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Lost Compression

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GV655

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Mar 24, 2013
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Im hoping to get some help/advice guys re my 2002 FZ1s. Just came home from a 5 day tour of Tasmania Bike performed faultlessly washed it put it away for 2 weeks went to start it got a backfire the starter sounded different and the old girl just does not want to go. Have just removed plugs and done a comp test and only 50psi on average accross all 4 cyls. Cam chain seems tight could it have jumped a tooth on a cam sprocket?? and maybe bent a valve? I have poked a bore scope down the 2 outside pots and nothing looks bent. Anyone else had anything like this happen??
Looking for some words of wisdom from all you techo fz1 fans
Rob
 
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Thx Guys
The starter is making a whining kind of noise but it is spinning the motor over plenty fast enough. Will try get hold of a leak down tester so i can see where my comp is going. Very strange all 4 pots being low hope i havent bent valves. Is it a motor out job to do the head on one of these ??
thx again in advance
Rob
 
donoharm said:
different like what? turns the engine slower? the given cyl pressure at 400rpm is 220psi for gen1 , so you have about 4 times lower compression, if the starter doesn't turn the engine fast enough you will see lower compression numbers ....
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It should still build plenty of compression even turning slow. There is another issue. I wouldn't imagine bent valves. When I bent a valve on my Duc I had nothing, wouldn't even move the needle.
 
Sebastian F7 said:
It should still build plenty of compression even turning slow. There is another issue. I wouldn't imagine bent valves. When I bent a valve on my Duc I had nothing, wouldn't even move the needle.
Click to expand...
That's why I said I would check the timing, may be opening the valves up before the pressure gets high enough. And have seen on car engines if the timing is off they can be hard to start and seems like the starter is working harder than usual. May not be it, but its just where I would start.




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Before going all out. Last time I checked compression on a car the throttle need to be WOT. How does it work with the secondary flies? Do you need to open them manually. In order to get 50ish PSi you need to have some bend valve or head gasket blow up!
 
I would slow down on the "engine is totally shot path" a bit . . .
Doubt your test procedure or equipment. Are you using some sort of long adapter? The volume of the adapter can have a ginormous effect on compression readings on a small combustion chamber. Do you know the gauge really works? . . .
It is incredibly unlikely that your engine (particularly after it was working fine) has become damaged in some amazing way that it yields very low compression reading evenly across the cylinders. Bending a valve (or valves )is a chaotic event and would give uneven results. Skipping a tooth on the cam/crank sprocket seems also unlikely given the condition of the bike when it last ran. It would also probably yield inconsistent results for compression. . .

Perhaps you have an electrical issue (from the washing) or water in your gas? Check for spark. Drain your bowls and see if you have water in there (use a clear glass jar).
 
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I agree with eurban,I would forget the compression test for a while, it seems your way ahead of yourself,onething I never do is wash any bike, then put it away with out taking it for a run first to dry out all the electrics etc first,I would first buy a can of wd40/crc/inox and spray all electric`s I could see eg plug wires coils etc.
 
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eurban said:
I would slow down on the "engine is totally shot path" a bit . . .
Doubt your test procedure or equipment. Are you using some sort of long adapter? The volume of the adapter can have a ginormous effect on compression readings on a small 250cc combustion chamber. Do you know the gauge really works? . . .
It is incredibly unlikely that your engine (particularly after it was working fine) has become damaged in some amazing way that it yields very low compression reading evenly across the cylinders. Bending a valve (or valves )is a chaotic event and would give uneven results. Skipping a tooth on the cam/crank sprocket seems also unlikely given the condition of the bike when it last ran. It would also probably yield inconsistent results for compression. . .

Perhaps you have an electrical issue (from the washing) or water in your gas? Check for spark. Drain your bowls and see if you have water in there (use a clear glass jar).
Click to expand...

Thanks Eurban and all others for your input
I am a snapon tools dealer comp gauge is brand new off the truck but i tested it again to make sure and yep no more than 50psi. i just put 60psi into the 2 outside cyls and turned the engine over slowly and i have constant air coming through the airbox also through exhaust when valves are open pretty much as it should be. and no air to speak of going into crank case which tells me the rings are probably fine. It is all pointing to bent /damaged inlet valves and i have no idea how or why this may have happened. The bike got a fair thrashing for 5 days solid i rode it home from the boat washed it and yes i do run the bike to dry any excess water off it fisherman and i parked it for 3 weeks. Time to go buy a manual i think and tear this baby down to see what the hell is going on. I will keep you posted as to what i find. Any recomendations with regards a w/shop manual digital or book form?
Rob
 
GV655 said:
Thanks Eurban and all others for your input
I am a snapon tools dealer comp gauge is brand new off the truck but i tested it again to make sure and yep no more than 50psi. i just put 60psi into the 2 outside cyls and turned the engine over slowly and i have constant air coming through the airbox also through exhaust when valves are open pretty much as it should be. and no air to speak of going into crank case which tells me the rings are probably fine. It is all pointing to bent /damaged inlet valves and i have no idea how or why this may have happened. The bike got a fair thrashing for 5 days solid i rode it home from the boat washed it and yes i do run the bike to dry any excess water off it fisherman and i parked it for 3 weeks. Time to go buy a manual i think and tear this baby down to see what the hell is going on. I will keep you posted as to what i find. Any recomendations with regards a w/shop manual digital or book form?
Rob
Click to expand...
Well then I would first check the valve clearances if you have some bent valves their clearances should be way out,then like others have said, check the timing also timing chain and sprocket`s teeth etc before ripping off the head. how many klms do you have on the bike,and good luck with it,
 
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