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[Duncan]

Good evening all.

New to the forum and have a question that desperately needs answering.

I have a 1994 500cc Bullet that has a total loss of compression.
Bike was running fine then one day started misfiring when i blipped the throttle, a kind of Bang-Bang-Bang like it was trying to fire like a two stroke.
Then when I tried to start it the following day there was zero compression.
I've had the top end off and cleaned up the piston which is the European made item and that and the rings look fine. The bore also looks fine with no scoring.
I reassembled it with new gaskets and a new decompressor blanking plug(yes with the correct washers). Valves are adjusted as should be. There are no visible cracks in the head and no blow-bye marks to indicate a warped head. I've not had the valves out as they are relatively new in the head.

When it was all assmbled I gave it a few kicks and there was a fair amount of compression then nothing and nothing sinse and I cant figure it out.
I though maybe a stuck valve because when kicking it over even with no compression there was an almighty backfire.

I slowly turned the engine over to different positions to check pushrod play thinking that if there is a stuck valve the pushrod on either valve would be really loose but this is not the case, they remain as should be, just the right amount of looseness on top dead centre and tight on either the inlet or exhaust stroke.

Your help is greatly appreciated.

Regards, Duncan

[Norm]

Duncan were the rings nice and free, not starting to bind then I would squirt a bit of oil in through the plug hole and kick it over and compression should return, these things do this from time to time

[Duncan]

Hi Norm

Yes the rings are free and in good condition. Had the barrel off to check the piston, rings and bore.
The one thing I didnt check was the valves as I dont have a suitable valve spring compressor. Im thinking maybe a stuck valve but like I said I dont think this is the case as I'd imagine if a valve was sticking open the pushrod would have a lot of play if the valve remained open as the cam "Shut".

[Gwilly]

Sounds intriguing Duncan, if the pushrods and rockers are moving as they should then i guess it can only be the sealing face of the valve or seat which has broken /chipped/burnt..

Maybe the exhaust valve letting by and igniting charge in the pipe..

Are you absolutely certain that the decompressor plug is sealing the exit to the exhaust?. Correct length and washers still intact..

Wondered if refitting the original decomp might help before removing the head again..

[simon]

A quick test for the valves is simply to listen as the bike is kicked over, If you hear a hissing on the compression stroke either through the carb (inlet valve) or exhaust (exhaust valve) then you've got a seating issue or a burnt valve.

[John R]

Mysterious loss of compression is not all that uncommon. I have a 1989 350. Occasionally, for no particular reason, I find that there is no compression just keep kicking it over and you'll probably find that it starts and then has good compression. Don't know why; I suspect that the first time it fires it knocks a slightly stuck valve into its seat.

[Alan R]

Hi guys---------- Bent exhaust pushrod ??

[The rider formaly known as Lone Rider]

I had the very same problem. The Indian heads have (had) at one time too smaller exhaust valves fitted. The valve would not maintain compression, and constant valve tappet adjustment was needed to maintain compression.

[Norm]

There is also the possibility of a loose valve seat that has moved and not set back properly

[Beezabryan]

Long time ago before I realised the vagaries of these ancient (design) nails I had the head on & off more times than a whores drawers. never was there anything adrift.