A10 exhaust valves & guides

[TT John]

Hi All.
I have been having trouble with my 1957 plunger A10, twice now, I have been riding then the exhaust valve siezes, push rod comes out and when I strip it down find that the valve has bent, most likely where the piston has hit it, although it does not appear to have done any damage to the piston. With this happening twice I wondered if when I had the head done originally whether the correct guide was fitted ie inlet instead of outlet, is there any difference? with part numbers etc, it seems that it is the same one, right hand exhaust, on both occasions, I did manage to get home with the bike by taking out the plug on the damaged side and riding it slowly on one cylinder but got my new jeans well oiled up on that side.
I am taking the head back to where it was done originally, just wondering whether to go back to the Ariel Huntmaster head that I had on before.
 
kind regards TTJohn

[BSA_54A10]

Did you do the plasticine on top of the pistons trick ?
.045" minimum between the top of the piston & the bottom of the valve.
Overall length of the guide will not make any real difference.
Height from the heat to the top of the guide will.

[trevinoz]

John,
                   Do you have enough clearance between the guide and the valve stem?

  Trev.

[beezermacc]

My mate managed to seize both exhaust valves! The problem turned out to be retarded ignition causing the engine to run too hot. A common problem is imbalanced points causing one cylinder to run retarded, accompanied by blue exhaust. If you have imbalanced points you really need to get the mag fixed but in the meantime set the smaller gap to 0.010" and set the timing on that side. If the imbalance is really bad this may cause pinking on the other side which is also to be avoided!

[TT John]

Hi All.

Thanks for all the helpfull hints etc, I have had a new guide and valve fitted and I will definitely check ignition timing before doing any milage on it just to see if it was running a bit retarded on that one side. Today is re-assemby day so its got to be correct, after all I am hoping to ride to Sweden on it in August for the rally and I hope to meet some of you there.

Kind regards TTJohn

[Flatboy 1950]

I have read somewhere (Tuning for speed ??) about counter-boring the exhaust valve guides a small amount at the exhaust port side .... to prevent this problem... !! ??

Regards , Elijah.

[TT John]

Well, a new valve guide & exhaust piston fitted, I did check & adjust the timing just to be sure it wasn't too far retarded, start the old girl up and the engine ran as sweet as a nut, switched off started up again & the right hand cylinder started playing up, then not firing at all on that side, after some checking found that the spark plug was dead, new one fitted and we are all systems go again. Its very off putting when after all the work you do to get the bike running, then you get a simple thing like this but with it being the same side as the previous trouble, my mind was thinking its all in vain but, no its all o.k. now.

A very happy TTJohn

[Goldy]

I had similar problems and it turned out that the small radial hole in the remanufactured rocker feed banjo bolts were too small. I was advised by the forum that they should be 3/64" and since drilling them out I have had not problems at all.

[beezermacc]

I had similar problems and it turned out that the small radial hole in the remanufactured rocker feed banjo bolts were too small. I was advised by the forum that they should be 3/64" and since drilling them out I have had not problems at all.

Very interesting - not heard of this before but makes sense. With ref to the misfire and dodgy plug make sure you have best quality pickup carbons fitted. I get lots of mags to fix where the cause of failure is the pickup carbons manufactured from the wrong grade carbon, tracking around the slip ring and sparks all over the place! Have a look in your pick up 'window' on the mag - you'll need a small mirror and check for a conspicuous black line all round your slip ring. I know this has got nothing to with valves and guides but it is certainly the cause of many a misfire often attributed mistakenly to the plug. You can be looking at the plug that should be sparking whilst it is sparking on the other side because of the carbon trace on the slipring!

[wilko]

Have you looked at the last plug? Could it have hit the top of the piston? Wrong extended tip type?

[TT John]

Took the A10 out for a run today covered about 90miles, all systems go, I had already checked for tracking Beezamacc and that was o.k. as I am using decent hard brushes, Wilko, the spark plug was dead, correct lenth, no damage. The bike ran quite nice today thanks to all your input its a great site and very helpfull.

Regards TTJohn

[Topdad]

Good morning John, just a thought and my apologises for posting this late ,it's slightly similar to Goldy's udea but in view of all the work you've done and this problem just wondered if you'd checked out your oil tank for any sediment /debris .The only probem I have encountered on my engine was a stuck exhaust valve ,like you didn't damage the piston but required replacement . It happened after a very short distance approx 1 mile following the complete rebuild somehow I'd missed some debris in the tank despite I thought cleaning it completely . The whole rocker assembly needed to be cleaned out and after that haven't had any further probs. Seemed to me that the rocker feed was surceptible to collecting this muck and like goldy's thought restricting flow with serious results, hope it's fine ,best wishes BobH

[bikerbob]

Hi there.  Something the guy who helped me on my A10 restoration told me was that everytime that you did a top end overhaul after first starting the engine take off the oil cap and place your finger over the oil return hole just for a few seconds as this forces the oil up into the rockers his explanation was that the feed to the rockers is on the return side and there is very little pressure and it does not take much to hold up the oil he maintained that you could possibly get an airlock and his remedy would solve that.