Fazer Owners Club - Unofficial

General => General => Topic started by: ogri48 on 29 June 2014, 09:19:40 pm

Title: Compression test readings..
Post by: ogri48 on 29 June 2014, 09:19:40 pm
I'm a tad confused..bikes running great but cylinder compression readings aren't particularly high, in fact they are low..110 hot. Would the cv carbs mean holding the throttle open to get air in is ineffective? Would it make more sense to get me local bike shop to do a leak down test? Just done it again with oil in the bores and it went up about 20 psi..is that bad? Was fun burning off the oil even if I couldn't go lairy in norwichs leafy suburbs..
http://youtu.be/aKMW-wKjKJg (http://youtu.be/aKMW-wKjKJg)[/t]
Title: Re: Compression test readings..
Post by: red98 on 30 June 2014, 06:57:48 am
morning ogri.......ummmm.....the oil in the bores trick is to check for worn rings,as you probably know.the oil will temporarily seal any gaps between the rings/pistons and bores and give you a higher reading,if theres no change when using oil and you have a low reading the valves are to blame...assuming the head gasket is ok....not got a good screen at home but as i look at your vid do i see a faint plume of smoke or is that my fading eyesight  :rolleyes ....whats the reason for you doing a compression test ?
Title: Re: Compression test readings..
Post by: TonyW on 30 June 2014, 10:33:51 am
The 20psi change does show a reasonable amount of wear on the bores/rings but not massively so. The 110psi is very low though if the bike isn't smoking or lacking power. I'd check the gauge against another in case its faulty. Also what are the valve clearances like? Too loose or tight will drop the pressure without smoke (power would be down though)
Title: Re: Compression test readings..
Post by: ogri48 on 30 June 2014, 07:09:23 pm
Cheers guys yeah it's smoking a bit.. However..was building a wall fir a mechanic mate in warboys today, he pointed out the bike was dry stored for twenty years, then re commissioned three years ago but hardly used since..he's saying redex in the bores for a coupla nights, then just use the bugger..reckons some decent miles on it will free up the rings if there a bit gummy and bang the valves down to seal them better. I will check valve tolerances though mate, should have done that as a matter of course. Only checked the compression because I will probably have to sell it to fund some spraying gear once it's painted, and want to make sure it's all good :)
Title: Re: Compression test readings..
Post by: ogri48 on 30 June 2014, 07:11:11 pm
Quote from: TonyW on 30 June 2014, 10:33:51 am
The 20psi change does show a reasonable amount of wear on the bores/rings but not massively so. The 110psi is very low though if the bike isn't smoking or lacking power. I'd check the gauge against another in case its faulty. Also what are the valve clearances like? Too loose or tight will drop the pressure without smoke (power would be down though)
Yeah, it's an old gunson, mate has a real good quality one I'll borrow that once I've got some miles on it and see what it says
It's smoking a bit, but not excessively. I was concerned because the plugs didn't seem that old in it but were fucked, so thinking maybe oil was getting to them and knocking them early.
Checked the lv side of the coils shows 11.8 volts where the batteries showing 12.7.. I know there's a common mod to use relays to get the full voltage to the coils without the slight voltage drop old wiring gives..do you think it's worth doing or is 11.8 about right? 
Having an old bike to work on is teaching me more about bikes than all the modern stuff I've had fir the past twenty years..
Title: Re: Compression test readings..
Post by: sadlonelygit on 30 June 2014, 07:51:39 pm
do you know what the cr is for that engine.
yank spec motors tended to have low comp pistons
time to get the syringe out :b
Title: Re: Compression test readings..
Post by: ogri48 on 30 June 2014, 08:06:46 pm
No I don't mate, but I've joined the z1 forum hoping to glean a lot of info from that..I know it originally had a 80 mph speedo and a berluddy great 46 tooth rear.. :)
Title: Re: Compression test readings..
Post by: sadlonelygit on 01 July 2014, 10:42:01 am
bike on sidestand
no4 plug out and find TDC
fill cylinder with oil to bottom of threads with syringe noting how much you put in.
998/4 + volume of oil/volume of oil...................simples.

remember to suck out the oil afterwards otherwise the motor don't turn over :rolleyes
Title: Re: Compression test readings..
Post by: ogri48 on 01 July 2014, 07:08:35 pm
Aaa I get it...Oakley dokely mate. Found on a website comp ratio is 9.2-1 stock...is that lowish?
Title: Re: Compression test readings..
Post by: TonyW on 01 July 2014, 08:29:27 pm
Fairly low for 2 star fuel. Compression pressure on a z1 should be 130-160psi.

Assuming the valve clearances are set right:

If its been stood it could just be gummed up rings or even corrosion on the valve seats if it wasn't laid up properly. Take the plugs out and drop a thimble full of diesel down the bores. Just enough to cover the top of the piston. leave it overnight it will act like penetrating oil and hopefully break free the rings if they are stuck. Make sure you spin over the engine to get any left over diesel out before refitting any of the spark plugs. Bare in mind that most of the diesel will end up in the sump so you either do an oil change afterwards or on the cheap just drain the oil into a clean container the pour it back in afterwards.

Run it for a few days at various loads and speeds then do another comp test to see if there's an improvement.
Title: Re: Compression test readings..
Post by: ogri48 on 01 July 2014, 09:23:34 pm
Good advice mate I'll take it..just changed oil and filter for expensive semi synth so I'll drain that off first...
Title: Re: Compression test readings..
Post by: unfazed on 02 July 2014, 12:00:08 am
Quote from: sadlonelygit on 01 July 2014, 10:42:01 am

remember to suck out the oil afterwards otherwise the motor don't turn over :rolleyes

 :lol Would not be the first to forget it.

I have a Z1 full service manual for the Us and Europe models, (downloaded by mistake a few years ago when I was looking for the GPZ900 manual).

Compression ratio is 8.5:1 and Compression when hot is 121psi
See below