Tell me what you think........

[jetta90]

This question is not pertinent to the GS series motorcycles covered on this forum but it does relate to a slightly younger GS bike. Hope it's ok to post this question here.

Picked up a 1993 Suzuki Katana GSXF 750 project some time ago and have just recently started digging into it to find the issue(s). The bike had not been used for quite a while and I was told there was a compression issue in #3 and possibly more cylinders.
Once I started getting into it I took compression readings myself and the results were horrible - 90/95/30/50. 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.......
Top piston rings on #3 and #4 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. Both piston #3 and #4 have identical damage. Pistons 1 and 2 don't appear to have any issues at all. 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? Lack of oil? Engine laid up for a long period of time (years) and rings partially seized up in their grooves and broke off when the engine was started?
See attached picture.

[jetta90]

Here's another pic.....

[Nessism]

Hard to say what caused this. The piston doesn't have evidence of a lot of blow by so I doubt the failure was occurring slowly.

I wouldn't focus much effort on trying to figure out what happened as opposed to working to fix the bike. They sold a ton of those bikes so finding a low mileage cylinder and set of pistons shouldn't be too hard.

Of course as with any old bike I suggest you go though the carbs and make sure the engine isn't running lean. Basic stuff.

[jamminjimmy]

From the pics you have shown us, it looks like high oil consumption. Lots of black on those pistons. Hard call on the original problem, lack of proper maintance is what we see here at our shop and yours looks the same. The cylinders could be sent to Millenium Tech and redone tel:920-893-5595, they are in Plymouth WI. I havent looked but I would be sure that Wiseco has got your pistons.

[jetta90]

You're right, one would think that with the number of Katanas out there one could quite easily find a used motor or at least a gently worn top end. I'm beginning to wonder if there are any out there at all!!!
I've searched and have had a couple of close calls but thus far nothing.......they seem to be harder to find than I expected. If anyone knows of one let me know please.

[Graham]

Check for bent valves. Maybe oil passage clogged in head?