Wana see a fancy looking piston?

**Crasherfromwayback** · 7th February 2009, 23:17

Originally Posted by RM125king

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** · 7th February 2009, 23:20

We will see what the pics come back like.

**pete376403** · 8th February 2009, 00:15

What size engine is that?

**camchain** · 8th February 2009, 00:18

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:Me** · 8th February 2009, 07:24

Originally Posted by B0000M

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.

Originally Posted by Crasherfromwayback

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** · 8th February 2009, 07:49

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** · 8th February 2009, 08:30

Originally Posted by 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.

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

**B0000M** · 8th February 2009, 08:55

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** · 8th February 2009, 09:00

Originally Posted by B0000M

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** · 8th February 2009, 10:44

Originally Posted by 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

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** · 8th February 2009, 10:57

Originally Posted by barty5

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** · 8th February 2009, 11:05

Originally Posted by B0000M

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** · 8th February 2009, 11:08

Originally Posted by B0000M

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.