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+--- Thread: Cylinder Compression... (/showthread.php?tid=77557)
Cylinder Compression... - anutz - 04-03-17
Hi,
I have been having issues with the bike just not feeling like its got the power it should have....
It also seemed hard to start, always needs full choke and even after warming a little is easy to stall, unless its been ridden for a while and its red hot...
I have checked a few things, Carb Sync, all but one are spot on, cylinder 3 shows a little less reading than the rest, 20 less, so is an issue there.
I also took the chance to measure the cylinder compression and get from 1-4 readings of 110, 100, 115, 102, so varied and well off what the service manual states.
Will be trying to pop some oil in the cylinders tommorow or Monday see what a re-test shows.
Engine has done 47K, and i had to replace the Water Pump and rear wheel bearing when i got it, not well looked after...
I also changed all exhaust studs and replaced the cylinder head gasked whilst in there, replaced spark plugs also.
Anyone any comments, do these readings seem well out or reasonable for a bike of this mileage/age
Anutz
Re: Cylinder Compression... - ram - 04-03-17
when you changed the gasket did you see any obvious wear on the bores?
have you checked the valve gaps? if tight they could have burnt the seats
oil test should show if valves or bores but i think valves
Re: Cylinder Compression... - anutz - 05-03-17
bores looked fine, no obvious signs of issues, looked nice and well honed
will be doing some more checks Monday i think..depends on time tmrw
will do an oil test and then check clearances, its one thing i have not done yet, clearances.
Re: Cylinder Compression... - old son - 05-03-17
A stealer told me that too tight clearances cause poor starting. Maybe that is the cause of your issues?
Re: Cylinder Compression... - tommyardin - 05-03-17
Question:
I ask because I do not know, the last time I had a cylinder head off a motorcycle Noah had not started building his ark.
When you replaced the head gasket did you set up the valve clearances afterwards?
Not sure how it works nowadays but after an initial bedding in period the head use to have to be torqued down again and the valve clearances reset. I don't know if this applies to modern engines or not., but on my old BSA Super Rocket of many years ago this was the case, mind you that was a push rod engine with under-slung cam shaft.
The top end was serviced I.e valves and compression tests on my FZS when I bought it as apart of the purchase service.
Re: Cylinder Compression... - tommyardin - 05-03-17
Dunno if this helps Haynes manual info.
Re: Cylinder Compression... - fazerscotty - 05-03-17
If a cylinder is showing approx 100 psi it could be well poorly.
When you describe the bores as well honed, do you mean polished shiney or can you see faint cross hatching marks?
Re: Cylinder Compression... - unfazed - 05-03-17
(04-03-17, 07:55 PM)anutz link Wrote: Hi,
I have been having issues with the bike just not feeling like its got the power it should have....
It also seemed hard to start, always needs full choke and even after warming a little is easy to stall, unless its been ridden for a while and its red hot...
I have checked a few things, Carb Sync, all but one are spot on, cylinder 3 shows a little less reading than the rest, 20 less, so is an issue there
I also took the chance to measure the cylinder compression and get from 1-4 readings of 110, 100, 115, 102, so varied and well off what the service manual states.
Will be trying to pop some oil in the cylinders tommorow or Monday see what a re-test shows.
Engine has done 47K, and i had to replace the Water Pump and rear wheel bearing when i got it, not well looked after...
I also changed all exhaust studs and replaced the cylinder head gasked whilst in there, replaced spark plugs also.
Anyone any comments, do these readings seem well out or reasonable for a bike of this mileage/age
Anutz
Did you have the throttle opened full when doing the compression test and kept it spinning until the gauge did not go any further. Those figures are like ones you get with a closed throttle
The engine is pretty robust and a few have gone well past the 120000 mile mark.
Re: Cylinder Compression... - anutz - 05-03-17
Hi All,
thanks for the input...
when i did the head gasket i just noted where the shims were i did not re-check it all, i only did the gasket due to removing the head to get all studs removed and replaced with SS, so was not looking at a running issue.....but it had a difficult start, i got it with other issues and they took priority, only now have i had chance to realise there is an issue with the engine
unfazed, when i did the test i have the carbs off, is this a stupid mistake or is that ok, i figured it would make no difference but may be wrong?
I am going to try some oil soon in each barrel, but they are darn low figures....especially in relation to what tommy posted....
the low compression explains the crap starting and less than what i expected in terms of brute power.
Re: Cylinder Compression... - unfazed - 05-03-17
having the carbs off was perfect for doing the compression test, no restrictions :thumbup
Oil in the bores will tell if cylinder or valves are the issue
Re: Cylinder Compression... - anutz - 05-03-17
OK i am gonna do all the tests again, to be sure, with no oil and then with a pipette of oil, i actually hope they don't change, as i am thinking a few un-seated valves due to wrong clearances will be easier to fix, unless they are burnt and there are other issues, anyway getting ahead of myself here...
shall report back with pics and a video i hope once i have these tests done
Re: Cylinder Compression... - anutz - 05-03-17
So done cylinder 1 and 2, and no difference, actually got worse a tad on cylinder 2, stopped now to let battery re-charge.
Assuming i now need to go check valve clearnaces and see if they are too tight i.e. shim too big and so holding the valve off its seat...
Will get coolant drained so i can get the water pipes sticking out of the head disconnected etc
:b
Re: Cylinder Compression... - fazerscotty - 05-03-17
A quick method to find where the compression is going is to carry out a leak down test.
Cylinder at TDC (you may have to hold the crank with a spanner) then feed approx 80 psi into the cylinder (convert a spark plug to take an air line). If the rings/bores are worn you'll hear the escaping air from the crankcase breather/oil filler, if its an exhaust valve you'll hear it from the exhaust etc.
Years and years ago I had a GS550, which one day refused to start - checked the compression's and they were all around the 100 mark, which is not enough to encourage combustion. A rebore on all pots had the wee beasty running sweet again.
Re: Cylinder Compression... - anutz - 05-03-17
thanks fazerscotty, would i not see pickup in pressures with the oil trick here?
If it is a re-bore job then its going to be a real carry on as i don't think the barrels can be removed like on the fzs 600....
I will check the clearances and make sure they are perfect, if not i will get them sorted and re-test, hoping it does the trick...
Re: Cylinder Compression... - anutz - 05-03-17
(05-03-17, 06:59 PM)fazerscotty link Wrote: A quick method to find where the compression is going is to carry out a leak down test.
Cylinder at TDC (you may have to hold the crank with a spanner) then feed approx 80 psi into the cylinder (convert a spark plug to take an air line). If the rings/bores are worn you'll hear the escaping air from the crankcase breather/oil filler, if its an exhaust valve you'll hear it from the exhaust etc.
Years and years ago I had a GS550, which one day refused to start - checked the compression's and they were all around the 100 mark, which is not enough to encourage combustion. A rebore on all pots had the wee beasty running sweet again.
I have an old air compressor so i may have a look at this
Re: Cylinder Compression... - anutz - 05-03-17
still to check the clearances but for info, how much does a re-bore cost, and would you need oversized piston rings once its re-bored, or do the normal rings just push out a fraction more to seal etc
Re: Cylinder Compression... - Graham53 - 05-03-17
Tommy posted the compression figures from the 600 , these are the ones from the 1000
Dont know why it came out sideways , bloody camera phones
Re: Cylinder Compression... - The Male Whale - 06-03-17
Valve clearances.
I will add an explanation why:
Adding oil to the bores will put up the compression by temporarily sealing the gap around the rings.
It won't seal a leaky valve caused by poor clearances.
Whale
Re: Cylinder Compression... - tommyardin - 06-03-17
(05-03-17, 10:30 PM)Graham53 link Wrote: Tommy posted the compression figures from the 600 , these are the ones from the 1000
Dont know why it came out sideways , bloody camera phones
Doh!
Re: Cylinder Compression... - sirgalahad3 - 06-03-17
All the problems described could be caused by incorrect valve timing. As the cylinder head has been off check and check again.
That's timing, not valve clearances.