Just got back from little Sahara sand dunes. Pilot ran great for two days with no problems.On my last ride of the day Friday I could tell it did not have the top end and the power that it previously had but thought it was just a jetting problem.Fl670 was checking compression on his buggy so I thought well let me check mine, and lo and behold it was only 75 psi.
So I am just starting to tear into it. Before I started tearing it apart I did a radiator pressure test to make sure the head gasket did not blow and it passed with flying colors.
For those of you that don’t know I am running a 400 cylinder with a sleeve from LA sleeve bored out to take CR 500 piston,currently running 89.50 mm

The head looks good although the gasket is messed up, anybody know where I can get another gasket?

Spark plug looks like crap

Top of piston

Another pic

Two of the cylinder bolts Came out of the bottom end and two stayed in

Nice work, good luck and keep posting. What if anything did you I do make the 500 setup burn?
Wrist pin, rod? Etc
Thanks

I’m sorry Go oddy I’m not understanding your question. Are you asking me what did I do to make the Engine blow up? If that is your question I don’t know the answer besides running it wide ass open trying to keep up with these high powered machines I was chasing

Sorry for the confusion....no not how you blew it but how you built it originally?

I bought the pilot With this Engine in it but it had sat outside and got water in it so as soon as I receive the pilot I took the Engine out and send it to Hoser Who completely rebuilt it from the bottom up

Looks like There is some rust on the crank, I am guessing this happened when I was Bitten by that rattlesnake a couple years ago when I was out riding my pilot at the beach.I went to the hospital meanwhile my buddy picked up my pilot and took it home, but he did not cover the air filter and it poured rain for a couple of days.So when I got well enough to pick up the pilot I figured out what had happened

To me It looks like this cylinder looks pretty damn good to me but I will let the experts chime in

I'm sure as heck no expert, but you had to loose compression for a reason. Thinks look good in the pictures. Could you have a stuck ring not seating properly? Why would the plug look so crappy?

Another pic of crank,doesnt Look like any rust is on the bears

Winner winner chicken dinner
When trying to remove circlips from piston I had one of the rings fall out in 2 pieces.Faulty ring? Who knows.
You can see in the pic the damage to the piston

So what do the experts say?
I’m thinking a hone will work for cylinder and should be able to go back with same size piston,what say yee?
Also any gaskets available for this cool head?
I need the one that lays in the head and the big O ring

I would measure the cylinder before I bought a piston just to make sure.

You are damn lucky pieces of the ring didn't get on top of the piston and chew up the head.

Even luckier the cylinder didn't get damaged.

I'm betting a new piston and rings, hone, and good to go.

I would closely examine the ports, are they properly relieved around the edges?

Hoser built the Engine right? So I bet they are, but I still wonder what caused the ring to fail.

Wish I could help you on the head gaskets, but when you find them, but a few extra.

Can you line the piston backup the same way you took it out? Keying off the piston damaged section will tell you where to look and see if the ring got snagged. If you just replace the parts, it may happen again if there is a problem with the cyilider.

If you find the o rings for the head please post up. I have one that also needs both of them. Mine is a Pro Design cool head and they no longer list any parts on their site for the Pilot.

It looks like the top ring may have rotated past the locator pins? Take the bottom ring off the piston and push it into the cylinder. Measure ring-end-gap and post back.

Also measure your current piston-to-cylinder wall clearance. I'd say if the clearance is <8thou you might get away with a new piston and just a hone, but is doubtful. Think about your piston costs, hone costs, and consider going to 90mm. BTW on a CR500 sleeve you should be able to get all the way out to 91mm on Wiseco. that's a lot of bores/years.

Finally on your O-Rings. This one is easy.

The inner O-Ring you should use measure the diameter of the slot on the dome, and the thickness of the slot. You can refer to various sized O-Rings at http://www.mcmaster.com. You want to be very careful with your selection however, because with the heat I would highly suggest you get Viton O-Rings for chemical and temperature resistance. Look here:
https://www.mcmaster.com/viton-fluoroelastomer-o-rings

The outer O-Ring is going to be EASY. Either you can try to lay it out and measure the diameter, ordering O-Rings 3 times, which isn't a bad idea... OR, McMaster sells O-Ring cord stock where you can make your own O-Rings. Look here:
https://www.mcmaster.com/viton-fluoroelastomer-o-rings
All you need is the diameter, and then cut the O_Ring to length. I'd use Permatex Water Pump and Thermostat RTV at the joining end to attach the O-Ring back onto itself. Clean cut the ends with a razor blade. Hell; I'd use that stuff to dress the entire O-Ring honestly. Let it dry for a few days before coolant is added. This is how we do it with large 2-cylinder JetSki heads with the outer o-ring.

morning REDMAN,

My first thought from looking at pics is Ring flutter.
My second thought, Check your exhaust port chamfer and cord width
My third thought Plug, kinda normal as it goes away. I would say you lost the ring before your trip.
My fourth. look at your exhaust flange. This will confirm

Remember your were running it with a coolant issue a while back. It is a good idea when this happens you pull the piston and change the rings. What happens is the pressure loss between the ring land can and will cause ring flutter and fracture of the top ring or break the top of the piston. Look for evidence of combustion marks on the bottom of the top ring and its groove. Also measure the lands width on the side (90 degrees from exhaust center). You should notice a some sort of taper in the groove from ring twist. This will happen if ring flutter and loss of pressure took place. If you do find this you may need to change ring end gap on rebuild to help with pressure between lands. Measure the distance down the cylinder to the change in wear mark on the cylinder. This will give an idea of peak cylinder pressure and timing for your fuel set up. Then check the from that mark to exhaust port opening. Get me those numbers along with cord width. Take a hard look at the exhaust port roof chamfer. Look at the book and get an idea of how the taper is in relation to the ports width. Wider the width the more aggressive the taper in an elliptical port. The ring is at static presssure at the point from port open to port close. So with any ring twist in the land from flutter can lead to port snag.
Or heck it could have just went boom. no matter what look hard at the port and read up on presure balance between the ring for seal and anti flutter at (high) rpm.

Thanks for advice on where to get o-rings and stuff.I'm hoping it will just need hone but if not I'm thinking I should be able to do the 89.75mm piston and not have to go all the way up to 90.I don't trust my mechanical skills to do the measurements,I am going to bring it to shop along with old piston and see what they think.

Yes,I will try and do that tonight,thanks

Thanks for advice,but most of what you asked me to do is beyond my skill set and I don't have proper measuring tools.
As far as the coolant problem,I think that was an anomaly and there was never a problem.It only happened that one time last year in Oct,and red overheating light came on within 2 or 3 minutes of riding,I don't see how it would have got that hot in 70 degree weather that quick?
What am I looking for when I look at exhaust flange?

So does this look heat related or something different?
One thing that has changed before this trip was I put a different pipe on it a couple months ago because the other one cracked,and I don’t believe I’ve done any hard riding with the new pipe.And with the new pipe I did not drill hole for digitron sensor so that wasn't hooked up.My fan has to be manually turned on and I never turned it on on this trip because the weather was 55 and I didn’t think it was needed.We didn’t ride that long between stops or stay that long when we were on the dunes.But one thing I did do when we were riding(and you can tell me if this is a good or bad thing)is during the rides at WOT (Wide Open Throttle) I would turn the pilot off and pump the throttle a couple times to dump fuel in cylinder to help cool it off then switch Pilot back on and continue at WOT (Wide Open Throttle)