Advice on compression readings...

Hi,

(bike: KZ750-R1 aka GPz 750 1982)

Before doing winter maintenance in a few months i decided to give a try with the engine compression tester.
I know i need to change the head gasket (little oil leaking at the oil passage on the side and the valve cover gasket)

Check out the readings:

Cyl by number

#1: 150 psi, #2: 121 psi, #3: 156 psi, #4: 145 psi

I put a teaspoon of oil in the cylinder #2 to check the rings.... pressure as increased to 152 psi on the second try... that's mean the rings on the piston #2 are shot ? The bike has only 21 000 miles!

Manual says usable range between 124 - 191 psi and less than 14 psi difference between any 2 cylinders.

What do you think ?

best regards,

laurent

Without accomplishing a leak down test...
run her as is....

Leak down test could inform you maybe a valve seat leaking a tad or so.... If your not blowing smoke, sparkies look good, performance within specifications, she idles, pulls hard etc... again run her....

Just my 2 worthless cents...

Leak down test could inform you maybe a valve seat leaking a tad or so.... If your not blowing smoke, sparkies look good, performance within specifications, she idles, pulls hard etc... again run her....

- I'm not blowing any smoke.

- By looking at the spark plug idle seems rich and leaking oil inside all the four cylinders a little bit (valve guide seals maybe...these dries with age) and at WOT mixture is #1 (nearly white insulator just a faint of brown)

- i don't know if it's performance is nearly the same as new... never ridden a bike in 1982 ... jeez i wasn't even born. :laugh:



For the winter maintenance i will have the top end rebuilt (valve seals,valve clearance check, valve lapping if needed) cam chain slack, valve cover gasket and head gasket changed.

I think this should improve a little bit the engine overall.

EDIT: btw, i know it's offtopic but OMR i think you've saw alot of vintage bike in your life... In average how long does these kawa engines tend to last (in miles) before going very major rebuild (crankshaft bearing changed, tranny rebuild etc etc)?

thank you very much!

best regards,
laurent

The factory specs on compression are for a hot engine, not cold and dry. I think yours will be a lot better tested hot. If it runs OK, ride it.

Maw Kaw overengineered these old bikes.Ride em until something major breaks,THEN worry about a major overhaul.Keep the maintenance up, ride sensibly and the bike may outlast you.bj

The factory specs on compression are for a hot engine, not cold and dry. I think yours will be a lot better tested hot. If it runs OK, ride it.

you are right, make sense to check it while it's hot.
I will do that tomorrow.

Maw Kaw overengineered these old bikes.Ride em until something major breaks,THEN worry about a major overhaul.Keep the maintenance up, ride sensibly and the bike may outlast you.bj

I will do my best to keep her running on the road in a good healthy condition

thanks guys for your help!

regards,
laurent

I got this from www.kawasakimotorcycle.org

Kawasaki Valve Clearances

83 Kz1100 D spectre help with valve, emissions, etc

100PSI will light it off , 125PSI will run reasonably well , 150PSI will run well , 180PSI is about a fresh engine.
all readings are cold with a fully charged battery and dry (no oil in cylinders .

Valve adjust can drastically affect cranking compression .
in thousandths of an inch anything less than .005" put the next thinner shim in .
.008" is about the max clearance . .006" if you like to check often . Any less and you risk closing up a valve through inattention and covering up a marginal valve clearance with carb sync , ignition advance and idle adjustment until you actually hold a valve open . Translation ? neglect your valve adjust = $$$ .

Refer to the FACTORY MANUAL for the procedure . Remember to back off the tensioner before replacing the cam cover and replace after the cover is tightened down . Think about that for a moment .

ELCouz wrote:

Hi,

(bike: KZ750-R1 aka GPz 750 1982)

Before doing winter maintenance in a few months i decided to give a try with the engine compression tester.
I know i need to change the head gasket (little oil leaking at the oil passage on the side and the valve cover gasket)

Check out the readings:

Cyl by number

#1: 150 psi, #2: 121 psi, #3: 156 psi, #4: 145 psi

I put a teaspoon of oil in the cylinder #2 to check the rings.... pressure as increased to 152 psi on the second try... that's mean the rings on the piston #2 are shot ? The bike has only 21 000 miles!

Manual says usable range between 124 - 191 psi and less than 14 psi difference between any 2 cylinders.

What do you think ?

best regards,

laurent

i would consider, redoing the compression test before u tare it apart. just to verify that it was done right the first time, unless u already verified #2.
things can go wrong during the test. the gauge may not have been sealing properly for example. did u have the throttle wide open during the test? it should be. and redo all cyls with oil as well.
if #2 is still down, it would be nice to address it if u are going to take the head off anyways.
Has the bike ever sat for years unused? u may just have sticky rings in #2. u could try and engine cleaner like Seafoam.
Otakar, has a good eng cleaning meathod as i recall.if u want to do a good cleaning send him a PM.
Good luck
Mark.

Here's a Yamaha product created to free stuck piston rings:

www.amazon.com/Yamaha-Ring-Additive-32oz...-32-00/dp/B002GUCLH2 (Yamaha Ring Free)

I'd try spraying some PB-Blaster in the sparkplug holes,re-install the plugs, and let sit for a few days, then do a re-test before tearing into the engine.

For the piston rings stuck... I've ridden my bike for nearly 1000 miles since i bought it... would that release the sticky rings ?

Also, you think beside pressure lost I'm scratching my cylinder walls because rings cannot rotate as they wish?

regards,
laurent

ELCouz wrote:

For the piston rings stuck... I've ridden my bike for nearly 1000 miles since i bought it... would that release the sticky rings ?

Also, you think beside pressure lost I'm scratching my cylinder walls because rings cannot rotate as they wish?

regards,
laurent

well lets not jump to conclusions. it may not be stuck. i'm just suggesting a simple remidy that MAY help IF the rings are stuck, they may not be.
1000miles may or may not release the ring? who knows, did the bike even sit for a long time?
i i dont think u will scratch the wall with the ring. if the ring is indeed stuck,it is not aplying preasure.

1000miles may or may not release the ring? who knows, did the bike even sit for a long time?

around 23-24 years but has been ridden once or twice in the last 5 years (new set of tire and the bike required no carb cleaning starting like a champ)

Also I've rescued just in time this bike from major problem the PO has already let the girl get covered in snow for 1 season.

Back to your suggestions guys, I've put a little bit of PB Blaster inside #2 but i was so excited to test if it would make a difference I've only waited half an hour before starting the girl. After an hour long ride pulled the spark plugs while it was hot like a freshly baked cake did the compression test.

The result are nearly the same for all cylinders +/- 1 or 2 psi.

I will put PB Blaster for a few days in all cylinders and test later if it helps.

BTW, i hear some valve clicking while riding maybe clearance is out of tolerance BUT i don't think it's my problem since i've put a teaspoon of oil in #2 cylinder that increase dramatically the pressure to 152 psi.


any ideas on that?

Wish you a very nice riding season to all!

Regards,
laurent