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Bsa A50 Royal Star Valves #788390 10/27/19 10:25 pm
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tridentdude75 Offline OP
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I have discovered that my Bsa cylinder head intake valve seat has been cut to many times. The stock replacement valve will not cover the entire seat area . My machinist has informed me that i could use a stock valve but it might not hold up very long. I have seen Kibble/ White Black Diamond oversize valves sold by our vendors marked for Bsa B25 and A50 models. Would this work? The machinist also could cut down a A65 intake valve to size or install new seats. Any suggestions ? Thanks. Jeff

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Re: Bsa A50 Royal Star Valves [Re: tridentdude75] #788397 10/27/19 11:02 pm
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Ignoramus Offline
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might be best to get a new hardened insert (seat) , do exhaust ones at the same time i would say


"There's the way it ought to be and there's the way it is" (Sgt Barnes)
Re: Bsa A50 Royal Star Valves [Re: tridentdude75] #788404 10/27/19 11:48 pm
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gavin eisler Online Content
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I have fitted oversize valves to stock seats, yes it should work, the original seats are worth saving if you can, its a fair old job to replace them . if your machinist is willing , go for it. Seats were originally cast in , machining them out, then making a new one fit so it doesnt fall out is a tricky job. My pals trident motor was wrecked when a replacement valve seat dropped out. Do watch out for installed spring length.


71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
Re: Bsa A50 Royal Star Valves [Re: tridentdude75] #788424 10/28/19 5:21 am
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John Goodwin Offline
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I had stellite valve seat inserts put in the T160 Trident I raced back in the 80's
I was running some W&S valve springs and after maybe 2 laps of Amaroo park I'd lose 1500 to 2000 rpm as the valves climbed into the head.
Once I had the seats done (Bernie at Rams Head Service) I'd go from meeting to meeting without having to adjust the clearances.
I think a cheaper option would be to try and source a good condition replacement head though.

Last edited by John Goodwin; 10/28/19 5:21 am.

Current: 2 x 1966 A65S, 1 x 1967 A65SA, 1 x 69/70? A65LA space Y, 1 X D14/4 & 1 x B175
Past: 4 x 1976 T160V, 1 74/5 T150V, 83 model GSX 750 ESD, Z650, Katana 1100(Bathurst Model), 79 T140V, 70's TR6, 2 x 1971 BSA 250 Gold Stars, 50's 350 Goldie, A65 Spitfire semi basket case, 1965/6? A65 LC, Tiger 21 350 & a D14/4 Bantam, 175 Bridgestone Twin with Zimmerman discs!
Re: Bsa A50 Royal Star Valves [Re: tridentdude75] #788429 10/28/19 6:14 am
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NickL Offline
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If you can find suitable oversize valves for the bike the beezer seats can be cut a fair bit bigger than they are as standard.
I've had seats put in an a65 that fell out and several other blokes i know have had the same problem. The inserts are put into
the original austenitic iron seats as machining them right out is very difficult. If you go that way i suggest you use albronze inserts.
That way the rate of expansion keeps them in.
Getting the job done by someone who has a Serdi or similar is a good idea, finding someone who'll gaurentee it, is harder.
If you use A65 valves they will need to be shortened from memory, that will mean using lash-caps and re-cutting collett grooves.
You may be able to find some that will fit if you can persuade a stockist to let you rummage through his stock, it may mean fitting
different colletts springs etc etc. For instance I have fitted Triumph 500 daytone valves in a B40 with no issue, but you need all the bits.
If you do fit bigger valves, check your piston clearances, when done, you may have to cut a little more out of the pockets.

Re: Bsa A50 Royal Star Valves [Re: NickL] #788442 10/28/19 1:33 pm
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Allan Gill Online Happy
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Originally Posted by NickL

If you use A65 valves they will need to be shortened from memory,


Interesting point Nick, never realised that A65 valves were longer.


beerchug
Re: Bsa A50 Royal Star Valves [Re: tridentdude75] #788446 10/28/19 2:53 pm
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DMadigan Offline
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Many nitrided auto valves available for less than $10 that can be modified to fit.

Re: Bsa A50 Royal Star Valves [Re: tridentdude75] #788461 10/28/19 5:03 pm
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VicCyclone Offline
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Are you using the correct A50 valves? Early valves are smaller than 66 onwards.


VicCyclone

1965 A50 Cyclone Clubman
1966 Victor GP
1967 Victor Special
1968 Victor Special
1968 A65L

2009 HD FXDC
Re: Bsa A50 Royal Star Valves [Re: tridentdude75] #788488 10/28/19 11:00 pm
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tridentdude75 Offline OP
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The new valves are in correct spec for a 1970 Bsa A50. Ordered 2 oversize intake valves, my machinist say's this will solve the problem. Thank you for the input. Jeff


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