1955 Plunger B31
The old girl has been stood for about 9 months at the back of the workshop and when I came to start it I found that there is very little compression and obviously won't go. I did a complete engine strip down and rebuild about a year ago and when she was put away she was absolutely fine.
My initial thought was that the exhaust valve had stuck- but this is free.
So.. I've stripped the head and barrel off and everything looks ok; piston ring gap is a tad over 12thou.
It hasn't wet sumped.
Any thoughts ?
have you tried to see if the valves are seated properly . petrol on an upturned head and torch down the inlet or exhaust port will tell you .
Probably hard to check now that the head is off, but could the exhaust lifter have been stuck after the stand time?
as long as the head-barrel is Ok, it can only be rings or valves. I would put the head back on without pushrods etc and see if you have compression, if not you may be able to hear where it is escaping from. A leakdown tester is brilliant for these problems!
Possibly the tappet clearances were not 100%?
Anyway, good luck and let us know how you get on.
cheers
Pete
Thanks guys
Will report back
finish of the bore good enough? too smooth wont seal or maybe ring quality?
did you check valve stem clearances , too much will allow valves to move, stopped it seats but moving it may not
Hi BeenyBoy,
As the bike was fine when put away it is possible that a valve was suck open a bit and during the removal of the head and barrel it sorted itself out. As you have not found a problem with any parts then the best thing would be to put it all back together again. Odds are it will be fine.
Dave.
Are you sure its not a clutch issue? Some how cable too tight so the clutch is giving the feel of no compression. I am sure this is a dumb comment but thougt I would throw it out there. I had a similar feel to my bike after intalling new cable and the cable length was too short which meant the clutch was I guess bypassing the motor at kick over?
Quote from: WayneBergman on 09 Jan, 2021, 22:39
Are you sure its not a clutch issue? Some how cable too tight so the clutch is giving the feel of no compression. I am sure this is a dumb comment but thougt I would throw it out there. I had a similar feel to my bike after intalling new cable and the cable length was too short which meant the clutch was I guess bypassing the motor at kick over?
An easy way to check this (after putting it all back together) is to take the points cover off. Kick the bike over, and if the points are turning, so is the crank.
Quote from: DAVE BRADY on 09 Jan, 2021, 17:03
Hi BeenyBoy,
As the bike was fine when put away it is possible that a valve was suck open a bit and during the removal of the head and barrel it sorted itself out. As you have not found a problem with any parts then the best thing would be to put it all back together again. Odds are it will be fine.
Dave.
That was my first thought but the valves are operating
Quote from: WayneBergman on 09 Jan, 2021, 22:39
Are you sure its not a clutch issue? Some how cable too tight so the clutch is giving the feel of no compression. I am sure this is a dumb comment but thougt I would throw it out there. I had a similar feel to my bike after intalling new cable and the cable length was too short which meant the clutch was I guess bypassing the motor at kick over?
Interesting thought - but the engine is turning over
:) :) :)
Drop of oil poured around the edge of the piston will help to stop air bypass and to some degree get behind the piston rings, forcing them up against the cylinder wall. it could be as simple as the rings stuck, the oil will help them to "unstick". Not an answer for wear tho.
If you already have the head back on you'll get the same effect by pouring the oil down the plug hole.
Mike 8) 8) 8)
Had a bit of a fiddle today....head back on minus pushrods.... very little compression... some 'whooshing' from the exhaust port.... head off again and torch up the valve ports- no light visible ... valves out just to double check and the - seals looks good....BUT... its now clear that the little end bush is b***g*ed and there is some lateral movement of the piston in the bore... so new bush on order..need to find my reamer...but what about the lateral play in piston...- is this a result of the b****d little end or are we talking a re-bore ? I'll check the piston skirt clearance tomorrow which should give a better idea......all good fun eh !!
Beeny, bit worried here. How do you know the small end is knackered?
Quote from: Willie Dee on 13 Jan, 2021, 15:52
Beeny, bit worried here. How do you know the small end is knackered?
Cos I can waggle the piston- there's an appreciable amount of free movement up and down.
Update- checked the piston skirt clearance and its about 3thou- so this seems ok
Had a look at the valve springs.... outer is a tad under 48mm- should be 54.75 and the inner is a gnats under 40mm- should be 46mm.... according to the book....so ....might not be the cause of the problem but it aint gonna help !
Is the piston out the barrel?