93 Katana engine failure

[jetta90]

Hello everyone. This is one of my first posts on this forum ......so, an introduction as well at the same time.
This past spring I purchased a 93 Suzuki Katana 750 project with a known weak compression issue in at least one cylinder. Valve adjustment produced a slight improvement in compression numbers but it was obvious head and barrels would need to come off for proper inspection.
This is what was found.......
It appears to me top piston rings on 3 and 4 jugs broke and caused massive ring land failure. Bits of ring found embedded into head combustion chamber domes adjacent to exhaust valves. Piston crowns around same area showing identical "punctures" caused by piston rings debris propelled withing cylinder while engine was running. Cylinder walls on cylinders 3 and 4 are also gouged along full length of stroke.
Quite a coincidence 2 pistons would fail the same way at the same time. Most definitely the PO enjoyed spinning this engine at higher revs but I just can't imagine 2 pistons having identical failures at the same time. Pistons 1 and 2 don't appear to have any issues. Perhaps a previous overheating episode on this engine caused the rings to lose their temper and consequently failed due to high rpm at a later time?? What do you folks think?
Probably find a good used motor or complete top end at this point would be my best bet?

[hardlydangerous]

cold seize

or AKA 4 point seizure
on multi cyl engines though the engines dont usually seize because there is still 1 or more good cylinders.
its caused by reving the engine or running the engine without warming it up slowly.

the pistons and cylinders expand at different speed and a nice slow warm up is needed to prevent this damage.
most common on #2 and #3 cylinders on inline fours but I have seen all 4 chewed to **** because of dumb people that rev a cold engine

[Wild-Bill]

...Probably find a good used motor or complete top end at this point would be my best bet?

Ouch! You're looking at replacing the cylinder block, head and two pistons plus new rings on the other two at the very least. Then there's the question of what else did the PO do to that engine. I'd go for either a complete rebuild (you get an engine you KNOW is good) or a used engine (Hard to be worse off than this one).

[hardlydangerous]

I agree
buy another engine to use while you rebuild this one.
if two pistons are shot the other two will likely need to be repalced.
Your looking at the very least, 4 pistons and rings, cylinder, main bearings, head, base and pan gaskets. The cyl head may be ok but you will want to check the valve seats for any wear or carbon build up.

FWIW this is why I run a cap full of 2 strok oil in every tank. greatly reduces the cyl wear on cold start, lubricates the top end and reduces then risk of a 4 point cold seize

[jetta90]

Thank you both for your responses.
Never thought of or heard of the cold seize you referred to. Very interesting indeed, and I'm glad I just learned something new here.
Odd that only # 3 and # 4 have had the issue and pretty much identical as far as damage goes. Only the top ring on both pistons have incurred this identical failure. Second compression ring and oil rings seem to have been spared from the carnage on both pistons. Pistons and cylinders on # 1 and # 2 have no signs of any damage or ring seizure in their respective ring lands.
I have been told that perhaps the bike was laid up for an extended period of time allowing rings to sieze up in their ring lands. Bike was then started at the end of this long hibernation and rings snapped?? Possible? What do you guys think?

I'll be digging into this project a little deeper shortly as I would like to eventually get this bike fixed up and running. I have a couple other older GS's I can use this coming riding season so I don"t have to get this one on the go right away............ although it would be nice to do so.
As far as used engines go, I understand the 88 to 97 Katana 750 engines were the same? I could use a GSXR 750 engine from 89 as well? I'm thinking dropping in a replacement with no mods required to make an engine fit would be the best route for me.
Thank you again guys for your responses......please keep your ideas and thoughts coming.

[scottynoface]

Oh wow...munch munch munch...

[jetta90]

Yea - it's an ugly one for sure.
Anyone have a used engine around? or......

Used head and cylinders/pistons wanting to sell?????

[woobie]

If I were you I'd post up a wanted to buy thread on one of the BC bike Forums. There's at least one major sport bike forum and maybe you could find a local Kat 600/750 bandit or even an older gsxr 750/1100 motor.