Compression disappeared while sat in lockup (350 bullet)

[stinkwheel]

Really odd. On my Royal Enfield 350 bullet (pre-unit, air cooled, OHV, 350cc single).

I last rode it at the beginning of December. Rode it into the lockup, squirted liberally with corrosion inhibitor and shut the door.

Hauled it out today to find it has no compression at all. Kick it over and the engine just spins. Now this is a motor that would normally bump over compression without the decompressor only if I were to put my full weight on it and bounce.

I suspected the decompressor at first but having stripped that (and dropped the decompressor valve into the cylinder then retrieved it again with a magnetised allen key) I can pretty confidently say it's not that.

The sparkplug is in properly too.

This leads me to conclude the exhaust valve must be stuck open. Any ideas how or why that would happen to a bike that was running fine when put away and has been sitting in a dry lockup for 6 weeks?

Obviously I'll know more when I get the rocker covers and (if necessary) head off it but I can't do anything with it until Friday when I'm off work. Thought I'd get planning now.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Alexio]

I guess your valve clearances for what ever reason could now be very far out? All I know is that when an OHV engine is turning over is puts oil up to the top of the engine to lubricate the push rod and valve stuff right? So while your engine was sitting, there was no oil up there. While there was no oil "protecting" your valves anything from minor corrosion to weird expansion or cohesion of parts could happen.

As you say though, you'll know once you have a look. I really don't know that much about diagnosing engine problems, I just really enjoy speculating (and learning!)

How many miles has the bike done any way? How old is the oil? (just curious)
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will never give up his CG. I look at my fuel gauge more as a progress bar than a fuel gauge.
G: With my GSXR I do often effectively use it as a scooter with a clutch in town.
ms51ves3: why does it need 500 miles? Are you teaching it how to be a piston?

[ms51ves3]

[stinkwheel]

[hmmmnz]

maybee the valve has wedged itself against the guide,
although it doesnt seem very plausible,
maybe the collet has broken and the spring has come loose
allowing the valve to stay open....


bugger if i could even guess
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the humans are dead
I kick arse for the lord
Wiring Diagrams BIDNIP it bitches

[The Shaggy D.A.]

From Pete Snidal's manual :-

[STONEY!]

the shaggy da has got it in one (well hopefully!) very common with cb250rs singles

[Alexio]

If that turns out to be the diagnosis then at least I know that my thinking wasn't too far off of the mark. We'll be curious to find out the problem and hopefully won't have to wait all the way until Friday to find out!

That makes sense actually because don't you put a bit of oil down the spark plug hole to test if it increases compression if you are testing your piston rings anyway?
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will never give up his CG. I look at my fuel gauge more as a progress bar than a fuel gauge.
G: With my GSXR I do often effectively use it as a scooter with a clutch in town.
ms51ves3: why does it need 500 miles? Are you teaching it how to be a piston?

[The Shaggy D.A.]

[.]

I always leave mine at TDC on the compression stroke (even overnight) This removes all strain from the valve gear and ensures the valves are closed which as a welcome bonus will prevent moisture entering the cylinder. Ths really is a must when storing this particular engine for any length of time because it will also prevent wet sumping.

On the assuption that it is a valve problem, knowing how slack the indian tollerances are, I would be very surprised if the valve had got itself stuck in the guide.
A valve/guide problem, which is easy enough to diagnose (the pushrod will remain tight no matter what position the crank is in) can often be solved with a rap on the valve tip to loosen it off.

I would guess either a tight rocker or a dropped valve seat is the culprit.

[Frost]

I was going to say oil until someone beat me too it

You could try a squirt of 2 stroke oil into the cylinder and see if that helps make a seal and gives a bit of compression. Worst case scenario, it'll smell nice

[stinkwheel]

Well. It starts and idles now after bunging some oil down there by the light of my car headlights after work (blows perfect smoke rings out of the exhaust too).

There is still remarkably little compression at the kick start though. Maybe it'll sort itself out after its wee run. Failing that, I'll have a look at the valvegear on friday.

I'd have tried a test run but I also stripped the thread out of one of the front axle nuts at the weekend. Well, it more stripped itself to be honest, I only had 2 fingers on the spanner at the time and it must be an M18 thread at a minimum. Seriously ropy machining. Need to replace that before I can ride it.

[mr.kris]

you planing on comeing to the fezze up? this year sir? alittle off subject i know
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[stinkwheel]