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Mystery Piston Damage / Marks

JTGS850GL said:
Could also be the result of a lean mixture on that cylinder from an issue with the carb that's causing detonation. That could also cause burnt valves as well. What did the plug from that cylinder look like? How much carbon buildup on that cylinder?
Click to expand...

I am just trying to talk him into checking things that should be checked anyway. In my option that does not look like a cylinder getting hot or running lean. It looks like a piston kissing the head. More pics would be helpful in finding what caused the problem. Or a couple of measurements Would tell all. It already has aftermarket pistons and the carbon look dark. Buy hey if everyone else wants him to put it back together the way it is then more power to him. You should see the rings he posted up a pic of asking if he could reuse them. If he was a good friend of mine sitting on the couch next to me he would be getting slapped upside of his head with me saying what the fuk is wrong with you.
Go to the link in this thread and look on page 48 & 49 and and page 44 you will see what I am talking about. http://www.boosttown.com/engine/piston_damage.pdf maybe the carbon build up caused the piston to kiss the head in which case the rod bearings meet to be checked.
The marks on the piston was not caused from melting. I have voiced my option and will keep quite from here out.
 
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That sits too close to the liner for that to be the piston high-fiving the valves. that's definitely hot gasses erroding the piston. if the piston was high-fiving the valves, you'd see it in the valve pockets in the piston quench area. i see this all the time in piston driven firearms on the heads of the pistons after i get all of the hard carbon scraped off. it's too much heat. but i would definitely take some measurements as stetracer has suggested, because sometimes it takes fixing one issue to find other issues. and since this is a turbo bike, tollerances are way more crucial than on a NA motor
 
60ratrod said:
That sits too close to the liner for that to be the piston high-fiving the valves. that's definitely hot gasses erroding the piston. if the piston was high-fiving the valves, you'd see it in the valve pockets in the piston quench area. i see this all the time in piston driven firearms on the heads of the pistons after i get all of the hard carbon scraped off. it's too much heat. but i would definitely take some measurements as stetracer has suggested, because sometimes it takes fixing one issue to find other issues. and since this is a turbo bike, tollerances are way more crucial than on a NA motor
Click to expand...

Not saying the valves hit the pistons every time once the valves hit the carbon in the valve pocket one time they would slightly bend and be out of the way never to hit again. I am saying the piston is kissing the flat part of the head right behind the valve over and over so slightly.
( Who said this was a turbo bike? )
Tolerances are critical on any build once aftermarket pistons are added and cylinders are decked for the replaced liners.

If it was from hot gasses why is it only on the top of the piston and not down the sides to the top ring?



.
 
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"and since this is a turbo bike, tolerances are way more crucial than on a NA motor"

odd statement...a monkey can put together a GS turbo engine..big power N/A engines take some measuring and fitting.
plus i think he has this thread confused with some of turbojonn's threads :D
 
I haven't got the head with me at the moment. I will look in due course. Thanks.

The thing is: is that piston OK to re-use?

Greetings
 
I'd reuse the piston as long as the ring land isn't crushed down. Measure the ring vertical clearance and if it's in spec, I'd run the piston again.
 
I thought that i had seen it mentioned in this thread that this was a turbo'd bike. and i may be confusing it with another thread. point is, i would be way more concerned with what the measurements were on a forced induction motor than i would be on an na motor, although i do get concerned where it counts(ex: ring end gaps and bearing clearances)
 
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60ratrod said:
I thought that i had seen it mentioned in this thread that this was a turbo'd bike. and i may be confusing it with another thread. point is, i would be way more concerned with what the measurements were on a forced induction motor than i would be on an na motor, although i do get concerned where it counts(ex: ring end gaps and bearing clearances)
Click to expand...

Ratrod your lack of knowledge is showing. Turbo or N/A it matters the same on both.
Your most important measurements besides the bearings, piston to cylinder wall , and ring gap are to know are valve to piston (.050 intake)(.070 exhaust) and head to piston clearance (.040). They always seemed to get over looked. If you don't have enough clearance there your gonna grenade your motor. Since he is working on a GSX1100 or as we call them here in the USA a GS1150 it is a roller bearing crank and a visual check of those bearings should be fine. But I have never been able to settle for fine. For me everything has to be perfect and exact.

Londonboards,
yes you can more than likely use that piston if you check what Ed told you to. But please don't use those rings you asked about in your other post don't even think about it. Only a hack would re use those rings.
 
stetracer - the motor that this piston came out of had been breathed on. I have APE cylinder studs, Ti retainers and probably HD valve springs (they are way over specified minimums). The pistons are also .5 over standard. I think the head, which is now shot, also had hot cams, which are completely gone. The metal remnants I took out also show the thin cylinder liner associated with big bore stuff before it was taken back to standard. This motor was abused at some stage. Probably drag racing! You guys!

Greetings
 
londonboards said:
stetracer - the motor that this piston came out of had been breathed on. I have APE cylinder studs, Ti retainers and probably HD valve springs (they are way over specified minimums). The pistons are also .5 over standard. I think the head, which is now shot, also had hot cams, which are completely gone. The metal remnants I took out also show the thin cylinder liner associated with big bore stuff before it was taken back to standard. This motor was abused at some stage. Probably drag racing! You guys!

Greetings
Click to expand...

Londonboard,
What I see in the motor you have been posting up pics of with cam damage was put together by someone that should not even be allowed to have a tool kit. The pistons you posted pics of looked to be 76mm aftermarket pistons the same ones that have been in my 85 GS1150 for 15 years. If a motor is put together correctly it will last a very long time. If it is just assembled with some parts aftermarket to make it go faster then it is gonna blow up. "Drag racing" a motor is easier on a motor than riding it on the street unless your winding it way up in the rpms like over 11,000rpm.
look at the build specs of my 85 GS1150 in my sig. And the size of the cams I use how much I milled off the head. I put that motor together 15 years ago. Oh I also run 80hp shot of nitrous on it. I have pics of the bike in my photo albums in my profile it is the red and black bike it is a street bike that I drag raced every week end for many years and road all around Daytona bike week with the wife on the back and was my daily ride for a long time. Again I will say drag racing a motor is not hard on it if built correctly. Bad mechanics are very hard on a motor.
 
Copy stet. I shall relegate back to asking questions. Seems my knowledge base is getting a tad rusty from not being able to work on stuff cause of my ex, who i couldn't pry off her computer with a 10' crowbar. I also have machine shops check that stuff for me since i didn't do any more than mild sbc builds before i was married
 
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