Wana see a fancy looking piston?

[B0000M]

my jetski made an unkind noise yesterday, heres the results...

the last piston shows both pistons. runs twin carbs with a big mixing section between them so i dont see how its jetting....

top bearings on the fucked one were totally rooted.

[RM125king]

Looks to me something has fallen in there and has been bouncing between the head and piston. Are the piston rings still complete?

Its that or a serious case of detonation/pinging. What was the compression? Anything over 180 PSI and you should be using AV gas.

[B0000M]

Looks to me something has fallen in there and has been bouncing between the head and piston. Are the piston rings still complete?

Its that or a serious case of detonation/pinging. What was the compression? Anything over 180 PSI and you should be using AV gas.

well i havnt found the casing for the top end bearing on that cylinder.... the other one fell apart as i took it out- quite likely it was them.

compression, unsure, but when i did pistons and rings on my old 650 i got 185psi on each cylinder, so i presume this is less as ive had it a while and not done any work to it

[Crasherfromwayback]

Has gone through it mate! I'm guessing bits of big end thrust washer or needles from the big end...or if you're saying the gudgeon pin brg is rooted...bits from that. Either way...you're gonna have to split the cases and check the crank.

[RM125king]

Yeah i would say it was the bearing cages bouncing around in the top.

Try and find an after market head or you can use that one again with a bit of a clean up. Get a couple of new pistons and bearings and your away again for another 10 years.

[Crasherfromwayback]

well i havnt found the casing for the top end bearing on that cylinder.... the other one fell apart as i took it out- quite likely it was them.


You've just answered my question. Major melt down.

[Crasherfromwayback]

Yeah i would say it was the bearing cages bouncing around in the top.

Try and find an after market head or you can get that one welded up and machined. Get a couple of new pistons and bearings and your away again for another 10 years.

Incorrect. Crank cases split...crank rebuild. That shit that's mashed the piston and head has also gone through the mains/big ends...and that's if it's not the big ends in the first place.

Total rebuild.

[B0000M]

yeah, thats the plan, ive got a mate whos up for repairing the head, the cylinder definately needs a hone or a re sleeve, not sure which yet, im not expert on whats good enough and whats not on that topic.

note in one of the pics the broken skirt - that bit is a concern...

[RM125king]

Yeah he will def have to split the cases but if the pieces got to the head they must be pretty small. Theres still a chance the crank might be alright. Will still def have to pull apart and check.

[RM125king]

Yeah i didnt notice that. Your up for a new cylinder. Fark mate it might be cheaper/easier to source a second hand motor or Write the ski off.

[Crasherfromwayback]

yeah, thats the plan, ive got a mate whos up for repairing the head, the cylinder definately needs a hone or a re sleeve, not sure which yet, im not expert on whats good enough and whats not on that topic.

note in one of the pics the broken skirt - that bit is a concern...

Mate...the whole thing is a 'concern'. I'm totally guessing here...but I think the ski has been put away without having being 'flushed' properly at some stage. As I'm sure you know...the exhaust systems are full of water. If you put the ski away after riding it...and don't run the ski to get the water out of the exhaust...the water sloshes into the crankcase back through the exhaust port and then rusts the crank and the mains/big ends.

The mains/big ends then fly apart and mash your piston/head and barrels.

Major rebuild. Then ALWAYS flush the ski when you're done riding it.

[Crasherfromwayback]

Yeah he will def have to split the cases but if the pieces got to the head they must be pretty small. Theres still a chance the crank might be alright. Will still def have to pull apart and check.

Not true sorry mate. If you're familiar with how two strokes work...you'll know that that shit has gone through the big ends/mains. She's over.

[B0000M]

Mate...the whole thing is a 'concern'. I'm totally guessing here...but I think the ski has been put away without having being 'flushed' properly at some stage. As I'm sure you know...the exhaust systems are full of water. If you put the ski away after riding it...and don't run the ski to get the water out of the exhaust...the water sloshes into the crankcase back through the exhaust port and then rusts the crank and the mains/big ends.

The mains/big ends then fly apart and mash your piston/head and barrels.

Major rebuild. Then ALWAYS flush the ski when you're done riding it.

na, you've guessed completely wronge. always flushed for about 5 minutes after riding, im religious about that, and other cleaning for that matter, then run till water stops coming out the exaust, also make a habit of pulling the bottom end bung cord before putting away just in case. the bottom end and mains feel perfect, so im not going to point the finger in that direction at all.

[RM125king]

Not true sorry mate. If you're familiar with how two strokes work...you'll know that that shit has gone through the big ends/mains. She's over.

I have seen a few let go and i havent seen one yet to take out the crank and cases.

Split the cases mate and check it out. Put some pics of what you find.

Cheers

[Crasherfromwayback]

na, you've guessed completely wronge. always flushed for about 5 minutes after riding, im religious about that, and other cleaning for that matter, then run till water stops coming out the exaust, also make a habit of pulling the bottom end bung cord before putting away just in case. the bottom end and mains feel perfect, so im not going to point the finger in that direction at all.

Well good to see you get rid of the water mate. But if you're missing a little end brg case and it's needles...you're gonna have to pull the crank out. If you don't...and you simply fit new pistons and s/e brgs...you'll be doing it all over again real soon.

[Crasherfromwayback]

I have seen a few let go and i havent seen one yet to take out the crank and cases.

Split the cases mate and check it out. Put some pics of what you find.

Cheers

Never said the cases would be in trouble. But the big ends and mains will be.

A two stroke...like any engine...is a pump. When the fuel/air is drawn through the manifold and reed cage, it enters the crankcase. It lubes the big ends/mains as it does so. When the piston comes down...it's pressurizes the crankcase and forces the fuel/air up through the transfer ports.

If the small end brg has collapsed...it's put bits of it into the crankcase. Those bits have then been munched up by the crank before they've been spat back up through the transfer ports and made that pretty little pattern on the top of the piston and cyl head.

Crank rebuild. End of story.

[RM125king]

We will see what the pics come back like.

[pete376403]

What size engine is that?

[camchain]

Those things are a real Dr Jekyl and Mr Hyde pair. Very weird but also very impressive damage. One for the Burt Munro shrine "offerings to the god of speed." How's that carb arrangement work? Does seem like the likely culprit. Excellent photos BTW. I got lousy detail shots until I figured out camera needed to be set to centre focus.

I seem to remember the melting point of aluminium being somewhere around 700 C. Probably even a fair bit higher on pistons made with a few special ingredients. Booom did you hoodoo yourself when you reckoned no probs with pro-x pistons?!

[Kiwi Graham]

na, you've guessed completely wronge. always flushed for about 5 minutes after riding, im religious about that, and other cleaning for that matter, then run till water stops coming out the exaust, also make a habit of pulling the bottom end bung cord before putting away just in case. the bottom end and mains feel perfect, so im not going to point the finger in that direction at all.

Yep always flush my motor (boat outboard) until the neighbours are pissed of, salt water/water is a killer.


Never said the cases would be in trouble. But the big ends and mains will be.

A two stroke...like any engine...is a pump. When the fuel/air is drawn through the manifold and reed cage, it enters the crankcase. It lubes the big ends/mains as it does so. When the piston comes down...it's pressurizes the crankcase and forces the fuel/air up through the transfer ports.

If the small end brg has collapsed...it's put bits of it into the crankcase. Those bits have then been munched up by the crank before they've been spat back up through the transfer ports and made that pretty little pattern on the top of the piston and cyl head.

Crank rebuild. End of story.

Sounds like the only option, pull it apart, apraise the damage and cost it verses a second hand re-ferb motor. Bit of a bugger it happens now and not in a few months time......good winter project eh

[barty5]

measure them up or check what size the piston is i can get matched sets Best way to go and do a rebore thats what i did with mine when it shat its self. if it a kawaka 650 the crank arent relly rebuidable with out extreme cost as they dont come appart very well for the center bearing best to get either new $$$$ go a goood second hand one. Check the water cooling intake and outlet for blockages as this is what killed mine think from memory it was the rear that went suxed up some shit and it was all over few min later.

Let us know re: pistons should be able do do a good deal.

[Crasherfromwayback]

measure them up or check what size the piston is i can get matched sets Best way to go and do a rebore thats what i did with mine when it shat its self. if it a kawaka 650 the crank arent relly rebuidable with out extreme cost as they dont come appart very well for the center bearing best to get either new $$$$ go a goood second hand one. Check the water cooling intake and outlet for blockages as this is what killed mine think from memory it was the rear that went suxed up some shit and it was all over few min later.

Let us know re: pistons should be able do do a good deal.

Certainly looks like a 650 to me...and you're right about their cranks!

[B0000M]

lots of guessing going on.....

its a 750, never touched this engine before.

carb setup is twin carb, but has a pretty decent sized 'mixing tube' section of the intake manifold, so i wouldnt expect such huge variation between cylinders. heat could be an issue as the way the motor had been put together the base and head gaskets had gasket poo on them as wel which was blocking the cooling jacket in some areas on that cylinder

[Crasherfromwayback]

lots of guessing going on.....

its a 750, never touched this engine before.



Guessing is all we can do unless we see it in the flesh!

[barty5]

lots of guessing going on.....

its a 750, never touched this engine before.

carb setup is twin carb, but has a pretty decent sized 'mixing tube' section of the intake manifold, so i wouldnt expect such huge variation between cylinders. heat could be an issue as the way the motor had been put together the base and head gaskets had gasket poo on them as wel which was blocking the cooling jacket in some areas on that cylinder

yeh well heat can be a major prob. 750 cranks will be the same big hassle to do bearings i think you can get hot rod cranks for them and wiseco do them as well depending on how old it is both of which i can get at real good price DONT get unmatched pistons.

[B0000M]

yeh well heat can be a major prob. 750 cranks will be the same big hassle to do bearings i think you can get hot rod cranks for them and wiseco do them as well depending on how old it is both of which i can get at real good price DONT get unmatched pistons.

yeah im not going to do the bottom end at all. ive flushed it out with shitloads of supercheap degreaser, and its currently bathing in some motor oil. i can feel no play in there and nothing is making any noise, a bit of debris has come out which has now stopped. feels and sounds good to me. ill leave it. the cylinder is a sleeveable type, so a new cylinder sleeve will fix that up, including the broken collar thing at the bottom. so new pistons, sleeves, rings, top bearings, gudgeon pins, circlips, gaskets, check out the carbs and repair as needed and shes all go again.

[barty5]

yeah im not going to do the bottom end at all. ive flushed it out with shitloads of supercheap degreaser, and its currently bathing in some motor oil. i can feel no play in there and nothing is making any noise, a bit of debris has come out which has now stopped. feels and sounds good to me. ill leave it. the cylinder is a sleeveable type, so a new cylinder sleeve will fix that up, including the broken collar thing at the bottom. so new pistons, sleeves, rings, top bearings, gudgeon pins, circlips, gaskets, check out the carbs and repair as needed and shes all go again.

what year/ model isit ill price it up for yah can get it all from wiseco at trade $$

[Crasherfromwayback]

yeah im not going to do the bottom end at all. ive flushed it out with shitloads of supercheap degreaser, and its currently bathing in some motor oil. i can feel no play in there and nothing is making any noise, a bit of debris has come out which has now stopped. feels and sounds good to me. ill leave it. the cylinder is a sleeveable type, so a new cylinder sleeve will fix that up, including the broken collar thing at the bottom. so new pistons, sleeves, rings, top bearings, gudgeon pins, circlips, gaskets, check out the carbs and repair as needed and shes all go again.

Well I genuinely hope I'm wrong mate...but I think you'll be replacing those bits again quite soon.

[pete376403]

lots of guessing going on.....

its a 750, never touched this engine before.

750 two stroke twin - woohoo. What sort of power do they make?
I'm starting to have ideas....

[barty5]

750 two stroke twin - woohoo. What sort of power do they make?
I'm starting to have ideas....
my 650 was rated at bout 65 70hp

[hospitalfood]

i was surprised at the damage! looks like there is more going on than bits being crunched around in there.
check the carbs for sure.
i would also check those lead anode things just to be sure, as odd at that sounds.

[B0000M]

750 two stroke twin - woohoo. What sort of power do they make?
I'm starting to have ideas....

they claim 72hp standard, but who wants to ride a standard! lol

keep in mind there is nothing in the way of a transmission, theres a crankshaft, which connects to the jet shaft

[crazyxr250rider]

Genuine rough barstard, split the cases.