Author Topic: Sticking Valves?  (Read 1329 times)

Offline LJ.

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Sticking Valves?
« on: 03.08. 2010 10:49 »
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?
Ride Safely Lads! LJ.
**********************
1940 BSA M20 500cc Girder/Rigid- (SOLD)
1947 BSA M21 600cc Girder/Rigid-Green
1949 BSA A7   500cc Girder/Plunger Star Twin-(SOLD)
1953 BSA B33  500cc Teles/Plunger-Maroon
1961 BSA A10  650cc Golden Flash-Blue
1961 BSA A10  650cc Golden Flash-Red

Offline MG

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Re: Sticking Valves?
« Reply #1 on: 03.08. 2010 12:51 »
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

The stuff is called extralube zx1.
1955 A7 Shooting Star
1956 A10 Golden Flash
1961 Matchless G12 CSR

www.histo-tech.at - Restoration, Repairs, Racing

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Offline terryk

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Re: Sticking Valves?
« Reply #2 on: 03.08. 2010 13:30 »
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.
1950-53 A10 rigid/plungers, 1958-61 A10 super rockets, 1947-50 A7 longstrokes, 1949 Star twin,
1951-54 A7 plungers, 1940s M21, WDM20s,
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Offline chaterlea25

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Re: Sticking Valves?
« Reply #3 on: 04.08. 2010 01:01 »
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

1961 Super Rocket
1963 RGS (ongoing)

Online Triton Thrasher

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Re: Sticking Valves?
« Reply #4 on: 04.08. 2010 08:37 »
. 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?

Offline LJ.

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Re: Sticking Valves?
« Reply #5 on: 04.08. 2010 10:59 »
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.
Ride Safely Lads! LJ.
**********************
1940 BSA M20 500cc Girder/Rigid- (SOLD)
1947 BSA M21 600cc Girder/Rigid-Green
1949 BSA A7   500cc Girder/Plunger Star Twin-(SOLD)
1953 BSA B33  500cc Teles/Plunger-Maroon
1961 BSA A10  650cc Golden Flash-Blue
1961 BSA A10  650cc Golden Flash-Red