Advice on compression readings...

When you do your work, pull the jugs+pistons and have them checked for barrelling/warp. You may need to have them bored over + new pistons + new rings.

Or not...

GL.

When you do your work, pull the jugs+pistons and have them checked for barrelling/warp. You may need to have them bored over + new pistons + new rings.

I hope not :ohmy: since it's a low mileage bike !! /me is going to pray for the best until the winter maintenance


regards,
laurent

"EDIT: btw, i know it's off topic but OMR i think you've saw alot of vintage bike in your life"...

Actually no I haven't in the KZ family... I have ridden motorcycles most of my 52 years yes but I have been extremely fortunate in the friendships I have developed here regarding KZ's...

I also have a weird brain (electronics engineering :S) where I

research & study

the manuals/literature and discuss it (theory and mechanics) with the guys who truly know these beautiful machines...

Guys like Plummen & Larry Cavanaugh (main mentors and life long friends) and Steve, Craig, Greggy-Poo, Sax, Mark Saunders, Sandy, timebomb just to mention a few who have become really good friends as well share their knowledge and experience with me...

Then there's Patton, Loudhvx, BountyHunter, Mfolks, Tekie9, Otto etc... who provide accurate advice....

As I have mentioned in numerous tech writings... All I'm doing is passing on what these guys where so kind enough to share with me... The rest is what I learned on my own (Dupli-Color painting/mod fabrications) & witnessed while going through the process of accomplishing what I learned from them.

Stick around awhile and you'll learn as well who to truly listen and pay attention to when they speak/write.
Studying (not just reading) the OEM service manuals provides pretty much everything you need...

As far as wear and tear... depends on way too many factors to say... Keep in mind, some of these old girls are 30 years old going strong... Proper & scheduled lubrication, maintenance and tuning, riding style etc... and she'll go another 30 years...


OMR

If the pressure didnt change with oil you have to tear it down. Probly rings. could be an exhuast valve with a beat up seat. Just took a head apart 10mns ago and see this alot. It's likely it's the rings, that's alot of miles. Whenever u do take it apart try rocking the piston kiddy corner in the bores without the rings. If they rock this way and even if they dont't rock back and forth (skirt to skirt) the bores and likely the pistons are shot too.

If the pressure didnt change with oil you have to tear it down

Pressure did change drastically with a teaspoon of oil. I will finish my season then I'll tear it apart anyway

One thing i like with the KZ750-R1 frame variant you have much clearance to work on the engine.It's basically the same frame as my KZ550 1983 spectre but the main tube is in the way when working on the engine head. I guess they did this to accommodate a larger fuel tank (13L vs 21L).

ELCouz wrote:

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

regards,
laurent

The rings don't rotate they stay where you put them, hence the reason they are carefully aligned at installation.

bountyhunter wrote:

ELCouz wrote:

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

regards,
laurent

The rings don't rotate they stay where you put them, hence the reason they are carefully aligned at installation.

If that's true then why do two strokes have pins in the ring lands to keep the rings from rotating and lining up a ring end in the ports?

Rings "can" rotate, there's nothing to stop them.

___________________________________________________________________

And back on the original subject, just how many compression tests have you folks done?

I've done a few hundred and what I'm reading here is not jiving with my experience.

31 psi increase in compression after adding oil is nothing, if the rings were worn the oil would have upped the compression to 170-200 psi.

I have never seen a KZ motor wear rings unevenly, if you have worn rings in one cylinder you have them in all cylinders.

Low compression in one cylinder indicates valve leakage, combined with the minimal 31 psi increase after adding oil nails it.

As a learning experience for my nephew (I believe in hands on training), we did compression checks on five KZ's one Saturday.
Checked compression stone cold, then rechecked compression after the motor had reached operating temp. In every case there was an average 10 psi increase between cold test and hot test in each cylinder.

Had a KZ650 motor that someone gave me that had over 100k miles on it. Cold compression test showed 60 psi in all cylinders. Re-checked after adding oil and all cylinders were 190-200 psi.
That's worn rings

steell wrote:

bountyhunter wrote:

ELCouz wrote:

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

regards,
laurent

The rings don't rotate they stay where you put them, hence the reason they are carefully aligned at installation.

If that's true then why do two strokes have pins in the ring lands to keep the rings from rotating and lining up a ring end in the ports?

Rings "can" rotate, there's nothing to stop them.

_

They could rotate if something twists on them. Seems like the forces acting on them are are going up and down. All I know is, after the 75k miles I put on my 750 twin engine, I lifted the cylinder off the pots and the ring gaps were EXACTLY where they are installed (gaps facing front/rear staggered going top to bottom) as shown in the FSM. Seems like the odds would be astronomically high against that being the case if they moved on their own.

If they are going to wander at random, why align the end gaps at all?

I can't speak to two-strokes, all I have worked on is four strokes.

They can rotate, but usually don't. I have seen a couple of instances where the rings have actually rotated around until the both top ring gaps aligned. Left a vertical ridge in the cylinder.

Over a fifty year span of being a professional and amateur gear head, I've seen a lot of things

And I learned a bunch from all the mistakes I made

steell wrote:

bountyhunter wrote:

ELCouz wrote:

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

regards,
laurent

The rings don't rotate they stay where you put them, hence the reason they are carefully aligned at installation.

If that's true then why do two strokes have pins in the ring lands to keep the rings from rotating and lining up a ring end in the ports?

Rings "can" rotate, there's nothing to stop them.

___________________________________________________________________

And back on the original subject, just how many compression tests have you folks done?

I've done a few hundred and what I'm reading here is not jiving with my experience.

31 psi increase in compression after adding oil is nothing, if the rings were worn the oil would have upped the compression to 170-200 psi.

I have never seen a KZ motor wear rings unevenly, if you have worn rings in one cylinder you have them in all cylinders.

Low compression in one cylinder indicates valve leakage, combined with the minimal 31 psi increase after adding oil nails it.

As a learning experience for my nephew (I believe in hands on training), we did compression checks on five KZ's one Saturday.
Checked compression stone cold, then rechecked compression after the motor had reached operating temp. In every case there was an average 10 psi increase between cold test and hot test in each cylinder.

Had a KZ650 motor that someone gave me that had over 100k miles on it. Cold compression test showed 60 psi in all cylinders. Re-checked after adding oil and all cylinders were 190-200 psi.
That's worn rings

Sixety psi is more like broken rings and bad valve seals. Would not run with 60psi. Less it was one strange cat.

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 = $$$ .

Just finished checking valve clearance today

here's the numbers:



all clearance are within specs.

Looks like it's either a bad valve seat or a blown head gasket leaking (maybe after all its leaking at the oil passage on the side) into the cam chain passage.

I can't find any other explanation for the low compression (121psi) on cyl #2. As for the rings being shot I'm very skeptical about that but i will still continue to investigate this «issue».

Does what i think make sense ?

thank you,

sincerely,
laurent

Didn't you add oil and the compression came up?

That means it isnt the valves...

The cylinder can be barreled or coned, warped... lots of strange crap.

You could do a leak-down test, but at this point its almost easier to just pull the cams and get her done.

Only way to figure out exactly is to pull those jugs and clean everything up and start measuring.

GL!