top end

Information relating to the Matchless G5 or AJS Model 8 350cc Lightweight
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Re: top end

Postby clanger9 » Fri Feb 02, 2018 3:09 pm

Did you move or loosen the fuel pipe union on the top of the float chamber? If fuel comes out of the inlet, then either the float valve is sticking, the float level is too high or the little spacer on the float pivot shaft is missing (unlikely if Martyn just rebuilt it!)
1966 AJS Model 14 250 CSR cafe racer
1989 Moto Morini Dart 350
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Re: top end

Postby red_dog49 » Fri Feb 02, 2018 5:06 pm

all, nothing has been done to the engine,last October I had two 20 min runs around the village and thought then as I could not get a good tickover when hot would send to martin bratby, who I think has done a fine job on the carb, fuel is coming out of the carb inlet at some pressure, that's
why I thought something was amiss with the inlet valve.
what is a good cylinder psi for a compression test.
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Re: top end

Postby Ozmadman » Fri Feb 02, 2018 5:13 pm

Duncan wrote:
red_dog49 wrote:HI, yes ok but would that cause fuel to exit the carb ????.
Rob.

Normally a sticking float/dirt on the seat of the carb fuel cut off.

Martin Bratby usually re-seats the float valve seat and fits a brass needle valve as he doesn't like the Viton tipped ones as he says they still stick and that Has been my experience too so I can't see it being that or any other carb problem to be honest as he is meticulous in his work.
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Re: top end

Postby clanger9 » Fri Feb 02, 2018 5:25 pm

Ah, if it’s *blowing* fuel out of the inlet, then it’s not the carb or float - sorry, I’d misunderstood your description.
Back-pressure through the inlet suggests a valve timing problem, inlet valve sticking open or exhaust valve sticking shut.

I’d check the inlet valve tappet clearance. It sounds like it’s too tight.
1966 AJS Model 14 250 CSR cafe racer
1989 Moto Morini Dart 350
1993 Ducati 750SS

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Re: top end

Postby Ozmadman » Fri Feb 02, 2018 11:58 pm

clanger9 wrote:I’d check the inlet valve tappet clearance. It sounds like it’s too tight.
just to add if you are unaware, the correct method is no discernible play between rocker and push rod when the engine is just warm (not hot) you should be able to spin the push rod easily. To make sure clanger is on the right track you could always set them with a bit of play just to see if that cures your problem and then re-set them correctly after.
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1960 Model 8
1974 Yamaha RD250B US Model 6 speed

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Re: top end

Postby red_dog49 » Sat Feb 03, 2018 9:34 am

thanks for the replies more checks imminent.
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Re: top end photos

Postby red_dog49 » Sat Feb 03, 2018 2:08 pm

hi, going to find new springs ,pics don't show me any other problem, although i'm happy to be corrected.
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Re: top end

Postby clive » Sat Feb 03, 2018 2:21 pm

I take it that is the inlet valve seat showing. Looks to me as though it is only making clear contact between the valve and seat in the bottom left "corner". If this is the case might the valve be slightly bent? If it is not going fully home then it would tend to blow back out of carb as the engine comes up to compression. I would try lightly grinding it back in and see if you get a nice finish all the way round the valve.
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Re: top end

Postby red_dog49 » Sat Feb 03, 2018 3:02 pm

no, that's the exhaust seat.
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Re: top end

Postby Mick D » Sat Feb 03, 2018 4:01 pm

Hi

You've gone this far so it would be missing a trick to not check both valve stems for evidence of distortion or binding, also to regrind both valves. Once the head is back together you can check the valve sealing by filling the inverted head with petrol and seeing how quickly it leaks away.

Regards Mick

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