The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: LJ. on 03.08. 2010 10:49
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Working on the 62 Super Rocket the bike starts up easy enough but almost nearly every revolution there is a backfiring through the carburettor, the bike had been standing ten years. Now through laziness I'm reluctant to remove the head as I'm suspecting a sticking valve. Are there any tips or tricks to ease the valves? Turning the engine over feels very low in compression, my standard A10s have much more compression than this Super Rocket what could be the problem here? I'm told the bike was imported when it's owner emigrated here to the UK, so the bike must have been good at that time or he'd have sold it before coming here. Doe's it look like a head and barrel pull?
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LJ,
Is the compression the same on both cylinder? If not, this could indicate a burnt (inlet) valve.
There was a thread recently about a sticking valve cured with some oil additive, but I couldn't find it now.
***edit***
Found it:
http://www.a7a10.net/forum/index.php/topic,2802.40.html (http://www.a7a10.net/forum/index.php/topic,2802.40.html)
The stuff is called extralube zx1.
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I would check ignition timing and valve timing you never know when someone has fiddled with things.
Check the carby is clean and no jets loose etc just to be sure.
Compression test on both cylinders should show if there is a compression problem. If compression is low on one side you know the problem. If its the same on both sides but it doesnt blow smoke then both sides have valve problems. It may be both sides if its been sitting for a long time.
Take the tappet covers off and turn over the engine with the plugs out and check that the valves close. Sometimes you can see a sticky valve. It might free up with a good squirt of oil into the valve through the valve spings and then give it heaps of kicks with the plugs out and fuel turned off of course. See if it
If compression doesnt come up it may be burnt or bent. You will need to take the head off and service the valves.
Sometimes when the valves are serviced and the engine is reassembled, the rings tend to start to blow smoke because of the extra compression. Its probably a good idea while the head is off to check the bore and pistons and rings also to feel the bigends. Hmmm on it goes.
If it is just a sticky valve run some upper cylinder lubricant for a while.
I hope it is an easy fix for you LJ.
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Hi LJ,
It could also be a valve spring gone soft !! If the engine was sitting for years with one compressed then it may have
compressed to the point of being very lazy!!!!
Another consideration is that when an engine is idle for years the rings get stuck in the grooves
what can happen when the engine is started is the rings give enough comp to start but wear rapidly or break as the heat builds up leading to consequentual damage *sad2*
Ask me how I know *eek*
My RGS hasnt been started since around 1992, Iiwont risk starting it until I have had it all apart and the sludge at least cleaned out
I hope you do not have the black cloud following you around like me ;) ;)
Good luck
JOhn o R
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. Now through laziness I'm reluctant
Are you industrious enough to check the valve clearances?
"Almost nearly every revolution" sounds strange. Is it a regular noise? Is it a hiss or more of a "sneeze?" At what engine speed and throttle opening is it happening?
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Hmmmmm lots of advice there including a couple of emails! thanks for the tips... all thats needed now is to switch off computer for a while and wave spanners! thanks again much appreciated.