Author Topic: Would you ignore this? (Read 11820 times)

rablack21 · « **on:** February 21, 2014, 08:14:38 AM »

I tore me engine down last night to put new piston rings in, and this is what I found. The piston has a light seizure/scuffing on the left side between the exhaust port and boost port. No other places, just this one. I have no way of knowing when it actually happened, I'm guessing sometime last year.It appears to be a cold seizure, but strange that it is only in one place and this particular location. I have a race this Sunday so my question is: would you put it back together and run it anyway, or would you sit this race out and get a new piston and bore the cylinder?

Stakes:The is technically a season warmer race for us and doesn't count for our regular season. It is a large race to raise money for ST. Jude and you do get a few points for participation. The first race of the season starts in two weeks.

Cost: if I put it back together and race it, it will cost me a gasket set and the time to put it back together only to tear it apart again to put a new piston in it before the next race.
Worst case scenario: if I raced it "as is", and it seized on the track.

So, what would you guys do?

08IRS · « **Reply #1 on:** February 21, 2014, 08:31:44 AM »

I'd fix it while it's apart. Nothing worse than the engine locking up before a jump and causing you to get injured.

KASEY · « **Reply #2 on:** February 21, 2014, 09:08:56 AM »

I am as budget minded as anyone,, and I would polish the piston up with some 1200 grit and run it,,, maybe not a whole season ,, but to get by I see no reason not to,,

JesseA420 · « **Reply #3 on:** February 21, 2014, 09:20:04 AM »

top ends are so easy to pull off, i would just buff that piston up, put it back together, then go put a piston on order, and replace next week after you run this weekend to see if you have problems.

rk88r · « **Reply #4 on:** February 21, 2014, 09:22:51 AM »

I'd run it and stock it's replacement.

havinnoj · « **Reply #5 on:** February 21, 2014, 09:25:58 AM »

That scuffing could very well be the piston slap I mentioned in your coolant thread. Do you have scuffing on the cylinder wall as well?

rablack21 · « **Reply #6 on:** February 21, 2014, 09:29:02 AM »

Quote from: havinnoj;26345

That scuffing could very well be the piston slap I mentioned in your coolant thread. Do you have scuffing on the cylinder wall as well?

The cylinder wall is smooth. You can tell where the cross hatching has been "rubbed out" where that piston was moving up and down. But other than that the cylinder is completely smooth on the inside.

trx88 · « **Reply #7 on:** February 21, 2014, 09:30:29 AM »

put it together and ride it

trx88 · « **Reply #8 on:** February 21, 2014, 09:32:20 AM »

looks like whatever was there rode its way out the bottom

what are the last two pictures showing the ring gap?

why did you pull it apart in the first place?

trx88 · « **Reply #9 on:** February 21, 2014, 09:35:32 AM »

if you have the money fix it but i woulndnt let that scare me too much. if i wanted to ride.

Rupp250 · « **Reply #10 on:** February 21, 2014, 09:42:01 AM »

I have had pistons look much worse than that. Sanded, ran a hone through the cylinder and re-install.

havinnoj · « **Reply #11 on:** February 21, 2014, 09:45:38 AM »

My bigger concern is that you're racing this weekend with a motor that you noted as overheating regularly. If you're going to get a new piston soon I'd try to get it honed or bored and throw a new piston in before the race.

rablack21 · « **Reply #12 on:** February 21, 2014, 09:52:41 AM »

Quote from: trx88;26348

looks like whatever was there rode its way out the bottom

what are the last two pictures showing the ring gap?

why did you pull it apart in the first place?

To put new piston rings in.

Quote from: Rupp250;26351

I have had pistons look much worse than that. Sanded, ran a hone through the cylinder and re-install.

Thanks, this is starting to make me feel a little better about it.

It will be just for one race, but I didn't really want to get out there and it seize up on my either. Any idea on cause? I tend to agree with OJ, I think it was due to piston slap. If so, this is why I was installing new rings.

C-Leigh Racing · « **Reply #13 on:** February 21, 2014, 11:06:41 AM »

Think about this.
If you have had over heating problems in the past, you know the hottest places in the cylinder bore will be around the exhaust. Since theres no bridge in the main exhaust port, the only part like a bridge, is the part of the sleeve between the main & aux exhaust ports.
With over heating, the higher heat will cause that small part of the bridge, in the exhaust area, to bulge out & take up piston to bore clearance & sometime result in piston seizure.
Note, that all these after market cylinders, Pro-x & ESR, tend to run hotter on the left front side & top of those cylinders & if you've noticed, most of the time when a inner o ring has blown, it will be in that left front corner that it happens on.
I would say sometime in the past, that area of the lite seizure must have got super hot for a real shot time & the small amount of damage was the result of it.
Now this might sound crazy from me & I'm a big boy if some of you want to laugh at me for this, but that small seize spot on the piston, the aluminum has melted & metal has been removed, so if you sand off that little spot, smooth out the ruffness, you know that part of the pistons not going to touch the bore any more.

Only things to think about afterwards, what was causing that one area in the cylinder to run hotter. Was it the fact, that side of the cylinder will run leaner than the right side & cause it to run hotter. Could it be an issue of port linking, on that side from the edge of the aux exhaust port window linking up with the machined area on the side of that old model piston.
Next thing, is all those up & down scars on the exhaust side of the piston ?. Could it be the pipes not sealed at every joint & raw air & maybe dust being sucked back in on the returning wave, or old burnt carbon inside the pipe flaking off & being pushed back in by the returning wave. Lot of scars on the exhaus side & hardly any on the intake side.
Every piece of an engine inside, when you look at it has a story to tell, like that black look to the piston between the top & second ring, its saying that top rings not sealing & letting burnt gas & oil blow by & collect on the piston in that area.

Even with all this going on, I would check the piston real close for cracks because of hours used & if none, smooth that spot out, put those new rings in & let it ride, but fatten up that main jet just a hair.
Neil

Jerry Hall · « **Reply #14 on:** February 21, 2014, 11:34:30 AM »

Quote from: rablack21;26338

I tore me engine down last night to put new piston rings in, and this is what I found. The piston has a light seizure/scuffing on the left side between the exhaust port and boost port. No other places, just this one. I have no way of knowing when it actually happened, I'm guessing sometime last year.It appears to be a cold seizure, but strange that it is only in one place and this particular location. I have a race this Sunday so my question is: would you put it back together and run it anyway, or would you sit this race out and get a new piston and bore the cylinder?

Stakes:The is technically a season warmer race for us and doesn't count for our regular season. It is a large race to raise money for ST. Jude and you do get a few points for participation. The first race of the season starts in two weeks.

Cost: if I put it back together and race it, it will cost me a gasket set and the time to put it back together only to tear it apart again to put a new piston in it before the next race.
Worst case scenario: if I raced it "as is", and it seized on the track.

So, what would you guys do?

The top of the piston shows that the piston crown temperature is normal to a little cool. The scuff (seized spot) is old. The piston has been run at least and hour or so since the seizure occurred. If it was a cold seizure or insufficient piston to cylinder wall clearance there will usually be a similar spot about 180 degrees from the spot you are showing.

Scuffs on the exhaust side of the piston skirt are common in the areas where the piston makes contact with the bridges between the exhaust ports. The areas around the exhaust port, especially the bridge areas run extremely hot. The hot areas really test the lubricants ability to do its job at extremely high temperatures. These hot areas also test the oil films THICKNESS to transfer heat from the hot surface to a cooler surface. The oil films thickness is primarily controlled by the temperature of the oil and premix oil ratio.

Look at the color of the big end of your connecting rod. I would not be surprised if the rod shows a slightly darker color in the area where the rod surrounds the crank pin. If this area is a little darker, this is a sign of insufficient lubrication and insufficient oil film thickness to transfer heat to the crank pin and crank webs. The bore and the rest of the piston skirt show some lubrications problems.

I would suggest that you take an oiled stone like you use to sharpen a knife and polish off the scuffed spot, put the engine back together, increase the amount of oil you put in the fuel and go racing.