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zero compression!
Moderators: KeithZ1R, chrisu, paul doran, Taffus
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dreadmanbastard
zero compression!
hey chaps, having just fitted new piston rings i finally tried to start the bike today and had no joy. No even a flutter, so i thought id try a compression test. Zero! all 4 cylinders. oil in there makes no difference. i have been browseing old posts and discovered im supposed to hold the throttle open. I cant belive this would result in getting zero compression. the starter motor spins the engine freely. What could have gone wrong? i remember the top of a valve falling off when i turned the head on its side to prize out the exhaust gaskets, but it slotted back in nicely , i though naught of it. if its not cylinders, then it can only be valves cant it.
Even if throttle closed you'd get something, on a stone cold engine with throttle closed, you should get about 6 bar pressure.
About 7 on a warm engine with throttle open.
Have you checked the valve clearances? if theres no clearance this'll leave valves open and give zero compression, head torqued down properly?, new gasket?
you did put the piston rings in didn't you?
If oil makes no difference and rings definitely in then it's summat up t'top end
Just re-read the post, when you say top of the valve falling off, can you clarify? mainly becuase there should be nothing to fall off bar a Shim possibly if over bucket shims and clearances very loose
About 7 on a warm engine with throttle open.
Have you checked the valve clearances? if theres no clearance this'll leave valves open and give zero compression, head torqued down properly?, new gasket?
you did put the piston rings in didn't you?
If oil makes no difference and rings definitely in then it's summat up t'top end
Just re-read the post, when you say top of the valve falling off, can you clarify? mainly becuase there should be nothing to fall off bar a Shim possibly if over bucket shims and clearances very loose
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dreadmanbastard
when i had the cams out and the head off on its side the shim and lifter fell out. it just slid back into place.
after the headache of getting cylinder back on , theres no doubt the rings went on/in!
I bolted down the head with torque settings, with all new gaskets.
I assumed (always a bad move) that valves would be ok as had just done them prior to ring changing. could all this work to cylinders have changed the clearances?
its too late now for mechaincs but will do throttle open compression checks , get my feeler gauges out and report back.
after the headache of getting cylinder back on , theres no doubt the rings went on/in!
I bolted down the head with torque settings, with all new gaskets.
I assumed (always a bad move) that valves would be ok as had just done them prior to ring changing. could all this work to cylinders have changed the clearances?
its too late now for mechaincs but will do throttle open compression checks , get my feeler gauges out and report back.
No, the beauty of OHC engines is all amounts of head off work and new gaskets and whathaveyou will make no difference to the clearances as the cams are bolted in place above the buckets and shims, unless you unbolted the cams for any reason then the clearances can't change.
That said the clearances shouldn't have allowed a shim to fall out of the bucket, removing and changing them requires a bolt on compression tool to compress the bucket, possibly buckets sticking in the bores?
I'd certainly whip the rocker cover off and check them again to be sure, don't mean to offend but is there a possibility that you've confused your guage type? mm - in
First time I set clearances I recall confusing the two and winding up with a gap big enough to park a family hatchback in.
just occured, the flipside of the OHC engine is the incredibly easy ability to get the valve timing way out when refitting, it easy as anything to get it 180 degrees off, though this shouldn't cause the zero compression and may possibly cause valve strike depending on clearance and compression ratio.
(the good reason for always turning two full revolutions by hand before spinning on the starter)
i.e. if you have minor valve strike but not enough to notice it you can bend the valves, the valves don't seat properly and you lose compression, guess how I found that out, well technically it wasn't quite like that I had a valve strip it's collets and 'drop' onto the piston crown bending it.
Another thought albeit not a nice one, hope it's not that!
That said the clearances shouldn't have allowed a shim to fall out of the bucket, removing and changing them requires a bolt on compression tool to compress the bucket, possibly buckets sticking in the bores?
I'd certainly whip the rocker cover off and check them again to be sure, don't mean to offend but is there a possibility that you've confused your guage type? mm - in
First time I set clearances I recall confusing the two and winding up with a gap big enough to park a family hatchback in.
just occured, the flipside of the OHC engine is the incredibly easy ability to get the valve timing way out when refitting, it easy as anything to get it 180 degrees off, though this shouldn't cause the zero compression and may possibly cause valve strike depending on clearance and compression ratio.
(the good reason for always turning two full revolutions by hand before spinning on the starter)
i.e. if you have minor valve strike but not enough to notice it you can bend the valves, the valves don't seat properly and you lose compression, guess how I found that out, well technically it wasn't quite like that I had a valve strip it's collets and 'drop' onto the piston crown bending it.
Another thought albeit not a nice one, hope it's not that!
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kev edwards
- Hardcore
- Posts: 1487
- Joined: 3rd Apr 2009
- Location: leverington UK
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dreadmanbastard
yes rings are right way up i made sure when installingt. as far as i can tell i did everything right. i tried this morning with throttles open. still no compression, with oil and without. nil, nothing. im stumped. i checked my valve clearance, all fine. tightened head bolts all fine. maybe i should spray wd40 all over the engine to assertain if there is a leak.
what i have done, is taken the oil breather mechanism of pipes out. and there is alot of air pumping out of there. could i have done something wrong in removing that?
what i have done, is taken the oil breather mechanism of pipes out. and there is alot of air pumping out of there. could i have done something wrong in removing that?
no compression is usually one of 3 things ..............
rings - for NO compression they'd have to be almost missing.
Valves - bent or timing way out.
compression tester - broken.
I hope its the last one but I'm fearing the second. It doesn't take a lot to ding/bend a valve or two if you get the timing wrong - see the thread by bigmac103 with photo evidence to prove it......
rings - for NO compression they'd have to be almost missing.
Valves - bent or timing way out.
compression tester - broken.
I hope its the last one but I'm fearing the second. It doesn't take a lot to ding/bend a valve or two if you get the timing wrong - see the thread by bigmac103 with photo evidence to prove it......
This must be doing your head in! I am no expert but:-
Have you tried a different compression tester? Or check the one you are using on a different engine to make sure its working ok?
I am trying to remember from previous thread, was there a pic of pistons, and did someone raise the point they looked like low comp. turbo pistons? If this is the case is the compression tester you are using able to go low enough?
Have you checked cam timing?
Taking the breather pipes out should not matter, fact there is air pumping there suggests problem is with top end not pistons, rings I think.
The gasket , piano wire set up isnt leaking is it?
Did this engine run before with these components in or have you built it up from scratch?
Have you tried a different compression tester? Or check the one you are using on a different engine to make sure its working ok?
I am trying to remember from previous thread, was there a pic of pistons, and did someone raise the point they looked like low comp. turbo pistons? If this is the case is the compression tester you are using able to go low enough?
Have you checked cam timing?
Taking the breather pipes out should not matter, fact there is air pumping there suggests problem is with top end not pistons, rings I think.
The gasket , piano wire set up isnt leaking is it?
Did this engine run before with these components in or have you built it up from scratch?
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dreadmanbastard
whats the piano wire set up?
the engine was running fine expet for oil in number 2, and bad carberation.
i turned the engine by hand after rebuilding, seemed fine,. ill have to take the head off i think, its the only way to have a look see.
the compression tester was working prior to dismantaleling engine.
i was getting 200psi.
its something strange cause its all four cylinders on zero compression. not one or two.
timing is a black space in my knowledge. i can check the point on the front cam and count the 28 links. fine. but the dyna black thing and the numbers behind allude my comprehention. as does spelling
the engine was running fine expet for oil in number 2, and bad carberation.
i turned the engine by hand after rebuilding, seemed fine,. ill have to take the head off i think, its the only way to have a look see.
the compression tester was working prior to dismantaleling engine.
i was getting 200psi.
its something strange cause its all four cylinders on zero compression. not one or two.
timing is a black space in my knowledge. i can check the point on the front cam and count the 28 links. fine. but the dyna black thing and the numbers behind allude my comprehention. as does spelling
Ignition off 
Sorry getting yours mixed up with hillbillys hence referance to pistons and piano wire.
This may help with cam timing
http://www.z1ownersclub.co.uk/forum/vie ... cam+timing
This may help with cam timing
http://www.z1ownersclub.co.uk/forum/vie ... cam+timing
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kev edwards
- Hardcore
- Posts: 1487
- Joined: 3rd Apr 2009
- Location: leverington UK
200 psi???Are you running a high compression engine or is it standard?No standard 900 engine would get that high. If it is standard then check your tester. Even if you had the rings fitted wrong you would get some compression.You say you have tightened the head down properly so its not that. Are you sure the valve timing was right? As said in a previous message, if your tappet clearances are right it is unlikely you have bent the valves. That said it sounds like a valve timing issue to me. Zero compression is very unusual so my money is on valve timing.
Gez
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dreadmanbastard
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