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Yeah it’s out and the barrel condition is questionable so definitely definitely boring it in some capacity.

Hopefully a machine shop can repair the case cover but if I find one cheap enough used I’ll likely just replace it.

Money isn’t too tight. Im not a rich man by any means but I’m 24 and live with my parents with a decent job. So I don’t have a mortgage to worry about. My life plan always was do the projects I want to do while I’m young and have the energy and money for them. Because once I buy a house I’m sure the money and the energy will be depleted a bit so may as well restore what I want to restore now and then all I’ll have to do is maintain my toys while I get older and have real bills to worry about. And this bsa was always on that bucket list project.

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Thank you!
Where did you find that info seems like they must have some useful documents like that.

So definitely going to try to seek out some hasting rings. Hopefully in .020 over. Interesting

Or maybe I’ll try to find that Hepolie piston and ring set. I’ll see what’s out there and report back before I make a final decision. Can’t thank you or the rest of you all enough for the advice. It’s little things like this as to why I post on forums like this. Im more than capable of just rebuilding a 1cylinder engine but it’s that tribal knowledge built from experience that is the big difference between a decent rebuild and a really good one.

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Competition cycle uses center auto machine ( it's just about across the street) but their guy who really knew the Brit stuff is on an an extended leave. They're mainly automotive. Job cycle does machining but again uncasville. Center was able to do my b44 valve job don't think they'd go much beyond without Rob.

Tracy tools UK for the tap and dies.
I'm pretty much a tool addict also.


65 TR6R 68A65T 69 B44VS. 74 T150V 19 Chieftain
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George……message Mike King ( aka Mr Mike). He’s successfully done some of the mods you’re considering.

Be patient he’s not online as much as he used to be.


Gordon Gray in NC, USA........"STOP blaming the bike!!!!”
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Originally Posted by Gtv6george
Yeah it’s out and the barrel condition is questionable so definitely definitely boring it in some capacity.

Hopefully a machine shop can repair the case cover but if I find one cheap enough used I’ll likely just replace it.

Money isn’t too tight. Im not a rich man by any means but I’m 24 and live with my parents with a decent job. So I don’t have a mortgage to worry about. My life plan always was do the projects I want to do while I’m young and have the energy and money for them. Because once I buy a house I’m sure the money and the energy will be depleted a bit so may as well restore what I want to restore now and then all I’ll have to do is maintain my toys while I get older and have real bills to worry about. And this bsa was always on that bucket list project.

Definitely. That’s what i did… And glad I did.


Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (now rebuilt)
67’ D10 sportsman (undergoing restoration)
68’ D14 trials (undergoing transformation)

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So I found out the reason I can’t find an oversize exhaust valve is because they don’t make them!

Interesting you can get an intake oversized but no exhaust. I’m wondering if it’s even worth it to do just the intake. As the intake is already larger than the exhaust valve. According to Peter there isn’t much room for an oversized exhaust valve which I can see now the seat is close to the edge of the head. So I wonder if the b50 valves are bigger and would possibly fit.

I also wonder if just installing an oversize intake valve would help or hurt performance. I’d imagine shoving more air and fuel in with not a lot of a area for that stuff to escape could be bad. But I guess the exhaust is being forced out by the piston either way. I’m not an expert on the subject.

I’ll have to message mr Mike and see what he did. In the meantime if anyone has b50 valves they could give me measurements of diameter of head, stem and overall length let me know.

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Originally Posted by Gtv6george
So I found out the reason I can’t find an oversize exhaust valve is because they don’t make them! .....Interesting you can get an intake oversized but no exhaust.......
Modern knowledge has found that older engines often have excessively big exhaust valves and do just fine with smaller ones. The spent gasses are still super hot and highly pressurized when the exhaust valve opens so they escape easily with the piston pumping to finish the job.

Normally aspirated induction only has atmospheric pressure (14.7 psi at sea level) to push the fuel/air mixture in. That's the basic reason that intake valves are usually bigger than the exhausts. Even lawnmower engines are built that way.

So consider this, fit a smaller exhaust valve to make room for a bigger intake valve? Not that I'm suggesting that for you, but some tuners do exactly that.

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“The spent gases show little reluctance to leave the cylinder,” as a wise tuner may have said.

Yes, forget bigger exhaust valves.

On the inlet side, a bigger valve is an improvement, if the present valve is too small. Do you have any reason to think it is too small?

A bigger valve was a common modification to keep an old head in service by cutting a bigger diameter seat area in an old pocketed seat.

A bigger valve has a similar effect to a longer duration cam, because it has more open area when it’s just opening and when nearly closed. It is possible to overdo it, especially if you already have a sporty cam and then you find that you’ve lost the midrange power and low speed behaviour that makes a bike enjoyable to ride.


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Gordon Gray in NC, USA........"STOP blaming the bike!!!!”
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