Morris Minor Owners Club

hows this then, splitt screen has been off road for a year but started at least once a fortnight,run up to temp and up and down drive to keep clutch and brakes free.Went to it today started first pull left ticking over up to temp and pushed choke in ran for a few minutes then splutterd and stoped.Petrol pump me thinks,taps it ,no go,took pipe off at carb pumping ok. took top off carb,full,checked ht good spark checked at plugs good spark,still no go,checked at jet,ok petrol at jet batterydown by now so out with starting handle,vertually No compression on each piston.Broken rocker shaft may be ,took cover off ,ok,valves moving ok,now suspect sudden head gasket failure,last attempt give it a doze of easy start on full throttle fires up and slowly picks up revs ,now runs ok reving freely,switch off,stick handle in and nearly breaks my wrist back up to full compression on every pot,hardle able to turn it over just like it was when I rebuilt the engine 5 years ago.now starts first pull on starter or first click over on handle.Now what was that all about then,it's old petrol but why the no compression and I mean vertually none,could only feel slight resistance on one cylinder,Got me beat,only hope it was just a one off,if i'd tryed the handle first I could put it down to no oil at the rings after standing for a couple of weeks,but it had been running for 5 minutes or so,will try the handle next time and see what it feels like,and I think the no start could be down to old petrol so will be putting fresh in,Its great to mess with old cars gets the old brain matter working.

Most likely a valve sticking open. Not really any other way to lose compression!

My guess would be gummed up exhaust valve stems. Revving it up has now freed them.
(Of course I could be talking out of my nether regions!)

yes what I thought but on all cylinders at the same time,and after starting and running fine for 5 mins just been to it now comp is fine and started first pull ,got me beat,but has to be valves As bm says only way to loose compression.

If you are running it up to temp on choke then you will have petrol blowing up the exhaust valve stems and very little oil coming down them, but it is very puzzling that it seems to have affected them all at the same time!

when I suspected a problem with the rocker shaft(may be timing chain) took cover off and turned engine on handle and could see all valves working ok and still very little compression,(Yes plugs were fitted before anyone asks ) to facilitate warm up I have the tickeover set highish so I can start then push the choke in after a few seconds,to prevent flooding.Got me beat can't think of anything that would cause it,If it hadn't started first off then I would have looked at stuck valves or compression rings but it only happened after about 5 mins running,when it stalled I knew something was wrong cause the starter was spinning much faster than normal as if there were no plugs fitted.been fine since,when it stalled it gave the classic running out of petrol sound slight increase in revs then a falter and stall.On reflection I remember it doing this about 10 years ago after a short run and then stall took some starting then but put it down to petrol pump at that time. Anyway twice in 10 years I can live with but just a puzzle .