Compression testing

[reds]

Got teh bugger in teh post today - loads of a daptors etc.... had a look in manual too at top end section - do i screw the end of the compression tester into where the spark plug should be ?

[masterofinsanity]

yes mate, and you are supposed to remove the wires from the cdi or coils to stop it firing up otherwise bang goes your compression tester, read the instructions i think you have to have the engine slightly warm too.

[reds]

nothing in manual about unhooking CDI - but its not very detailed to say the least !!!

says to warm engine, and also hold throttle full open as you crank the starter - (i assume this means ignition switch ?)

when / if i come to do cam chain / headgasket i assume i am best of stripping it all down to the head, and then replacing gasket, then when re assembling put in a new cam chain - is there anything else thats worth replacing whilst ive got it all in bits ???

[reds]

cocking compression guage doesnt have an adaptor that fits theres two their but both much too big - bollox

did notice however, and need to ask about oil level.

when cold / stood upright, oil in bubble is close to max line - however whilst i was running engine to warm it, tilted the bike upright and the oil is right at the lower level - possibly under - should i top up, im pretty sure the manual says to take the reading when the engine is cold though !

[extonyg]

you should check the oil level with the engine running!!as the oil is traveling around the engine and not sitting in the sump, if it was at max without it running then its ok.
the oil level will always be slightly higher when the bike is warmed up as the viscosity of the oil changes it becomes thinner.

[extonyg]

sorry that should say ......'should NOT check'.......

[RedexRobB]

cocking compression guage doesnt have an adaptor that fits theres two their but both much too big - bollox

Im sure you can get one for bikes, im sure Gunsons do them.

[reds]

going to have a look in motorfactors tommorw, may try b+q too as when typed compression adaptor into ebay loads of plumbing bits came up

dont know if i could drill out one of the old spark plugs to use, as the guage itself slots over the adaptors, and its not a particulary tight fit

[masterofinsanity]

my compression tester was a gunsons and fitted the zxr400

[reds]

its a 10mm thread, kit i got came with 14 and 18 !!!! so need to get an adaptor, which costs half of the cost of the whole set (£10 !)

any idea how much a new head gasket will be ???

[reds]

anyone local (west mids) got a 10mm extension i could borrow just to test it quickly ? cheapest adaptor i could find was £23.99 !!!! and halfords only had the gunson tester with 14mm and 18mm ends

[tk400]

How are you going, when choosing a compression tester for small capacity cylinders like the 400, Be sure that the schrader valve (check valve) is located in the fitting that actually threads into the head. Ideally this fitting will be a dummy sparkplug, As you do not want to decrease the comp ratio by using a fitting that either does not protrude far enough down the spark plug socket or does not have the check valve in this fitting.
All volume before the check valve will effect the comp reading, so if you use an extension to get down into the plug area this will reduce the comp ratio if there is no valve in it at the end. For this reason it also important to crank the engine a reasonable amount of times so that the volume after the check valve is at a pressure reasonably close to the actual max reading before you take the reading.
This is why the comp gauge increases in what appears to be stages. Of course you could just use what ever setup but you will then not be able to compare to the manual as a reference, you would at least be able to compare cylinders I suppose. cheers.

Regards TK400

[reds]

Seems to be fixed !!! thanks for all the help.

Checked the compresson ratio (after finally tracking down a 10mm compression tester (QB bikes in Quarry Bank - god bless em) all 4 cylinders were firing out at 100 psi - which is just within the limit ! so dont think its head gasket - thank god. Figured the compression would be higher in reality, was trying to get bike warmed up but next door neighbour come to ask not to make noise as they had a "dieing child trying to sleep" suffice to say i didnt keep the engine running, so figure compression would pos be a bit higher ???

Anyway - started to look around radiator etc.. for issues, giving the fittings a good yank, did it to the thermostatic fan switch, and it just came off in my hand ! had completly corroded and one of the plugs had snapped off. went to cradley for a new one (£34 with the 10% members discout - nice one baz) fitted it, and drained coolant. Took the bike on a 10 mile razz and no issues at all with overheating, stayed within the first two white lines, no issues

weirdest thing of all is the odd rattling, that i thought was cam chain (between 4-5K revs) has now also disappeared. Dont know if this is anything to do with the thermostatic valve - or if its a loose bolt or similar on fairing - as i went out on it yesterday without re-attaching the fairings !

so thank good its all done ready for bulldog in a couple of week

thanks all, especially baz and rob for all the input / help

[tk400]

My post above may explain your low comp result...

[saka_ZXR]

Although probably not advised i was incredibly low on funds at the time so just used the halfords gunson tester with the 14mm adaptor and just held it down tight! the compression read correctly. I then took the tester back to halfords for my money back as i was stone broke at the time and that £20 was my petrol money for a month I was looking at adaptors but halfords had to order one in which would have been like £15 and i only had 4days to find out if the head gasket needed replacing