Cylinder Pressure

freddie 136 · Post by **freddie 136** » Fri Jul 04, 2008 8:59 pm

Hello again, Just been testing the cylinder pressure on my G11[ 600cc ] Does any one have the pressure in lbs sq inch please from there engin rebuild, With the engin hot and throttle full open and one good kick i got 85lbs in R,h,cylinder and 90 lbs in L,H, one does this sound o.k. or is it a bit on the low side, any help appreciated,cheers Fred

Biscuit · Post by **Biscuit** » Fri Jul 04, 2008 10:07 pm

Quite a lot has been written on this near irrelevant topic. Do a Forum search (compression pressures/cylinder pressures- all members)

clive · Post by **clive** » Fri Jul 04, 2008 10:53 pm

Alan, this is a relatively new club member judging by the number of posts. Your information is always helpful, sad it tends to have a negative edge. Not all of us understand the concept of a forum search even if we can post messages. Helpful of you to tell people hown to do them but negativity can put off new members and we need everyone we can to keep the club vibrant. If you are bored by the questions raised on the site perhaps you should get out on your bike more and on the computer less?

bjork · Post by **bjork** » Sat Jul 05, 2008 12:56 am

Hang on Clive, Alan is just playing his regular part of the 'Straight man' , Itma will be along shortly with the punchline. Timing is everything in comedy you know!

GSAX1 · Post by **GSAX1** » Sat Jul 05, 2008 10:21 am

Hi Fred. One kick is not enough to give correct readings. Make it 4-5 kicks. Have someone to hold the bike while you kick it . You should be looking for a compression of 125-150 PSI max. Both cylinders should be equal (ideally).

Hope this helps.

MichaelEdited by - GSAX1 on 05 Jul 2008 09:23:22 AM

itma · Post by **itma** » Sat Jul 05, 2008 12:30 pm

leave me out Bjork

my advice is be gentle with the poor bloke, we have enough to deal with with one worrier, our very own fishy

freddie, stop worrying, as long as both cylinders are more or less the same forget it, as long as it runs sweet, 10PSI or 100 its as the man says, irrelevant.
If you are looking for somethin to worry about,
turn tellie on.

bjork · Post by **bjork** » Sat Jul 05, 2008 1:28 pm

quote:
leave me out Bjork

my advice is be gentle with the poor bloke, we have enough to deal with with one worrier, our very own fishy

freddie, stop worrying, as long as both cylinders are more or less the same forget it, as long as it runs sweet, 10PSI or 100 its as the man says, irrelevant.
If you are looking for somethin to worry about,
turn tellie on.

Sorry Ken, just couldn't resist the urge to drop you in it. Good punch line/catch phrase all the same!

As for the answers to the original query, it's difficult as pointed out above, to get a meaningful reading. You need to keep turning it over till the needle stops rising. Electric starters help here, and if it takes many turns of the motor to bring the reading up that suggests problems too.
A much more meaningful test is a cylinder leak test, but for this you need even more equipment. The idea is, set piston at TDC on compression stroke-both valves closed-and with the crank locked to prevent it rotating, apply compressed air via the plug hole. Then you listen/look around for clues as to where the air is leaking. I'ts easy for example to listen to the exhaust pipe to check the exhaust valve and open the throttle to listen if it gets past the inlet. Then listen to the breathers to see how much of it gets past the rings. Head joints are easy to check too.

To do this you'll need a compressor or a charged portable air tank, a spark plug adaptor that can be made up using the fittings from your compression tester, hoses and connectors and some way of stopping the crank from turning-plenty of obvious ways of doing that. If you buy a test kit ready made, they come with clocks to tell you the pressure differential between cylinder and supply and charts to tell you how much leakage is acceptable. All great ways of justifying the price tags of something you can mackle up in your shed.
In the end though, is all worth it? I dunno. It can provide lasting memories if you try doing it on the sidestand with the engine in gear. Warning-your investment can go backwards or forwards, and you won't have time to do a thing about it! Hilarious, and no, it wasn't me this time. I bet you've done the job by now though? Yes, you can worry too much, the internet is great for that-you end up with loads of waffle written by well meaning do-gooders that only makes you wish you hadn't asked- they do go on a bit sometimes, don't they? Not like workshop manuals that at least were written by factory staff or contractors with relevant knowledge and experience. Hope your bikes ok and/or easily fixed.

Steve

freddie 136 · Post by **freddie 136** » Sat Jul 05, 2008 4:40 pm

Thanks chaps for the answers, don't want to start any arguments between you people, i am new to this forum but not to biking, so you can treat me rough , Had a few bikes, but this is my first matchles. Reason for my question was that i am a bit dissapointed with the speed of the 600cc engine [not that i need the speed as i have a more modern Triuph as well ]but i thought i would check the pressure in the cylinders to see what you knowlegable chaps would come up with, thanks for the answers, Fred

bjork · Post by **bjork** » Sat Jul 05, 2008 6:35 pm

After all that, the figures you quoted wouldn't actually be bad for one kick. So probably nothing to worry about there.
It might be worth pointing out that these twin engines are meant to be more of a 'revver' than a slogger, and don't seem at all lively at low revs. Even compared to other british twins they feel a bit lacking, but if revved a little they cover ground quite respectably.
Don't worry about starting arguments either, it's the norm round here and we all love each other really all round.

Steve

lawrence · Post by **lawrence** » Sat Jul 05, 2008 8:56 pm

Fred seems a sensible young lad. I don't think he'll be scared off.

It's not as if Alan was rude. He simply stated the facts in a businesslike and helpful way. None of us here are public relations managers

Lets all stay mellow