When I say hatred, what I meant was why are you looking at a 670 when you got this monster Engine in it already ?? That should be more than enough power. You spent considerable amount of money and time on this Engine so why not just have some fun with it rather than spending more time and money on your machine.
When I said twisted axels, what I meant was that one miss calculation with either this Engine or a 670 and its all over. Check out ZeroClient's thread: viewtopic.php?f=4&t=18074 and if you start right at the beginning you can tell that the previous owners ran the hell out of it. Probably jumping it and landing with throttle on, because those previous owners were racers. Then Zero gets it and does a tremendous job at restoration. He goes for one puzzy type ride and blows the gearbox. That shaft was already fractured because when I look at it, you can see the spiral twist in the metal at the break. I seen this all my life on the large line shafts that I used to repair. We used to slack off the belts on the gearboxes at work or just run one belt so the homo's don't twist off the 2 7/16" shafts. This is what happens when you high load a shaft. It starts to metal fatigue and spiral fracture in two.

Edit: I know that wasn't your first test flight with that thing and you have been on this site long enough to know, but just saying here what I am thinking when ever I hear someone talk about putting in a bigger Engine. Honda engineers are not stupid people. They design this stuff to take a certain load.

Hey check this out (see pic below).
No I didn't do that. It came with a bunch of parts I bought several years ago. Yup it also came with a blown gearbox.
How did the fag do that ?? You have three guesses.
Anything look familiar guys ??

Wow that looks like the input shaft on my 350. Mine is running the 350 Engine but a 10” driven clutch! It’s Grenaded the reduction box probably more than once.

Hey, if you are having to use more than one gasket and cutting your domes to get your compression dialed, this tells me you have some room to raise your port timing some on your exhaust port. This will give you better top end and then also you can run a tighter chamber to keep the compression higher. I’m just saying if you are looking to improve what you got now there’s room to do so there.

yeah I think over the winter I will tear it apart and send the cylinder south to have some work done to it, maybe a hone and some new rings to get the compression back up

so today I decide to pull the cylinder off and just a have look at things..sure glad I did. was surprised at what I found. I am going to guess that I had a bit of a cylinder head leak, or it could of sucked some water in when I washed it up.

Few more

No idea where the wet line is

that's an interesting failure you've got there. My first guess was that the crank bearings or bottom bearing is coming undone, but usually when that happens you'll see pin-like markings in the head and piston. Here I see only large circular pit markings - which is weird. It doesn't look like detonation either. No seizure marks either. Usually water ingestion washes the oil film from the falls and causes the piston to mark the cylinder walls, like a seizure - but from lack of lubrications due to water wash. Don't see that here either. In fact the cylinder and sides of the piston look alright. That cylinder probably just needs a hone or +bore. Something was ingested. Nonetheless you saved yourself from a bigger failure obviously.

Take a magnet and see if anything embedded in your head or piston sticks to it.

Is there water/antifreeze in the bottom of the crankcase? Any water anywhere else inside the Engine?

You'll need to split the cases and really check everything over if you intend on re-doing this.

Could you have ingested sand? K&N? Single or Dual filters? The exhaust passage looks like melted sand/blasted?

I am starting to think this just happened. the last time I was out I ran it hard all day long. no issues, washed it up, checked compression, ran it for a few minutes and backed it into garage. I believe it ingested something, possibly when I was checking compression, the marks on the head and piston are new, and only running it for a few minutes would actually make sense to me.

as for a filter I am running a uni filter in the air box, with two inlets, but no prefilters, this is where I think I may have ingested some water, after washing it the filter box had some water in it. I don't think there was any coolant inside the Engine other than what I may have spilled.

the exhaust does look really weird, not sure how to clean it..

Did the one-way valve drop out of your compression test gauge? I don't think that was it.

I don't think water should have caused this either. Usually just a little water entering the Engine will cause it to flutter and stall. Not cause Engine damage. Did you hydrolock? If so, your crank may have bent.

no I don't believe it hydrolocked. it started and ran like normal. only ran it for a few minutes like I do after every wash just to flush out any water that may get in through the filter or the exhaust, I am gonna go look at my test now lol.

compression test is fine..but it is possible that there was a piece of debris stuck to it. grasping at straws here, its just he marks on the piston look to fresh to be run for any amount of time



that was taken minutes after I pulled the cylinder off..didnt wipe it or touch it..those look pretty fresh. only thing I found was that one little piece in the head but dropped it and never found again. so I believe one little piece did this in a short amount of time running

Fully,

I just posted some of your pictures on another forum; guys who know watercraft 2-strokes.

A couple people are saying its not water, nor bottom/crank, but they are saying it could be a reed screw. I looked back and your intake and reed cage is still installed. Better remove them and check it out.

Fully,

I just posted some of your pictures on another forum; guys who know watercraft 2-strokes.

A couple people are saying its not water, nor bottom/crank, but they are saying it could be a reed screw. I looked back and your intake and reed cage is still installed. Better remove them and check it out.

Also verify ring locator pins are still in position

I did think about the pin bosses and they are still there..

yes the reeds are still installed. I sill go and remove them and see

Just tore the entire Engine now on in the bottom man looks fine to me bearings seals all seem to be good only thing missing is that one thrust washer on the crank. But if you go through pics of the last time I rebuilt this Engine it looks like that was missing before and I just overlooked it when I rebuilt.

Only thing I noticed was I was very low on balancer oil and there was a bit of coolant in it. Not sure how that happened.

Im not sure then. Only thing I can think is sand ingestion?

Reed pedals look worn but that wouldn't cause the damage.

If you plan to re-use this Engine then best replace ALL bearings. How does the wrist pin and needle bearing look? Any slop in the bottom bearing?

Reeds are actually in really good shape. Wrist pin and bearing seem fine. No up or down play in rod bearing. But can be wiggled a bit because of missing shim.
I don’t have a press so I can’t get big bearing off crank

also for anyone interested in these reeds, I bought them through boyesen, but they are a FMF reed, part number FMF002 they are for a 1988-89 CR250

One more thing to note. The exhaust has been modified on this and on the top and bottom there used to be small pieces of the flange that fit into the cylinder I know the top piece has been broken off for quite some time but the bottom piece I’m not to sure. There some carbon buildup but not much.

I have come to the conclusion that when I took the plug out a piece of debris fell in the cylinder. There was still some build up of crap around the plug base. It seems to make sense in my head anyway cause there’s no damage to the cylinder walls or anything else other than the head and piston. And I only ran it for a few minutes. Less than five minutes. I cannot find anything else wrong other than the shim on the crank and the exhaust flange.

Well, That sucks if that was the case.

So, the crank is missing one of the thrust washers next to the bottom bearing? I'm thinking that would cause the bearing cage to overheat and possible even throw sparks or metal bits. The thrust washers are very important pieces. I see your crank is welded and so not sure what you are going to do there.

What have you decided to do?

the welds can always be cut out, I do have another crank, but the stator thread got mushroomed out. I have sent the Engine to methodical and he's gonna work some magic on it. hopefully fix the head if I can be, this head has had lots of work done in the past so hopefully he can figure something out. not sure if you could tig weld to add aluminum then machine it back down, probably a new piston, hone, and most importantly some port work. the cylinder has all ready been shaved down +-3mm. and I think there is lots of port work that can still be done. for what I have invested and the child that I am going to have to sell, I could of done a 583 or 670 conversion, but I like seeing the faces of people when I am keeping up with them on there new fancy machines

THE MOOSE IS IN THE KAYAK!

You forgot to take your meds meth !!
Now take your meds and post some good stuff for us. You haven't done that in a while.