: Timed breather, what is the actual timing?
« Last post by Swarfcut on 23.02. 2020 10:07 »
SF.. Like Musky says....DON'T TOUCH IT!   That's how it it should be.  The lower blanked off hole in the inner timing case is simply where the casting was drilled to form the breather duct. So that answers the second question. Following the duct across the crankcase, the drilling exits above the gearbox sprocket, and should be a free flowing unobstructed path for crankcase vapours.

  The question is how does it work? Well, goodness knows, but it does.  The breather sleeve rotates at half engine speed, located and driven by the peg on the cam drive gear. Pistons rising and falling together will produce alternate high and low pressure within the crankcase. At some point the breather holes align for a fraction of a second, connecting the crankcase to atmosphere, and in theory the engine "breathes." That's it, a minor miracle.

   Things to remember.

    The cork washer that fits between the breather sleeve and the cam gear pushes the cam towards the drive side, in effect eliminating cam end float. It pushes the breather sleeve towards the timing side and should be in light compression when assembled, to keep the cam and breather sleeve in their respective places. It is available in various thicknesses to suit variations in the parts. Too thick will put too much load on the breather flange, and it will wear away itself and the inner timing case. You may find a witness mark. Too thin and the sleeve and cam can float, and the breather won't work properly because the holes will not align fully.

  The holes in the breather sleeve should line up perfectly with the holes in the inner cover. Worth checking, I have come across breather sleeves that only half match the holes. Also the breather sleeve design changed  slightly over the years, but seems to have little  improvement on its function. Whether this is the position or size of the holes is just a guess, so to recap, check the breather sleeve you have matches your timing cover. The drive pin on the cam gear needs to be long enough to ensure a positive drive to the breather sleeve.

 At best it is simply a design for everyday use, tuned and race engines need a better system as detailed elsewhere.

 Apologies to those folks who know this old news, but I can bet a good few wonder how it works.

A7 & A10 Engine / Re: Engine misses and loses power
« Last post by JulianS on 23.02. 2020 09:39 »
For info during 1957 BSA changed the guide material for light alloy heads from Hidural 5 to cast iron.
Frame / Re: POR 15
« Last post by Greybeard on 23.02. 2020 09:24 »
I remember when I used POR15 the instructions said damp helps it set but someone, (here? ) denied that. That made me wonder if the formulation had changed.
A7 & A10 Engine / Re: Timed breather, what is the actual timing?
« Last post by muskrat on 23.02. 2020 09:08 »
G'day Sf.
Don't touch it. The breathing is through the top hole and exits on the other side of the motor.
A7 & A10 Engine / Re: Engine misses and loses power
« Last post by Beeza on 23.02. 2020 07:54 »
Hi Jim, I’m just checking, on your first post you never mentioned new valve springs, but you did make reference to reinstalling the old springs. Do you have new springs in this head mate ?
Valve spring pressure is important for a good engine, many old (original) valve springs do lose pressure/ability to preform well.

Cheers Thomas 
A7 & A10 Engine / Re: Timed breather, what is the actual timing?
« Last post by Superflash on 23.02. 2020 05:43 »
Gents. Resurrecting a fairly old thread here, however I've been reading through a lot of the past posts about this subject trying to understand how it all works from a practical side of things. I understand the theory of having a breather etc, I'm just struggling with how it all actually works. Example....the breather itself sits on a peg located on the cam pinion. A cork spacer is used to get the cam end float to where it needs to be. the 2 holes in the breather will line up with the 2 holes in the inner timing case as it spins, thus allowing the expulsion of pressurised all that. 2 things have left me baffled though. is it only the inner timing case hole that the breather slides into, all that stops it falling off the cam pinion pin? And secondly, the inner timing case has 2 leads upwards and appears to vent into a hole in the main case. The other leads down, and presumably out of the case? I ask this last question because the tube leading downwards has been plugged. Should it be, and do I need to drill it out to create a clear pathway for escaping gases? Cheers
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